Diel patterns of fish activity in the Vistula Lagoon’s littoral zone: integrating acoustic and net fishing methods

The study investigated summer diel variability in fish abundance and movement within a highly eutrophic Baltic lagoon, with a focus on horizontal migrations between reed beds and open water. A combination of multibeam ARIS sonar and traditional net fishing was employed, allowing for continuous, non-invasive monitoring of fish behavior alongside assessments of species composition and size structure. The dominant species caught included roach, bleak, silver bream, and juvenile perch. Acoustic recordings revealed consistently higher fish activity during the day compared to night, with activity elevated during the full moon relative to the new moon. Morning migrations to open water were observed, whereas mass evening migrations back to the reed beds occurred only once. The study suggests the presence of reverse migration patterns, potentially driven by improved night visibility and predation pressure from sander.