2 research outputs found
Ontogenetic trophic segregation between two threatened smooth-hound sharks in the Central Mediterranean Sea
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 \u201cvulnerable\u201d 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
Sharks Do Not Always Grow Slowly: Tagging Data Reveal a Different Pattern of Growth, Longevity and Maturity for Threatened Smooth-Hounds in the Central Mediterranean Sea
Elasmobranchs are among the marine species more threatened by overfishing. Their
conservation is often impaired by the lack of knowledge of species’ life history traits. We filled
knowledge gaps on age and growth of two threatened smooth-hound sharks (Mustelus mustelus, Mm;
Mustelus punctulatus, Mp) in the central Mediterranean Sea, combining standard vertebrae analysis
with growth increment data from a tagging survey. Our data revealed that the two species grow at a
faster rate than previously estimated using vertebrae reading only. The maximum age/size found
was higher for Mm (16 years, 170 cm TL) than Mp (8 years, 120 cm TL), the first species attaining larger
size-at-age than the second one. Mp reaches maturity at earlier ages (A50 3 years for both females
and males) than Mm (A50 females: 4 years; males: 3 years). The use of the tag-recapture method to
validate the growth rate, firstly derived by sectioned vertebrae readings, highlighted the presence
of false check marks. The new estimates of growth and longevity have important implications for
the assessment of natural mortality, productivity, and stock resilience to fishing pressure which,
combined with the high site fidelity highlighted by tagging data, may have crucial implications for
the conservation of these two threatened sharks in the Mediterranean Sea