A Comparative Analysis of Feeding and Trophic Level Ecology in Stingrays (Rajiformes; Myliobatoidei) and Electric Rays (Rajiformes: Torpedinoidei)

Standardised diets and trophic level (T-L) estimates were calculated for 75 ray species from the suborders Myliobatoidei (67 spp.) and Torpedinoidei (8 spp.). Decapod crustaceans (31.71 +/- 3.92%) and teleost fishes (16.45 +/- 3.43%) made the largest contribution to the standardised diet of the Myliobatoidei. Teleost fishes (37.40 +/- 16.09%) and polychaete worms (31.96 +/- 14.22%) were the most prominent prey categories in the standardised diet of the suborder Torpedinoidei. Cluster analysis identified nine major trophic guilds the largest of which were decapod crustaceans (24 species), teleost fishes (11 species) and molluscs (11 species). Trophic level estimates for rays ranged from 3.10 for Potamotrygon falkneri to 4.24 for Gymnura australis, Torpedo marmorata and T. nobiliana. Secondary consumers with a T-L <4.00 represented 84% of the species examined, with the remaining 12 species (16%) classified as tertiary consumers (T-L >= 4.00). Tertiary consumers included electric rays (Torpedo, 3 spp. and Hypnos, 1 sp.), butterfly rays (Gymnura, 4 spp.), stingrays (2 spp.) and Potamotrygonid stingrays (2 spp.). Feeding strategies were identified as the primary factor of influence with respect to Myliobatoidei and Torpedinoidei T-L estimates with inter-family comparisons providing the greatest insight into Myliobatoidei and Torpedinoidei relationships.