MEPS 325:243-253 (2006)  -  doi:10.3354/meps325243

Prey switching of cod and whiting in the North Sea

Anna Rindorf*, Henrik Gislason, Peter Lewy

Danish Institute for Fisheries Research, Charlottenlund Castle, 2920 Charlottenlund, Denmark

ABSTRACT: Predator–prey switching may stabilise predator–prey interactions, promote co-existence of prey that share a common predator, and increase the overall stability of homogeneous systems of interacting species. This study presents an investigation of prey switching of 2 major North Sea fish predators, cod Gadus morhua and whiting Merlangius merlangus. Relative food composition derived from analysis of more than 36000 stomachs is compared to the relative density of fish prey reflected by trawl survey catches, and generalised linear models are used to examine how prey switching is affected by predator length and prey species and length. Possible effects of stomach sample size and predator density are also investigated. Prey preference is a decreasing function of the relative density of the prey (negative prey switching), in particular for large cod (40 to 100 cm). This was neither the result of variations in stomach sample size, nor of changes in local predator abundance. If not counteracted by compensatory changes in spatial overlap or total food intake, negative switching is likely to destabilise the interactions between cod and whiting and their fish prey.

KEY WORDS: Prey switching · Piscivorous fishes · North Sea · Ecosystem stability

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