Population dynamics and stock assessment of Delegoa threadfin bream, Nemipterus bipunctatus (Nemipteridae), from the Wadge Bank, South India

Abstract

Fishery, population characteristics and stock estimates of Nemipterus bipunctatus were studied during June 2015 to May 2016 from Wadge Bank, South India. This region is characterised by rich biodiversity and has a conducive influence of the Indian Ocean and Arabian Sea. The asymptotic length (L?), growth coefficient (K) and arbitrary origin of growth (t0) were estimated as 30.5 cm, 0.85/year and 0.18 respectively. The mortality parameters, total mortality rate (Z), fishing mortality rate and natural mortality rate (M) were estimated as 2.20, 0.95 and 1.25 respectively. Exploitation ratio (E) was found to be 0.57 which showed marginal over exploitation of the species at Wadge Bank. This species has two recruitment seasons, one major season from October to December and another minor season in August. The length structured Virtual population analysis revealed heavy fishing pressure on the length group 24 to 28 cm and hence the delegoa threadfin bream was not found to suffer due to recruitment overfishing in Wadge Bank. Estimated total stock, Maximum Sustainable Yield (MSY) and annual catch were 5625.9348 tonnes, 1935.321t, 2419.152t respectively. Present level of Exploitation rate (U) and Exploitation ratio (F/Z) were estimated to be 0.43 and 0.57 respectively. The study infers the cod end mesh size of the trawls operated at Wadge Bank coast has to be increase from 10 to 25 mm to increase the yield per recruit, the effort could also be maintained as the exploitation ratio of 0.50 to have maximum yield per recruit. The study suggests reducing the present level of effort by 8 percent may be needed to sustain the stock of N. bipunctatus in Wadge Bank, South India