Esben Moland Olsen

• Prchalová, Marie; Arlinghaus, Robert; Westrelin, Samuel; Jarić, Ivan; Bertram, Michael G. & Alós, Josep [Show all 26 contributors for this article] (2026). Behavioural Diversity of Fishes: Concepts, Drivers and Its Role in Conservation and Management. Fish and Fisheries. ISSN 1467-2960. doi: 10.1111/faf.70107. Full text in Research Archive Show summary

  Human activity has altered nearly all ecosystems on Earth, contributing to substantial biodiversity loss across taxonomic, genetic and functional dimensions, from the intraspecific to the ecosystem scale. Yet some components of biodiversity remain hidden or underappreciated, including behavioural diversity. Behaviour is often among the earliest whole-organism responses to environmental change, and diversity in behaviour can occur within individuals, among individuals, among populations and across communities and ecosystems. This variation may influence growth, survival, reproduction, ecological interactions and responses to anthropogenic pressures, although its effects on population stability and resilience are likely context-, scale- and component-dependent. In this review, we examine behavioural diversity in fishes, defined here as variation in behavioural traits across levels of biological organisation, from individuals to ecosystems. Our review has two complementary aims. First, we provide a conceptual overview of behavioural diversity, clarify how it differs from related constructs such as personality, plasticity, and behavioural syndromes, and summarise the evolutionary, ontogenetic, ecological, stochastic and anthropogenic processes that generate or erode it. Second, we evaluate why behavioural diversity matters for fish ecology, fisheries management, aquaculture, restoration and conservation. We conclude by identifying key research needs, including improved quantification, stronger empirical links between behavioural diversity and ecological outcomes, and the development of management approaches sensitive to behavioural diversity. More explicit consideration of behavioural diversity should improve our ability to predict fish behavioural diversity responses and to design conservation and management measures that account for variation rather than only average behavioural responses.

• Fernández-Chacón, Albert; Buttay, Lucie; Villegas-Ríos, David; Thorbjørnsen, Susanna Huneide & Olsen, Esben Moland (2026). Effects of protection on the spatial range of a long-lived harvested species. ICES Journal of Marine Science. ISSN 1054-3139. 83(9), p. 1–13. doi: 10.1093/icesjms/fsag172. Full text in Research Archive Show summary

  Abstract Marine protected areas (MPAs) are globally seen as useful tools to preserve marine biodiversity and restore depleted fisheries. However, high fishing pressure around MPAs could disfavour individuals with large home ranges crossing protected area borders and thereby cause a shift towards less mobile individuals within MPAs. Eventually, this could reduce the benefits of protected areas for both conservation (i.e. phenotypic diversity) and fisheries (i.e. spillover). Here, we tested whether MPAs select against highly mobile phenotypes of European lobster (Homarus gammarus) by using multi-year data (2006–2019) on captures and recaptures of 8020 tagged individuals collected at three MPA-fished area pairs along the Norwegian Skagerrak coast. By applying spatially explicit capture-recapture models to this dataset, we could estimate sigma, a model parameter that reflects the spatial range of the populations, and test for temporal, sex, and size-specific variation in sigma across populations. We found no general evidence that lobsters exhibited higher sigma values in fished areas than in MPAs, nor that spatial range consistently declined through time within protected areas. Although models including temporal variation in sigma performed better than time-constant models, significant declines through time were only statistically supported for male lobsters at one MPA. Furthermore, sex- and size-specific mobility patterns varied markedly among populations. Overall, while selection against mobility may occur in some protected populations, our results suggest that this is not a general consequence of MPA implementation and that the mechanisms regulating lobster spatial behaviour are likely context dependent.

• Rohtla, Mehis; Moland, Even; Thorstad, Eva Bonsak; Skiftesvik, Anne Berit; Bosgraaf, Sebastian & Olsen, Esben Moland [Show all 8 contributors for this article] (2026). Behaviour of European eel Anguilla anguilla transitioning from the yellow resident to the silver migratory stage in marine waters. Journal of Fish Biology. ISSN 0022-1112. doi: 10.1111/jfb.70564. Full text in Research Archive Show summary

  Current knowledge on the continental shelf and transatlantic spawning migration of the European eel (Anguilla anguilla) is based on silver eels outmigrating from fresh water. However, an unknown proportion of eels grow in marine coastal waters during the continental part of their lifecycle and therefore start their spawning migration while they are already in marine waters. To study the onset of the European eel's spawning migration in marine waters, we tagged yellow eels in Sandnesfjord, Norway. One hundred yellow and pre-migratory eels (stage FII or FIII) were tagged with acoustic transmitters in August, September or October in 2018–2019 and their subsequent movements were recorded within a hydrophone array until May 2023. Twenty-two eels left the fjord in a period spanning from early October to early December, which partly coincides with the usual downstream migratory period among European eels. These eels were never detected again and had thus presumably transitioned to the silver eel stage. This transition occurred from a few months to up to 3 years after tagging. In all silver eels, an increase in vertical and horizontal movements within the fjord preceded their exit from the fjord. This sudden increase in activity occurred only for a few days before they left the fjord in most individuals, but this period was as long as 1 month in other individuals. Five of the silver eels undertook migrations up to several kilometres to a tidal stream before leaving the fjord. Eel migration was largely nocturnal, independent of moon or tidal phase. We conclude that the relatively short migration season and individual migration duration within the fjord, combined with the absence of significant environmental, physiological or anthropogenic stressors, may contribute to higher survival rates during the continental phase of the spawning migration compared to eels that start their spawning migration from fresh water, but this needs to be investigated in future studies.

• Olsen, Esben Moland; Strøm, John Fredrik; Skjæraasen, Jon Egil; Meeren, Terje van der; Jorde, Per Erik & Johansen, Torild [Show all 10 contributors for this article] (2026). Intraspecific diversity in Atlantic cod Gadus morhua spatial ecology within subarctic fjords during the foraging season. Marine Ecology Progress Series. ISSN 0171-8630. 782, p. 1–11. doi: 10.3354/meps15087. Full text in Research Archive Show summary

  Intraspecific diversity in life histories and movement behaviour can buffer population dynamics of animals against environmental change and potentially improve the reliability of ecosystem services such as fisheries yields. We used a combination of acoustic telemetry and genetics to study the movement behaviour of 2 sympatric ecotypes of Atlantic cod Gadus morhua across a wide range of body sizes (N = 389, body lengths = 35-101 cm), during their foraging season (July-December) within 3 subarctic fjords in northern Norway. As expected, most tagged fish belonged to a coastal ecotype (93%). In addition, a migratory Northeast Arctic ecotype was also seen in all 3 fjords during the foraging season (7%). On average, individuals belonging to the Northeast Arctic ecotype used deeper locations in the fjords compared to the coastal ecotype. The 2 ecotypes behaved similarly in terms of horizontal and vertical movements. Larger individuals were typically detected at more locations (i.e. a higher horizontal movement activity) and greater depths, while smaller individuals on average had more extensive vertical movements. Females (N = 200) and males (N = 189) showed similar movement behaviours. Our findings imply that conservation measures, such as marine protected areas, should connect shallow and deep fjord habitats to effectively preserve Atlantic cod. Similarly, the biodiversity impact of anthropogenic pressures such as fishing and aquaculture will likely depend on their specific location within fjords

• Nickel, Anja K.; Espeland, Sigurd Heiberg; Campana, Steven E.; Olsen, Esben Moland & Ólafsdóttir, Guðbjörg Ásta (2026). Seasonal shifts and individual variation in juvenile Atlantic cod diel migration at nearshore nurseries. Marine Ecology Progress Series. ISSN 0171-8630. 778. doi: 10.3354/meps15056. Full text in Research Archive Show summary

  Diel migration (DM) is a common behavior among aquatic species, supporting optimal foraging, predator avoidance, and energy balance. While often perceived as uniform, DM patterns vary significantly across populations and individuals due to both intrinsic and extrinsic factors. We investigated diel horizontal migration in acoustically tagged juvenile Atlantic cod Gadus morhua in nearshore nurseries in Iceland and Norway, examining spatial, seasonal, and individual variation. By applying a novel method to estimate horizontal DM from acoustic telemetry data for individuals too small to carry depth-logging transmitters, we detected clear DM patterns when a distinct day-night cycle was present. In Iceland, fish consistently migrated nearshore at night and farther from land during the day. In contrast, Norwegian G. morhua displayed both typical and reverse DM patterns. During the Icelandic summer, when daylight was continuous, DM was not observed, and fish remained farther from shore. Migration timing at both sites aligned closely with seasonal changes in daylength, particularly with shifts in light levels at dawn and dusk, indicating that seasonal variation in DM is largely governed by photoperiod. While seasonal DM patterns were broadly consistent across sites and between individuals, variation in the tendency to migrate and migration direction between individuals suggests that intrinsic factors specifically influence finer-scale variation in DM. Understanding these dynamics is critical for predicting behavioral responses to shifting light regimes and habitat availability under climate-driven changes, including poleward range expansions.

• Johannesen, Edda; Ottersen, Geir; Berg, Florian; Bogstad, Bjarte; Dalpadado, Padmini & Denechaud, Côme [Show all 17 contributors for this article] (2026). The Abrupt and Persistent Decline in Recruitment Success in Northeast Arctic Cod: A Review of Probable Causes. Fish and Fisheries. ISSN 1467-2960. doi: 10.1111/faf.70074. Full text in Research Archive Show summary

  Most of the previously large cod stocks in the North Atlantic are depleted to very low levels. A notable exception has been the Northeast Arctic cod inhabiting the Barents Sea. This cod stock reached a record high level around 2013, but since then has declined sharply, with older fish being fished out and few new recruits entering the stock. More specifically, since 2006 the average recruitment at age 3 per unit spawning stock biomass has dropped to a very low level. Here we review recent literature and data to evaluate potential causes of poor recruitment. We find that in most years the large spawning stock was successful in producing offspring up to the 0-group stage, but the survival thereafter was reduced—leading to few recruits into the fishable stock. Evidence points to consequences of northwards shifts of spawning locations, reduced inflow of Calanus and density dependent factors influencing pre-recruit survival at times when the spawning stock was at a record high level. However, large uncertainties in the causes of recruitment failure remain at a time when the Barents Sea ecosystem is experiencing unprecedented warming. A precautionary measure to avoid further decline and potential stock collapse in the current situation is to lower fishing pressure and improve management by setting reference points based on the recent period with low productivity. Including demographic characteristics like age diversity as explicit management targets to ensure spatial and temporal spread in spawning should be a goal for future method development.

• Opdal, Anders Martin Frugård; Alix, Maud; Kjesbu, Olav Sigurd; Jørgensen, Christian; Langangen, Øystein Ole Gahr & Karlsen, Ørjan [Show all 11 contributors for this article] (2026). Despite temperature effects on gonad development, timing of spawning is remarkably flexible in Atlantic cod. ICES Journal of Marine Science. ISSN 1054-3139. 83(2), p. 1–12. doi: 10.1093/icesjms/fsag020. Full text in Research Archive Show summary

  At high latitudes, early life stage survival of fish is often associated with how spawning time relates to the timing of the spring bloom. With ocean warming, basic physiological rates of ectotherms, like fish, will speed up—including gonadal development rates, which dictate spawning time. Since warmer water is thought to influence the spring bloom timing differently than that of fish spawning time, the two may fall out of synchrony in the future. The precise mechanisms between temperature and gonadal development and spawning time have, however, been difficult to disentangle. Here, we take advantage of a series of independent laboratory experiments measuring individual oocyte development up to or near spawning for 153 Atlantic cod (Gadus morhua) kept between 3 and 12°C. From these data we derive a predictive, mechanistic equation for daily oocyte growth rate as a function of temperature and oocyte developmental status (diameter). The vitellogenic oocyte growth follows an accelerating pattern, and the model predicts that spawning can advance by up to 7 days per 1°C increase. Within-treatment variation is, however, of comparable magnitude to between-treatment temperature effects. The model was also tested in the field by back-calculating oocyte development of 82 fish (2018–2021) sampled at two locations along the Norwegian coast, using daily ambient temperatures from telemetry tags during vitellogenesis as model input. We find that Atlantic cod are able to initiate vitellogenesis over a period of several months in late summer and autumn, as well as regulate the oocyte development rate across a wide range of temperatures—both leading to significant phenotypic plasticity in spawning phenology.

• Hočevar, Sara; Perälä, Tommi; Olsen, Esben Moland; Falkenhaug, Tone; Naustvoll, Lars Johan & Kuparinen, Anna (2026). Intraspecific diversity in Atlantic cod drives divergent trophic cascades across a coastal food web. Canadian Journal of Fisheries and Aquatic Sciences. ISSN 0706-652X. 83, p. 1–11. doi: 10.1139/cjfas-2025-0195. Full text in Research Archive Show summary

  Intraspecific diversity can profoundly shape ecological interactions, yet its role within complex food webs remains challenging to quantify. We explored how eco-evolutionary divergence within Atlantic cod (Gadus morhua), specifically between the resident Fjord and migratory North Sea ecotypes, influences food web structure and function in a coastal marine ecosystem. Using key trait differences, including growth rate, age and size at maturation, reproductive investment, and ontogenetic dietary shifts, we parameterized an allometric trophic network model with empirical data from the Norwegian Skagerrak. The high-resolution network comprised 148 trophic guilds and 2054 feeding links, permitting resolution of ecotype-specific interactions. We found pronounced intraspecific divergence: North Sea cod reached higher trophic position earlier, exerting greater interspecific influence, whereas Fjord cod retained higher early-stage biomass, intensifying intraspecific competition between ecotypes. Together, these complementary roles indicate that variation within a single species can both dampen and amplify food web interactions across life stages, enhancing ecosystem connectivity, and triggering cascading ecological effects. To sustain this natural buffer, conservation and management must move beyond species-level metrics and actively protect intraspecific diversity.

• Skjæraasen, Jon Egil; Arechavala-Lopez, P.; Karlsen, Ørjan; Olsen, Esben Moland; Meager, Justin James & Nyqvist, Daniel [Show all 12 contributors for this article] (2026). Male Agonistic Behavior on Atlantic Cod Spawning Grounds. Ecology and Evolution. 16(4). doi: 10.1002/ece3.73316. Full text in Research Archive Show summary

  The mating system of the iconic Atlantic cod (Gadus morhua) has been described as a lek, a mating system where male–male agonistic interactions are expected. However, observing such behaviors directly in marine environments is challenging. So far, the evidence supporting the importance of agonistic interactions between males is mainly derived from laboratory studies with fish kept in close confinement, possibly elevating the observed levels and their perceived importance. In natural aquatic systems, agonistic interactions may be inferred from acoustic telemetry transmitters fitted with accelerometers, given that they are associated with high activity levels. A large telemetry dataset on Atlantic cod was collected during (i) a field study at two Western Norway spawning grounds from 2019 to 2024 and (ii) a close confinement net—pen study in 2019–2020. A total of 154 sexed mature Atlantic cod were tagged with acoustic transmitters fitted with accelerometers and depth sensors, yielding ~1.5 million accelerometer detections for subsequent activity analyses. In the net-pens, male cod showed much higher activity levels than females. Overall activity levels were reduced in the field, but male activity levels remained higher than those of females during the spawning period. A prominent feature of coastal cod spawning along the Norwegian coast is that males tend to dwell deeper than females. We therefore explored whether depth influenced activity patterns of males and females. This was indeed the case with males being more active than females at fish depths > 20 m and no sex-difference in activity levels closer to the surface (< 20 m depth). No sex difference in activity levels was found outside the spawning period. Our data suggest that male–male agonistic interactions, inferred from activity levels, are present on natural spawning grounds for Atlantic cod, albeit at reduced levels compared to levels exhibited in net–pen confinement. We hypothesize that the heightened activity levels of males compared to females when occupying deeper waters are related to their overall deeper distribution and territorial and agonistic behavior at these depths, agreeing with the lek description of the cod mating system.

