Statistical evaluation and modelling of the stomach contents of Icelandic cod (Gadus morhua)

A model is proposed for investigating the statistical properties inherent in data on fish stomach contents of cod (Gadus morhua) taken on board Icelandic research vessels. The model explicitly incorporates components to describe the spatial distribution of prey species. It is found that combined delta-gamma (a presence-absence model and an abundance where present model, respectively) generalized additive models are useful in the analysis and explain a considerable portion of the variability in this type of data set, but a fairly large number of degrees of freedom is required to describe the behaviour of the data. A feature of the proposed model is the ability to combine information on the stomach contents from several predator length groups into a single analysis. Analytical results indicate that sampling procedures that base the analysis on the contents of individual stomachs are preferable to those based on combining the contents of several stomachs into aggregate samples.

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