Preliminary assessment of the trophic structure of demersal fish community in the Sea of Oman

Detailed knowledge on the trophic ecology of marine species is an essential asset for the development of appropriate ecosystem-based management of marine fisheries. In the Sea of Oman, no studies to date have addressed the diet of demersal fish inhabiting soft-bottom habitats, despite the importance of these habitats for local fisheries. This study provides a preliminary investigation of feeding strategies displayed by demersal fish communities at two seasons in the Sea of Oman, Muscat waters, based on stomach content and dorsal muscle δ¹⁵N, δ¹³C and δ³⁴S analyses. A total of 46 fishes from 15 species, 14 families and 7 orders were collected in December 2013 and March 2014. All species displayed a carnivorous diet, with variable contributions of invertebrate and fish prey. While stomach content data suggested that Fistularia petimba (Fistulariidae), Saurida tumbil (Synodontidae) and Ulua mentalis (Carangidae) were mostly piscivorous, their δ¹⁵N values strongly overlapped with other species found to feed mostly on invertebrates, suggesting a mixed fish-invertebrate feeding on a longer time scale. No significant variations were found between months in terms of mean isotopic values, but larger range values and variances were observed for δ¹³C and δ³⁴S in December, possibly indicating the consumption of food resources from more diverse mixture and origin during that month. Only δ¹⁵N was weakly but significantly related to fish size at the community level, suggesting a poor size-related structuration of the demersal fish community at the spatial and temporal scale examined, consistent with other studies in the study area. However, the low number of samples analyzed limited the scope of our conclusions, and further investigations based on stable isotope methodology are needed to obtain essential biological knowledge for ecosystem-based management of fisheries in the Sea of Oman.