Some biological factors of blue whiting in the north-east Atlantic

Abstract

Total mortality coefficients of blue whiting in the spawning area as well as in the feeding area, were obtained for various years and for various yearclasses, by calculating the regressions of the natural logarithms of age frequency against age. Together with established fishing mortality coefficients, a mean value of 0.18 was calculated for the natural mortality coefficient; compared to 0.2 used by the Blue Whiting Assessment Working Group. The index of the larval Anisakis parasite on the liver surface of blue whiting was found to increase with host`s age. The burden of accumulation of this parasite did not seem to affect neither the condition factor nor the length growth in blue whiting. While the condition factor increased with age in the spawning area, the contrary was observed in the feeding area.