Predation on herring (Clupea harengus) eggs and young larvae.
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The study presented here is part of a greater project dealing with recruitment studies of a local herring stock in Lindåspollene north of Bergen. Fish predators on herring spawn, mainly cod and haddock, were trapped in entangling nets near the spawning ground during 1978, 1979 and 1980. On the basis of stomach contents of these fish species, one has tried to estimate to which degree fish predation on herring spawn influences total egg mortality. During years with moderate and heavy spawning, fish feeding on herring eggs seems to play a minor role in Lindåspollene, but during years with ligh spawn (1978), fish predation was estimated to make up maximum 40-60% of total egg number. These estimates depend closely on fish abundance which is insufficiently known. On the basis of mean stomach contents and values obtained from the literature on food consumption and daily energy requirements, a cod specimen has been calculated to ingest about 15-20 000 eggs daily. Staging of herring eggs in fish stomachs indicates that the natural mortality of herring eggs is variable, and increases towards the time of hatching. In situ observations of planktonic invertebrates preying on newly hatched herring larvae, confirm the presumably high predator potential of planktonic invertebrates previously reported (FOSSUM and JOHANNESSEN 1979). Bolinopsis sp. and Sarsia sp. especially, but also Pleurobrachia sp. and other medusae-species were recorded in situ preying on herring larvae.