Potential reasons for the changes in the abundance of pike, Esox lucius, in the western Gulf of Finland, 1939–2007

Abstract

Pike, Esox lucius L., catch-per-unit-effort (CPUE) in rod and line fishing fluctuated considerably in the western Gulf of Finland between 1939 and 2007. Since the beginning of the 1980s, CPUE has been only 3-4% of the highest CPUE during the period, suggesting a drastic decrease in population size. The collapse of the population coincided with a rise in the nutrient level in the Baltic Sea and consequent changes in productivity, turbidity and vegetation. The differences in the food web that followed the environmental change may partly explain the variation both in CPUE and in the mean weight of pike caught. Long-term fluctuations in salinity and temperature, however, did not seem to affect the population size. The mean weight of pike fluctuated inversely with CPUE, indicating changes in the recruitment of pike to the study area.

Abiotic and fishing-related correlates of angling catch rates in pike (Esox lucius)

“…van Poorten and Post, 2005). Secondly, if catch rates in angling are applied as a proxy for population density (e.g., Pierce and Tomcko, 2003;Lehtonen et al, 2009), fishing effort over the previous days should be kept constant because it influences catch rates and might therefore influence the abundance index derived using angling gear.…”

“…Therefore, quantifying the vulnerability of fish to angling gear necessitates identifying environmental variation in angling catch rates, but this has rarely been investigated in detail using rod-and-reel-type angling. Moreover, as stock assessments are sometimes conducted using angling methods (e.g., Myers and Worm, 2003;Pierce and Tomcko, 2003;Hansen et al, 2005;Lehtonen et al, 2009), distinguishing environmental variations in angling catch per unit effort (CPUE; an index of relative abundance) from variation arising from differences in population density is vital for obtaining reliable information about the population size (Stoner, 2004).…”

Pike (Esox lucius L.) on the edge: consistent individual movement patterns in transitional waters of the western Baltic

“…In most areas of the Baltic Sea including the Danish straits, commercial catches of pike have declined considerably since the 1970s-1980s suggesting a drastic population decrease (Nilsson et al, 2004;Nilsson, 2006;Lehtonen et al, 2009;Ljungren et al, 2010). Reasons for these declines in the different areas are not well determined, whether due to poor recruitment, habitat deterioration, eutrophication or other reasons.…”

Temporally stable, weak genetic structuring in brackish water northern pike (Esox lucius) in the Baltic Sea indicates a contrasting divergence pattern relative to freshwater populations

“…In addition, pike is a much appreciated target for primarily recreational but also small-scale coastal commercial fisheries and thus of obvious socioeconomical value (Karlsson et al 2014). Severe local declines of Baltic pike have been reported (Andersson et al 2000;Westin and Limburg 2002;Lehtonen et al 2009;Rohtla et al 2012), and although pike is not regarded as threatened in the Baltic Sea, there is still reason for conservation concern .…”