Predation rates by North Sea cod (Gadus morhua) – predictions from models on gastric evacuation and bioenergetics

Abstract

P. E. 1996. Predation rates by North Sea cod (Gadus morhua) -predictions from models on gastric evacuation and bioenergetics. -ICES J. mar. Sci., 53: 107-114.We compared four different methods for estimating predation rates by North Sea cod (Gadus morhua). Three estimates, based on gastric evacuation rates, came from an ICES multispecies working group and the fourth from a bioenergetics model. The bioenergetics model was developed from a review of literature on cod physiology. The three gastric evacuation 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 intermediate to those predicted by the gastric evacuation models.Using the standard ICES model and the average population abundance and age structure for 1974-1989, annual prey consumption by the North Sea cod population (age d1) was 840 kilotons. The other two evacuation rate models produced estimates of 1020 and 1640 kilotons, respectively. The bioenergetics model estimate was 1420 kilotons. The major differences between models were due to consumption rate estimates for younger age groups of cod.1996 International Council for the Exploration of the Sea

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Quota implementation of the maximum sustainable yield for age-structured fisheries

“…For example, the population for the North Sea cod is dominated by the age (or year) classes one and two. Estimated average values for cod population year-class abundance are 273 million for age class one (wet weight 32 grams), 84.3 million for age class two (wet weight 466 grams), 24.8 million for age class three (wet weight 1856 grams), 8.86 million for age class four (wet weight 3980 grams), 3.56 million for age class five (wet weight 5990 grams), 1.44 million for age class six (wet weight 8212 grams), 0.60 million for age class seven (wet weight 9420 grams), 0.27 million for age class eight (wet weight 10622 grams), 0.12 million for age class two (wet weight 11543 grams), 0.079 million for age class two (wet weight 12235 grams) (Hansson et al 1996). Given that North Sea cod usually reach maturity at the age of 3-5 years, we can label age classes 3 to 5 as young mature fish and age classes 6 to 10 as old mature fish.…”