Migratory patterns and cyanotoxin concentrations of pikeperch (Sander lucioperca) in the coastal waters of the Baltic Sea

We used stable isotopes of sulfur (δ34S) and carbon (δ13C) to distinguish resident and migratory pikeperch (Sander lucioperca) among individuals captured from a coastal freshwater lagoon (Curonian Lagoon) and adjacent Baltic Sea waters. We found that non-migratory pikeperch collected from the lagoon had negative δ34S ratios (–1.84‰ to –0.17‰), whereas migrating individuals exhibited higher and more variable δ34S values (4.4‰ to 18.5‰). Our findings suggest that S isotopes may be a valuable tool for assessing migratory habits in the brackish waters. We also compared cyanotoxin concentrations among the resident individuals of Curonian Lagoon and the migratory individuals in or returning from the Baltic Sea. No difference in toxin levels was observed among the resident and migratory pikeperch, although toxin concentrations were frequently close to or exceeded the recommended concentrations for safe long-term human consumption.