Abstract
In order to monitor the demersal resources of the Persian Gulf and Oman Sea, and estimation of the catch per unit of area (CPUA) and biomass, 15 research cruises using R/V Ferdows 1, equipped with a bottom trawl net from the western waters of Khuzestan Province (49° 00' east longitude) to Gwatr Bay in the waters of Sistan and Baluchestan Province (61° 25' east longitude) was implemented from 2017 to 2020. The whole study area was divided into 17 strata from A to Q, of which 10 areas are in the Persian Gulf (A to J) and 7 areas in the Oman Sea (K to Q). The water depths in the Persian Gulf and Oman Sea were at the range of 10-50 m and 10-100 m, respectively. Due to the size of the regions, 288 stations in the Oman Sea and 274 stations in the Persian Gulf were randomly selected for sampling during this four years study. The amounts of biomass and average catch per unit area (CPUA) of the demersal resources were calculated using the swept area method.
Based on the results obtained from the amount of biomass in the trawl catch, it was found that the portion of the Persian Gulf in the density of demersal fish during the years 2017-2020 was equal to 71440.5 tons and 58.4% of the total biomass. In this study, the highest amount of total biomass, commercial and non-commercial demersal fishes in the Oman Sea was in K and L (Sirik to Meidani) areas, respectively, in the water basin of Hormuzgan province and in the Persian Gulf was in D (Bordkhoon to Dir) from the fishing grounds of Bushehr and J stratum (Bandar Abbas to Sirik) at the western fishing grounds of Hormuzgan Province, respectively. The lowest amount of total biomass for commercial and non-commercial demersal fishes was observed in A (west of Khuzestan to Doha Deylam) region during the 2017 to 2020. The average CPUA of all aquatic animals during the 2017 to 2020 in the Oman Sea was 2.2 times more than the Persian Gulf. The highest average of CPUA and consequently the abundance of total and commercial demersal fish during the period of 2017 to 2020 were observed in K, L and O regions of the Oman Sea and the highest value of non-commercial demersal fish was in the O and P regions (eastern basin of the Oman Sea). In the Persian Gulf, the highest amount of CPUA and total fish abundance were observed in F (fishing grounds of Hormuzgan Province) region and for commercial and non-commercial demersal fishes were observed in I and F regions in Hormuzgan province, respectively. In this study, during 2017 to 2020, the lowest average CPUA and the lowest fish abundance were observed in A (west of Khuzestan to Doheh-Deylam) region in Khuzestan Province and then in Q (Beris, Pasabander and Gwatr) region in Sistan and Baluchestan Province. .
In the Oman Sea and the Persian Gulf, the highest average of CPUA for all aquatic animals during the 2017 to 2020 years were both observed in the depth layer of 20-30 m. The lowest value of this index in the Oman Sea and the Persian Gulf were both in the depth layer of 10-20 m. However, the highest amount of biomass and the average CPUA of all aquatic animals in the Persian Gulf basin were both observed in the depth layer of 30-50 m.
Commercial demersal fishes during the period of 2017-2020 had about 50% of the total biomass of the southern waters of Iran. The portion of non-commercial demersal organisms in the total aquatic biomass of southern waters was also calculated to be about 30.9%. The most abundant aquatic species in the Oman Sea were large-head hairtail, carangids, Japanese threadfin bream, barracuda, silver pomfret and rays, respectively, and in the Persian Gulf waters, barracuda, carangids, rays, common lizardfish, Japanese threadfin bream, and goatfish were recorded, respectively.
Keywords: Biomass, CPUA, Commercial fishes, Non-commercial fishes, Persian Gulf, Oman Sea