Stock-environment recruitment models for Norwegian spring spawning herring (Clupea harengus)

Different stock-environment recruitment models for Norwegian spring spawning herring (Clupea harengus) are fitted to a time series of spawning stock, recruitment, and temperature data extending back to 1907. In addition to the traditional temperature index from the Barents Sea (the average annual temperature in the Kola transect), we also developed a new index based on the temperature in the larval drift trajectories during early larval life. The models show highly significant effects of both spawning stock and temperature. The inclusion of the temperature term in the stock-recruitment models removes the autocorrelation from the residuals and improves their explanatory ability by 6-9%. We explore the interdependence between recruitment success and subsequent spawning stock biomass and conclude that this is not likely to generate the stock-recruitment relationship. Our analysis suggests that the collapse of the Norwegian spring spawning herring stock in the period 1950-1970 was not caused by reduced recruitment, but by the drop in spawning stock biomass induced by the increased fisheries in this period.