Biology and exploitation of Trichiurus lepturus Linnaeus from Visakhapatnam waters

Length-weight relationship, relative condition factor, growth, maturity, mortality, exploitation, fishery, food and feeding and sex ratio of Trichiurus lepturus from Visakhapatnam were studied. Length-weight relationship obtained for male and female was, male : W = 0.000273 L3245862 (r=0.9961) and female : W = 0.000223 L3298627 (r = 0.9950). Growth parameters estimated for von Bertalanffy's growth function were, LM = 106.8251 cm, K = 0.6117 per year and to = -0.1399 years. The fish attained maturity at 42.5 cm and has a longevity of 4.9 years. The total mortality and fishing mortality were estimated as 2.4170 and 1.5236 respectively. The exploitation ratio, E = 0.6304 and exploitation rate, U = 0.5741, indicated overexploited state of the stock. The seasonal abundance in major gears and the annual abundance in the small trawler landings during the decade 1982-'91 are also presented. Growth performance index, PHI1 ( ') for this species was calculated based on five sets of parameters given by different authors and a mean ' value was arrived at. The fish was found to be a voracious carnivore, often exhibiting cannibalism. Incidence of differential fishing noticed in this case is briefly discussed.