• Gjelland, Karl Øystein; Strøm, John Fredrik; Olsen, Esben Moland; Baktoft, Henrik; Skjæraasen, Jon Egil & Johansen, Torild [Show all 11 contributors for this article] (2026). Precise positioning of Atlantic cod reveals size-dependent preferences for substrate and bathymetric terrain. Marine Ecology Progress Series. ISSN 0171-8630. 778. doi: 10.3354/meps15039. Full text in Research Archive Show summary

  Atlantic cod Gadus morhua is a keystone species in the North Atlantic and Barents Sea ecosystems. Coastal Atlantic cod stocks have declined in recent decades, raising concerns about their recovery. Knowledge about cod behaviour, ecology and habitat use is vital to a management that ensures better costal cod population resilience and recovery. In this study, we aimed to quantify seascape use by Atlantic cod, using 3-dimensional acoustic telemetry to track 82 coastal cod (35-118 cm) from April through September in a 20 km 2 subarctic Norwegian fjord. We calculated continuous swimming trajectories in individual Atlantic cod with high precision (~15 m) and combined this with high-resolution bottom substrate classification and bathymetric maps with derivatives such as terrain slope and bathymetric position index. Bedrock and mixed gravel/stone substrates were among the least available habitats in the fjord, yet small cod (<55 cm) spent the most time in these habitats and avoided substrates containing mud and/or sand. Large cod (>55 cm) spent the most time in association with mud and sandy substrate. Large cod used deeper fjord parts than small cod, with only 24% overlap between the average depth distributions of the 2 size groups. Small cod were associated with steeper terrain slopes. The combination of the precise tracking method, detailed bathymetry and high-resolution habitat mapping provided new understanding of the size-dependent habitat use by Atlantic cod, and may serve as an important tool for marine research as well as coastal planning and management.

• Stanley, R. R.E.; Abad-Uribarren, A.; Belackova, A.; Belgrano, A.; Bergström, U. & Boerder, K. [Show all 25 contributors for this article] (2025). Five key opportunities to enhance the effectiveness of area-based marine conservation. npj Ocean Sustainability. 4(1). doi: 10.1038/s44183-025-00172-z. Full text in Research Archive Show summary

  Abstract Effective area-based conservation is central in global efforts to reverse marine biodiversity loss and safeguard ecosystem functioning. Here, we identify five key opportunities to maximize conservation potential as nations progress towards the Convention on Biological Diversity’s 2030 area-based management targets. These include enhancing accountability, elevating conservation in spatial planning, implementing adaptive management, coordinating conservation efforts across scales, and reconciling design with expected outcomes. Addressing these collectively will advance global marine conservation and maximize its contributions to biodiversity protection and human society.

• Keeley, Nigel B.; Meier, Sonnich; Laroche, Olivier; Steiner, Konstanze; Bøhn, Thomas & Olsen, Esben Moland [Show all 8 contributors for this article] (2025). Connecting the dots: evidence of interactions between wild Atlantic cod Gadus morhua, the benthic environment and salmon farm discharges. Aquaculture Environment Interactions. ISSN 1869-215X. 17, p. 85–106. doi: 10.3354/aei00496. Full text in Research Archive Show summary

  Rapid expansion in coastal salmon farming has coincided with declines in coastal Atlantic cod Gadus morhua populations in Norway, raising suspicions over a causal relationship. One established effects pathway concerns the discharge of exogenous waste feed; however, food-web-related pathways remain poorly understood. Here we present a study conducted in 3 neighbouring fjords that are also important cod spawning areas, one of which has several active salmon farms. The study combines spatially explicit information on benthic ecology, cod stomach contents (via eDNA), dietary groups (via fatty acid profiling) and cod source-stock and demographics. Results confirmed that in addition to an anticipated fish diet, wild cod fed on a diverse array of benthic invertebrates, including shrimps, echinoderms, crabs, benthic worms and other infauna. Cod diets differed strongly with proximity to fish farms. Most (69%) cod caught adjacent to a farm had fatty acid trophic markers in their stomachs and/or livers consistent with a salmon pellet diet, and their stomachs contained benthic fauna that proliferate with organic enrichment. This trend was very localised, indicating a degree of residency and feeding specialisation or adaptability. When feeding off the bottom, cod are also likely to ingest contaminated sediments, which can (1) be toxic to marine life, (2) have a strongly altered microbiome and (3) contain known fish pathogens. We conclude that cod are influenced by farm-induced changes to food-web pathways, both in terms of the type and availability of suitable prey species and the composition of their tissues.

• Skjæraasen, Jon Egil; Karlsen, Ørjan & Olsen, Esben Moland (2025). Stability and spatial scale of Atlantic cod Gadus morhua communities within a network of coastal spawning grounds. Animal Biotelemetry. 13(1). doi: 10.1186/s40317-025-00423-3. Full text in Research Archive Show summary

  Background Knowledge about the spatial dynamics of fish populations, including social dynamics during the spawning season, is important for ensuring that fisheries management is rooted in ecology. Yet such detailed information about individual fish movement is hard to obtain and therefore typically lacking. Methods We applied network analyses to acoustic telemetry data to study movements and spatial associations of sexually mature Atlantic cod (Gadus morhua) in amid-Norway fjord complex. Cod were caught at five known spawning grounds, acoustically tagged, and released annually at these grounds during 2017–2019. Network analyses using community detection algorithms were then performed on bipartite network graphs for each spawning period (February–April) and feeding period (June–December) to identify spatial groupings or communities of the cod selected for analyses (ntotal = 352). Additionally, edge use, i.e. movement between receivers, was analysed for individual cod in the spawning and feeding periods. Results Spawning communities were typically dominated by cod captured and released locally, but commonly also contained fish from other grounds. A tendency for temporal and spatial stability in spawning communities was evident, with 67% of cod monitored over several spawning periods (n = 119) assigned to communities containing at least one common station across years. However, seven cod clearly utilized different spawning sites in different years. Cod detected during both the feeding and spawning period (n = 88) tended to have similar edge use during both periods, with said edge use increasing with fish size. However, eight cod showed either limited movement during spawning and much more extensive movements outside the spawning period or vice versa. Conclusions The network analyses revealed temporal and spatial stability in communities of mature cod during the spawning period. Notwithstanding this, some cod switched their spawning site locality within our regional study area between years. Individual cod tended to have similar edge use during the spawning and feeding periods, although there were examples of cod moving a lot during the spawning period and little outside this period and vice versa. Management should consider such networks of spawning grounds to preserve the intraspecific diversity of movements and the mating system of cod.

• Dornelas, Maria; Antão, Laura H.; Bates, Amanda E.; Brambilla, Viviana; Chase, Jonathan M. & Chow, Cher F. Y. [Show all 485 contributors for this article] (2025). BioTIME 2.0: Expanding and Improving a Database of Biodiversity Time Series. Global Ecology and Biogeography. ISSN 1466-822X. 34(5), p. 1–18. doi: 10.1111/geb.70003. Full text in Research Archive Show summary

  Motivation Here, we make available a second version of the BioTIME database, which compiles records of abundance estimates for species in sample events of ecological assemblages through time. The updated version expands version 1.0 of the database by doubling the number of studies and includes substantial additional curation to the taxonomic accuracy of the records, as well as the metadata. Moreover, we now provide an R package (BioTIMEr) to facilitate use of the database. Main Types of Variables Included The database is composed of one main data table containing the abundance records and 11 metadata tables. The data are organised in a hierarchy of scales where 11,989,233 records are nested in 1,603,067 sample events, from 553,253 sampling locations, which are nested in 708 studies. A study is defined as a sampling methodology applied to an assemblage for a minimum of 2 years. Spatial Location and Grain Sampling locations in BioTIME are distributed across the planet, including marine, terrestrial and freshwater realms. Spatial grain size and extent vary across studies depending on sampling methodology. We recommend gridding of sampling locations into areas of consistent size. Time Period and Grain The earliest time series in BioTIME start in 1874, and the most recent records are from 2023. Temporal grain and duration vary across studies. We recommend doing sample‐level rarefaction to ensure consistent sampling effort through time before calculating any diversity metric. Major Taxa and Level of Measurement The database includes any eukaryotic taxa, with a combined total of 56,400 taxa. Software Format csv and. SQL.

• Martorell‐Barceló, Martina; Abecasis, David; Akaarir, Mourad; Alonso‐Fernández, Alexandre; Arlinghaus, Robert & Aspillaga, Eneko [Show all 28 contributors for this article] (2025). Revealing Chronotypes Across Aquatic Species Using Acoustic Telemetry. Fish and Fisheries. ISSN 1467-2960. 26(6), p. 1134–1145. doi: 10.1111/faf.70022. Full text in Research Archive Show summary

  ABSTRACT Acoustic telemetry offers valuable opportunities to investigate individual variability in circadian‐related and other behaviours and how environmental cues shape these patterns in wild fish populations. However, this potential has not yet been fully exploited. We conducted a meta‐analysis on 44 datasets from 34 distinct marine and freshwater species and different types of data (acoustic detections, depth, acceleration and positioning). Our aim was to explore the potential of acoustic telemetry in identifying chronotypes as consistent among‐individual differences in circadian‐related behaviours. First, we applied hidden semi‐Markov models to classify individual time series into active and rest states. Subsequently, we computed two classical circadian‐related behavioural traits: awakening time (as the activity onset) and rest onset (as the activity offset). Subsequently, we identified distinct phenotypes by decomposing behavioural variation into within‐ and among‐individual components based on repeatability scores. We found evidence of distinct chronotypes in 17 species, with average repeatability scores of 0.52 for awakening time and 0.43 for rest onset, revealing that chronotypes are common in aquatic species. Our findings highlight that both the data type, particularly acceleration sensors, and the number of detections are effective tools for exploring chronotypes. Our study proposes a novel approach to characterising daily activity patterns in aquatic species, predominantly in fishes, and provides guidelines for investigating chronotypes across diverse taxa. We emphasise the promise of biotelemetry and advanced statistical models for improving our understanding of the behaviour of aquatic species and highlight the value of synthesising across large data sets collected in networks of biotelemetryprojects.

• Olsen, Esben Moland & Strand, Hans Kristian (2025). Conservation translocation of Atlantic wolffish (Anarhichas lupus) to a depleted Arctic fjord ecosystem. Canadian Journal of Fisheries and Aquatic Sciences. ISSN 0706-652X. 82, p. 1–10. doi: 10.1139/cjfas-2024-0253. Full text in Research Archive Show summary

  Predators have important functional roles in coastal ecosystems. In cases where such species are locally depleted or extirpated, a proactive restoration strategy may include conservation translocation. This study reports on such translocations of Atlantic wolffish (Anarhichas lupus) to fjord habitats in northern Norway where the species is currently severely depleted. A total of 20 pioneer individuals measuring 42–80 cm in length were captured in outer coastal habitats and subsequently tagged, released, and tracked within a fjord using acoustic telemetry. A first group of seven individuals were monitored for 14 months during 2017 and 2018, while a second group of 13 individuals were monitored for 4 months during 2019. Up to 40% of translocated wolffish remained inside their new fjord environment until the study was terminated, while the remaining 60% likely dispersed. Weekly home range size decreased substantially with time for larger fish, while this trend was weaker for smaller fish. Our study implies that there is reason for cautious optimism regarding the implementation of conservation translocation of wolffish in coastal ecosystems, while acknowledging the challenge of accounting for animal dispersal in aquatic systems.

• McQueen, Kate; Sivle, Lise Doksæter; Khodabandeloo, Babak; Skjæraasen, Jon Egil; Olsen, Esben Moland & Karlsen, Ørjan (2025). Free-ranging Atlantic cod did not change their behaviour in response to a sparker seismic sound source. Marine Environmental Research. ISSN 0141-1136. 210. doi: 10.1016/j.marenvres.2025.107254. Full text in Research Archive Show summary

  Sparkers are seismic sources commonly used to survey the seabed in areas planned for offshore wind farms. The almost continuous sounds produced by sparkers, with most energy in the frequency range 50Hz - 4 kHz, are audible to both fish and marine mammals and may cause disturbance and behavioural reactions. Here, we conducted a sparker exposure experiment with wild, free-ranging, tagged Atlantic cod (Gadus morhua). The fish were exposed to sound from a real sparker, experiencing varying sound exposure levels up to 130 dB re 1μPa2s over 10 s. During a 40 h exposure period, we used a randomised block design with three source levels, where the highest was as used in normal sparker operations with this source (800 J). The movement behaviours of cod were monitored using acoustic telemetry. Only one tagged cod left the test site during the exposure. The remaining tagged cod (n = 11) neither changed their location within the test site, nor did we detect any changes in swimming depth, activity levels or displacement attributable to the exposure. Although the sample size and number of replicates in this study were limited, these results indicate that the relatively low sound levels produced by a sparker source do not greatly disturb cod during the feeding season.

• Bøhn, Thomas; Strøm, John Fredrik; Sanchez-Jerez, Pablo; Keeley, Nigel B.; Johansen, Torild & Gjelland, Karl Øystein [Show all 14 contributors for this article] (2024). Ecological interactions between farmed Atlantic salmon and wild Atlantic cod populations in Norway: A review of risk sources and knowledge gaps. Reviews in Aquaculture. ISSN 1753-5123. 16(3), p. 1333–1350. doi: 10.1111/raq.12899. Full text in Research Archive Show summary

  Aquaculture provides an important and expanding source of protein rich and healthy food to the world. However, to minimize environmental harm from aquaculture, interactions with wild fish communities need to be thoroughly assessed. Here, we characterize the existing knowledge pertaining to such interactions, exemplified with Atlantic salmon (Salmo salar) farming in open net pens along the Norwegian coast and potential consequences for wild Atlantic cod (Gadus morhua) populations. Importantly, the wild cod fishery also provides a protein rich, high quality food source with high economic value. We identify seven risk sources that may affect behaviour, physiology, and survival in wild cod. Of particular importance is the large amount of waste feed that causes wild fish to aggregate around farms, thereby altering a multitude of ecological interactions including predation and disease transmission. Moreover, altered food quality in pellets may alter physiological processes and cause mortality to vulnerable life-stages in wild cod. More research is needed on mechanisms and thresholds for harm. As the most important cod fisheries are found in northern Norway, where climate change also is rapid, we expect stronger and potentially more harmful interactions between fish farming and wild cod fisheries as aquaculture continues to expand. We hope that our analysis will inspire further research, on farmed salmon and wild cod interactions, but also on aquaculture and wild fish interactions in general. Such research is fundamental for the development of management systems that can reduce the impact of aquaculture on fisheries and the environment.

• Skjæraasen, Jon Egil; Olsen, Esben Moland; McQueen, Kate; Nyqvist, Daniel; Meager, Justin James & Karlsen, Ørjan [Show all 7 contributors for this article] (2024). Sex-specific vertical movements of spawning atlantic cod in coastal habitats inferred from acoustic telemetry. Scientific Reports. 14(1), p. 23242–23242. doi: 10.1038/s41598-024-74896-2. Full text in Research Archive Show summary

  Fish spawning location and behaviour can be challenging to detect, especially in deep water. Here we utilise two large acoustic telemetry datasets from western and mid Norway to study the vertical movement dimension of individual Atlantic cod Gadus morhua spawning behaviour in their natural habitats. The datasets comprise ~ 6 million depth detections from 644 sexed, mature cod, collected at seven different Norwegian coastal cod spawning grounds during 2017–2021. During the spawning period, females were typically found at shallower depths compared to males, while this pattern was much less pronounced or absent outside this period. Furthermore, we identify a hitherto undescribed sex-dependent vertical movement behaviour: periodic descents, where females made deep dives, putatively associated with egg release and spawning, approximately every third day. Females not showing this behaviour tended to occupy deeper positions in the water column than the “periodic descent” females and hence may approach and retreat from spawning males more horizontally. These observed sex-specific behaviours correspond well to the lek-like description of the cod mating system and with cod reproductive physiology, where females are known to mature and release batches of eggs at intervals of several days as part of a bet-hedging strategy.

