Early estimates of recruitment of the Belt Sea cod stock
Keywords:Baltic Sea, cod, year class strength, reproduction, condition, maturity stage
The Belt Sea cod stock produced very different year class abundances from 1993 to 1999. After the strong year class 1994 a poor year class 1995 followed. Stronger year classes were observed again in 1996 and in 1997. Comparative analyses of the maturity development of female cods, of the fecundity and of the year class abundance demonstrated the following: The maturity development of female cods from November to March was very different in the years investigated. However, the analyses showed that an early or late beginning of the maturity development did not give any indications concerning the new year class abundance. The year class strength of Belt Sea cod is mainly determined by the portions of female cod having a maturity stage of more than II at the beginning of the main spawning season in March. A trawl survey during the beginning of the spawning season for estimating the portions of active female spawners can be used for assessing the actual potential population fecundity and arriving at a first estimate of the new year class abundance with acceptable accuracy. These data are available before the spawning season of the Belt Sea cod is finished. The large variations of the portions of active female spawners are influenced by the abundance and the spatial distribution of the main prey component age group 1 herring and by the temperature conditions during the prespawning period.
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