Effects of predation from juvenile herring on mortality rates of capelin larvae in the Barents Sea

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In this study, we examine whether predation from juvenile herring has a significant effect on mortality rates of capelin larvae in the Barents Sea, which in turn might affect the year class strength in the capelin stock. Surveys were carried out in summer 2001, 2002, 2003 and 2004. Juvenile herring were sampled by pelagic trawl, and a Gulf III was used to sample capelin larvae and other zooplankton. Hydrographical and acoustic data were also collected. The stomach contents of herring and the zooplankton samples were dominated by Calanus finmarchicus and euphausiids. Capelin larvae with lengths in the range 7-25 mm dominated the ichthyoplankton. In 2001, juvenile herring were widely distributed and overlapped with capelin larvae over a wide area. At 11 of 24 stations where herring was caught, capelin larvae were observed in the herring stomachs. Average frequency of occurrence for capelin larvae was 7% (n = 612 herring stomachs). In 2002 and 2004, herring was almost absent from the trawl catches. Herring abundance in 2003 appeared to be higher than in 2002, but lower than in 2001. Large schools of herring were observed in one area, and analysis of three trawl samples from these schools revealed that the herring had been feeding intensively on capelin larvae. Five hundred nine capelin larvae were found in 330 herring and 39.7 of the herring stomachs contained capelin larvae. The effects of abundance of herring and capelin larvae and drift patterns on mortality rates were analysed and are discussed. A total estimate of 7.3% and 9.9% of the capelin larvae were eaten by herring per day in 2001 and 2003, respectively. This refers to stations where herring was presented in the trawl catches.