Abstract
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.
Highlights
The increased level of information on elasmobranch (Chondrichthyes: Elasmobranchii) diets has seen a shift away from broad generalisations characterising all elasmobranchs as apex predators to more quantitative multi-species dietary assessments [1,2,3]
Diet standardisation and trophic level (TL) calculations were performed in accordance with Cortes [1] and Ebert & Bizzarro [2] with quantitative dietary data summarized from peer-reviewed journal articles, graduate theses and grey literature
Standardised diets and TL estimates were calculated for 67 Myliobatoidei species and eight Torpedinoidei species
Summary
The increased level of information on elasmobranch (Chondrichthyes: Elasmobranchii) diets has seen a shift away from broad generalisations characterising all elasmobranchs (sharks, skates, rays) as apex predators to more quantitative multi-species dietary assessments [1,2,3]. A similar analysis was undertaken by Ebert & Bizzarro [2] for 60 species of skate (Rajiformes: Rajoidei). In so doing, both studies provided a more holistic account of how elasmobranchs influence regional ecosystems. The Myliobatoidei is second largest suborder within the Rajiformes and comprises a morphologically diverse group of seven families, three subfamilies and over 200 recognised species [9,10,11]. While there are notable exceptions, such as the giant stingaree Plesiobatis daviesi (Wallace, 1967), species from the Myliobatoidei tend to inhabit relatively shallow, warm temperate to tropical waters and are common within the Indo-
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