Pikeperch (Sander lucioperca (L.)) in Decline: High Mortality of Three Populations in the Northern Baltic Sea |
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Authors: | Noora Mustam?ki Ulf Bergstr?m Kaj ?djers Alf Sevastik Johanna Mattila |
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Affiliation: | .Environmental and Marine Biology & Husö Biological Station, Åbo Akademi University, Tykistökatu 6, 20520 Turku, Finland ;.Department of Aquatic Resources, Swedish University of Agricultural Sciences, Skolgatan 6, 74242 Öregrund, Sweden ;.Provincial Government of Åland Islands, Fisheries Division, PB 1060, 22111 Mariehamn, Åland Islands Finland ;.Ulriksgatan 43, 74234 Östhammar, Sweden |
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Abstract: | 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.Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-013-0429-z) contains supplementary material, which is available to authorized users. |
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Keywords: | Year-class strength Commercial fishing Multimesh gillnet monitoring Mortality Great cormorant |
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