Individual behavioural differences, not body size or sex, structure spatial connectivity in coastal northern pike (Esox lucius) in the southern Baltic Sea

Individual variation in movement is fundamental to understanding population structure and dynamics in coastal fish. Here, we examine size- and sex-specific patterns of movement, spatial connectivity, and spawning site fidelity in coastal northern pike (Esox lucius) within and across years in a spatially extensive lagoon network in the southern Baltic Sea. We analysed capture–mark–recapture data for 666 recaptured pike (of 4597 tagged) and acoustic tracking data from 318 individuals, spanning total lengths from 28 to 126  cm. Neither mark–recapture nor telemetry data revealed a relationship between individual body length and sex, distance between capture and recapture, connectivity, maximum horizontal displacement, and among-year spawning site fidelity. Instead, spatial connectivity and movement ranges were significantly correlated between years and statistically repeatable, indicating stable inter-individual variation in movement behaviour independent of body size or sex. These patterns point to a population in which movement roles are not structured by size or sex, but rather by stable individual-level differences in behavioural types. That said, events of significant spatial connectivity were rare, pointing to local recruitment dynamics within lagoons being dominant in coastal northern pike.