Fishery resource characteristics and stock assessment of ribbonfish, Trichiurus lepturus (Linnaeus)

Ribbonfish, Trichiurus lepturus (Linnaeus) has become one of the most important exploited resources in the northwest coast of India. It was landed as bycatch of shrimp trawler earlier but on account of emerging export demand it is now increasingly targeted. The resource has been monitored for more than ten years. The landings of ribbonfishes varied between 16,000 t (1995) and 63,000 t (2000) with an average catch of 33,000 t. The trawl contributed about 93 % of the total landing. Peak catch rates were observed in September and November-December. T. lepturus is a carnivorous predator feeding on crustaceans, fishes and cephalopods. Spawning season is prolonged from October-May. Individual fish spawns once in a year and the minimum size at maturity is 75 cm. The fecundity varied between 4,900 and 81,000 with a relative fecundity of 65 ova/gm of body weight. It grows at faster rate and attains 65.1 cm, 98.0 and 114.7 cm. at the end of first, second and third year respectively. The estimated L” is 127.3 cm. and K 0.67 (annual). The average total mortality coefficient (Z) for the period 1992’97 was 3.3 whereas it was 3.64 during 1998-2001. The estimated fishing mortality (F) was 2.49 with exploitation ratio (F/Z) 0.756 and F 2.96 with F/Z 0.815 during the same quiniqual periods respectively. During the last two years of 2000-2001, the rate of exploitation was very high and the average Z was 3.97 with F/Z 0.814. The average F was 3.232, the yield was about 60,000 t and the biomass was 46,391 t. The yield can be optimized at 70 % of the current fishing effort.