NATURAL MORTALITY AND FISHING MORTALITY IN A COASTAL COD POPULATION: A RELEASE–RECAPTURE EXPERIMENT

Abstract

As with most teleosts, the life cycle of the cod (Gadus morhua) is characterized by high productivity of eggs leading to high concentration of larvae. These stages are known to be associated with high mortality rates. Mortality of older stages (juveniles and adults) has been relatively poorly studied. We use capture–mark–recapture (CMR) methodology to estimate time and age variation of natural mortality and fishing mortality in a coastal cod population within the Norwegian Skagerrak coast. A total of 36 728 reared 6-mo-old, and 2415 wild-caught mostly 18-mo-old, individually tagged cod were released in four consecutive years, leading to 4155 recaptures by fishermen. Tag loss and mortality due to tagging appeared negligible for reared young fish, but up to 60% of the wild-caught tagged fish disappeared just after release. Tag return by fishermen was ∼50–60%. Natural mortality was found to be high in the 6–12 mo range, but subsequently it decreased rapidly and was no longer age-dependent. Fishing mortality ...