Assessment of the diets of cod and whiting larvae in a frontal region close to the Norwegian trench: co- existence or competition?

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Frontal regions are important hydrographic features that enhance the primary and secondary productivity of the North Sea and cause the aggregation of planktonic organisms, including fish larvae. As part of the EU-LIFECO project, we analysed the zooplankton prey availability and stomach contents of over 200 0-group cod (Gadus morhua) and whiting (Merlangius melangius) sampled in spring 2001 at stations inside and outside of a frontal region close to the Norwegian Trench. Whiting larvae appeared to feed on a more diverse sub-sample of the zooplankton community, whereas cod larvae appeared to preferentially select Pseudocalanus spp., even though these prey items were not the dominant component of the prey community.Our results show that whiting and cod are direct competitors for zooplanktonic prey. In addition, because they are more opportunistic, whiting larvae may be more robust to changes in the species composition of the prey community, and therefore out- compete cod larvae at times of low preferred prey abundance or under changing environmental conditions.