• Olsen, Esben Moland; Hutchings, Jeffrey; Rogers, Lauren; Stenseth, Nils Christian & Vøllestad, Leif Asbjørn (2024). Plasticity and Evolution in Atlantic Cod Populations during Climate Change. In Kulatska, Nataliia; Howell, Daniel; Wright, Peter J. & Jonsdottir, Ingibjörg G. (Ed.), Biology and Ecology of Atlantic Cod. CRC Press. ISSN 9781003120872. p. 1–21. doi: 10.1201/9781003120872. Full text in Research Archive Show summary

  It is increasingly recognised that ecology and evolution may interact on contemporary time scales and result in ongoing eco-evolutionary dynamics at population- community- and ecosystem levels. Therefore, an eco-evolutionary perspective is needed to better understand how fish populations may respond to ongoing and future climate change. This chapter highlights research on the impact of climate warming on population dynamics, life history and behaviour of Atlantic cod (Gadus morhua), specifically making the case of integrating ecological and evolutionary perspectives for understanding local adaptations and broader responses to climate change. The chapter focuses particularly on the interactions between genotypes and the environment, a reflection of phenotypic plasticity that can be graphically described as a reaction norm. With some exceptions, fish tend to be highly plastic, meaning that the phenotype being expressed by an individual will depend on the environment that it experiences during its lifetime, and potentially that experienced by its parents. Understanding the mechanisms and constraints related to such plasticity is therefore relevant for studies on the effects of climate change.

• Ohayon, Sarah; Abecasis, David; Almeida, Pedro R.; Alós, Josep; Aspillaga, Eneko & Belo, Ana Filipa [Show all 21 contributors for this article] (2024). Fully protected marine areas linked to reduced home ranges of fishes. Fish and Fisheries. ISSN 1467-2960. 25(6), p. 985–996. doi: 10.1111/faf.12859. Full text in Research Archive Show summary

  Home range size is a fundamental trait that can affect the probability of fish being harvested and, at the same time, may be affected by fishing. The relationship between home range size and fishing will impact the effectiveness of fully protected areas (FPAs), as it will influence the number of fish moving into fished areas, affecting both spillover and edge effects. One hypothesis is that individuals within FPAs will present reduced home range size relative to individuals in fished areas. This pattern can be driven by demographic selection (e.g. fishing of individuals with large home ranges leaving the FPAs), improved habitat requiring less foraging movements, or behavioural changes associated with reduced fishing threats. To test the relationship between home range size and protection, we compiled 1143 individual-level home range sizes based on acoustic tracking, covering 17 species from 11 FPAs in 7 countries, with information on distance from FPA borders. A dichotomic analysis (in/out of FPAs) did not support a significant change in the home range size between FPAs and fished areas. However, continuous analysis across the FPA borders demonstrated reduced home range size within the FPAs. We did not find an effect of FPA age or size on this pattern. While we cannot pinpoint the underlying mechanism for the pattern revealed, we suggest behavioural changes as the main driver for reduced home range within FPAs. This mechanism will lead to more resident populations within FPAs, reducing fishing mortality within FPAs yet limiting spillover benefits to adjacent fisheries.

• Poulton, Anna J.; Villegas-Ríos, David; Freitas, Carla; Moland, Even; Olsen, Esben Moland & Sethi, Suresh A. [Show all 7 contributors for this article] (2024). Bayesian estimation of spatially varying mortality risk using tagged animal data. Methods in Ecology and Evolution. 15(11), p. 2101–2117. doi: 10.1111/2041-210X.14428. Full text in Research Archive Show summary

  The survival of animals is impacted by landscapes of spatially varying mortality factors including habitat type, predation risk or harvest risk, among others. Characterization of these spatial mortality processes is important for managing animal populations and their habitats, yet this information has proved challenging to capture. Advances in telemetry now make it possible to monitor tagged individuals' locations through time for a wide range of taxa, providing opportunity to assess movement and mortality simultaneously through spatial time-to-event data. Existing time-to-event modelling frameworks have largely ignored spatially varying mortality processes or have treated an animal's location as fixed at a regional level. Here we present a general spatial survival model for analysing time-to-event data arising from animal telemetry. Our model has a flexible Cox regression form and can estimate the effects of conventional non-spatial risk factors (size, seasonality, etc.), spatial covariates (e.g. habitat type) and spatial variation in risk not explained by covariates on mortality. We show how to fit our model using Bayesian methods and demonstrate applications of our model with several simulated examples and two animal telemetry case studies. Our model produced consistent and unbiased parameter estimates throughout simulations with a variety of spatial and non-spatial hazards. In the first case study, data from 147 tagged caribou in British Columbia, Canada, revealed a spatially heterogeneous mortality landscape with caribou survival varying by elevation, likely in response to space use by predators. Our second case study involved a dataset of 390 acoustically tagged Atlantic cod in a southern Norwegian fjord where a marine protected area (MPA) was established during the study. We found that the MPA led to a shift from mostly fishing mortality to mostly natural mortality within the fjord and that these risks had markedly different spatial hazard patterns. Our spatial time-to-event model can make use of data from a variety of widely used telemetry technologies to characterize landscapes of mortality risks for different taxa. Our work provides new opportunities to inform the spatial ecology and management of fish and wildlife populations.

• Koeck, Barbara; Olsen, Esben Moland; Závorka, Libor; Crespel, Amélie; Freitas, Carla & Enberg, Katja [Show all 11 contributors for this article] (2024). Conservation benefits of marine reserves depend on knowledge integration of genotypic and phenotypic diversity. Biological Conservation. ISSN 0006-3207. 299. doi: 10.1016/j.biocon.2024.110831. Full text in Research Archive Show summary

  Conserving intraspecific trait variation is vital for maintaining the viability of species. It ensures a species to adapt to warming and increasingly stochastic environments, and to recover following extreme events. Here we investigate the selective effects of spatial management on intraspecific genetic and phenotypic variation of two sympatric but genetically distinct Atlantic cod ecotypes in a Norwegian fjord. We found that phenotypic differences between sympatric cod genotypes were mainly driven by morphological and metabolic traits. Offshore cod had higher metabolic maintenance costs at cool temperatures but lower aerobic capacity at warm acclimation than coastal ecotypes, indicative of thermal constraint of aerobic physiological processes beyond metabolic maintenance. Offshore cod also had larger and thicker peduncles and better body condition. We found that protection benefits from the no-take zone (NTZ) of the Tvedestrand marine protected area were independent of individual space-use size, but instead resulted from ecotype-specific differences in habitat occupation. Results specifically show that the current delimitations of the NTZ do not cover habitats occupied by the coastal and highly resident cod ecotype which shows greater metabolic thermal tolerance but is considered to already be in a depleted state. Our study exemplifies why protecting intraspecific diversity is directly relevant for management implementations aimed at reducing the impact of further selection pressures such as ongoing environmental change. Careful investigation of intraspecific diversity and integration of such knowledge to fisheries management and design of protected areas may prevent unwanted additional selective pressures and contribute to offer broad protection to genotypes and phenotypes.

• McQueen, Kate; Sivle, Lise Doksæter; Forland, Tonje Nesse; Meager, Justin James; Skjæraasen, Jon Egil & Olsen, Esben Moland [Show all 9 contributors for this article] (2024). Continuous sound from a marine vibrator causes behavioural responses of free-ranging, spawning Atlantic cod (Gadus morhua). Environmental Pollution (1987). ISSN 0269-7491. 344. doi: 10.1016/j.envpol.2024.123322. Full text in Research Archive Show summary

  Marine vibrators are a new technology being developed for seismic surveys. These devices can transmit continuous instead of impulsive sound and operate over a narrower frequency band and at lower peak pressure than airguns, which is assumed to reduce their environmental impacts. We exposed spawning Atlantic cod (Gadus morhua) to sound produced by a prototype, but full-scale, marine vibrator, and monitored behavioural responses of tagged cod using acoustic telemetry. Fish were exposed to 10 × 3 h continuous sound treatments over a 4-day period using a randomised-block design. Sound exposure levels were comparable to airgun exposure experiments conducted previously with the same set-up ranging from ∼115 to 145 dB re 1 μPa2s during exposure. Telemetry data were used to assess 1) whether marine vibrator exposure displaced cod from the spawning ground, through estimation of residence and survival probabilities, and 2) fine-scale behavioural responses within the test site, namely swimming depth, activity levels, displacement, and home ranges. Forty-two spawning cod were tagged prior to the exposure, with 22 present during the exposure. All 22 tags were equipped with pressure sensors and ten of these additionally with accelerometers. While no premature departure from the spawning site was observed, cod reacted to the exposure by decreasing their activity levels (by up to 50%, SE = 7%) and increasing their swimming depth (by up to 2.5 m, SE = 1.0 m) within the test site during the exposure period. These behavioural responses varied by sex and time of day. Cod reactions to a marine vibrator may be more pronounced than reactions to airguns, possibly because continuous sound is more disturbing to fish than intermittent sound at the same exposure levels. However, given sample size limitations of the present study, further studies with continuous sound are necessary to fully understand its impact and biological significance.

• Varnes, Bjørg Karin & Olsen, Esben Moland (2023). Fish community dynamics in a coastal no-take marine protected area compared to a harvested area before and after protection from fishing. ICES Journal of Marine Science. ISSN 1054-3139. 80(5), p. 1462–1471. doi: 10.1093/icesjms/fsad074. Full text in Research Archive Show summary

  An ecosystem's ability to maintain key functions during environmental change is largely determined by its biodiversity. We compared fish species composition, richness, diversity, catch per unit effort (CPUE), and fish size between a 1.5 km2 no-take marine protected area (MPA) and a nearby fished area on the southern Norwegian coast annually for one decade (2011–2021), including before-protection status. In total, >26 thousand fish representing 31 species were sampled using a beach seine. No significant effect of protection was detected on either species richness, diversity, or evenness. For selected species of small-bodied intermediate predators, there was a significant decline in mean body size in the MPA area compared to the fished area, indicative of a response to protection involving trophic interactions. No significant effect of the MPA was detected on either CPUE or body size of Atlantic cod (Gadus morhua), a top predator mainly captured at the juvenile stage by our sampling. The limited responses seen in this study may be linked to the small size of the MPA compared to the dispersal and movement capabilities of species such as the cod.

• Olsen, Esben Moland; Karlsen, Ørjan & Skjæraasen, Jon Egil (2023). Large females connect Atlantic cod spawning sites. Science. ISSN 0036-8075. 382(6675), p. 1181–1184. doi: 10.1126/science.adi1826. Full text in Research Archive
• Monk, Christopher; Power, Michael; Freitas, Carla; Harrison, Philip M.; Heupel, Michelle & Kuparinen, Anna [Show all 10 contributors for this article] (2023). Atlantic cod individual spatial behaviour and stable isotope associations in a no-take marine reserve. Journal of Animal Ecology. ISSN 0021-8790. 92(12), p. 2333–2347. doi: 10.1111/1365-2656.14014. Full text in Research Archive Show summary

  Foraging is a behavioural process and, therefore, individual behaviour and diet are theorized to covary. However, few comparisons of individual behaviour type and diet exist in the wild. We tested whether behaviour type and diet covary in a protected population of Atlantic cod, Gadus morhua. Working in a no-take marine reserve, we could collect data on natural behavioural variation and diet choice with minimal anthropogenic disturbance. We inferred behaviour using acoustic telemetry and diet from stable isotope compositions (expressed as δ13C and δ15N values). We further investigated whether behaviour and diet could have survival costs. We found cod with shorter diel vertical migration distances fed at higher trophic levels. Cod δ13C and δ15N values scaled positively with body size. Neither behaviour nor diet predicted survival, indicating phenotypic diversity is maintained without survival costs for cod in a protected ecosystem. The links between diet and diel vertical migration highlight that future work is needed to understand whether the shifts in this behaviour during environmental change (e.g. fishing or climate), could lead to trophic cascades.

• Durif, Caroline; Arts, M.; Bertolini, F.; Cresci, Alessandro; Daverat, F. & Karlsbakk, Egil Erlingsson [Show all 16 contributors for this article] (2023). The evolving story of catadromy in the European eel (Anguilla anguilla). ICES Journal of Marine Science. ISSN 1054-3139. 80(9), p. 2253–2265. doi: 10.1093/icesjms/fsad149. Full text in Research Archive Show summary

  Anguillid eels were once considered to be the classic example of catadromy. However, alternative life cycles have been reported, including skipping the freshwater phase and habitat shifting between fresh, brackish, and saltwater throughout the growth phase. There is a lack of knowledge regarding these alternate life strategies, for example, the proportion of individuals in the population that adopt them compared to classic catadromy. We provide a description of these alternate life cycle strategies in temperate anguillids, their possible drivers, and the methods available to investigate them. These methods (lethal and non-lethal), include otolith microchemistry, fatty acid and stable isotope analyses, parasite identification, blood transcriptomics, and electronic tags. We argue that since the current management framework for the European eel and other temperate eels is based mainly on the freshwater component of the population, it ignores eels growing in saline waters. Many of the factors that are thought to be responsible for the precipitous decline of the eel population are more prevalent in freshwater systems. Therefore, the contribution of saline eels may be more important than currently estimated. The habitat-shifting ability of eels may be all the more crucial for the persistence and recovery of those species that are endangered.

• Strøm, John Fredrik; Bøhn, Thomas; Skjæraasen, Jon Egil; Gjelland, Karl Øystein; Karlsen, Ørjan & Johansen, Torild [Show all 9 contributors for this article] (2023). Movement diversity and partial sympatry of coastal and Northeast Arctic cod ecotypes at high latitudes. Journal of Animal Ecology. ISSN 0021-8790. 92(10), p. 1966–1978. doi: 10.1111/1365-2656.13989. Full text in Research Archive Show summary

  Movement diversity within species represent an important but often neglected, component of biodiversity that affects ecological and genetic interactions, as well as the productivity of exploited systems. By combining individual tracking data from acoustic telemetry with novel genetic analyses, we describe the movement diversity of two Atlantic cod Gadus morhua ecotypes in two high-latitude fjord systems: the highly migratory Northeast Arctic cod (NEA cod) that supports the largest cod fishery in the world, and the more sedentary Norwegian coastal cod, which is currently in a depleted state. As predicted, coastal cod displayed a higher level of fjord residency than NEA cod. Of the cod tagged during the spawning season, NEA cod left the fjords permanently to a greater extent and earlier compared to coastal cod, which to a greater extent remained resident and left the fjords temporarily. Despite this overall pattern, horizontal movements atypical for the ecotypes were common with some NEA cod remaining within the fjords year-round and some coastal cod displaying a low fjord fidelity. Fjord residency and exit timing also differed with spawning status and body size, with spawning cod and large individuals tagged during the feeding season more prone to leave the fjords and earlier than non-spawning and smaller individuals. While our results confirm a lower fjord dependency for NEA cod, they highlight a movement diversity within each ecotype and sympatric residency between ecotypes, previously undetected by population-level monitoring. This new knowledge is relevant for the management, which should base their fisheries advice for these interacting ecotypes on their habitat use and seasonal movements.

