Migratory patterns and productivity potential of juvenile Sea Trout (MAPS)

In Sweden, sea trout is an important resource with increasing interest from anglers, but little is known about factors determining its population size. In 2016, sea trout in Sweden were red listed by the World Wildlife Fund, as stocks are not currently sustainable. Sea trout spawn in streams and after 2-3years the juveniles (smolts) migrate to sea.

Previously we showed that both temperature and discharge affect the outward migration of smolt. However, there is much variation in survival and migration pattern, within and between streams.

By tagging young trout with transponders and using fixed antenna arrays in multiple streams across Europe we will investigate how stream habitat complexity, altitude and length of adult spawning migration correlates with the performance of juvenile trout in terms of smoltification, residence time, survival and growth.

Using smolt traps near river mouths we will validate and fine tune models to assess smolt production based on the proportion anddistribution of freshwater habitats.

In addition, behavioural and physiological differences between fry originating from short and long distance migrant parents will be examined in controlled laboratory experiments. We predict that offspring from long distance migrant parents will be more exploratory and have a higher metabolic rate.

The project will generate key information on sea trout biology and produce important guidelines on how to prioritise restoration work for sustaining their populations.