Estimation of the ratio of cephalopods' biomass by bottom trawl in the 12 nautical miles distance from Sistan and Baluchestan's shorelines

Cephalopods have short life and global distribution except freshwater that these make them importance for study of their dynamics population. So, the purpose of this study was to estimate the biomass of cephalopods (Amphioctopus marginatus, Uroteuthis (Photololigo) edulis, Uroteuthis (Photololigo) duvaucelii, Sepia saya, Sepia prashadi, Sepia omani, Sepia stellifera and Sepia pharaonis) with the catch dynamics model (generalized depletion model) in the NE Gulf of Oman at the end of the fishing season (of bottom trawlers) in the summer and autumn of 2020. The catch data of these valuable fisheries species were obtained through field sampling from commercial fishing in the depths of 74-212 meters by an industrial bottom trawler for 17 consecutive days in the "Gowater-Pasabandar-Beris" fishing grounds (at least 12 nautical miles from the shoreline according to the new move-on rule). The highest total abundance and biomass belonged to Sepia pharaonis by 23431 individuals and 27005.78 kg. Also, the lowest total abundance and biomass belonged to Uroteuthis (Photololigo) edulis by 8 individuals and Sepia saya by 0.397 kg, respectively. The abundance response for most of the stocks was a hyperdepletion (β > 1), while the fishing effort response for most of them was an effort synergy (α > 1). Also, most of the selected models were executed in the presence (open population) of perturbations (pulses). Cuttlefishes had the highest and octopuses had the lowest biomass, respectively. Probably, this study was the first survey of biomass for mentioned species in the waters of the Islamic Republic of Iran - except Uroteuthis(Photololigo)duvaucelii and Sepia pharaonis. The advantages of implementing catch dynamics model based on commercial fisheries activities are practical, operational, and close-to-reality estimates, lack of some costs of scientific surveys, also lack of additional pressure on aquatic resources (especially in nursery grounds) due to the implementation of fisheries activities (fishing operations) within the permitted limits (spatial-temporal).