Investigation of biomass and catch per unite area changes of demersal resources based on swept area method in the northern waters of Oman Sea (Sistan and Baluchestan Province)

For more than two decades, assessment and monitoring of Oman Sea demersal resources has been carried out using swept area method. The study area starts from western water of Iran to border of Iran and Pakistan in the east of Oman Sea and total study area were divided into 5 sub-areas M to Q in different depth layers of 10-20, 20-30, 30-50 and 50 -100 meters. In general, the average amount of biomass has a downward trend in different depths of 2003 to 2021 years. Due to the changes in the average biomass at different depths, it can be said that the average biomass at depths of less than 20 meters has decreased. Average biomass of depths less than 20 meters have decreased significantly from about 14 thousand tons in 2003 to about 1.5 thousand tons in 2021 (P<0.05), and benthic biomass accumulation has shifted from coastal and shallow areas to deeper areas. Also, average catch per unit area of different areas had a decreasing trend in 2003 to 2021 and usually regions O and Q had higher values than other regions in different years (P <0.05). Some species fish such as Otolitus ruber, Lethrinidae, Ray and sharks have decreased sharply and some species fish such as Nemipterus japonicus, Saurida tumbil and Sphyraena sp. have increased in fishing composition. Considering the mentioned conditions, it seems that the amount of demersal resources caught is not in a good condition and measures should be taken to reduce the catch of these fish.