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Modelling the distribution of fish accounting for spatial correlation and overdispersion

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Abstract:

The spatial distribution of cod (Gadus morhua) in the North Sea and the Skagerrak was analysed over a 24-year period using the Log Gaussian Cox Process (LGCP). In contrast to other spatial models of the distribution of fish, LGCP avoids problems with zero observations and includes the spatial correlation between observations. It is therefore possible to predict and interpolate unobserved densities at any location in the area. This is important for obtaining unbiased estimates of stock concentration and other measures depending on the distribution in the entire area. Results show that the spatial correlation and dispersion of cod catches remained unchanged during winter throughout the period, in spite of a drastic decline in stock abundance and a movement of the centre of gravity of the distribution towards the northeast in the same period. For the age groups considered, the concentration of the stock was found to be constant or declining in the period. This means that cod does not follow the theory of density-dependent habitat selection, as the concentration of the stock does not increase when stock abundance decreases.

Nous avons analysé la répartition spatiale de la morue (Gadus morhua) dans la mer du Nord et le Skagerrak sur une période de 24 ans à l’aide du processus log-gaussien de Cox (LGCP). Contrairement aux autres modèles spatiaux de répartition des poissons, le LGCP évite les problèmes reliés à l’absence d’observations et inclut la corrélation spatiale entre les observations. Il est, par conséquent, possible de prédire et d’interpoler les densités non mesurées dans n’importe quel site dans la région. Cela est important pour obtenir des estimations non erronées de la concentration du stock et d’autres mesures qui dépendent de la répartition dans la région toute entière. Les résultats montrent que la corrélation spatiale et la dispersion des captures de morues restent inchangées durant l’hiver pendant toute la période, malgré un déclin spectaculaire de l’abondance du stock et un déplacement vers le nord-est du centre de gravité de la répartition durant la même période. Pour les groupes d’âge considérés, la concentration du stock est demeurée constante ou a décliné durant la période. Cela signifie que les morues ne se conforment pas à la théorie de la sélection des habitats dépendante de la densité, puisque la concentration du stock n’augmente pas lorsque l’abondance du stock diminue.

Document Type: Research Article

Publication date: 2009-10-01

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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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