Abstract
Elasmobranchs are among the species most threatened by overfishing and a large body of evidence reports their decline around the world. As they are large predators occupying the highest levels of marine food webs, their removal can alter the trophic web dynamic through predatory release effects and trophic cascade. Suitable management of threatened shark species requires a good understanding of their behaviour and feeding ecology. In this study we provide one of the first assessments of the trophic ecology of the “vulnerable” smooth-hounds Mustelus mustelus and M. punctulatus in the Central Mediterranean Sea, based on stomach contents and stable isotope analyses. Ontogenetic diet changes were addressed by comparing the feeding habits of three groups of individuals: juveniles, maturing and adults. Our results highlighted that the two species share a similar diet based mostly on the consumption of benthic crustaceans (e.g. hermit crabs). Their trophic level increases during ontogeny, with adults increasing their consumption of large-sized crustaceans (e.g. Calappa granulata, Palinurus elephas), cephalopods (e.g. Octopus vulgaris) and fish (e.g. Trachurus trachurus). Our results provide also evidence of ontogenetic shifts in diet for both species showing a progressive reduction of interspecific trophic overlap during growth. The results of this study contribute to improve the current knowledge on the trophic ecology of these two threatened sharks in the Strait of Sicily, thus providing a better understanding of their role in the food web.
Highlights
Elasmobranchs are among the species most threatened by overfishing and a large body of evidence reports their decline around the world
In this study we focused on the trophic ecology of the common (M. mustelus) and blackspotted smooth-hound (M. punctulatus) in the Northern sector of the Strait of Sicily (SoS), an area that probably hosts some of the last viable populations of these species in European Mediterranean w aters[29]
Crustaceans, mainly Brachiura and Anomura, were the most important prey for mmus juveniles (%index of relative importance (IRI) = 68.6) and adults (%IRI = 85.3), while Teleostea were the main prey for maturing specimens (%IRI = 49.4) (Table 2; Fig. 4)
Summary
Elasmobranchs are among the species most threatened by overfishing and a large body of evidence reports their decline around the world. The results of this study contribute to improve the current knowledge on the trophic ecology of these two threatened sharks in the Strait of Sicily, providing a better understanding of their role in the food web. Improved knowledge about the elasmobranch trophic ecology, including the prey consumed, trophic level, ontogenetic diet changes, especially in the Mediterranean species, can play a crucial role in the development of new fishery management strategies. Commonly known as smooth-hounds, have a high level of regional endemicity and are commonly distributed on the continental shelf in temperate to tropical w aters[21,22] They are small to medium-sized demersal mesopredator sharks commonly exploited as target species or caught as by-catch by several different types of fisheries (e.g. artisanal, trawlers, recreational) in many oceanic a reas[2,23]. Smooth-hounds are still exploited or caught as by-catch in trawling and artisanal fisheries in the few Mediterranean areas where viable populations are still existing, such as Tunisia[32], Northern Adriatic[33,34] and Mediterranean Turkish c oasts[26,35,36]
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