AbstractsBiology & Animal Science

The northern blue whiting is a small mesopelagic gadoid, widely distributed in the north‐east Atlantic. The fishery on this species is extensive and is of commercial importance for several states, also Norway. There have been large variations in the abundance of the blue whiting the last 30 years, and what causes these variations has partially been an open question. By analysing the population dynamics of the northern blue whiting stock, using descriptive statistics, Leslie matrix models, multiple regression analyses, and general additive models (GAM) I here demonstrate that there have been extensive changes in the population structure of the northern blue whiting population mainly caused by a general decline in mean weight and mean age of the spawning stock. The variation in the population intrinsic growth rate is influenced by the heavy fisheries on the stock, the population size (N) and the mean age of the spawning stock, and the variation in recruitment can partially be explained by the size of the spawning stock, the mean age of the spawners and by the intensity of the north Atlantic subpolar gyre. I also demonstrate that survival in the spawning stock is density‐dependent and the density‐dependent effect is most evident in a spawning‐stock with where the mean weight of the spawners is high. There are clear signs of density dependent survival in the spawning stock and indications of a density dependent effect also in the egg and/or larval stages.