TROPHIC RELATIONSHIPS AND FEEDING HABITS OF FOUR DEEP-SEA SHARK SPECIES OFF THE SOUTH COAST OF PORTUGAL

In the present work, the feeding habits of four deep-sea shark species (Etmopterus pusillus, E. spinax, Galeus melastomus and Scyliorhinus canicula), taken as bycatch and discarded by commercial trawl fisheries, are studied also as part of some scientific projects that aim to study discards off the south coast of Portugal. Data was collected during 1997 to 1999. Stomach contents were analysed to infer trophic interactions between these four species through their diet composition. Some indices (frequency of occurrence, percentage by number, percentage by weight and index of relative importance) were used in order to express the importance of different prey in the feeding habits of these species. Multivariate analysis (Detrended Component Analysis, Principal Component Analysis, ReDundancy Analysis) were applied in order to determine major patterns of variation in prey data, and to examine which variables can best account for dietary variation in these deep-sea elasmobranch species. Two more and well defined groups (S. canicula and E. pusillus) and one non-defined group (G. melastomus and E. spinax) of predators were identified. Between these two groups, distinct feeding habits are evident being the sample distributions of the