Abstract:
The Swept Area Project was conducted during 2018-2021 from the waters of Ganaveh (E 50° 30´) to Nayband Bay (E 52° 30´), to monitor the stocks of demersal fishes in waters of Bushehr Province, calculate the amount of catch per unit area (CPUA) and determining the amount of biomass of aquatic life in the study areas. In this research, the R/V Ferdows 1, equipped with a fish trawl net, was used. The total of the studied areas was 2551.7 Sq miles. In 2018, 2019 and 2021, eighty-two stations were trawled in three stratums named C, D, E, and depth layers of 10-20, 20-30 and 30-50 meters. This project was performed based on the Swept Area method.
The results of this research in 2018 indicated that the total biomass of targeted biota species in the study area was estimated to be 30098.3 tons. The biomass of commercial demersal species in the catch composition was 18817.3 tons (62.5%), the biomass of non-commercial demersal species was 6117.9 tons (20.3%), and the biomass of pelagic species was 5163.2 tons (17.2%). The highest amount of total biomass was recorded in the stratum D (Bordkhoon to Bandar Dayyr) with total biomass of 14246.4 tons (47.3%), and the depth layer of 30-50 meters depth layer of 30-50 meters with total biomass of 14789.1 tons (49.1%). The lowest amount of the total biomass was recorded in zone E with total biomass of 2559.9 tons (8.5%), and depth layer of 20-30 m with total biomass of 6549.3 tons (21.8%). The average catch per unit area of total targeted aquatic fish species was calculated to be 5897.7 kilogram per square mile (kg/Sq mile).
The highest average catch per unit area (CPUA) of targeted species was obtained in stratum D with 7835.4 and the lowest value of the index was obtained in stratum C (Genaveh to Bordkhoon) with 4696.6 kg/Sq mile. The highest amount of CPUA was calculated in the depth layer of 10-20 m with 7939.3 kg/Sq mile. The highest CPUA of commercial demersal fish was observed in stratum D with 4472.7 kg/Sq mile. The highest and lowest CPUA of non-commercial benthic fish were obtained in stratums D and C, respectively.
The results of this research in 2019 showed that the amount of total biomass was 32416.9 tons. The highest amount of total biomass was recorded in the stratum D with total biomass of 17765.1 tons (54.8%), and the depth layer of 30-50 meters with total biomass of 24337.4 tons (75.1%). The lowest amount of the total biomass was recorded in stratum E (Dayyer – Nayband Bay) with total biomass of 735.3 tons (2.3%), and depth layer of 10-20 m with total biomass of 1813.3 tons (5.6%).
The total biomass of commercial demersal species in the catch composition was 17630.5 tons (54.4%). The highest biomass of commercial benthic species with 9994.7 tons (56.7%) was recorded in stratum C, while zone E had the lowest amount of biomass. The amount of biomass of non-commercial demersal species in stratum D was 8174.1 tons (59.4%). The highest and lowest biomass of commercial benthos were estimated in the depth layer of 30-50 m, with 0.14007 tons (79.4%), and the depth layer of 10-20 m, with 1026.3 tons (4.3%), respectively. The highest and lowest biomass of non-commercial demersal species were obtained at depths of 30-30 and 10-20 meters with values of 8252.1 tons (33.9%) and 542.2 tons (29.9%), respectively. The average CPUA of total targeted species was calculated to be 0.6352 kg/Sq mile. The highest average CPUA of commercial demersal was calculated in stratum D with 9770.7 and the lowest value of this index was recorded in stratum E with 1615.9 kg/Sq mile. The highest amount of CPUA was obtained in the depth layer of 30-50 m with 9090.6 kg/Sq mile. The maximum and minimum CPUA of non-commercial demersal species were calculated to be 4495.7 and 382.1 kg/Sq mile in stratums D and E, respectively. The portion of pelagic species in the total trawl catch composition was 10.8%. It should be noted; The assessment of Bushehr benthic reserves was not carried out in 2020 due to technical problems of Ferdows 1 research ship and some social considerations.
The results of this study in 2021, the amount of total biomass of marine biota was estimated to be 12263.3 tons. The biomass of commercial benthic species in the catch composition was 9494.0 tons (77.4%), the biomass of non-commercial demersal species was 1882.5 tons (15.4%), and the biomass of pelagic species was 886.8 tons (7.2%). The highest amount of total biomass was recorded in the stratum C with total biomass of 7598.8 tons (62.0%), and the depth layer of 30-50 meters with total biomass of 6012.9 tons (49.0%). The lowest amount of the total biomass was recorded in stratum E with total biomass of 2559.9 tons (8.5%), and depth layer of 10-20 with total biomass of 2708.2 tons (22.1%).
The average amount of CPUA of marine biota in 2021 was calculated to be 2403 kg/Sq mile. The highest average value of CPUA was obtained in stratum E with 3139.6 and the lowest mean value of this index was in stratum D with 17799.8 kg/Sq mile. The highest amount of CPUA of commercial benthic species was related to stratum C with 2146.9, and the lowest amount of this index was observed in stratum D with 0.1353 kg/Sq mile. The highest amount of CPUA for non-commercial benthic species was calculated in stratums E and C, and the lowest amount was calculated in stratum D.
The predominant fish species of the trawl catch in the waters of Bushehr Province include Nemipterus japonicus, Saurida tumbil,CARANGIDAE, MULLIDAE, Trichiurus lepturus, LEIOGNATHIDAE, Ilisha spp, Rays, SPHYRAENIDAE, GERREIDAE, ARIIDAE and HAEMULIDAE. Graph of depth and regional distribution of important economic and non-economic fish species was drawn using the data of CPUA. Excel software was applied to perform data entry, calculations and data analysis.
Comparison of all studied zones showed that stratum D has a better situation than other zones in terms of abundance and density of demersal fish species. It is important to be noted that according to the results of this study, the density of commercial demersal species was higher than those of non-commercial species.
The results of the statistical analysis of variance and Tukey and Duncan's post hoc test related to the average abundance and catch per unit area of the total demersal, commercial demersal, non-commercial demersal, and total demersal fish by three zones and depth layers showed that there was no significants difference. Although the results of the analysis of some tests showed that the average of the above indices in the zones and depth layers was sometimes significant.
Keywords: Biomass, Commercial benthos, CPUA, Non-commercial benthos, Waters of Bushehr Province