Abstract
Demersal fish communities in marine ecosystems are affected by a diverse set of biological and anthropogenic factors, each of which can change their structure on a temporal and temporal scale. In this study, in four separate projects, the geomorphology of the Persian Gulf and Oman Sea and the effect of anthropogenic factors including heavy metals and total petroleum hydrocarbons, as well as, physicochemical factors and on biomass of demersal fish was investigated during 2018 to 2020. The results of heavy metal pollutants showed that there are spatial variations between the studied stations in four coastal provinces indicating environmental heterogeneity in terms of metal accumulation. Cadmium was identified as the most dangerous metal in the Persian Gulf and Oman Sea, and the stations around Chabahar Bay, Jask and Gabrik protected areas and Nakhilo Bushehr area were identified as the most polluted areas according to ecological indices. In terms of total petroleum hydrocarbons, the findings of the sediment quality evaluation showed that the sediments of the Persian Gulf and the Oman Sea are classified as non-polluted to slightly polluted, and the concentrations closest to the threshold are observed in the sediments of Khuzestan province. The findings of the spatial and temporal changes of the physicochemical variables showed that most of the variables, except temperature and salinity, had significant spatial fluctuations between the Persian Gulf and Oman Sea stations. Environmental variables showed a significant correlation with each other, so that with increasing temperature and silicate concentration, and decreasing salinity, the amount of chlorophyll-a increased in two ecosystems. Significant changes were observed in the environmental variables during three years, so that among the variables, about half of them showed an increasing trend from 2018 to 2020. Based on bottom geomorphology, 13 geomorphological landforms in the coastal area of Khuzestan province, 22 landforms in Bushehr province, 22 landforms in the coastal area of Hormozgan province, and 22 landforms in the coastal area of Sistan and Baluchistan province, were identified and separated. Based on the amount of biomass of aquatic fish in bottom trawling fishing, the contribution of the Persian Gulf in the density of demersal fish was equal to 71440.5 tons and 58.4% of the total biomass. The highest amount of total biomass, commercial and non-commercial benthos was observed in the areas of Sirik to Meidani of Hormozgan province in Oman Sea, as well as, in Bardkhon areas to Dayyer from the fishing grounds of Bushehr and Bandar Abbas to Sirik from the fishing grounds of the west of Hormozgan province in Persian Gulf. CCA (Canonical Correlation Analysis) showed that all the investigated variables in the first axis and all axes were significant and the significant relationship between the biomass of fish and environmental variables were observed. Environmental factors explained the variability of 48.64% of the data, compared to all available factors, on fish biomass. Significant correlations were observed between pollutants, nutrients and physicochemical factors. Most of the demersal fish had optimal conditions in the average concentration of environmental factors. The biomass of fish including Diodontidae, Serranidae, Priacanthidae, Ephippus orbis, Sparidentex hasta, Sparidae, Lutjanidae and Lethrinus nebulosus, have not noticeable decrease with the increase in the concentration of pollutants, which indicates their less sensitivity to the pollutant and their potential as biological indicators in the Persian Gulf and Oman Sea. The findings indicate that demersal fish communities in the ecosystem of the Persian Gulf and Oman are affected by a diverse set of human and environmental factors. Comprehensive and impressive strategies to control and reduce pollution, especially heavy metals in polluted areas, should be considered to identify and manage the sources of these pollutions.
Keywords: Demersal fish, environmental factors, Catch per unit area (CPUA), Coasts of Persian Gulf and Oman Sea