• Synnes, Ann-Elin; Olsen, Esben Moland; Jorde, Per Erik; Knutsen, Halvor & Moland, Even (2023). Contrasting management regimes indicative of mesopredator release in temperate coastal fish assemblages. Ecology and Evolution. 13(12). doi: 10.1002/ece3.10745. Full text in Research Archive Show summary

  The absence of functional top predators has been proposed as a mechanism acting to shape fish assemblages in temperate marine ecosystems, with cascading effects on lower trophic levels. We explore this scenario by comparing the trophic and functional status of fish assemblages in Norwegian marine national parks, open to fishing, to a nearby coastal seascape that harbors a system of marine protected areas (MPAs) including a no-take zone. Demersal fish assemblages were sampled using fyke nets over three consecutive seasons. Atlantic cod (Gadus morhua) is potentially a dominant top predator in this ecosystem, and historically, this and other gadids have been targeted by the full range of former and present fisheries. In the present study, we find that average body size of the Atlantic cod was significantly larger in the zoned seascape compared to the unprotected areas (mean ± SD: 36.6 cm ± 14.38 vs. 23.4 ± 7.50; p < .001) and that the unprotected seascape was characterized by a higher abundance of mesopredator fish species. These observations are consistent with the hypothesis that the protection of top predators within MPAs aids to control the mesopredator populations and provides empirical support to the notion that the present state of many coastal fish assemblages is driven by mesopredator release linked to functional depletion of large top predators.

• McQueen, Kate; Skjæraasen, Jon Egil; Nyqvist, D; Olsen, Esben Moland; Karlsen, Ørjan & Meager, Justin James [Show all 11 contributors for this article] (2023). Behavioural responses of wild, spawning Atlantic cod (Gadus morhua L.) to seismic airgun exposure. ICES Journal of Marine Science. ISSN 1054-3139. 80(4). doi: 10.1093/icesjms/fsad032. Full text in Research Archive Show summary

  Seismic airgun surveys to map petroleum deposits in the seabed may impact behaviour of marine animals over large distances. Understandingwhether fish spawning behaviour is affected by this anthropogenic noise source is important because reproductive success may be impacted.The fine-scale behavioural responses of Atlantic cod to airgun exposure over an extended period were investigated using an acoustic telemetrypositioning system on a spawning ground in Norway. During 2019 to 2021, 135 spawning cod were equipped with telemetry sensor tags andwere exposed to airgun shooting during the spawning periods of 2020 and 2021, with varying received sound levels comparable to a full-scalesurvey at distances of 5 to >40 km. Cod demonstrated only weak responses to the disturbance from repeated 3-h treatment periods over 5-d,swimming on average slightly deeper during seismic exposure compared to silent control periods. This response varied between individuals.Longer-term effects of seismic exposure on swimming depth were not detected. No changes in swimming acceleration, displacement, or areause occurred. These results suggest that relatively distant seismic surveys do not substantially alter cod behaviour during the spawning periodat received sound exposure levels varying between 115 and 145 dB re 1 μPa2s over a 5-d period.

• Skjæraasen, Jon Egil; Karlsen, Ørjan; Langangen, Øystein Ole Gahr; Meier, Sonnich; Dunlop, Katherine Mary & Meeren, Terje van der [Show all 14 contributors for this article] (2022). Attraction of cod Gadus morhua from coastal spawning grounds to salmon farms. Aquaculture Environment Interactions. ISSN 1869-215X. 14, p. 229–242. doi: 10.3354/aei00440. Full text in Research Archive Show summary

  Wild fish aggregate at aquaculture net-pens, but the underlying mechanisms are not fully understood. This study examined how salmon farms attract coastal Atlantic cod Gadus morhua from their inshore spawning grounds. Acoustic receivers were deployed at 5 known cod spawning grounds and 6 salmon Salmo salar farms located at varying distances from these grounds in a mid-Norway study site. Cod were caught at each spawning ground annually from 2017-2019, fitted with acoustic transmitters and released (n = 535). A total of 289 tagged cod (54%) were detected at the salmon farms, with more cod detected at farms closest to the focal spawning grounds and at operational farms. The latter result is likely linked to the availability of feeding opportunities at farm locations. Those cod that were detected by the receivers spent less time at farms farther from their release locations. For the farm-associated cod, 70% were detected for <1 wk at the farms. However, 48 cod spent >1 mo close to the farms, with 1 individual staying 720 d underneath the farm. A total of 135 cod visited 2 or more farms, with farms in proximity more connected in terms of inter-farm movement. Some of the cod utilizing these local spawning grounds likely have considerable dietary input from salmon feed.

• Villegas-Ríos, David; Freitas, Carla; Moland, Even & Olsen, Esben Moland (2022). Eco-evolutionary dynamics of Atlantic cod spatial behavior maintained after the implementation of a marine reserve. Evolutionary Applications. doi: 10.1111/eva.13483. Full text in Research Archive Show summary

  The effects of marine reserves on the life history and demography of the protected populations are well-established, typically increasing population density and body size. However, little is known about how marine reserves may alter the behavior of the populations that are the target of protection. In theory, marine reserves can relax selection on spatial behavioral phenotypes that were previously targeted by the fishery and also drive selection in favor of less mobile individuals. In this study, we used acoustic telemetry to monitor the individual spatial behavior of 566 Atlantic cod (Gadus morhua Linnaeus, 1758) moving within a marine reserve and a control site in southern Norway, starting 1 year before the implementation of the marine reserve and lasting up to 9 years after. Following a before-after-control-impact approach, we investigated changes in (1) survival, (2) selection acting on behavioral traits, and (3) mean behavioral phenotypes, after the implementation of the marine reserve. We focused on three behavioral traits commonly used to describe the mobility of aquatic animals: home range size, depth position, and diel vertical migration range. Survival increased after reserve implementation, but contrary to our expectations, it subsequently decreased to preprotection levels after just 3 years. Further, we found no significance in selection patterns acting on any of the three behavioral traits after reserve implementation. Although some changes related to water column use (the tendency to occupy deeper waters) were observed in the marine reserve after 9 years, they cannot unequivocally be attributed to protection. Our results show that survival and behavioral responses to marine reserves in some cases may be more complex than previously anticipated and highlight the need for appropriately scaled management experiments and more integrated approaches to understand the effects of marine protected areas on harvested aquatic species.

• Johansen, Kurt; Olsen, Esben Moland; Haraldstad, Tormod; Arlinghaus, Robert & Höglund, Erik (2022). Digital Data Help Explain Drivers of Angler Satisfaction: An Example from Southern Norway. North American Journal of Fisheries Management. ISSN 0275-5947. 42(5), p. 1165–1172. doi: 10.1002/nafm.10810. Full text in Research Archive Show summary

  We analyzed trip-level self-reports collected by a cell phone app to understand angler satisfaction of fishing for sea trout Salmo trutta (anadromous Brown Trout) in southern Norway. We found no clear support for a positive relationship between trip outcome (catch or no catch) and angler satisfaction level. In the cases where sea trout was caught, however, there was a positive relationship between fish size and angler satisfaction level. A total of 52% of the captured sea trout were voluntarily released, and releases were unrelated to fish size. In conclusion, digital data collected via a cell phone app are useful to reveal patterns of angler behavior and satisfaction.

• Haraldstad, Tormod; Forseth, Torbjørn; Olsen, Esben Moland; Haugen, Thrond Oddvar & Höglund, Erik (2022). Empirical support for sequential imprinting during downstream migration in Atlantic salmon (Salmo salar) smolts. Scientific Reports. 12. doi: 10.1038/s41598-022-17690-2. Full text in Research Archive Show summary

  The precise homing of Atlantic salmon to their natal river and spawning grounds is the foundation for locally adapted genetically differentiated populations across rivers or across river sections. A sequential imprinting hypothesis states that salmon smolts may imprint on environmental clues along the outward migration route and then use this in reverse order to direct the spawning migration later in life. In this study, we provide empirical support for this hypothesis. PIT-tagged wild Atlantic salmon using a 2 km hydropower tunnel as downstream migrating smolts had a 18% (1SW) and 23% (2SW) lower probability of successfully migrating through the parallel river stretch as adult spawners compared to spawners that migrated through the same river stretch as smolts. These findings highlight how a fine-scale riverine migration route may be imprinted in wild Atlantic salmon smolts. From an applied perspective, these results stress the importance of not depriving smolts from parts of their migration route to ensure successful return of adults to their natal spawning grounds.

• Rohtla, Mehis; Moland, Even; Skiftesvik, Anne Berit; Thorstad, Eva Bonsak; Bosgraaf, Sebastian & Olsen, Esben Moland [Show all 8 contributors for this article] (2022). Overwintering behaviour of yellow-stage European eel (Anguilla anguilla) in a natural marine fjord system. Estuarine, Coastal and Shelf Science. ISSN 0272-7714. 276. doi: 10.1016/j.ecss.2022.108016. Full text in Research Archive Show summary

  Like many animals, northern temperate eel can enter a hibernation-like state and become dormant during the winter. Knowledge of overwintering behaviour in eel is sparse and mainly based on anecdotal observations and a few experimental studies on thermal tolerance. We studied European eel (Anguilla anguilla) overwintering behaviour in a Skagerrak fjord in Southern Norway, during three consecutive years, using an array of acoustic receivers and acoustic tags with depth and temperature sensors. We obtained results from 55 yellow eel, of which 19 were studied for one winter, 35 for two winters and one for three winters. Dormancy was inferred to begin in September for the earliest individuals and lasted until May for the last, with the majority of eel dormant from at least late October–November until mid-April. The timing of dormancy was mainly related to photoperiod and less to temperature. More than 50% of eel became dormant when day length was <9 h and became active when day length was >14 h. Approximately 10% of eel remained active during the winter and 31% of eel changed their pattern between consecutive years. Some dormant individuals exhibited activity periods that interrupted their dormancy. Eel in the outer fjord nearer the open sea became dormant before eel in the inner more freshwater part of the fjord, and were dormant longer. Acoustic telemetry Overwintering North sea Winter ecology Dormancy Photoperiod

• Knutsen, Jan Atle; Kleiven, Alf Ring; Olsen, Esben Moland; Knutsen, Halvor; Espeland, Sigurd Heiberg & Sørdalen, Tonje Knutsen [Show all 15 contributors for this article] (2022). Lobster reserves as a management tool in coastal waters: Two decades of experience in Norway. Marine Policy. ISSN 0308-597X. 136. doi: 10.1016/j.marpol.2021.104908. Full text in Research Archive Show summary

  The positive effects of reduced fishing pressure in marine protected areas (MPAs) are now well documented globally. Yet, evidence of MPA benefits from long-term replicated before-after control-impact (BACI) studies and their usefulness in protecting target species are still rare, especially in northern temperate areas. Scientific rigor in the monitoring of MPAs is considered important for obtaining trust and compliance and can increase interest and enthusiasm for the benefits of marine conservation. Off the coast of southern Norway, a MPA imple- mentation process started up in 2002. Based on comprehensive consultations with local fishers and managers, four experimental lobster reserves were appointed in 2004. Two years later (2006), the reserves came into effect as the Norwegian Directorate of Fisheries implemented regulations as a by-law of the Saltwater Fisheries Act that effectively banned all fixed gear. Long-term monitoring of the MPAs and adjacent control areas has enabled a rigorous scientific evaluation of the effects of these MPAs on lobster populations, including effects on density, growth, demography, behavior, and phenotypic diversity. As protection effects started to manifest, the lobster reserves attracted high public attention and were soon considered a credible supplement to traditional fisheries management. In the period from 2002 to 2021, more than 50 lobster reserves have been implemented in Norway. Here, we review the experiences since the lobster reserves were designated, implemented, and embraced by local communities in Norway, and over two decades have become an important tool for fishery management. Thoughts on the future of MPAs along the coast of Norway are discussed.

• Sodeland, Marte; Jentoft, Sissel; Jorde, Per Erik; Mattingsdal, Morten; Albretsen, Jon & Kleiven, Alf Ring [Show all 12 contributors for this article] (2022). Stabilizing selection on Atlantic cod supergenes through a millennium of extensive exploitation. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 119(8). doi: 10.1073/pnas.2114904119. Full text in Research Archive Show summary

  Life on Earth has been characterized by recurring cycles of ecological stasis and disruption, relating biological eras to geological and climatic transitions through the history of our planet. Due to the increasing degree of ecological abruption caused by human influences many advocate that we now have entered the geological era of the Anthropocene, or “the age of man.” Considering the ongoing mass extinction and ecosystem reshuffling observed worldwide, a better understanding of the drivers of ecological stasis will be a requisite for identifying routes of intervention and mitigation. Ecosystem stability may rely on one or a few keystone species, and the loss of such species could potentially have detrimental effects. The Atlantic cod (Gadus morhua) has historically been highly abundant and is considered a keystone species in ecosystems of the northern Atlantic Ocean. Collapses of cod stocks have been observed on both sides of the Atlantic and reported to have detrimental effects that include vast ecosystem reshuffling. By whole-genome resequencing we demonstrate that stabilizing selection maintains three extensive “supergenes” in Atlantic cod, linking these genes to species persistence and ecological stasis. Genomic inference of historic effective population sizes shows continued declines for cod in the North Sea–Skagerrak–Kattegat system through the past millennia, consistent with an early onset of the marine Anthropocene through industrialization and commercialization of fisheries throughout the medieval period.

• Oomen, Rebekah Alice; Knutsen, Halvor; Olsen, Esben Moland; Jentoft, Sissel; Stenseth, Nils Christian & Hutchings, Jeffrey (2022). Warming Accelerates the Onset of the Molecular Stress Response and Increases Mortality of Larval Atlantic Cod. Integrative and Comparative Biology. ISSN 1540-7063. 62(6), p. 1784–1801. doi: 10.1093/icb/icac145. Full text in Research Archive Show summary

  Temperature profoundly affects ectotherm physiology. Although differential thermal responses influence fitness, thus driving population dynamics and species distributions, our understanding of the molecular architecture underlying these responses is limited, especially during the critical larval stage. Here, using RNA-sequencing of laboratory-reared Atlantic cod (Gadus morhua) larvae of wild origin, we find changes in gene expression in thousands of transcripts consistent with a severe cellular stress response at both ambient and projected (+2°C and +4°C) temperatures. In addition, specific responses to stress, heat, and hypoxia were commonly identified in gene ontology enrichment analyses and 33 of the 44 genes comprising the minimum stress proteome of all organisms were upregulated. Earlier onset of the stress response was evident at higher temperatures; concomitant increased growth and mortality suggests a reduction in fitness. Temporal differences in gene expression levels do not correspond to differences in growing degree days, suggesting negative physiological consequences of warming beyond accelerated development. Because gene expression is costly, we infer that the upregulation of thousands of transcripts in response to warming in larval cod might act as an energetic drain. We hypothesize that the energetically costly stress response, coupled with increased growth rate at warmer temperatures, leads to faster depletion of energy reserves and increased risk of mortality in larval cod. As sea surface temperatures continue to rise over the next century, reduced fitness of Atlantic cod larvae might lead to population declines in this ecologically and socioeconomically important species. Further, our findings expand our understanding of transcriptomic responses to temperature by ectothermic vertebrate larvae beyond the critical first-feeding stage, a time when organisms begin balancing the energetic demands of growth, foraging, development, and maintenance. Linking the molecular basis of a thermal response to key fitness-related traits is fundamentally important to predicting how global warming will affect ectotherms.

