The fishery, biology and stock assessment of Nemipterus delagoae Smith off Tuticorin, Gulf of Mannar

Abstract

Nemipterus delagoae is the dominant threadfin-bream landed at Tuticorin. An estimated 158.15 t and 226.9 t were landed by trawl net at the catch rate of 6.31 and 10.13 kg/unit in 1987 and 1988 respectively constituting on an average 3.6% of the total catch by trawl net. The peak period of fishing season is during September - December. The estimated growth parameters from length frequency data are Loo = 362.0 mm, K = 1.0586 (annual) and tj = -0.0087 yr. The sexwise length-weight relationship did not exhibit any significant difference and hence a common length-weight relationship is proposed. Fishes (25.6%), prawns (21.9%), crabs (14.3%) formed the dominant food items of this species in addition to brittle-stars, cuttlefishes, gastropods, bivalves, Squilla, polychaetes, alphids, isopods and amphipods. The natural mortality coefficient (M) is 1.625 and the average annual total mortality coefficient (Z) is 3.29 by trawl net. The yield per recruit studies indicate that the prevailing F i.e. 1.665 by trawl net which is well below the V^^^ which can produce the highest yield ( Y^^^) for the prevailing age at first capture 0.4687 yr for the M/K ratio 1.535. This indicate that the fishery of N. delagoae is not exposed to higher fishing pressure and there is scope for further increase in the fishing effort of trawl net.