Effects of temperature, wind and spawning stock biomass on recruitment of Arcto‐Norwegian cod

Abstract

ABSTRACTSea temperature has earlier been shown to have a large influence on the recruitment of Arcto‐Norwegian cod, Gadus morhua. We here hypothesize that this linkage is partly due to the direct effect of temperature on larval and juvenile growth. Secondly, temperature acts as a proxy for both biotic and abiotic factors influencing recruitment. Indices of abundance of early juvenile cod (2–3 months old), 0‐group cod (4–5 months old) and 3‐year‐old cod are analysed in more detail against the environmental temperature, wind stress components, wind‐induced turbulent energy and the spawning stock biomass. To deal with autocorrelation, non‐stationar‐time and nun‐normality, which complicate a statistical time series analysis, randomization and Box‐Jenkins methods are applied. In addition to the important effect of high sea temperature during the early life stage in forming strong year classes, the results show that the spawning stock biomass is nearly as important. Also, alongshore southerly wind stress anomalies during the period of pelagic drift (from April through summer) and offshore wind stress anomalies during egg and early larval stages (in April) act favourably on recruitment. The beneficial effect of southerly wind anomalies could he linked partly to high temperature, but the flux of zooplankton‐rich water from the Norwegian Sea into the feeding areas of the Barents Sea may also be increased. The favourable influence of offshore winds in April is less predominant and causal links are also less clear; possible explanations for this might be increased offshore spreading of eggs and early larvae, resulting in reduced risk of predation, and increased compensation inflow of intermediate Norwegian Sea water which, in this restricted period of time, has a high concentration of spawning copepods suitable as prey for the developing cod larvae.