A MODEL FOR THE PHENOTYPIC PLASTICITY OF NORTH-SEA HERRING GROWTH IN RELATION TO TROPHIC CONDITIONS

An adaptation of the von Bertalanffy growth model is formulated to des cribe the phenotypic plasticity of fish somatic growth in relation to trophic conditions. The model is developed for the North sea Downs her ring (Clupea harengus). II suggests that annual growth variability dur ing 1974-1990 was mainly due to the combined effects of herring abunda nce and wind-induced turbulence (coincident with the spring stratifica tion of the water column). Springtime turbulences cause reduced and de layed planktonic blooms preceding the annual foraging period of Downs herring. The negative relation observed between herring abundance and growth is hypothesized to be due to intra-specific competition for tro phic resources. Incorporated into the calculation of yield per recruit , the established growth model provides slightly more optimistic diagn oses while dropping the classic assumption of constant weight at age. (C) Ifremer/Elsevier, Paris.