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

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.