• Dunlop, Katherine Mary; Staby, Arved; Meeren, Terje van der; Keeley, Nigel B.; Olsen, Esben Moland & Bannister, Raymond [Show all 7 contributors for this article] (2022). Habitat associations of juvenile Atlantic cod (Gadus morhua L.) and sympatric demersal fish communities within shallow inshore nursery grounds. Estuarine, Coastal and Shelf Science. ISSN 0272-7714. 279. doi: 10.1016/j.ecss.2022.108111. Full text in Research Archive Show summary

  Resolving the relationship between demersal fish and sublittoral biotic habitats and substrates is a key element in the protection of important nursery grounds for strengthening fish recruitment. In Norway, coastal Atlantic cod (Gadus morhua L.) is a commercially and culturally important demersal fish for Norwegian coastal communities, and in recent decades the stock has declined to such an extent that a plan to rebuild the stock to biologically safe limits has been implemented. Yet, little is known about the specific biotic and abiotic habitat associations of the early-life stages of coastal cod, which is important for the management and protection of the species. The same shallow, sublittoral zones are inhabited by juveniles and adults of other commercial demersal gadoids and wrasses. This study presents novel findings on associations between juvenile coastal cod and other demersal fish species with seafloor substrates and biological habitats, inferred from five years of extensive fyke net surveys. Newly settled 0-group cod were typically associated with eel grass and red algae biotic habitats on sand and shell sand substrates. However, there was an ontogenic habitat shift amongst one year old (1-group) individuals that became more ubiquitous with their biotic habitat or substrate type choices. The juvenile gadoids saithe (Pollachius virens) and pollack (Pollachius pollachius), were most associated with hard bottom dominated sites with saithe being more abundant at exposed sites, compared to pollack. Goldsinny wrasse (Ctenolabrus rupestris) and corkwing wrasse (Symphodus melops) appeared to favor sugar kelp forests and red algae. Overall, the study identifies the specific sublittoral biotic habitats and substrates important to different early life stages of juvenile coastal cod and other commercially important demersal fish, providing critical information needed for identifying candidate coastal habitats for protection.

• Kleiven, Alf Ring; Espeland, Sigurd Heiberg; Stiansen, Stian; Ono, Kotaro; Zimmermann, Fabian & Olsen, Esben Moland (2022). Technological creep masks continued decline in a lobster (Homarus gammarus) fishery over a century. Scientific Reports. 12. doi: 10.1038/s41598-022-07293-2. Full text in Research Archive Show summary

  Fishery-dependent data are frequently used to inform management decisions. However, inferences about stock development based on commercial data such as Catch-Per-Unit-Effort (CPUE) can be severely biased due to a phenomenon known as technological creep, where fishing technology improves over time. Here we show how trap improvement over nine decades has driven technological creep in a European lobster (Homarus gammarus) fishery. We combined fishing data, experimental fishing with contemporary and older trap types, and information on depletion effects during fishing seasons. The resulting standardized CPUE time series indicates a 92% decline in lobster abundance between 1928 and 2019 compared to 70% if technological creep is not corrected for. Differences are most pronounced within the last 40 years when the most substantial shift in gear technology occurred: an uncorrected CPUE index suggests an 8% increase in lobster abundance during this period, while the corrected CPUE index declined by 57%. We conclude that technological creep has masked a continuous stock decline, particularly in recent decades and largely driven by the shift from one- to two-chambered traps, as well as the ability of newer trap designs to capture larger lobsters. Our study confirms the importance of adequate standardization, including technological development, when using fishery dependent CPUE for monitoring and management of data-limited fisheries.

• Sørdalen, Tonje Knutsen; Halvorsen, Kim Aleksander Tallaksen & Olsen, Esben Moland (2022). Protection from fishing improves body growth of an exploited species. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 289(1987). doi: 10.1098/rspb.2022.1718. Full text in Research Archive Show summary

  Hunting and fishing are often size-selective, which favours slow body growth. In addition, fast growth rate has been shown to be positively correlated with behavioural traits that increase encounter rates and catchability in passive fishing gears such as baited traps. This harvest-induced selection should be effectively eliminated in no-take marine-protected areas (MPAs) unless strong density dependence results in reduced growth rates. We compared body growth of European lobster (Homarus gammarus) between three MPAs and three fished areas. After 14 years of protection from intensive, size-selective lobster fisheries, the densities in MPAs have increased considerably, and we demonstrate that females moult more frequently and grow more during each moult in the MPAs. A similar, but weaker pattern was evident for males. This study suggests that MPAs can shield a wild population from slow-growth selection, which can explain the rapid recovery of size structure following implementation. If slow-growth selection is a widespread phenomenon in fisheries, the effectiveness of MPAs as a management tool can be higher than currently anticipated.

• Benito-Abelló, Carmela De; Bentes, Luís; Sousa, Inês; Pedaccini, Marie; Villegas-Ríos, David & Olsen, Esben Moland [Show all 8 contributors for this article] (2022). Among-individual variation in white seabream (Diplodus sargus) spatial behaviour and protection in a coastal no-take area. ICES Journal of Marine Science. ISSN 1054-3139. 79(8), p. 2265–2276. doi: 10.1093/icesjms/fsac157. Full text in Research Archive
• McQueen, Kate; Meager, Justin James; Nyqvist, Daniel; Skjæraasen, Jon Egil; Olsen, Esben Moland & Karlsen, Ørjan [Show all 10 contributors for this article] (2022). Spawning Atlantic cod (Gadus morhua L.) exposed to noise from seismic airguns do not abandon their spawning site. ICES Journal of Marine Science. ISSN 1054-3139. 79(10). doi: 10.1093/icesjms/fsac203. Full text in Research Archive Show summary

  Seismic airgun surveys may disturb and displace fish at large ranges. If such displacement causes fish to abandon spawning grounds, reproductive success could be impacted. To investigate whether airgun sound causes cod (Gadus morhua L.) to leave their spawning grounds, acoustictelemetry arrays were deployed on two cod spawning grounds: a test and a reference site. From 2019 to 2021, 136 mature cod from the test siteand 45 from the reference site were tagged with acoustic transmitters. Intermittent seismic shooting of two 40 in.3 airguns for 1 week during thespawning periods of 2020–2021 resulted in fluctuating sound exposure levels (SEL) at the test site, comparable to a full-scale industrial survey5–>40 km away. Residency and survival of tagged cod were analysed with capture–mark–recapture models fitted to the detection and recapturedata. Departure rate of the mature cod varied between spawning seasons but was similar between the test and reference sites. Neither survivalnor departure significantly differed between seismic exposure and baseline periods. The results indicated that exposure to airguns at receivedSEL of up to ∼145 dB re 1 μPa2 s, comparable to a seismic survey occurring several kilometres away, did not displace tagged cod from spawninggrounds.

• Martin, Angela Helen; Pearson, Heidi; Saba, Grace & Olsen, Esben Moland (2021). Integral functions of marine vertebrates in the ocean carbon cycle and climate change mitigation. One Earth. ISSN 2590-3330. 4(5), p. 680–693. doi: 10.1016/j.oneear.2021.04.019. Full text in Research Archive Show summary

  In the last decade, the ocean has absorbed a quarter of the Earth’s greenhouse gas emissions through the carbon (C) cycle, a naturally occurring process. Aspects of the ocean C cycle are now being incorporated into climate change mitigation and adaptation plans. Currently, too little is known about marine vertebrate C functions for their inclusion in policies. Fortunately, marine vertebrate biology, behavior, and ecology through the lens of C and nutrient cycling and flux is an emerging area of research that is rich in existing data. This review uses literature and trusted data sources to describe marine vertebrate C interactions, provides quantification where possible, and highlights knowledge gaps. Implications of better understanding the integral functions of marine vertebrates in the ocean C cycle include the need for consideration of these functions both in policies on nature-based climate change mitigation and adaptation, and in management of marine vertebrate populations.

• Fernández-Chacón, Albert; Buttay, Lucie; Moland, Even; Knutsen, Halvor & Olsen, Esben Moland (2021). Demographic responses to protection from harvesting in a long-lived marine species. Biological Conservation. ISSN 0006-3207. 257, p. 1–10. doi: 10.1016/j.biocon.2021.109094. Full text in Research Archive Show summary

  Marine protected areas (MPAs) are usually considered to have positive effects on the recovery of over-exploited populations. However, resolving the extent to which MPAs function according to their conservation goals requires that essential demographic information such as individual survival and population size are quantified. To this end, we analyzed a 16-year replicated mark-recapture study on European lobster (Homarus gammarus, n = 8793) conducted at several protected and unprotected sites in southern Norway, quantifying the impact of MPAs on local population dynamics by means of a “before-after control-impact” study approach (BACI). Lobster survival and abundance were estimated by applying multi-state and robust design models to the mark-recapture data. These models revealed underlying positive responses to protection. Annual survival rates and population abundances reached higher values in the MPAs, compared to the unprotected sites (abundance range: MPAs = 96–1172, control areas = 92–747). In general, female survival was higher than male survival (range of survival: male = 0.13–0.75, female = 0.37–0.85), while larger males benefited more from protection compared to smaller males (range of increase in survival after protection: big = 100–125%, small = 55–101%). We also detected regional differences in demographic responses to protection, as not all MPAs showed the same changes in abundance over time. Our results show that MPAs can reach conservation goals by increasing the local survival and abundance of lobster, but they also highlight demographic differences between sexes and geographic areas that are worth considering for the management and design of both current and future MPAs.

• Kristensen, Martin Lykke; Olsen, Esben Moland; Moland, Even; Knutsen, Halvor; Grønkjær, Peter & Koed, Anders [Show all 8 contributors for this article] (2021). Disparate movement behavior and feeding ecology in sympatric ecotypes of Atlantic cod. Ecology and Evolution. 11(16), p. 11477–11490. doi: 10.1002/ece3.7939. Full text in Research Archive Show summary

  Coexistence of ecotypes, genetically divergent population units, is a widespread phenomenon, potentially affecting ecosystem functioning and local food web stability. In coastal Skagerrak, Atlantic cod (Gadus morhua) occur as two such coexisting ecotypes. We applied a combination of acoustic telemetry, genotyping, and stable isotope analysis to 72 individuals to investigate movement ecology and food niche of putative local “Fjord” and putative oceanic “North Sea” ecotypes—thus named based on previous molecular studies. Genotyping and individual origin assignment suggested 41 individuals were Fjord and 31 were North Sea ecotypes. Both ecotypes were found throughout the fjord. Seven percent of Fjord ecotype individuals left the study system during the study while 42% of North Sea individuals left, potentially homing to natal spawning grounds. Home range sizes were similar for the two ecotypes but highly variable among individuals. Fjord ecotype cod had significantly higher δ13C and δ15N stable isotope values than North Sea ecotype cod, suggesting they exploited different food niches. The results suggest coexisting ecotypes may possess innate differences in feeding and movement ecologies and may thus fill different functional roles in marine ecosystems. This highlights the importance of conserving interconnected populations to ensure stable ecosystem functioning and food web structures.

• Villegas-Ríos, David; Claudet, Joachim; Freitas, Carla; Moland, Even; Thorbjørnsen, Susanna Huneide & Alonso-Fernández, Alexandre [Show all 7 contributors for this article] (2021). Time at risk: Individual spatial behaviour drives effectiveness of marine protected areas and fitness. Biological Conservation. ISSN 0006-3207. 263, p. 1–11. doi: 10.1016/j.biocon.2021.109333. Full text in Research Archive
• Skjæraasen, Jon Egil; Karlsen, Ørjan; Langangen, Øystein Ole Gahr; Meeren, Terje van der; Keeley, Nigel B. & Myksvoll, Mari Skuggedal [Show all 12 contributors for this article] (2021). Impact of salmon farming on Atlantic cod spatio-temporal reproductive dynamics. Aquaculture Environment Interactions. ISSN 1869-215X. 13, p. 399–412. doi: 10.3354/AEI00415. Full text in Research Archive Show summary

  Salmon farming in marine net pens is a major activity in many temperate regions. This industry may affect coastal ecosystems in several ways, such as with waste pollution and parasite spillover. Less is known about the extent to which salmon farming disrupts the use of inshore spawning grounds by wild fish, such as the Atlantic cod Gadus morhua . Acoustic telemetry was therefore used to explore cod space use during the spawning season in a coastal region in mid-Norway with multiple salmon farms. Acoustic receivers were placed in clusters at 5 known cod spawning grounds and 6 nearby salmon farms. Data from 481 adult cod caught at the spawning grounds during 2017-2019 and equipped with acoustic telemetry transmitters were analysed. Overall, fewer fish were detected at farms than spawning grounds, even when accounting for distance from release point. Individual cod residency (days detected / duration of spawning period) was generally higher at the spawning grounds close to farms but low at the farms themselves, with little apparent spawning at the farm localities. In contrast, spawning was clearly occurring at the nearby spawning grounds, with cod spending weeks (n = 316) or months (n = 158) there during the spawning period. Males had longer residence times at spawning grounds than females, likely linked to the cod mating system. Overall, we found little support for the assertion that salmon farms disrupt inshore spawning dynamics of cod using nearby spawning grounds presently, either by attracting spawners to farms or causing fish to leave these grounds.

• Haraldstad, Tormod; Haugen, Thrond Oddvar; Olsen, Esben M.; Forseth, Torbjørn & Höglund, Erik (2021). Hydropower-induced selection of behavioural traits in Atlantic salmon (Salmo salar). Scientific Reports. 11. doi: 10.1038/s41598-021-95952-1. Full text in Research Archive Show summary

  Renewable energy projects such as hydropower facilities contribute towards meeting the world`s growing energy demands and urgent need for mitigating climate change. However, such infrastructure has the potential to substantially alter the environment which, in turn, can induce new challenges related to for instance fish migration conditions. As a consequence, local adaptations related to pre-development migration conditions may be affected for influenced populations. To explore selection regimes operating at a river hydropower plant, we monitored Atlantic salmon smolt individuals during their seaward migration. When passing the hydropower plant, the smolts chose between a surface fish passage or a submerged turbine intake. Smolts were scored for behavioural type (basal locomotor activity, net restrain (a measure of escape responses) and willingness to leave a familiar environment) prior to their migration choice, and we found that smolts with high basal activity had higher probability of using the fish passage than the turbine intake. In addition, migration route choice was a partly consistent trait in that fish that had previously passed a hydroelectric facility by using a fish passage rather than the turbine intake were significantly more likely to use it again when faced with the same choice. Higher mortality among turbine migrants could potentially reduce or eliminate particular behaviour types within populations- and the corresponding population genetic diversity that is essential to cope with future environmental challenges.

• Thorbjørnsen, Susanna Huneide; Moland, Even; Villegas-Ríos, David; Bleeker, Katinka; Knutsen, Halvor & Olsen, Esben Moland (2021). Selection on fish personality differs between a no-take marine reserve and fished areas. Evolutionary Applications. 14(7), p. 1807–1815. doi: 10.1111/eva.13242. Full text in Research Archive Show summary

  Marine reserves can protect fish populations by increasing abundance and body size, but less is known about the effect of protection on fish behaviour. We looked for individual consistency in movement behaviours of sea trout in the marine habitat using acoustic telemetry to investigate whether they represent personality traits and if so, do they affect survival in relation to protection offered by a marine reserve. Home range size had a repeatability of 0.21, suggesting that it represents a personality trait, while mean swimming depth, activity and diurnal vertical migration were not repeatable movement behaviours. The effect of home range size on survival differed depending on the proportion of time fish spent in the reserve, where individuals spending more time in the reserve experienced a decrease in survival with larger home ranges while individuals spending little time in the reserve experienced an increase in survival with larger home ranges. We suggest that the diversity of fish home range sizes could be preserved by establishing networks of marine reserves encompassing different habitat types, ensuring both a heterogeneity in environmental conditions and fishing pressure.

