A methodological approach based on fish ecomorphology was chosen to predict potential fish diet. This study tests a method used in earlier research on a marine ecosystem containing phylogenetically diverse organisms: the North Sea. Fish feeding morphology imposes constraints on feeding options. A bottom-up perspective was used to describe the demands that food makes on fish feeding morphology. A set of quantitative morphological variables were measured on fish and compared to the demands made by different food-categories. Common North Sea Gadiformes and Pleuronectiformes were analysed. The results of the measurements were used as a basis for predictions of potential diet. Five ‘morphotypes’ were identified: Large-mouthed flatfish, small-mouthed flatfish, soles, ling/rockling/haddock and other Gadiformes. The predictions on diet were checked by stomach content data from literature. The main conclusions were that morphology differed significantly among fish species indicating detailed morphological adaptations to specific food types. Furthermore the utilization of fast, relatively large prey were predicted better than the utilization of slow or sessile prey that is well hidden, hard to crack or otherwise ‘tough to handle’. Also the method failed to clearly separate different food types within this group of fast/large prey. Moreover, no clear distinction in stomach contents were found between Large-mouthed flatfish (being predicted as eating mostly shrimp) and Gadiformes (being predicted as eating mostly fish) within the group of fast prey hunters. Overall predictions succeed in separating different feeding guilds, but in some cases do not succeed in distinguishing between species. Knowledge on feeding behaviour on slow and sedentary benthic prey is a limiting factor. Also limiting the usefulness of the study is the incomplete knowledge and/or implementation of this knowledge on the distribution of both benthic fish and benthic prey items.
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