Pikeperch (Sander lucioperca (L.)) in Decline: High Mortality of Three Populations in the Northern Baltic Sea

Abstract

The development of three pikeperch (Sander lucioperca (L.)) populations in the northern Baltic Sea was monitored using standardized multimesh gillnets in [1995][1996][1997][1998][1999][2000][2001][2002][2003][2004][2005][2006][2007][2008][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.

Great cormorant (Phalacrocorax carbo) predation on pikeperch (Sander lucioperca L.) in shallow eutrophic lakes in Poland

“…These results agree with data in other publications that report pikeperch as being susceptible to cormorant predation (Engström 2001, Mustamäki et al 2014, Salmi et al 2015. In many areas where these two species occur together, it has been confirmed that the share of pikeperch in the cormorant diet fluctuates significantly (Emmrich and Düttmann 2011).…”

“…In Polish inland waters, the minimum pikeperch landing size is 45 cm, which is why cormorant feeding on pikeperch could be a significant factor influencing the successful management of this species. The cormorant has been confirmed to impact the abundance and size-age structure of pikeperch populations in the waters of the northern Baltic Sea (Mustamäki et al 2014).…”

Perch (Perca fluviatilis) and pikeperch (Sander lucioperca) in the diet of the great cormorant (Phalacrocorax carbo) and effects on catches in the Archipelago Sea, Southwest coast of Finland

“…Rudstam et al, 2004;Fielder, 2010;Jepsen et al, 2010;Vetemaa et al, 2010;Östman et al, 2012;Mustamäki et al, 2013) while in other studies no impact has been found (e.g. Engström, 2001;Liordos and Goutner, 2007;Lehikoinen et al, 2011).…”

“…The differences in the results depend on differences in the fish species studied, cormorant predation pressure, fishing pressure, fish community structure and research methods. Especially percids (Percidae) seem to be particularly vulnerable to cormorant predation (Rudstam et al, 2004;Fielder, 2010;Vetemaa et al, 2010;Östman et al, 2012;Mustamäki et al, 2013;Skov et al, 2014, but see Lehikoinen et al, 2011).…”

Length at maturity as a potential indicator of fishing pressure effects on coastal pikeperch (Sander lucioperca) stocks in the northern Baltic Sea

“…Unfortunately, no length distribution data are available for either the most critical time before the pikeperch fishery was closed in 2000, or from the time period shortly after it was reopened in 2007. Declines in the abundance of large individuals have also been reported in other pikeperch populations in the northern Baltic Sea (Mustamäki et al, 2014). The length distribution of the mature stock apparently reacts more rapidly to changes in fishing pressure than the TL50 values.…”