Winter mortality of pikeperch (Stizostedion lucioperca) at age 0 is dependent on size, based on samples collected with trawls during 1961-1994 in Pärnu Bay, Estonia. Mortality increased as mean length of pikeperch in the first autumn decreased. The size-dependent mortality was analysed as correlation between mean lengths at age 0 in autumn and changes in mean lengths between age 1 and age 0. When the varying lengths at age 0 were taken into account, the duration of winter also affected mortality; longer durations of ice cover resulted in less size-dependent winter mortality. Since mean length at age 0 in autumn correlated positively with summer water temperature, winter mortality can be expected to decrease the warmer the summer.
The abundance of 0+ pikeperch, Stizostedion lucioperca (L.), in trawls was compared with water temperature, water level and commercial catches 6–9 years later. The abundance of juveniles in autumn was positively correlated with the water temperature but not with water level in May or in June. The sum of a year abundance of juveniles showed a strong correlation with the catch years later. This abundance and the cumulative water temperature between August and October inclusive in five consecutive years one year prior to recruitment into the commercial fishery explained 86% of the variation in catches. This empirical model indicates that catches of pikeperch depend on both juvenile abundance and water temperature.
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