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Personality of sea trout and why it matters in management

Susanna Huneide Thorbjørnsen at the Faculty of Engineering and Science has submitted her thesis entitled «Personality of sea trout. A case study on ecology, conservation and dynamics in coastal Skagerrak”, and will defend the thesis for the PhD-degree Friday 10 May 2019. (Photo: Private)

Some fish are bold and take larger risks when they look for food. This might make them more vulnerable to being eaten by a larger fish or maybe get caught on your fishing hook. A shy fish will stay safe, but might take longer to find enough food to grow larger.

Susanna Huneide Thorbjørnsen

PhD-Candidate

Susanna Huneide Thorbjørnsen at the Faculty of Engineering and Science has submitted her thesis entitled «Personality of sea trout. A case study on ecology, conservation and dynamics in coastal Skagerrak”, and will defend the thesis for the PhD-degree Friday 10 May 2019.

She has followed the PhD-programme at the Faculty of Engineering and Science with a scientific direction of marine biology. Read more about the Centre for coastal research (CCR) at the UiA. Salary and travel funding covered by UiA, filed work costs covered by the Institute of Marine Research.

Summary of the thesis by Susanna Huneide Thorbjørnsen:

Personality of sea trout and why it matters in management

A fish always has to adapt to the environment it inhabits, but there are also differences in behaviour between each individual that makes them tackle challenges in different ways.

Personalities

Some fish are bold and take larger risks when they look for food. This might make them more vulnerable to being eaten by a larger fish or maybe get caught on your fishing hook.

A shy fish will stay safe, but might take longer to find enough food to grow larger.

The sea trout in the Tvedestrand fjord also has different personalities, according to Susanna Huneide Thorbjørnsen’s PhD dissertation.

She has tracked the sea trout using acoustic telemetry – a method where a small tag is operated into the fish and sends sound signals to receivers positioned around the fjord, revealing depth use and enabling positioning.

Different individuals of sea trout had different home range sizes in the fjord and also different activity levels. These patterns persisted from one period of time to the next.

Activity and home range size

Previous studies have shown that personality traits in animals can be heritable.

If this is the case, us humans may affect selection on fish behaviour for example by fishing the boldest fish. Maybe this fish is also the fish that grows the fastest and gets the most offspring?

By looking at sea trout survival in relation to the marine reserve in the Tvedestrand fjord, Susanna found that fish initially caught in the reserve experienced reduced survival with increasing home range size, while fish caught outside the reserve experienced increased survival with increasing home range size.

By providing variation in fishing pressure, marine reserves or networks of marine reserves can help us to maintain a spectrum of personalities and behaviours in fish populations. This will be important when fish populations adapt to environmental challenges.

Increasing sea trout population

Susanna has also looked into the population dynamics of sea trout along the southeastern Norwegian coast using 100 years of data from a beach sine survey carried out by the Institute of Marine Research.

Largely, the sea trout population has increased since the 80’s until today, all the way from the county of Vest-Agder to the Swedish border.

Disputation facts:

The Candidate: Susanna Huneide Thorbjørnsen (1990, Porsgrunn). BA from NTNU - Norwegian University of Science and Technology, Masters degree from the University in Bergen. Current position: Leading research technician, Institute of Marine Research.

The trial lecture and the public defence will take place at Gabriel Scotts auditorium – B1-001, Campus Kristiansand.

Professor Tove Margrethe Gabrielsen, Department of Natural Sciences, will chair the disputation.

Trial lecture at 10:30 a.m.

Public defense at 12:30 p.m.

Given topic for trial lecture: "The role of inheritance, learning and environment in shaping consistent individual differences in fish behaviour"

Thesis title: «Personality of sea trout. A case study on ecology, conservation and dynamics in coastal Skagerrak”

Search for the thesis in AURA - Agder University Research Archive, a digital archive of scientific papers, theses and dissertations from the academic staff and students at the University of Agder. The thesis will also be available at the University Library, and some copies will also be available for loan at the auditorium where the disputation takes place.

Opponents:

First opponent: Professor Anssi Vainikka, University of Eastern Finland, Joensuu, Finland

Second opponent: Researcher II Eva B. Thorstad, Norwegian Institute for Nature Research (NINA)

Professor Dag Olav Andersen, Head of Department at the Department of Natural Sciences, UiA, is appointed as the administrator for the assessment commitee.

Supervisors were Professor Esben Moland Olsen, Associate Professor Even Moland and Professor Halvor Knutsen - all three from the Department of Natural Sciences at the University of Agder (UiA) / the Institute of Marine Research (HI).

Susanna Huneide Thorbjørnsen hunting for trout to study. (Photo: Private)

Susanna Huneide Thorbjørnsen hunting for trout to study. (Photo: Private)

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