Pikeperch (Sander lucioperca (L.)) in Decline: High Mortality of Three Populations in the Northern Baltic Sea
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The development of three pikeperch (Sander lucioperca (L.)) populations in the northern Baltic Sea was monitored using standardized multimesh gillnets in 1995–2009. Declining trends in the abundances of pikeperch over 40 cm total length, low numbers of individuals older than 6 years, and high mortality rates were observed in all three populations. In the site with the largest commercial catches per unit area and a rapidly increased colony of great cormorants (Phalacrocorax carbo sinensis Blumenbach 1798), also the abundance of pikeperch below 40 cm total length and year-class strength showed declining trends. The adverse population level changes did not correlate with changes in water quality or eutrophication status. Together, the results suggest that in all study sites fisheries are harvesting a large proportion of the pikeperch soon after or even before reaching the maturity, and that predation from great cormorants may increase mortality of juveniles. Pikeperch is important not only for fisheries but also for ecosystem functioning, and our results point at the need for further management measures to ensure viable populations in the areas studied.
KeywordsYear-class strength Commercial fishing Multimesh gillnet monitoring Mortality Great cormorant
We thank the Environment Agency of the Provincial Government of Åland Islands, Husö biological station, Finnish Meteorological Institute and Svealand’s Coastal Water Management Association for providing data. Special thanks to Outi Heikinheimo, Tom Karlsson, Åsa Hägg, Kerstin Söderberg, Maria Boström and everyone involved in performing the gillnet monitoring. This study was financed by the Baltic Sea 2020 Foundation, Åbo Akademi University Endowment and Swedish Cultural Foundation in Finland.
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