Future management of Laisriver Brown trout : what life history and enhancement strategy should be prioritized?

Abstract: The life history and coexistence of subpopulations of brown trout in the same drainage area are relatively well known. The three forms of trout; sea-run, lake-run and resident, can all be present in the same location at some period of their life cycle, e.g. during the parr stage or at spawning. Despite the presence of all three forms, mostly the sea-run strategy is targeted in management actions from fishery organizations. Commonly this is done by compensatory stocking, even though the survival and fate of stocked individuals are not fully understood. This study investigates the fate of two groups of brown trout in the Laisriver in northern Sweden; stocked sea-run hatchery-reared juveniles and wild adult trout. This was done by tagging and tracking using acoustic telemetry during 2019 and 2020 to 2021. In addition, a genetic comparison of the adult trout with a genetic baseline for the whole Vindelriver system. My results indicate that survival of stocked hatchery-reared juvenile trout is low and that wild adult trout in Laisriver is from a common origin with a genetic profile partly unique to Laisriver and that they can adopt both resident and anadromous life histories. The home range size for the adult trout that has adopted a resident life history reached over 80 km including both stream sections and lakes but was limited to the Laisriver only. My conclusion is that future management actions should aim on enhancing the resident trout stock rather than stocks assumed to be purely sea-run. I suggest that this should be done by habitat restoration measures and improved fishing regulations to protect the important large trout individuals. Finally, I highlight the need for future monitoring of movement patterns of adult trout to increase the knowledge which will lead to further improved management actions in the future.