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

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Abstract:

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.

Nous avons analysé l’interaction entre les processus reliés à la température et la prédation pour expliquer la force du recrutement d’âge 1 entre 1992 et 2006 chez la morue de la mer du Nord (Gadus morhua) et le tacaud norvégien (Trisopterus esmarki). Dans ce but, nous avons calculé un indice de l’impact de la prédation (PI) à partir de données d’inventaire. Nous présupposons que PI est fonction de l’abondance des prédateurs et du chevauchement spatial entre les populations de prédateurs et de proies. Nous avons élaboré des modèles additifs généralisés (GAMs) dans lesquels la biomasse du stock reproducteur (SSB), la température de surface de la mer (SST) dans les zones respectives de fraye et de nourricerie, ainsi que PI sont les variables explicatives. Chez les deux espèces, SSB n’a pas d’impact significatif sur le recrutement durant cet intervalle de temps. Les SST au printemps et PI expliquent en grande partie la variabilité interannuelle de la force du recrutement (88 % de la variance totale chez la morue et 68 % chez le tacaud). La SST détermine ainsi le niveau global du recrutement. Au-delà de certaines SST, cependant, l’effet sur le recrutement n’est plus significatif. Dans ces gammes de température, l’effet dominant est celui de la prédation. Le sort des stocks de morue de la mer du Nord et de tacauds norvégiens dans les conditions de réchauffement global sera donc fortement influencé par la condition du réseau alimentaire de la mer du Nord.

Document Type: Research Article

Publication date: 2009-04-01

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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