Density-dependent growth and cannibalism in Northeast Arctic cod: Some implications for fishing strategies

Density-dependent growth of Northeast Arctic cod is studied empirically by regressing (i) the growth of different age groups of fish and (ii) the weight at age on the number of fish in the same and adjacent age groups. Density dependence is found for almost all age groups, but with the two approaches giving a somewhat contradictory evidence; using weight at age gives a correlation that rises with age, while growth gives the opposite result. The von Bertalanffy growth function is used to model fish growth, with density dependence modelled as affecting asymptotic weight. Cannibalistic mortality for younger cohorts is regressed on the number of fish in older cohorts, with a significant relationship found for fish over a certain age. Implications for catch-maximizing fishing mortality and gear selectivity are studied by examining the life history of normal versus large year classes. Fishing young age groups of large year classes to improve growth would not increase fish catches while increasing fishing mortality for older and cannibalistic year classes would increase catches by increasing the survival of young fish.