Modelling diet composition dynamics among North Sea predatory fish using a length-structured partial ecosystem model

McCaig, Chris and Speirs, Douglas and Thurlbeck, Ian and Needle, Coby and Heath, Michael (2012) Modelling diet composition dynamics among North Sea predatory fish using a length-structured partial ecosystem model. Canadian Journal of Fisheries and Aquatic Sciences. ISSN 1205-7533 (In Press)

Abstract

Studies of the gut contents of fishsh stocks in the North Sea show decadal changes in diet composition, as might be expected when the relative abundances of prey species change. In this paper we explore the extent to which a simple model of prey consumption deployed within a dynamic multispecies population model is able to capture those changes. We make use of a length-structured partial-ecosystem model (FishSUMS) in which the relative diet preferences are set by a combination of species weightings and predator-to-prey length ratios. Eleven species were included in the model with full length structure, together with other trophic resources represented in less detail. By tuning to various sources of data we show that, despite the simplicity of the representation of the predation process, it is capable of capturing some of the large observed changes in the sampled diets of predator species. We also quantify the rate at which individuals are lost to three sources of mortality; fishing, predation and density- dependent mortality.

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