Species composition and depth variation of cutlassfish (Trichiurus lepturus L. 1785) trawl bycatch in the fishing grounds of Bushehr waters, Persian Gulf

Abstract

Cutlassfish trawl fisheries have been used in the Persian Gulf, but very little information about species composition of the large rates of bycatch caught in this region is available. The data on total species composition of 40 hauls from vessels operating off the fishing grounds of Persian Gulf was collected from May 1^st 2009 to 10^th August 2010. From the estimated 952.3 tonnes of bycatch taken annually in the fishing grounds of cutlassfish, 39 species from 32 families were obtained which include: 30 teleost species with 88.3% of the total biomass (841.4 t) from the main composition of the catches and followed by 7 elasmobranchs with 8.3% (79.7 t) and 2 invertebrate with 3.3% (31.2 t) of the biomass. With 554.3 tonnes (58.2% of the total biomass), the major species in trawl bycatches were Nemipterus japonicas (234.1 t), Saurida tumbil (229.5) and Ilisha melastoma (90.5%). There was a significant difference in the total bycatch taken (biomass and number) from different depths. Some mean catch rates of the abundant species differed significantly between seasons which displayed dial differences in their catch values. This study provided the first comprehensive study of the species composition of cutlassfish trawl in fishing grounds of Bushehr waters in the Persian Gulf. The examination of the bycatch indicates the large impact on stocking density of commercial and non-commercial species in this region; which with respect to decline in stocking density of demersal fishes of Persian Gulf in recent years, has caused increasing concerns. The data collected in this study can be used in the quantitative assessments of fisheries pressure on bycatch stocks in the Persian Gulf.

Key words: Cutlassfish, Bushehr, bycatch, depth variation, trawl, Persian Gulf.