Personality of sea trout : A case study on ecology, conservation and dynamics in coastal Skagerrak

Abstract

Variation in fish behaviour seems to be an important part of species’ lifehistory and adaptation to environmental change. Interestingly, variation occurs not only in response to environmental cues, but can also be consistently different between individuals, reflecting differences in personality. By means of acoustic telemetry tracking, I set out to measure the movement and behavioural composition of sea trout (Salmo trutta) in the marine habitat. The study system was located in the Tvedestrand fjord, a Norwegian fjord bordering the Skagerrak coast, where a no-take marine reserve was also located. This enabled me to study how behavioural variation can be maintained in a population by means of spatial protection, by potentially protecting fish from fishing-induced evolution. Firstly, I found that home ranges varied both in size and location for individual sea trout. The amount of protection received by the marine reserve for individual sea trout was affected by both the home range size of the individual, and initial capture location (inside or outside of the reserve). Sea trout tagged in the reserve also spent the most time there, although an increase in home range size resulted in a marginal reduction in degree of protection. For individuals tagged outside of the reserve, an increase in home range size resulted in an increase in protection. Secondly, I found that sea trout spatial behaviour was repeatable, hereby representing differences in spatial personality which is likely to be partly heritable. Moreover, selection on fish ‘spatial personality’ differed between the reserve and the fished area. Here, individuals tagged inside the reserve experienced a decrease in survival with increasing home range size, whereas individuals tagged outside the reserve experienced an increase in survival with increasing home range size. Effectively, the fitness landscape of sea trout was affected by the no-take marine reserve as a spatial management measure. Third, using accelerometer tags, I obtained high-resolution spatial behaviour data, and found evidence of personality, temperature and light conditions (time of day) driving variation in activity of sea trout. Fourth and last, I investigated trends in sea trout catches along the Skagerrak coast using data from a scientific beach seine survey conducted during the past 100 years, and found that catches have been increasing for the past four decades in six Norwegian coastal regions. Conclusively, sea trout behaviour as measured in the wild, was found to vary both in response to environmental cues and as an effect of innate individual differences in behaviour, i.e. personality. To protect behavioural variation in a population from fishing-induced selection, marine reserves are a useful management tool, and optimally, a network of marine reserves can provide heterogeneity in fishing pressure and the selective landscape through which the sea trout moves when occupying its coastal marine habitats.