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

Maria Valls,Francesc Ordines,Antoni Quetglas,Joan Moranta

doi:10.3989/scimar.2011.75n4633

Abstract

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 .

Highlights

Trophic relationships are fundamental to understanding biological interactions in animal communities and how they respond to human exploitation
Considering depth strata, sample sizes ranged from 6 individuals of R. clavata caught on the US to 766 S. canicula individuals from the MS
The highest dietary diversity was found on the CS, where S. canicula and R. clavata showed the highest values in terms of numbers (4.10) and volume (4.55) respectively (Table 1)

Summary

Introduction

Trophic relationships are fundamental to understanding biological interactions in animal communities and how they respond to human exploitation. Elasmobranchs are top predators playing an important role in the marine ecosystems with a top-down control on the size and dynamics of many species (Wetherbee and Cortes, 2004). Despite the importance of feeding relationships to understand the food structure and dynamics of marine ecosystems, little is known about the feeding ecology of most elasmobranchs (Heithaus, 2004; Wetherbee and Cortes, 2004). This is especially true for batoids, which have received considerably less attention than sharks at a worldwide level (Ishihara, 1990; Motta, 2004). Few studies have focussed on the feeding ecology of batoids individual species in the Mediterranean Sea (Jardas et al, 2004; Romanelli et al, 2007; Saglam and Bascinar, 2008)

Methods

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Discussion

Conclusion