Eco-evolutionary dynamics of coastal fishes

Marine animals such as crustaceans and fish in the coastal zone live their lives attached to places. Many display a movement behavior characterized by a ‘home range’ – a space within which the animals conduct movement connected to foraging or hunting, sheltering and reproduction. In addition, anadromous and catadromous fish species utilize the coastal zone as habitat during parts of their life cycle. A multitude of extrinsic and intrinsic factors shape the utilized movement space.

In the highly variable environment experienced by fish species inhabiting the Skagerrak coastal system, how does natural selection act on individuals and populations? And how do human-induced selection pressures act on these same species and populations (see e.g. Moland et al. 2019, Haraldstad et al. 2020)? How will a phenotypic trait such as body size change in response to ongoing selection, and to what extent will such changes in phenotype influence population dynamics, community structure and ecosystem function? Will there be feedback-mechanisms altering the original selection regime, for instance by changes in food availability and density dependence?

Researchers acoustically marking fish.

To counteract the possible negative impact from human interventions on fish populations, mitigation measures have been put into action. Protection of habitats and marine fish assemblages through the introduction of spatial management using marine protected areas (MPAs) have created an opportunity to study contrasts to harvesting (Thorbjørnsen et al. 2019, Fernández-Chacón et al. 2020). However, other mitigation measures such as minimum size limits and measures to help migratory fish pass waterway barriers also have the potential to shape the selective ‘landscape’ experienced by crustaceans and fish (Moland et al., 2019, Haraldstad et al. 2019).

At CCRs’ Coastal FISH telemetry LAB (C-FISHLAB), eco-evolutionary dynamics and conservation of coastal fishes are explored, using state of the art technologies. The miniaturization of electronics and availability of such technologies tailored to biological research has opened exciting possibilities for natural science. The primary focus of C-FISHLAB is research on wild fish in their natural environments through long-term field studies with an ability to track the movement and fate of individual fish. In addition, the group conducts experiments in aquaria (Höglund et al. 2021) – sometimes in combination with field studies (e.g. Villegas-Ríos et al. 2018) – to increase the explanatory power of field- based work. In the Tvedestrand fjord acoustic telemetry array, several marine fish species in areas with different levels of protection are monitored. Study species are tagged with acoustic (sound-emitting) electronic tags, with signals that are detected by an array of hydrophone receivers (but not the fish themselves). The array of receivers allows for detailed three-dimensional studies of fish movement within the study area, sometimes in combination with habitat data (Freitas et al. 2016). Data from the Tvedestrand fjord acoustic telemetry array have been utilized in several master’s, PhD and postdoctoral projects at CCR and IMR. In these projects, molecular tools are often used in combination with telemetry to fully utilize the explanatory potential of assignment of individuals to sub-stocks or spawning populations.

The ongoing CODSIZE project, funded by the Research Council of Norway, explores the role of large fish for population productivity and ecosystem structure. The project is centred around data collection within Norway’s first no-take marine reserve in the Tvedestrand fjord, where cod has been protected from fishing since 2012. Specifically, the spawning and feeding behaviour of large cod versus smaller cod and their reproductive output and fitness in a natural system are explored. The project collaborates broadly with experts in stable isotope analyses, genetics and ecosystem modelling.

In other settings, passive integrated transponders (PIT- tags) are used to study migrations of anadromous (Atlantic salmon and brown trout) and catadromous species (European eel) in rivers and estuaries. These miniature tags are activated and detected when fish pass antennae placed strategically in places that fish must pass during migrations. Such systems allow long-term monitoring of the comings and goings of large numbers of individuals. Vital information can be obtained regarding life-history traits such as timing of migration to sea and survival of individuals during the sea phase, as well as the return rate in relation to age and body size (Haraldstad et al. 2019). What about fish that migrate further? In 2021, CCR’s C-FISHLAB will expand into the open Skagerrak sea and take part in a regional effort to increase the coverage of hydrophone receivers.
Together with national and international collaborators, the C-FISHLAB uses these cutting-edge acoustic technologies to conduct novel research within the rapidly developing field of eco-evolutionary dynamics of marine species. In light of this goal, CCR hosted the 5th International Conference on Fish Telemetry in Arendal in 2019, in cooperation with the Institute of Marine Research. This conference attracts the major international research community and provided a unique opportunity for communicating our science and identifying new potential collaborators.