PREDATION RATES BY NORTH-SEA COD (GADUS-MORHUA) - PREDICTIONS FROM MODELS ON GASTRIC EVACUATION AND BIOENERGETICS

We compared four different methods for estimating predation rates by N orth Sea cod (Gadus moi hua). Three estimates, based on gastric evacua tion rates, came from an ICES multispecies working group and the fourt h from a bioenergetics model. The bioenergetics model was developed fr om a review of literature on cod physiology. The three gastric evacuat ion rate models produced very different prey consumption estimates for small (<0.5 kg) and large (>2 kg) fish. For most size and age classes , the bioenergetics model predicted food consumption rates intermediat e to those predicted by the gastric evacuation models. Using the stand ard ICES model and the average population abundance and age structure for 1974-1989, annual, prey consumption by the North Sea cod populatio n (age greater than or equal to 1) was 840 kilotons. The other two eva cuation rate models produced estimates of 1020 and 1640 kilotons, resp ectively. The bioenergetics model estimate was 1420 kilotons. The majo r differences between models were due to consumption rate estimates fo r younger age groups of cod. (C) 1996 International Council for the Ex ploration of the Sea