Feeding ecology and trophic segregation of two sympatric mesopredatory sharks in the heavily exploited coastal ecosystem of the Adriatic Sea

Feeding ecology and reproductive biology of small coastal sharks in Malaysian waters

Small coastal demersal sharks form a major proportion of the sharks landed in Malaysia. However, little is known about their feeding ecology and reproduction. This study sought to elucidate the dietary patterns, role of ontogeny in prey consumption, and reproductive biology of four dominant small demersal shark species in Malaysian waters: the Hasselt's bamboo shark, Chiloscyllium hasseltii; brownbanded bamboo shark, C. punctatum; spadenose shark, Scoliodon laticaudus; and Pacific spadenose shark, S. macrorhynchos. Dietary analyses revealed a high overlap in prey taxa consumed; clear resource partitioning among co-occurring species based on the percentage Prey-specific Index of Relative Importance (%PSIRI), with higher fish %PSIRI for Chiloscyllium hasseltii, higher cephalopod %PSIRI for C. punctatum, and higher crustacean %PSIRI for both Scoliodon species; and an ontogenetic diet shift, seen through changes in prey size. Based on the examination of reproductive organs, the results showed larger sizes at maturity for males compared to females for all four species; no obvious reproductive cycles, based on hepatosomatic and gonadosomatic indices for all species; female bias in the sex ratio of the embryos of Scoliodon species; and increased reproductive output (number of eggs or embryos and size of eggs) with larger female size for C. hasseltii and Scoliodon species. The partitioning of food resources minimizes direct competition for food and supports coexistence within shared coastal habitats. The reproductive strategies of these small coastal sharks appear to be favorable for supporting short-term population productivity; although a reduction in fishing pressure, especially from bottom trawlers, is essential for the long-term sustainable use of these sharks.

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 "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.

Triloculotrema euzeti n. sp. (Monogenea, Monocotylidae) from the nasal tissues of the blackspotted smooth-hound Mustelus punctulatus (Carcharhiniformes, Triakidae) from off Tunisia

Triloculotrema euzeti n. sp. (Monogenea, Monocotylidae, Merizocotylinae) is described from the nasal tissues of the blackspotted smooth-hound Mustelus punctulatus collected from the coastal marine waters off Tunisia. The new parasite species is distinguished from the other two species of the genus, T. japanicae Kearn, 1993 and T. chisholmae Justine, 2009, by the morphology of the sclerotised male copulatory organ which has longitudinal ridges. The species is also characterised by its oötype with short descending and ascending limbs (long and more convoluted in the other two species). The presence of three peripheral loculi, which is the main characteristic of the genus Triloculotrema Kearn, 1993, is unconfirmed. This is the first description of a species of this genus in the Mediterranean Sea and the first record from a coastal shark.