f. ehteshami

Investigating the relations and mechanisms of coexistence among sympatric species is essential to comprehend their ecological roles in the food webs. In the present study, the diet and trophic interactions of 5 abundant teleost species coexisting in the northern Oman Sea were examined using stomach contents analyses. The cumulative prey curves showed that the sample size of each studied species was large enough to clarify the general dietary preferences. The vacuity indices of Netuma thalassina, Plicofollis dussumieri and Otolithes ruber were less than 50%, indicating the comparatively gluttonous behavior of these species, while the estimated vacuity indices of Lutjanus johnii and Carangoides malabaricus were more than 50%. Assessment of %IRI (index of relative importance) revealed that diets of N. thalassina, O. ruber and C. malabaricus were similar and consisted mostly of teleost fishes followed by crustaceans. Conversely, P dussumieri and L. johnii mostly fed on crustaceans followed by teleost fishes. Results showed that P. dussumieri and L. johnii occupied an intermediate trophic level, whereas N. thalassina, O. ruber and C. malabaricus occupied high trophic levels, placing them as top predators in the food web. In total, analyses indicated that there were no significant differences in diets between these 5 teleost species.

In the present study, a trophic structure model for some fish species of the northern Oman Sea is developed through using mass balance modeling software, Ecopath with Ecosim (EwE). In this model, we simulated 16 functional groups spread across an area of 3998.20 km2 from 2017 to 2018. Mean trophic level in the area of the present study was 3.49. Values calculated for system omnivory and connectance indices were 0.42 and 0.44, respectively. However, the values of ecotrophic efficiency in the model were high (>0.5) for most consumers of high trophic levels except for sharks and rays because of their high fishing mortality. Accordingly, mixed trophic impact showed that phytoplankton and detritus positively impacted almost all ecological groups. Also bentho-pelagics, the medium demersals, benthos, and crustaceans had a very negative impact on themselves due to cannibalism. Furthermore, the highest realized trophic level was 4.34 for sharks. The maximum omnivory index is calculated as 0.99 for medium demersals for feeding on a wide variety of preys. Also, the average catch per net primary production, i.e., the gross efficiency of the system was around 0.000198 (lower than the global average) indicating that the fishery is harvesting fishes high in the food chain. The primary production/respiration (PP/R) ratio is found to be 3.57 and the values of ascendancy (45.40%) and overhead (54.60%) showed stability of the ecosystem. Thus northern Oman Sea can be classified as an immature ecosystem (in the developmental stage), although it has some kind of system maturity. Accordingly, the food web of northern Oman Sea is consisted mostly of detritivorous, planktivorous, and carnivorous fish species. Besides, Ecopath with Ecosim (EwE) software can be an excellent option to examine interactions among ecological groups, and the impact of fishing in northern Oman Sea which is unquestionably helpful to develop concrete management strategies. The proper ecosystem-based fisheries management practice can improve the efficiency of this overexploited ecosystem.

In order to identify and determine the distribution of economic and ornamental seashells in the northern coasts of the Persian Gulf, sampling was done in upper, middle and bottom intertidal zone in all four seasons and in mud, sand and rocky substrates. Onshore samples were collected through diving and trawling. Identification of specimens was carried out inside the country and confirmed by Institute of Malacology, Tokyo, Japan.381 species belonging to 117 families and 231 genera were identified. There was no significant difference in the warm and cold months in terms of diversity, although the density of the species was much higher in the warm seasons. In terms of species diversity, Bandar-length, Faroor and Hendurabi islands were the most diverse. In terms of size, the largest shells found were Sepia pharaonius and Pinna muricata with a total length of 45 cm and the smallest one with a size of 1 mm was Acteocina involute.