Feeding ecology of demersal elasmobranchs from the shelf and slope off the Balearic Sea (western Mediterranean)

Abstract

SUMMARY: The feeding ecology of eight demersal elasmobranchs, three sharks (Etmopterus spinax, Scyliorhinus canicula and Galeus melastomus) and five batoids (Myliobatis aquila, Leucoraja naevus, Raja polystigma, R. miraletus and R. clavata), from the Balearic Sea (western Mediterranean) was analyzed. For each species, the diet and feeding habits were characterized by depth strata using quantitative indices such as diet overlap, diet breadth and prey diversity. Diet variation with size and depth were also tested for the most abundant species. For shelf-living species, natantian and reptantian crustaceans together with teleosts were the most important preys. On slope bottoms, euphausiids were the preferential prey for S. canicula and G. melastomus, while E. spinax fed mainly on cephalopods. The most specialist and generalist diet corresponded to G. melastomus living on the upper slope and S. canicula from the continental shelf, respectively. High overlap was found between all the skates on the continental shelf and the sympatric sharks S. canicula and G. melastomus on the slope. Significant overlap was also found between S. canicula and R. clavata on the continental shelf. Size was found to significantly affect the diet of S. canicula, G. melastomus and R. clavata, whereas depth affected exclusively S. canicula.Keywords: Elasmobranch, batoid, shark, feeding habits, diet overlap, niche breadth, Mediterranean. RESUMEN: Ecología alimentaria de elasmobranquios demersales de plataforma y talud en aguas de las Islas Baleares (Mediterráneo Occidental). -Se estudia la ecología alimentaria de ocho elasmobranquios demersales, tres tiburones (Etmopterus spinax, Scyliorhinus canicula y Galeus melastomus) y cinco rayas (Myliobatis aquila, Leucoraja naevus, Raja polystigma, R. miraletus y R. clavata), del mar Balear (Mediterráneo Occidental). Para cada especie se caracterizó la dieta y la estrategia alimentaria por estratos de profundidad mediante diferentes índices cuantitativos. También se analizó la variación intraespecífica de la dieta con la talla y la profundidad en las especies más abundantes. Las presas más frecuentes en especies de la plataforma continental fueron los peces y los crustáceos natantia y reptantia. En aguas del talud las presas principales de S. canicula y G. melastomus fueron los eufausiáceos, mientras que E. spinax consumió preferentemente cefalópodos. Las especies con la dieta más especializada y más generalista fueron G. melastomus del talud superior y S. canicula de la plataforma costera, respectivamente. En aguas de la plataforma se detectó solapamiento de dieta entre todas las especies de batoideos, así como entre S. canicula y R. clavata; el solapamiento fue significativo también entre S. canicula y G. melastomus del talud. Se observaron cambios ontogénicos en la dieta de S. canicula, G. melastomus y R. clavata, mientras que la única especie que mostró cambios de dieta con la profundidad fue S. canicula.Palabras clave: elasmobranquio, batoideo, tiburón, estrategia alimentaria, solapamiento de die...

A Tale on the Demersal and Bottom Dwelling Chondrichthyes in the South of Sicily through 20 Years of Scientific Survey

“…Analysis of the stomach contents of individuals caught in the northern Tyrrhenian Sea also found galley leftovers (in Ref. [28]). Blackmouth catshark is generally considered as having an awful taste and Sicilian fishers discard it immediately (in Refs.…”

“…E. spinax fed mainly on cephalopods (in Ref. [28]). The diet of E. spinax was composed primarily of mesopelagic fish, with decapod crustaceans and cephalopods of secondary importance (in Ref.…”

“…In particular, natantian and reptantian crustaceans together with teleosts were the most important preys (in Ref. [28]). S. canicula is taken in commercial fisheries across its range but only larger individuals are usually retained for human consumption; the juveniles discarded seem to have some possibility to survive.…”

“…Its maximum size is about 50-60 cm TL and it feeds mainly on crustaceans and bony fishes depending on the sex, size and also partly on the season (in Ref. [28]). The species is caught as bycatch in demersal trawl fisheries but is also fished with gillnets, longlines and handlines in artisanal fisheries (in Ref.…”

“…G. melastomus feeds mainly on shelf-living species, natantian and reptantian crustaceans together with teleosts (in Ref. [28]). Analysis of the stomach contents of individuals caught in the northern Tyrrhenian Sea also found galley leftovers (in Ref.…”