Recruitment of North Sea cod (Gadus morhua) and Norway pout (Trisopterus esmarkii) between 1992 and 2006: the interplay between climate influence and predation

The interplay between temperature-related processes and predation in determining age-1 recruitment strength between 1992 and 2006 was analysed for North Sea cod (Gadus morhua) and Norway pout (Trisopterus esmarkii). For this purpose, an predation impact index ( PI) was calculated out of survey data. PI was assumed to depend on the abundance of the predators and on the spatial overlap between predator and prey populations. Generalized additive models (GAMs) were created with spawning stock biomass (SSB) and sea surface temperature (SST) in the respective spawning and nursery areas and PI as explaining variables. SSB had no significant impact on recruitment during this time period for both species. SSTs during spring and PI explained the interannual variability in recruitment strength to a large extent (88% of the total variance for cod and 68% for Norway pout). The SST during spring determined the overall level of recruitment. At SSTs above a certain level, however, the effect on recruitment was no longer significant. In these temperature ranges, predation was the dominant effect. Therefore, the fate of North Sea cod and Norway pout stocks under global-warming conditions will be strongly influenced by the status of the North Sea food web.