Large female northern pike (Esox lucius) do not connect spawning areas across a lagoon network in the southern Baltic Sea

Olga Lukyanova, Robert Arlinghaus, Félicie Dhellemmes

Exceptionally large individuals may serve as keystone connectors among subpopulations and habitats, a role recently demonstrated in large Atlantic cod (Gadus morhua) in Norway. To examine whether this pattern extends to other coastal fish species, we analysed capture-mark-recapture data for over 5,800 coastal northern pike (Esox lucius) and acoustic tracking data from 317 pike individuals, using a large biotelemetry array covering 1,200 km² in brackish lagoons in the southern Baltic Sea in Germany. The pike in our study spanned a wide size range, with total lengths ranging from 28 cm to 126 cm. In the capture-mark-recapture dataset, we observed a positive relationship between body length and distance between capture and recapture, but this correlation was driven by the presence of two particularly large and mobile individuals in the sample. In the acoustic telemetry dataset, we found no relationship between individual body length, connectivity, and maximum horizontal displacement over two spawning seasons, and separately for spawning and non-spawning periods. These findings suggest that large northern pike may not serve as keystone connectors among spawning sites in brackish lagoons.