Epsilon Archive for Student Projects

Abstract

Northern pike (Esox lucius) play a crucial role in freshwater ecosystems, yet knowledge about their movement remains limited. With the increasing availability of telemetry technology, the traditional image of pike as sedentary ambush predators with limited migratory tendencies is being challenged, revealing more complex movement strategies with implications for ecology and management. In view of the particularly sparse data on large inland lakes, this study investigated the spatial and temporal movement patterns of pike in Lake Siljan, Sweden’s sixth-largest lake, using acoustic telemetry. Forty-five large adult pike were tagged at a wetland spawning site (Limsjön) and in the open lake (Storsiljan) in 2022 and 2023, and monitored over two years with a network of 28 receivers.

Movement patterns were highly variable across individuals, with maximum ranges spanning from less than 3 km to nearly 47 km, but mean ranges consistent across tagging groups (~26 km). Many pike used almost the entire system, although despite connectivity, none entered the northern basin, suggesting ecological avoidance rather than physical limitation. Seasonal dynamics were pronounced, pike expanded their ranges in autumn and winter and contracted them in spring when returning to spawning areas in some cases traversing almost the entire lake. Spawning behaviour showed strong site fidelity to Limsjön across years, with individuals returning in spring within a narrow thermal window of about 7 °C. While fish from the Storsiljan group mixed in the open lake outside the spawning season, only a small fraction used Limsjön which suggests that the Siljan population is composed of multiple spawning groups that remain largely distinct during reproduction but intermingle for the rest of the year.

Together, these results show that pike in large lakes can display the same ecological traits known from coastal systems, including spawning-site fidelity and subpopulation structuring. To safeguard population diversity and resilience, effective management will therefore require identifying and protecting multiple spawning habitats and recognizing the population as a mixed-stock fishery.