فهرست مطالب علیرضا راستگو

The present study aimed to the biodiversity of Chondrichthyes and distribution of this group of aquatic animals in the Persian Gulf and Oman Sea using biodiversity indices and finally, the maps were ploted using the GIS software. Data collection was carried out from October to December 2018 using bottom trawler by Ferdows from Sistan and Baluchestan and Hormozgan provinces waters in the Persian Gulf and Oman Sea. A total of 4014 specimens were caught in the study area, of which 245 specimens belonged to 10 species and 4 families of sharks and 3769 specimens belonged to 21 species and 12 families. The results showed that Margalef species richness index varied from zero to 1.82 for sharks and from zero to 2.65 for batoids. Also, the Pielou’s evenness index varied from 0.43 to 1 for sharks and from 0.11 to 1 for the batoids. Also, the Shannon index varied from zero to 1.9 for sharks and zero to 1.86 for batoids. The Shannon Diversity Index distribution for sharks only showed a range of 54 to 56 degrees longitude (range south of Qeshm Island to Bandar-lengeh) as a hotspot compared to the rest of the study area. On the other hand, the distribution of this index showed two points, range from 57 to 59 degrees longitude (Sirik to Meydani) and of 53 to 55 degrees longitude (Kish Island to Qeshm Island) as hotspots for the presence of batoids.

Current study was aimed effect of environmental factors on spatial ecology and habitat use of three sympatric elasmobranch species in the Iranian waters of Gulf of Oman. Sampling was carried out from the northern part of Gulf of Oman using bottom trawl of FERDOWS from October to November 2017. Environmental factors were recorded by CTD and the GAM model was used to determine the factors influencing on habitat preferences by species. The results showed that chlorophyll a is the most effective factor in the habitat use of Iago omanensis. On the other hand, the frequency of Rhinobatos annandalei had a significant correlation with the dissolved oxygen, chlorophyll a, temperature and electrical conductivity. Also, temperature and electrical conductivity had the most important role on the spatial ecology of Torpedo sinuspersici. The results of this study improve our knowledge and understanding of the ecology of the distribution of sympatric elasmobranch species in the Gulf of Oman, which can be used to introduce locations with the probability of these species and their spatial analysis for other interested researchers and future fishery management.

A new species of genus Acanthobothrium Blanchard, 1848 is described from the spiral intestine of Pastinachus cf. sephen (Forsskal, 1775) from Iranian coasts of the Gulf of Oman. The morphological characteristics of specimens were analyzed with light and scanning electron microscopy. Acanthobothrium chabahariense n. sp. is a category 1 species (with Pastinachus. It is distinguished from the other species from the region within the genus by a combination of the following morphological features: total length, number of proglottids, hook length, number of testes and ovarian lobe length. Pastinachus sephen is a complex group still with no taxonomic resolution; therefore, the identity of the host in this study area is in question. Because of the molecular study of specimens from the Gulf of Oman did not completely correspond with P. sephen since they were introduced as P. cf. sephen. This brings the total number of species of Acanthobothrium from Pastinachus to 11 and the total number of Acanthobothrium species described from the Persian Gulf and the Gulf of Oman to seven. In addition, an identification key to the Acanthobothrium species occurring in the Pastinachus species was provided.

This study aimed to investigate on species diversity of elasmobranches in the Iranian waters of the Persian Gulf (Hormozgan province) and Oman Sea, and length- weight relationships for dominant species were estimated. For this purpose, samples were collected using both industrial-research bottom trawlers of using“Ferdows” class ship and shrimp trawlers by-catch, between May 2014 and September 2015. A total of 709 individuals, belonging to 28 elasmobranch species (19 batoids from 11 families and 9 sharks from 5 families), were collected and studied. Between the species of batoids, seven species were dominant, including Torpedo sinuspersici (107 individuals), Himantura randalli (99 individuals), Gymnura poecilura (77 individuals), Brevitrygon imbricata (79 individuals), Rhinobatos punctifer (68 individuals), Pastinachus sephen (46 individuals) and Aetobatus flagellum (17 individuals), while among sharks, five species, including Iago omanensis (63 individuals), Rhizipriondon acutus (47 individuals), Carcharhinus macloti (35 individuals), R. oligolinx (17 individuals) and Chiloscyllium arabicum (18 individuals) were dominant in the sampling region, for which length –weight parameters were estimated. In general, most species showed positive allometric or isometric growth. Also, both the disk length-weight and disk width-weight relationships showed a good fit, indicating the credibility of these factors for investigating the length-weight relationships.

In this study, trophic interactions were studied among three elasmobranches including Iago omanensis, Rhinobatos punctifer and Torpedo sinuspersici coexisting in the depth ranging from 50 to 100 meters in the Oman Sea (Sistan and Balochistan waters). A total of 238 specimens were collected using industrial bottom trawlers of ‘FERDOWS’ during spring and summer,2014 and their stomach contents were analyzed based on VI, FO, %IRI indices and nMDS analysis. Results showed that I. omanensis fed mainly on teleosts, and crustacean and cephalopod were found in the several stomachs. Moreover, T. sinuspersici had specialized diets on teleosts. On the other hand, R. punctifer had a specialized diet on crustacean. An analysis of similarity showed significant differences among three studied species (R=0.574; P=0.001). Analysis of pair-wise tests detected the greatest dietary differences between R. punctifer and T. sinuspersici, while I. omanensis and T. sinuspersici showed the lowest differences. The results showed that there is resource partitioning, which can be related to morphology and feeding behavior of each species.

The estimation of fractional trophic levels is essential for the management of fisheries resources as well as for quantifying the ecosystem effects of fishing. The main aim of this study was estimation of trophic levels in different marine organisms using TrophLab software in the Persian Gulf and Oman Sea. We gathered all available information on diet that has been locally described. Usable diet data of 25 species resulted in 28 trophic level estimates that ranged from 2.28 to 4.50. For those fishes with more than one dietary study estimation of trophic level was found to vary, probably due to a combination of different size ranges, with bigger fish tending to have higher trophic levels. The maximum trophic levels were obtained for Euthynnus affinis, Sphyraena putnamae, Thunnus tonggol and Thunnus albacores with amount of 4.50, 4.50, 4.49 and 4.45, respectively. An ordinary regression model relating trophic level and body length was formulated. Result showed that trophic level and body length were moderately correlated. This is the result of the fact that as fish grow their relative success rates increase due to ontogenetic changes in sensory and swimming capacities. Trophic level and regression model should be of help in the formulation of trophic indicators and models marine ecosystems.