• Freitas, Carla; Villegas-Ríos, David; Moland, Even & Olsen, Esben Moland (2021). Sea temperature effects on depth use and habitat selection in a marine fish community. Journal of Animal Ecology. ISSN 0021-8790. 90(7), p. 1787–1800. doi: 10.1111/1365-2656.13497. Full text in Research Archive Show summary

  Understanding the responses of aquatic animals to temperature variability is essential to predict impacts of future climate change and to inform conservation and management. Most ectotherms such as fish are expected to adjust their behaviour to avoid extreme temperatures and minimize acute changes in body temperature. In coastal Skagerrak, Norway, sea surface temperature (SST) ranges seasonally from 0 to over 20°C, representing a challenge to the fish community which includes cold-, cool- and warm-water affinity species.

• Moland, Even; Fernández-Chacón, Albert; Sørdalen, Tonje Knutsen; Villegas-Rios, David; Thorbjørnsen, Susanna Huneide & Halvorsen, Kim Aleksander Tallaksen [Show all 14 contributors for this article] (2021). Restoration of Abundance and Dynamics of Coastal Fish and Lobster Within Northern Marine Protected Areas Across Two Decades. Frontiers in Marine Science. 8(674756). doi: 10.3389/fmars.2021.674756. Full text in Research Archive Show summary

  This article reviews a suite of studies conducted in a network of coastal Marine Protected Areas (MPAs) in Skagerrak, Southeast Norway. In 2006, Norway’s first lobster reserves were implemented, with the aim of protecting European lobster (Homarus gammarus) through a ban on fixed gear. A before–after control-impact paired series (BACIPS) monitoring program was initiated to evaluate effects of protection on depleted lobster populations. Experimental trapping and capture-recapture techniques were combined to track demography of populations, also including movement of individuals within and beyond MPAs and adjacent control areas. Further, population genetics and parentage studies were applied, allowing for estimation of gene flow, and novel work on sexual selection in lobsters. Additional studies have evaluated MPA effects on coastal cod (Gadus morhua), and on commercially harvested labrids (Ctenolabrus rupestris and Symphodus melops) and anadromous brown trout (Salmo trutta). Together, these studies reported effects of protection pertaining to increased population density, survival, body size and phenotypic diversity, changes in emigration and interaction with surrounding fisheries, and alteration of selection pressure on morphological- and behavioral traits. Designation of MPAs in close collaboration with fishers and managers, long-term monitoring, inclusion of citizen science and evolving research protocols—also including fisheries data—have revealed novel effects of protection and harvesting on marine populations, thus providing substantial contributions to conservation science. Moreover, knowledge of MPA effects on coastal species has impacted harvest regulations showing the utility of MPAs as empirically documented management tools in Norway.

• Fernández-Chacón, Albert; Villegas-Ríos, David; Moland, Even; Baskett, Marissa L.; Olsen, Esben Moland & Carlson, Stephanie M. (2020). Protected areas buffer against harvest selection and rebuild phenotypic complexity. Ecological Applications. ISSN 1051-0761. 30(5). doi: 10.1002/eap.2108. Full text in Research Archive Show summary

  Harvest mortality typically truncates the harvested species' size structure, thereby reducing phenotypic complexity, which can lead to reduced population productivity, increased population variability, and selection on an array of life history traits that can further alter these demographic processes. Marine protected areas (MPAs) are a potential tool to protect older, larger individuals and therefore mitigate such ecological and evolutionary effects of harvest, depending on the degree of connectivity among areas. Such MPA protection relies on a shift in size‐dependent mortality, the measurement of which can therefore serve as an early indicator of whether MPAs might achieve the desired longer‐term ecological and evolutionary responses. We directly measured MPA effects on size‐selective mortality and associated size structure using mark–recapture data on European lobster (Homarus gammarus) collected at three MPA–control area pairs in southern Norway during one decade (n = 5,943). Mark–recapture modeling, accounting for variation in recapture probabilities, revealed (1) that annual mean survival was higher inside MPAs (0.592) vs. control areas (0.298) and (2) that significant negative relationships between survival and body size occurred at the control areas but not in the MPAs, where the effect of body size was predominantly positive. Additionally, we found (3) that mean and maximum body size increased over time inside MPAs but not in control areas. Overall, our results suggest that MPAs can rebuild phenotypic complexity (i.e., size structure) and provide protection from harvest selection.

• Claireaux, Marion; Schmidt, Thassya C. Dos Santos; Olsen, Esben Moland; Slotte, Aril; Varpe, Øystein & Heino, Mikko [Show all 7 contributors for this article] (2020). Eight decades of adaptive changes in herring reproductive investment: The joint effect of environment and exploitation. ICES Journal of Marine Science. ISSN 1054-3139. 78(2), p. 631–639. doi: 10.1093/icesjms/fsaa123. Full text in Research Archive Show summary

  Reproductive investment is a central trait for population dynamics and productivity. Fishing and environmental variations are major drivers affecting population structure, dynamics, and adaptation of life-history and behavioural traits. However, those factors are often considered independently, and few studies take into account their joint effect. In this study, we investigate the contribution of environment, fishing pressure, and intra-specific competition to variation in the reproductive investment of the Norwegian spring-spawning herring (Clupea harengus), a stock that has been fished for centuries, and monitored for decades. Reproductive investment and post-spawning weight were affected differently by growth rate (measured as mean age-at-length), sea surface temperature, North Atlantic Oscillation, and spawning stock biomass in periods with no fishing, unselective fishing, and low but size-selective fishing. We hypothesize that those changes can be explained by direct effects of exploitation such as age truncation and changes in migration patterns. Our results highlight how fishing, by affecting population-level dynamics, can modify the impact of environmental variations on life-history traits. Clupea harengus, environmental variation, fishing, Norwegian spring-spawning herring, trade-offs

• Perälä, Tommi; Olsen, Esben Moland & Hutchings, Jeffrey (2020). Disentangling conditional effects of multiple regime shifts on Atlantic cod productivity. PLOS ONE. 15(11), p. 1–16. doi: 10.1371/journal.pone.0237414. Full text in Research Archive Show summary

  Regime shifts are increasingly prevalent in the ecological literature. However, definitions vary and detection methods are still developing. Here, we employ a novel statistical algorithm based on the Bayesian online change-point detection framework to simultaneously identify shifts in the mean and (or) variance of time series data. We detected multiple regime shifts in long-term (59–154 years) patterns of coastal Norwegian Atlantic cod (>70% decline) and putative drivers of cod productivity: North Atlantic Oscillation (NAO); sea-surface temperature; zooplankton abundance; fishing mortality (F). The consequences of an environmental or climate-related regime shift on cod productivity are accentuated when regime shifts coincide, fishing mortality is high, and populations are small. The analyses suggest that increasing F increasingly sensitized cod in the mid 1970s and late 1990s to regime shifts in NAO, zooplankton abundance, and water temperature. Our work underscores the necessity of accounting for human-induced mortality in regime shift analyses of marine ecosystems.

• Villegas-Ríos, David; Freitas, Carla; Moland, Even; Thorbjørnsen, Susanna Huneide & Olsen, Esben M. (2020). Inferring individual fate from aquatic acoustic telemetry data. Methods in Ecology and Evolution. 11(10), p. 1186–1198. doi: 10.1111/2041-210X.13446. Full text in Research Archive Show summary

  Acoustic telemetry has become a popular means of obtaining individual behavioural data from a wide array of species in marine and freshwater systems. Fate information is crucial to understand important aspects of population dynamics such as mortality, predation or dispersal rates. Here we present a method to infer individual fate from acoustic telemetry arrays of receivers with overlapping detection ranges. Our method depends exclusively on information on animal movements and the characteristics and configuration of the telemetry equipment. By answering a limited number of simple questions, our method identifies six different fates: tagging mortality, natural mortality, fishing mortality, predation, dispersal and survival. Applying the method to a cod telemetry dataset, we were able to determine the fate of 97% of the individuals. We validate the results using several external sources of information, such as recaptures from fishers and control fish with known fate. The method is readily applicable to a wide array of species with minimal adjustments, expanding the range of hypotheses that can be tested using telemetry data.

• Haraldstad, Tormod; Höglund, Erik; Kroglund, Frode; Olsen, Esben Moland; Hawley, Kate Louise & Haugen, Thrond Oddvar (2020). Anthropogenic and natural size-related selection act in concert during brown trout (Salmo trutta) smolt river descent. Hydrobiologia. ISSN 0018-8158. 2020. doi: 10.1007/s10750-020-04329-4. Full text in Research Archive Show summary

  By hindering migration and inducing direct turbine mortality during downstream migration, hydropower is regarded as one of the most serious threats to anadromous salmonids. Yet, little attention has been paid to long-term turbine-induced selection mechanisms effecting fish populations. This work evaluates turbine and post-turbine survival of PIT-tagged wild brown trout smolts. By estimating individual river and sea survival rates, we were able to compare survival rates of smolts that had migrated through the turbine with smolts that had bypassed the turbine, as well as investigate both natural and anthropogenic size-selective mechanisms operative on the population. Total river-descent survival probability was 0.20 for turbine migrants and 0.44 for bypass migrants. The surviving turbine migrants were significantly smaller than their bypass counterparts and more exposed to predation from Northern pike. The estimated mean-adjusted selection gradient was − 0.76 for turbine migrants and + 1.85 for the bypass migrants. The resulting disruptive selection may ultimately lead to increased phenotypic smolt size variation provided sufficient additive genetic variance associated with smolt size. Mitigation measures at hydropower plants are thus essential for preserving sustainable populations of anadromous fish and maintaining population genetic variation.

• Sørdalen, Tonje Knutsen; Halvorsen, Kim Aleksander Tallaksen; Vøllestad, Leif Asbjørn; Moland, Even & Olsen, Esben Moland (2020). Marine protected areas rescue a sexually selected trait in European lobster. Evolutionary Applications. 13(9), p. 2222–2233. doi: 10.1111/eva.12992. Full text in Research Archive Show summary

  Marine protected areas (MPAs) are increasingly implemented worldwide to maintain and restore depleted populations. However, despite our knowledge on the myriad of positive responses to protection, there are few empirical studies on the ability to conserve species’ mating patterns and secondary sexual traits. In male European lobsters (Homarus gammarus), the size of claws relative to body size correlates positively with male mating success and is presumably under sexual selection. At the same time, an intensive trap fishery exerts selection against large claws in males. MPAs could therefore be expected to resolve these conflicting selective pressures and preserve males with large claws. We explored this hypothesis by contrasting claw size of males and females in three pairs of MPAs and nearby fished areas in southern Norway. By finding that male lobsters have up to 8% larger claws inside MPAs compared to similarly sized males in fished areas, our study provides evidence that MPAs rescue a secondary sexual trait. Recovery from harvest selection acting on claws is the most likely explanation; however, the higher abundance of lobster inside MPAs does not rule out a plastic response on claw size due to increased competition. Regardless of the underlying cause, our study demonstrates (a) the value of protected areas as a management tool for mitigating fisheries‐induced evolution and (b) that MPAs help maintaining the scope for sexual selection in populations with vulnerable life histories and complex mating system.

• Ono, Kotaro; Knutsen, Halvor; Olsen, Esben M; Ruus, Anders; Hjermann, Dag Ø & Stenseth, Nils Chr (2019). Possible adverse impact of contaminants on Atlantic cod population dynamics in coastal ecosystems. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 286(1908), p. 1–9. doi: 10.1098/rspb.2019.1167. Full text in Research Archive Show summary

  While many in-laboratory ecotoxicological studies have shown the adverse impact of pollutants to the fitness of an individual, direct evidence from the field on the population dynamics of wildlife animals has been lacking. Here, we provide empirical support for a negative effect of pollution on Atlantic cod (Gadus morhua) population dynamics in coastal waters of Norway by combining unique time series of juvenile cod abundance, body size, environmental concentration of toxic contaminants and a spatially structured population dynamics model. The study shows that mercury concentration might have decreased the reproductive potential of cod in the region despite the general decline in the environmental concentration of mercury, cadmium and hexachlorobenzene since the implementation of national environmental laws. However, some cod populations appeared to be more resistant to mercury pollution than others, and the strength and shape of mercury effect on cod reproductive potential was fjord-specific. Additionally, cod growth rate changed at scales smaller than fjords with a gradient related to the exposure to the open ocean and offshore cod. These spatial differences in life-history traits emphasize the importance of local adaptation in shaping the dynamics of local wildlife populations. Finally, this study highlights the possibility to mitigate pollution effects on natural populations by reducing the overall pollution level, but also reveals that pollution reduction alone is not enough to rebuild local cod populations. Cod population recovery probably requires complementary efforts on fishing regulation and habitat restoration.

• Haraldstad, Tormod; Haugen, Thrond Oddvar; Kroglund, Frode; Olsen, Esben Moland & Höglund, Erik (2019). Migratory passage structures at hydropower plants as potential physiological and behavioural selective agents. Royal Society Open Science. 6(11). doi: 10.1098/rsos.190989. Full text in Research Archive Show summary

  Anthropogenic activities affect fish populations worldwide. River dams have profound impacts on ecosystems by changing habitats and hindering migration. In an effort to counteract such effects, a range of mitigation measures have been installed at hydroelectric power plants. However, not all individuals in a population use these measures, potentially creating strong selection processes at hydroelectric power plants. This may be especially true during migration; fish can get heavily delayed or pass through a hydropower turbine, thus facing increased mortality compared with those using a safe bypass route. In this study, we quantify migration route choices of descending wild passive integrated transponder (PIT)-tagged Atlantic salmon smolts released upstream from a hydroelectric plant. We demonstrate how only a few metres’ displacement of bypass canals can have a large impact on the fish guidance efficiency (FGE). The proportion of fish using the bypasses increased from 1% to 34% when water was released in surface gates closer to the turbine intake. During a period of low FGE, we observed two different smolt migratory strategies. While some individuals spent little time in the forebay before migrating through the turbine tunnel, others remained there. We suggest that these groups represent different behavioural types, and that suboptimal mitigation measures at hydropower intakes may, therefore, induce strong selection on salmon behavioural traits. The ultimate outcome of these selection mechanisms is discussed in light of potential trade-offs between turbine migration mortality coast and optimal sea entrance timing survival benefits.

• Barth, Julia Maria Isis; Villegas-Ríos, David; Freitas, Carla; Moland, Even; Star, Bastiaan & André, Carl [Show all 15 contributors for this article] (2019). Disentangling structural genomic and behavioral barriers in a sea of connectivity. Molecular Ecology. ISSN 0962-1083. 28(6), p. 1394–1411. doi: 10.1111/mec.15010. Full text in Research Archive Show summary

  Genetic divergence among populations arises through natural selection or drift and is counteracted by connectivity and gene flow. In sympatric populations, isolating mechanisms are thus needed to limit the homogenizing effects of gene flow to allow for adaptation and speciation. Chromosomal inversions act as an important mechanism maintaining isolating barriers, yet their role in sympatric populations and divergence with gene flow is not entirely understood. Here, we revisit the question of whether inversions play a role in the divergence of connected populations of the marine fish Atlantic cod (Gadus morhua), by exploring a unique data set combining whole‐genome sequencing data and behavioural data obtained with acoustic telemetry. Within a confined fjord environment, we find three genetically differentiated Atlantic cod types belonging to the oceanic North Sea population, the western Baltic population and a local fjord‐type cod. Continuous behavioural tracking over 4 year revealed temporally stable sympatry of these types within the fjord. Despite overall weak genetic differentiation consistent with high levels of gene flow, we detected significant frequency shifts of three previously identified inversions, indicating an adaptive barrier to gene flow. In addition, behavioural data indicated that North Sea cod and individuals homozygous for the LG12 inversion had lower fitness in the fjord environment. However, North Sea and fjord‐type cod also occupy different depths, possibly contributing to prezygotic reproductive isolation and representing a behavioural barrier to gene flow. Our results provide the first insights into a complex interplay of genomic and behavioural isolating barriers in Atlantic cod and establish a new model system towards an understanding of the role of genomic structural variants in adaptation and diversification.

