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Temporal and sexual effects in feeding ecology were examined in the marbled sand skate ( Psammobatis bergi). Of 137 stomachs analysed, 130 (95%) contained food. Among these, >50% contained between 2 and 4 items, with a maximum of 18 prey items found. Thirty taxonomic levels of prey items were identified: 18 crustaceans, 5 polychaetes, 3 molluscs, 3 teleosts, and 1 chondrichthyan. Coenophthalmus tridentatus and unidentified Brachyura were the dominant prey items by number, frequency of occurrence and index of relative importance (IRI). Libinia spinosa was the dominant item by mass and third most important by %IRI. Psammobatis bergi consumed mostly brachyurans and showed little variability in overall mean prey importance, hence, only a small number of stomachs was needed for a precise description of its dietary composition. There was no interaction between season and sex in the diet composition of P. bergi and there were no differences between the diets of males and females during winter and spring. However, a seasonal pattern was found. The most important prey in spring was C. tridentatus by number and L. spinosa by mass whereas in winter the most important prey was Peltarion spinosulum. The temporal pattern indicates that P. bergi probably modifies its diet in response to prey abundance. [ABSTRACT FROM AUTHOR]

Sources of variation in dietary composition were examined in the piked spurdog (Squalus megalops). The species is an opportunistic predator that consumes a wide range of prey items. When importance of prey was measured by weight or occurrence, S. megalops preyed largely on molluscs and teleosts. However, when number of prey was considered, the main items were crustaceans. A bootstrap analysis showed that considerable variability can be expected in the importance of prey items in the species'' overall diet. Regional, seasonal, and ontogenetic differences in dietary composition were found, but there were no differences between mature and immature sharks or between males and females. The spatial and temporal variation in diet exhibited by S. megalops and the intrinsic natural variability of the dietary composition of this opportunistic predator suggest that studies that infer predator–prey interactions from overall diet are likely to miss information on the ecological relationships among species and thus account for only part of these interactions. [Copyright &y& Elsevier]