Determinatio the optimum mesh size of gillnets for Largehead hairtail (Trichiurus lepturus) fishing by Hormozgan coastal waters

This study was performed in order to the optimization mesh size of Trichiurus lepturus´s gillnet-fishing in Hormozgan province. At first linear relationships between the total length and the different parts of the body of the Ribbonfish were obtained. In order to evaluate the efficiency and determine the appropriate mesh size, the classification of fish caught by this method was compared with the length at first maturity. The percentage of fish caught in different parts of the body was investigated. By using the length at first maturity of this species and proportion coefficient the optimal mesh size was obtained. More than 57% of the fish were caught in the head (around gill) as the highest part of body fish. The length modes of the various parts of the ribbonfish, including head (gilled), body, snout(snagged) circumference and entangled, were in the total length classifications of 50-55, 65-70, 65-70 and 80-85 cm, respectively. The proportion coefficient was equal to 0.036 and the optimal internal mesh (knot to knot opposite) was calculated to be 57 mm. Considering that more than 71% of the ribbonfish caught with common gillnets have been in sizes less than the length of maturity (78.7 cm total length), eliminating these gillnets and using the optimized mesh nets that proposed this research study,  reduces immature fish in the fishing.