• Olsen, Esben Moland; Halvorsen, Kim Aleksander Tallaksen; Larsen, Torkel & Kuparinen, Anna (2019). Potential for managing life history diversity in a commercially exploited intermediate predator, the goldsinny wrasse (Ctenolabrus rupestris). ICES Journal of Marine Science. ISSN 1054-3139. 76(2), p. 410–417. doi: 10.1093/icesjms/fsy183. Full text in Research Archive Show summary

  Small-bodied wrasse species are important for structuring coastal marine ecosystems but are also increasingly harvested as parasite cleaners on farmed salmon. Identifying management regulations that will support long-term sustainability of wrasse fisheries is challenging, because there is still limited knowledge about the impacts of fisheries on the demography of these intermediate predators in their natural environments. To this end, we studied individual growth histories of goldsinny wrasse (Ctenolabrus rupestris) at a fine spatial scale across replicated marine protected areas (MPAs) and areas open to commercial harvesting on the Norwegian coast. The MPAs were established 1–7 years prior to our sampling. We detected significant fine-scale spatial variation in wrasse asymptotic body size, but found no consistent difference between MPAs and fished areas. Male wrasses reached larger asymptotic body sizes than females, whereas fyke nets captured individuals with larger asymptotic body sizes compared with baited traps. These are the two commonly used gear types in wrasse fisheries. An extended use of baited traps, along with slot-size limits, could therefore aid in protecting large-growing phenotypes such as nest-guarding males.

• Kleiven, Portia Joy Nillos; Espeland, Sigurd Heiberg; Olsen, Esben Moland; Abesamis, Rene A.; Moland, Even & Kleiven, Alf Ring (2019). Fishing pressure impacts the abundance gradient of European lobsters across the borders of a newly established marine protected area. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 286(1894). doi: 10.1098/rspb.2018.2455. Full text in Research Archive Show summary

  Marine protected areas (MPAs) are considered viable fisheries management tools due to their potential benefits of adult spillover and recruitment subsidy to nearby fisheries. However, before–after control–impact studies that explore the biological and fishery effects of MPAs to surrounding fisheries are scarce. We present results from a fine-scale spatial gradient study conducted before and after the implementation of a 5 km2 lobster MPA in southern Norway. A significant nonlinear response in lobster abundance, estimated as catch-per-unit-effort (CPUE) from experimental fishing, was detected within 2 years of protection. After 4 years, CPUE values inside the MPA had increased by a magnitude of 2.6 compared to before-protection values. CPUE showed a significant nonlinear decline from the centre of the MPA, with a depression immediately outside the border and a plateau in fished areas. Overall fishing pressure almost doubled over the course of the study. The highest increase in fishing pressure (by a magnitude of 3) was recorded within 1 km of the MPA border, providing a plausible cause for the depression in CPUE. Taken together, these results demonstrate the need to regulate fishing pressure in surrounding areas when MPAs are implemented as fishery management tools.

• Moland, Even; Carlson, Stephanie; Villegas-Rios, David; Wiig, Jørgen Ree & Olsen, Esben Moland (2019). Harvest selection on multiple traits in the wild revealed by aquatic animal telemetry. Ecology and Evolution. 9(11), p. 6480–6491. doi: 10.1002/ece3.5224. Full text in Research Archive Show summary

  Harvesting can have profound impacts on the ecology and evolution of marine populations. However, little is known about the strength and direction of fisheries‐induced selection acting on multiple traits in the wild. Here, we used acoustic telemetry to directly monitor individual behavior and fate in an intensively harvested species, the European lobster (Homarus gammarus, n = 100), in southern Norway. Overall, 24% of the tracked lobsters survived the two‐month harvest season within the study area. Our results indicated that local survival was not random with respect to phenotype. We found no clear support for fisheries‐induced selection acting directly on body size. However, lobsters with large crusher claws relative to their body size, typical of socially dominant individuals, appeared at higher risk of being captured in the conventional trap fishery. We also detected a fine‐scale spatial gradient in survival. After accounting for this gradient, individuals displaying larger home ranges were more likely to survive the harvest season. Finally, we found significant repeatabilities for lobster behavior on a monthly timescale, indicating that individual behavioral attributes tended to persist and may reflect personality. Our study therefore provides empirical support for the need to consider an evolutionary enlightened approach to fisheries management that considers the influence of harvest on multiple traits of target species.

• Thorbjørnsen, Susanna Huneide; Moland, Even; Simpfendorfer, Colin A.; Heupel, Michelle R.; Knutsen, Halvor & Olsen, Esben Moland (2019). Potential of a no‐take marine reserve to protect home ranges of anadromous brown trout (Salmo trutta). Ecology and Evolution. 9(1), p. 417–426. doi: 10.1002/ece3.4760. Full text in Research Archive Show summary

  The extent to which no‐take marine reserves can benefit anadromous species requires examination. Here, we used acoustic telemetry to investigate the spatial behavior of anadromous brown trout (sea trout, Salmo trutta) in relation to a small marine reserve (~1.5 km2) located inside a fjord on the Norwegian Skagerrak coast. On average, sea trout spent 42.3 % (±5.0% SE) of their time in the fjord within the reserve, a proportion similar to the area of the reserve relative to that of the fjord. On average, sea trout tagged inside the reserve received the most protection, although the level of protection decreased marginally with increasing home range size. Furthermore, individuals tagged outside the reserve received more protection with increasing home range size, potentially opposing selection toward smaller home range sizes inflicted on fish residing within reserves, or through selective fishing methods like angling. Monthly sea trout home ranges in the marine environment were on average smaller than the reserve, with a mean of 0.430 (±0.0265 SE) km2. Hence, the reserve is large enough to protect the full home range of some individuals residing in the reserve. Synthesis and applications: In general, the reserve protects sea trout to a varying degree depending on their individual behavior. These findings highlight evolutionary implications of spatial protection and can guide managers in the design of marine reserves and networks that preserve variation in target species' home range size and movement behavior.

• Haraldstad, Tormod; Höglund, Erik; Kroglund, Frode; Lamberg, Anders; Olsen, Esben Moland & Haugen, Thrond Oddvar (2018). Condition-dependent skipped spawning in anadromous brown trout (Salmo trutta). Canadian Journal of Fisheries and Aquatic Sciences. ISSN 0706-652X. 75(12), p. 2313–2319. doi: 10.1139/cjfas-2017-0076. Full text in Research Archive Show summary

  Repeat spawners of anadromous salmonids may contribute significantly to population resilience by providing multiple cohorts to both seawater and freshwater life stages. In this study, winter survival of sea trout (Salmo trutta Linnaeus, 1758) post spawners (kelts) was 89%. Sea survival increased linearly with female length with a return probability between 30% and 50%, whereas males attained a maximum return probability of 60% at 520 mm. Of the returning sea trout, 40% skipped spawning and they had significantly lower condition factor as kelts compared with those who returned after one summer. These results suggest that sex-specific differences in individual post-spawning growth–survival trade-off exist and that energetic status of descending kelts may influence the probability to skip spawning. We discuss to what extent hydropower may reduce post-spawning survival due to blocking of river descent opportunities, potentially altering the fitness landscape and favouring new life-history adaptations. From a management perspective, it is concluded that it is crucial to maintain connectivity in regulated rivers, allowing fish to complete repetitive spawning and feeding migrations, thus contributing to population productivity.

• Roney, Nancy; Oomen, Rebekah Alice; Knutsen, Halvor; Olsen, Esben Moland & Hutchings, Jeffrey (2018). Temporal variability in offspring quality and individual reproductive output in a broadcast-spawning marine fish. ICES Journal of Marine Science. ISSN 1054-3139. 75(4), p. 1353–1361. doi: 10.1093/icesjms/fsx232. Full text in Research Archive
• Villegas-Rios, David; Réale, Denis; Freitas, Carla; Moland, Even & Olsen, Esben Moland (2018). Personalities influence spatial responses to environmental fluctuations in wild fish. Journal of Animal Ecology. ISSN 0021-8790. 87(5), p. 1309–1319. doi: 10.1111/1365-2656.12872. Full text in Research Archive Show summary

  Although growing evidence supports the idea that animal personality can explain plasticity in response to changes in the social environment, it remains to be tested whether it can explain spatial responses of individuals in the face of natural environmental fluctuations. This is a major challenge in ecology and evolution as spatial dynamics link individual‐ and population‐level processes. In this study, we investigated the potential of individual personalities to predict differences in fish behaviour in the wild. Specifically, our goal was to answer if individual differences in plasticity of space use to sea surface temperature could be explained by differences in personality along the reactive–proactive axis. To address this question, we first conducted repeated standard laboratory assays (i.e., open‐field test, novel object test and mirror stimulation test) to assess the personality type of 76 wild‐caught Atlantic cod (Gadus morhua). Next, we released the fish back into the sea and monitored their spatial behaviour over large temporal (16 months) and spatial (a whole fjord) scales, using high‐resolution acoustic tracking. We demonstrate that (a) cod personality traits are structured into a proactive–reactive syndrome (proactive fish being more bold, exploratory and aggressive), (b) mean depth use of individuals is mainly driven by sea temperature and (c) personality is a significant predictor of home range changes in the wild, where reactive, but not proactive, individuals reduced their home range as sea temperature increased. These findings expand our understanding of the ecological consequences of animal personality and the mechanisms shaping spatial dynamics of animals in nature.

• Sørdalen, Tonje Knutsen; Halvorsen, Kim Aleksander Tallaksen; Harrison, Hugo B.; Ellis, Charlie D.; Vøllestad, Leif Asbjørn & Knutsen, Halvor [Show all 8 contributors for this article] (2018). Harvesting changes mating behaviour in European lobster. Evolutionary Applications. 11(6), p. 963–977. doi: 10.1111/eva.12611. Full text in Research Archive Show summary

  Removing individuals from a wild population can affect the availability of prospective mates and the outcome of competitive interactions, with subsequent effects on mating patterns and sexual selection. Consequently, the rate of harvest‐induced evolution is predicted to be strongly dependent on the strength and dynamics of sexual selection, yet there is limited empirical knowledge on the interplay between selective harvesting and the mating systems of exploited species. In this study, we used genetic parentage assignment to compare mating patterns of the highly valued and overexploited European lobster (Homarus gammarus) in a designated lobster reserve and nearby fished area in southern Norway. In the area open to fishing, the fishery is regulated by a closed season, a minimum legal size and a ban on the harvest of egg‐bearing females. Due to the differences in size and sex‐specific fishing mortality between the two areas, males and females are of approximately equal average size in the fished area, whereas males tend to be larger in the reserve. Our results show that females would mate with males larger than their own body size, but the relative size difference was significantly larger in the reserve. Sexual selection acted positively on both body size and claw size in males in the reserve, while it was nonsignificant in fished areas. This strongly suggests that size truncation of males by fishing reduces the variability of traits that sexual selection acts upon. If fisheries continue to target large individuals (particularly males) with higher relative reproductive success, the weakening of sexual selection will likely accelerate fisheries‐induced evolution towards smaller body size.

• Jorde, Per Erik; Kleiven, Alf Ring; Sodeland, Marte; Olsen, Esben Moland; Ferter, Keno & Jentoft, Sissel [Show all 7 contributors for this article] (2018). Who is fishing on what stock: Population-of-origin of individual cod (Gadus morhua) in commercial and recreational fisheries. ICES Journal of Marine Science. ISSN 1054-3139. 75(6), p. 2153–2162. doi: 10.1093/icesjms/fsy080. Full text in Research Archive
• Knutsen, Halvor; Jorde, Per Erik; Hutchings, Jeffrey; Hemmer-Hansen, Jakob; Grønkjær, Peter & Jørgensen, Kris-Emil Mose [Show all 10 contributors for this article] (2018). Stable coexistence of genetically divergent Atlantic cod ecotypes at multiple spatial scales. Evolutionary Applications. 11(9), p. 1527–1539. doi: 10.1111/eva.12640. Full text in Research Archive Show summary

  Coexistence in the same habitat of closely related yet genetically different populations is a phenomenon that challenges our understanding of local population structure and adaptation. Identifying the underlying mechanisms for such coexistence can yield new insight into adaptive evolution, diversification and the potential for organisms to adapt and persist in response to a changing environment. Recent studies have documented cryptic, sympatric populations of Atlantic cod (Gadus morhua) in coastal areas. We analysed genetic origin of 6,483 individual cod sampled annually over 14 years from 125 locations along the Norwegian Skagerrak coast and document stable coexistence of two genetically divergent Atlantic cod ecotypes throughout the study area and study period. A “fjord” ecotype dominated in numbers deep inside fjords while a “North Sea” ecotype was the only type found in offshore North Sea. Both ecotypes coexisted in similar proportions throughout coastal habitats at all spatial scales. The size‐at‐age of the North Sea ecotype on average exceeded that of the fjord ecotype by 20% in length and 80% in weight across all habitats. Different growth and size among individuals of the two types might be one of several ecologically significant variables that allow for stable coexistence of closely related populations within the same habitat. Management plans, biodiversity initiatives and other mitigation strategies that do not account for the mixture of species ecotypes are unlikely to meet objectives related to the sustainability of fish and fisheries.

• Roney, Nancy; Oomen, Rebekah Alice; Knutsen, Halvor; Olsen, Esben Moland & Hutchings, Jeffrey (2018). Fine-Scale Population Differences in Atlantic Cod Reproductive Success: A Potential Mechanism for Ecological Speciation in a Marine Fish. Ecology and Evolution. p. 1–11. doi: 10.1002/ece3.4615. Full text in Research Archive Show summary

  Successful resource‐management and conservation outcomes ideally depend on matching the spatial scales of population demography, local adaptation, and threat mitigation. For marine fish with high dispersal capabilities, this remains a fundamental challenge. Based on daily parentage assignments of more than 4,000 offspring, we document fine‐scaled temporal differences in individual reproductive success for two spatially adjacent (<10 km) populations of a broadcast‐spawning marine fish. Distinguished by differences in genetics and life history, Atlantic cod (Gadus morhua) from inner‐ and outer‐fjord populations were allowed to compete for mating and reproductive opportunities. After accounting for phenotypic variability in several traits, reproductive success of outer‐fjord cod was significantly lower than that of inner‐fjord cod. This finding, given that genomically different cod ecotypes inhabit inner‐ and outer‐fjord waters, raises the intriguing hypothesis that the populations might be diverging because of ecological speciation. Individual reproductive success, skewed within both sexes (more so among males), was positively affected by body size, which also influenced the timing of reproduction, larger individuals spawning later among females but earlier among males. Our work suggests that spatial mismatches between management and biological units exist in marine fishes and that studies of reproductive interactions between putative populations or ecotypes can provide an informative basis on which determination of the scale of local adaptation can be ascertained.

• Dornelas, Maria; Antão, Laura H.; Moyes, Faye; Bates, Amanda E.; Magurran, Anne E. & Adam, Dusan [Show all 270 contributors for this article] (2018). BioTIME: A database of biodiversity time series for the Anthropocene. Global Ecology and Biogeography. ISSN 1466-822X. 27(7), p. 760–786. doi: 10.1111/geb.12729. Full text in Research Archive Show summary

  <p><i>Motivation</i>: The BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community‐led open‐source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene.</p> <p><i>Main types of variables included</i>: The database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record.</p> <p><i>Spatial location and grain</i>: BioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km² (158 cm²) to 100 km² (1,000,000,000,000 cm²).</p> <p><i>Time period and grain</i>: BioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year.</p> <p><i>Major taxa and level of measurement</i>: BioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates.</p> <p><i>Software format</i>: .csv and .SQL.

