A preliminary investigation of the feeding ecology of skates (Batoidea: Rajidae) off the west coast of southern Africa

Abstract

The diets of 14 species of skates (Rajiformes: Rajidae) collected along the coast of South-Western Africa between Walvis Bay and Cape Agulhas over a depth range of 50–1 016 m were analysed. Two distinct communities of skates could be recognized on the basis of depth zonation, the boundary between these communities being at approximately 380 m water depth. These two skate communities have similar species components: the so-called biscuit skate community (the shallow one) has two crustacean specialists (Cruriraja parcomaculata, Raja wallacei), one fish specialist (R. alba) and two generalists (R. pullopunctata, R. cf. clavata); the so-named grey skate community has two crustacean specialists (Raja caudaspinosa, R. confundens) and two generalists (Bathyraja smithii, R. leopardus). The grey skate community appears to be a more complex and dynamic assemblage with higher diversity (at least 13 species) than the biscuit skate community (five species). In both communities the most common prey items were crustaceans and small demersal fish. Cephalopods and polychaetes were uncommon prey in most species. Other potential prey items commonly trawled but absent from the skates' diet included bivalve molluscs, gastropods and echinoderms. Although their importance has hitherto not been recognized, skates are important predators on the demersal crustacean and fish fauna in the Benguela ecosystem.