THE DIET AND FOOD-CONSUMPTION OF WHITING (MERLANGIUS-MERLANGUS) IN THE NORTH-SEA

The stomachs of more than 19 000 North Sea whiting were examined in 1981. Almost 50% were either empty or were judged to have lost all or part of their contents through regurgitation. The contents of the remaining stomachs (approximately 9800) were analysed. The average weight of the stomach contents (S, g) including fish with empty stomachs, was related to the ungutted weight of the fish (W, g) as follows: S = 0.009 xW1057. Fish and Crustacea comprised at least 85% by weight of the stomach contents of whiting of all sizes, the proportion of fish increasing with predator size. Some geographical and seasonal differences in stomach contents were detected; annelids represented a significant proportion of the food of whiting in the southeastern North Sea, as did cephalopod molluscs in the north, during the first part of the year. Larger whiting eat larger prey. This is particularly noticeable in the case of fish prey where: Prey length = 0.57 X predator length087. The bulk of the fish prey consisted of seven species (cod, haddock, whiting, Norway pout, sprat, herring, and sandeels), each of which is of considerable economic importance. Although whiting feed on fish representing the entire range of age classes of the smaller fish species (Norway pout, sprat, and sandeels) they eat mainly the youngest (0 + and 1 +) age classes of herring, cod, haddock, and whiting. Quantifying the food requirements of fish species is notoriously difficult, but attempts have been made to estimate the annual food consumption by whiting in the North Sea. It is concluded that whiting may be one of the most important piscivorous fish in the North Sea. © 1991 Conseil International pour l'Exploration de la Mer.