• Thorbjørnsen, Susanna Huneide; Moland, Even; Huserbråten, Mats Brockstedt Olsen; Knutsen, Jan Atle; Knutsen, Halvor & Olsen, Esben Moland (2018). Replicated marine protected areas (MPAs) support movement of larger, but not more, European lobsters to neighbouring fished areas. Marine Ecology Progress Series. ISSN 0171-8630. 595, p. 123–133. doi: 10.3354/meps12546. Full text in Research Archive Show summary

  The European lobster Homarus gammarus is heavily exploited in the Norwegian fishery, and several management actions have been implemented to protect the species. Three marine protected areas (MPAs) excluding all but hook and line type fishing gear were established along the Skagerrak coast in 2006, effectively banning the trap-based fishery for European lobster. Lobster populations within MPAs and adjacent control areas were studied by capture-mark-recapture and recovery methods every year from prior to MPA establishment to the present. During 2006-2014, a total of 4682 and 3317 lobsters were captured (including recaptures) in the MPAs and control areas, respectively. In all MPAs, protection led to a shift in demography, with an increase in mean total length of 15% during 2006-2014, thereby opposing the effects of a size-selective fishery. No difference was found in rates of movement out from MPAs and control areas, but lobsters moving from MPAs and caught in fished areas were significantly larger than lobsters moving out of control areas. In instances where lobsters tagged in a control area moved into an MPA, the immigrating lobsters had a larger body size than the mean in their area of origin. The range of movement undertaken by recovered lobsters extended beyond the home range sizes suggested by previous shorter-term studies, and well beyond the sizes of the small coastal MPAs studied herein. In summary, demographic changes should be accounted for when interpreting the value of spillover from MPAs, and also potential ‘spill in’ from fished areas to MPAs.

• Villegas-Rios, David; Moland, Even & Olsen, Esben Moland (2017). Potential of contemporary evolution to erode fishery benefits from marine reserves. Fish and Fisheries. ISSN 1467-2960. 18(3), p. 571–577. doi: 10.1111/faf.12188. Full text in Research Archive
• Laurel, Benjamin J.; Cote, David; Gregory, Robert S.; Rogers, Lauren; Knutsen, Halvor & Olsen, Esben Moland (2017). Recruitment signals in juvenile cod surveys depend on thermal growth conditions. Canadian Journal of Fisheries and Aquatic Sciences. ISSN 0706-652X. 74(4), p. 511–523. doi: 10.1139/cjfas-2016-0035. Full text in Research Archive
• Halvorsen, Kim Aleksander Tallaksen; Larsen, Torkel; Sørdalen, Tonje Knutsen; Vøllestad, Leif Asbjørn; Knutsen, Halvor & Olsen, Esben Moland (2017). Impact of harvesting cleaner fish for salmonid aquaculture assessed from replicated coastal marine protected areas. Marine Biology Research. ISSN 1745-1000. 13(4), p. 359–369. doi: 10.1080/17451000.2016.1262042. Full text in Research Archive Show summary

  Wrasse (Labridae) fisheries have increased markedly in Norway since 2010. Wrasse are being used as cleaner fish in salmonid aquaculture to control sea-lice infestations. However, fundamental knowledge on the demography and abundance of the targeted wrasse populations in Norwegian waters is lacking, and the consequences of harvesting at the current intensity have not been assessed. Here, we compared catch per unit effort (CPUE), size, age and sex ratio of goldsinny wrasse (Ctenolabrus rupestris) and corkwing wrasse (Symphodus melops) between marine protected areas (MPAs) and control areas open for fishing at four localities on the Skagerrak coast in Southern Norway. The CPUE of goldsinny larger than the minimum size limit was 33–65% higher within MPAs, while for corkwing three of four MPAs had higher CPUE with the relative difference between MPAs and control areas ranging from −16% to 92%. Moreover, corkwing, but not goldsinny, was significantly older and larger within MPAs than in control areas. Sex ratios did not differ between MPAs and control areas for either species. Our study suggests that despite its short history, the wrasse fisheries have considerable impacts on the target populations and, further, that small MPAs hold promise as a management tool for maintaining natural population sizes and size structure. Goldsinny, being a smaller-sized species, also seems to benefit from the traditional minimum size limit management tool, which applies outside MPAs. The final version of this research has been published in Marine Biology Research. © 2017 Taylor & Francis

• Rogers, Lauren; Storvik, Geir Olve; Knutsen, Halvor; Olsen, Esben Moland & Stenseth, Nils Christian (2017). Fine-scale population dynamics in a marine fish species inferred from dynamic state-space models. Journal of Animal Ecology. ISSN 0021-8790. 86(4), p. 888–898. doi: 10.1111/1365-2656.12678. Full text in Research Archive Show summary

  Identifying the spatial scale of population structuring is critical for the conservation of natural populations and for drawing accurate ecological inferences. However, population studies often use spatially aggregated data to draw inferences about population trends and drivers, potentially masking ecologically relevant population sub-structure and dynamics. The goals of this study were to investigate how population dynamics models with and without spatial structure affect inferences on population trends and the identification of intrinsic drivers of population dynamics (e.g. density dependence). Specifically, we developed dynamic, age-structured, state-space models to test different hypotheses regarding the spatial structure of a population complex of coastal Atlantic cod (Gadus morhua). Data were from a 93-year survey of juvenile (age 0 and 1) cod sampled along >200 km of the Norwegian Skagerrak coast. We compared two models: one which assumes all sampled cod belong to one larger population, and a second which assumes that each fjord contains a unique population with locally determined dynamics. Using the best supported model, we then reconstructed the historical spatial and temporal dynamics of Skagerrak coastal cod. Cross-validation showed that the spatially structured model with local dynamics had better predictive ability. Furthermore, posterior predictive checks showed that a model which assumes one homogeneous population failed to capture the spatial correlation pattern present in the survey data. The spatially structured model indicated that population trends differed markedly among fjords, as did estimates of population parameters including density-dependent survival. Recent biomass was estimated to be at a near-record low all along the coast, but the finer scale model indicated that the decline occurred at different times in different regions. Warm temperatures were associated with poor recruitment, but local changes in habitat and fishing pressure may have played a role in driving local dynamics. More generally, we demonstrated how state-space models can be used to test evidence for population spatial structure based on survey time-series data. Our study shows the importance of considering spatially structured dynamics, as the inferences from such an approach can lead to a different ecological understanding of the drivers of population declines, and fundamentally different management actions to restore populations.

View all works in NVA

• McQueen, Kate; knaap, Inge Elisabeth Jacoba Van der; Olsen, Esben Moland; Biuw, Martin & Vikebø, Frode Bendiksen (2026). Monitoring effects of offshore wind development on fish and marine mammals using acoustic telemetry and passive acoustic monitoring . Full text in Research Archive
• Opdal, Anders Martin Frugård; Jørgensen, Christian; Sivle, Lise Doksæter; Karlsen, Ørjan; Langbehn, Tom & Ljungström, Anna Jeja Gabriella [Show all 11 contributors for this article] (2025). Seasonal dynamics in ocean temperatures can give false impression of thermal bottleneck for spawning fish. Full text in Research Archive
• Opdal, Anders Martin Frugård; Jørgensen, Christian; Sivle, Lise Doksæter; Karlsen, Ørjan; Langbehn, Tom & Ljungström, Anna Jeja Gabriella [Show all 11 contributors for this article] (2024). Seasonal dynamics in ocean temperatures can give false impression of thermal bottleneck for spawning fish. Full text in Research Archive
• Sivle, Lise Doksæter; McQueen, Kate; Jong, Karen de; Forland, Tonje Nesse; Skjæraasen, Jon Egil & Olsen, Esben Moland [Show all 7 contributors for this article] (2023). SpawnSeis. Påvirkning av luftkanon og marin vibrator på gytende torsk. Full text in Research Archive
• Oomen, Rebekah Alice; Knutsen, Halvor; Moland, Even; Olsen, Esben Moland; Knutsen, Jan Atle & Bernatchez, Louis [Show all 8 contributors for this article] (2022). Nothing so boundless, nothing so patient: Obituary for Professor Jeffrey Alexander Hutchings (1958–2022). Fish and Fisheries. ISSN 1467-2960. 23(3), p. 519–521. doi: 10.1111/faf.12661. Full text in Research Archive
• McQueen, Kate; Skjæraasen, Jon Egil; Nyqvist, Daniel; Olsen, Esben Moland; Karlsen, Ørjan & Meager, Justin James [Show all 10 contributors for this article] (2022). Behavioural responses of spawning Atlantic cod (Gadus morhua) to seismic airgun exposure. Full text in Research Archive
• Nyqvist, Daniel; Sivle, Lise Doksæter; Karlsen, Ørjan; Olsen, Esben Moland; Jong, Karen de & Forland, Tonje Nesse [Show all 7 contributors for this article] (2019). Behaviour of spawning cod in relation to marine seismic surveys. Full text in Research Archive
• Nyqvist, Daniel; Sivle, Lise Doksæter; Karlsen, Ørjan; Olsen, Esben Moland; Jong, Karen de & Forland, Tonje Nesse [Show all 7 contributors for this article] (2019). Do seismic surveys affect the behavior of spawning cod? Full text in Research Archive
• Sivle, Lise Doksæter; Nyqvist, Daniel; Olsen, Esben Moland & Karlsen, Ørjan (2019). Cyborg i forskinga si teneste. [Journal]. Marsteinen. Full text in Research Archive
• Olsen, Esben Moland; Halvorsen, Kim Aleksander Tallaksen; Larsen, Torkel & Kuparinen, Anna (2019). Erratum: Potential for managing life history diversity in a commercially exploited intermediate predator, the goldsinny wrasse (Ctenolabrus rupestris). ICES Journal of Marine Science. ISSN 1054-3139. 76(1), p. 357–357. doi: 10.1093/icesjms/fsy195. Full text in Research Archive
• Stige, Leif Christian; Langangen, Øystein; Durant, Joel Marcel; Knutsen, Halvor; Olsen, Esben Moland & Ottersen, Geir (2019). Forskning på torsk. Biolog. ISSN 0801-0722. 37(2), p. 46–49. Full text in Research Archive
• Meeren, Terje van der; Skjæraasen, Jon Egil; Myksvoll, Mari Skuggedal; Dahle, Geir; Olsen, Esben Moland & Karlsen, Ørjan [Show all 7 contributors for this article] (2018). Interaksjoner mellom lakseoppdrett og gyteområder for torsk (ICOD-prosjektet). Full text in Research Archive
• Oomen, Rebekah Alice; Knutsen, Halvor; Olsen, Esben Moland; Jentoft, Sissel; Stenseth, Nils Chr. & Hutchings, Jeffrey (2018). Transcriptomic variability in population responses of Atlantic cod to temperature. Full text in Research Archive
• Meeren, Terje van der; Skjæraasen, Jon Egil; Myksvoll, Mari Skuggedal; Dahle, Geir; Olsen, Esben Moland & Karlsen, Ørjan [Show all 7 contributors for this article] (2018). Interaksjoner mellom lakseoppdrett og gyteområder for torsk (ICOD-prosjektet). Full text in Research Archive
• Meeren, Terje van der; Skjæraasen, Jon Egil; Myksvoll, Mari Skuggedal; Dahle, Geir; Olsen, Esben Moland & Karlsen, Ørjan [Show all 7 contributors for this article] (2018). Interactions of salmon farming on Atlantic cod spawning grounds (ICOD prosjektet). Full text in Research Archive
• Meeren, Terje van der; Skjæraasen, Jon Egil; Myksvoll, Mari Skuggedal; Dahle, Geir; Olsen, Esben Moland & Karlsen, Ørjan [Show all 7 contributors for this article] (2018). Interactions of salmon farming on Atlantic cod spawning grounds. Full text in Research Archive Show summary

  There is increasing focus on finding optimal areas for fish farming of Atlantic salmon and rainbow trout in open cages in Norwegian fjords, along the coast and in Northern Norway. The potential for overlapping fish farming installations with areas that are important spawning/nursery areas for commercial fish species (i.e. Atlantic cod) may have implications for the success of these spawning and juvenile nursery grounds and subsequently may influence the long-term health and fitness of commercial fish species. Atlantic cod is one of the species that can be influenced by the presence of the aquaculture industry. With the growth of aquaculture it is anticipated that the competition for use of coastal area between aquaculture, fisheries, and other interests will escalate in the coming years and it is important to understand the potential interactions. This presentation details a large 5-year (2015-2020) research project focusing on understanding if the establishment of fish farming activities in the vicinity of a known spawning ground of Atlantic cod will affect the migration of adult cod and their spawning and recruitment success. This project is multidisciplinary in nature, using a combination of research methodologies to disentangle the effects of fin-fish aquaculture on cod spawning grounds. Here we discuss the use of 1) acoustic telemetry to study adult spawning cod behaviour, 2) spatial and temporal sampling of cod eggs and juvenile fish, 3) DNA identification of spawning cod, cod eggs and juvenile cod and 4) sampling of benthic environmental health. This data is combined using state-of-the-art-modelling tools to increase our understanding of the interactions of coastal aquaculture with cod spawning grounds, and to predict changes in spawning and juvenile populations. This presentation will present recent data on observed changes in cod spawning/juvenile nursery grounds and shifts in benthic environmental health due to the establishment of the fish farm. The project results presented here are important new knowledge that are essential for addressing the needs for managing natural resources and environments along the Norwegian coastline with the development of the aquaculture industry, as outlined by the Norwegian authorities.

• Thorbjørnsen, Susanna Huneide; Moland, Even; Villegas-Rios, David; Knutsen, Halvor & Olsen, Esben Moland (2018). Personality of sea trout and consequences for survival quantified using detailed movement data from a telemetry study in a southern Norwegian fjord. Full text in Research Archive
• Barth, Julia Maria Isis; Star, Bastiaan; Matschiner, Michael; André, Carl; Knutsen, Halvor & Bradbury, Ian [Show all 13 contributors for this article] (2017). Chromosomal rearrangements as barriers to homogenization in highly mobile fish. Full text in Research Archive
• Thorbjørnsen, Susanna Huneide; Moland, Even; Simpfendorfer, Colin A.; Heupel, Michelle R.; Knutsen, Halvor & Olsen, Esben Moland (2017). A no-take marine reserve provide benefits to anadromous sea trout (Salmo trutta). Full text in Research Archive
• Durif, Caroline; Axelsen, Bjørn Erik Eversvik; Bogstad, Bjarte; Huse, Geir; Eriksen, Elena & Olsen, Esben Moland (2025). Rognkjeks kvoterådgivning fra Havforskningsinstituttet for 2026. Havforskningsinstituttet. doi: https:/www.hi.no/hi/nettrapporter/rapport-fra-havforskningen-2025-70. Full text in Research Archive
• Moland, Even; Synnes, Ann-Elin; Naustvoll, Lars Johan; Freitas, Carla; Norderhaug, Kjell Magnus & Thormar, Jonas [Show all 15 contributors for this article] (2021). Krafttak for kysttorsken - Kunnskap for stedstilpasset gjenoppbygging av bestander, naturtyper og økosystem i Færder- og Ytre Hvaler nasjonalparker. Havforskningsinstituttet. Full text in Research Archive Show summary

  Ytre Oslofjord har en unik kystnatur av svært stor verdi for både fastboende og tilreisende. Færder- og Ytre Hvaler nasjonalparker ligger side om side ytterst i fjorden, og skal sikre naturverdiene for kommende generasjoner. Nasjonalparkene har utformet egne forvaltningsplaner og -mål, som gjenspeiler et ønske om å legge best mulig til rette for at fiskearter, fugler, planter og insekter skal fortsette å trives innenfor parkenes grenser. Generelle mål for naturverdiene er at de skal opprettholdes med god økologisk funksjon, og et høyt biologisk mangfold.

View all works in NVA