International Council for the Exploration of the Sea

Benthos-fish interactions were quantified for North Sea cod and haddock on the basis of stomach content data co11ected within the framework of the Stomach Samp1ing Project in 1981. For comparison avai1ab1e cod data for 1980 were also inc1uded. Taking into account the density distribution of the predators and their absolute stock sizes according to VPA, consumption rates were ca1cu1ated for major prey taxa in three different areas by season, indicating 1arge regional and seasona1 variations. However, interannua1 variations between the two sets of cod stomach content data appeared to be comparative1y sma11 and it is conc1uded that from a mu1tispecies point of view the assumption of a constant quantity of avai1ab1e benthic food is as good as any. Crustacea represent the dominant prey of cod and anne1ids, echinoderms and crustacea contribute approximate1y equa1 shares in the food of haddock. When comparing epibenthic species compositions in cod stomachs and trawl catches 1arge incongruencies were observed. Some species frequent1y observed in stomachs do not occur in trawl catches, whereas for others it is the other way round. Not on1y are fish high1y se1ective, but apparent1y also samp1ing gear does not catch benthic anima1s indiscriminant1y. In the absence of re1iab1e quantitative data on relative prey abundance, analysis of prey se1ection is hampered. The estimated rate of consumption per unit area by the cod and haddock stocks combined decreases progressive1y from the southern (0.8 g.C.m2.y-l) to the northern North Sea (0.5). The resu1ts are compared with avai1ab1e production figures, indicating that either consumption is estimated too high or production figures are too 10w. One outstanding problem in such, comparisons is that benthos represents a high1y heterogeneous aggregate of organisms with very differenet positions in the food chain. Fish feed on1y on specific components, which are rare1y sing1ed out in benthos studies.