Population dynamics and stock assessment of spadenose shark Scoliodon laticaudus Muller and Henle 1839 along Gujarat coast of India

Abstract

Stock assessment of Scoliodon laticaudus Muller and Henle, 1839 was made along with analysis of its few biological characteristics from its commercial landings during 2012-2016 from Gujarat waters of India to understand the population dynamics and stock status of the species. The average annual landing of the species was 5442 t, which constituted about 67% of the total shark landings at Gujarat coast. L∞, K and t0 were estimated as 75.53 cm and 0.54/yr, and -0.4 yr, respectively. Total mortality rate, fishing mortality rate and natural mortality rate were estimated as 1.95 yr-1, 1.04 yr-1 and 0.91 yr-1, respectively. The length at capture (Lc50) and length at maturity (Lm50) were 39.74 cm and 35.79 cm, respectively, which indicate that most of the sharks are exploited after attaining the sexual maturity. Length-weight relationship showed that the growth was isometric. The species was a continuous breeder and showed peak recruitment during September. The current exploitation ratio (Ecur) was found to be 0.53, which is lower than E0.1 estimated for the species using Beverton and Holt yield per recruit analysis. Thompson and Bell prediction model showed that maximum sustainable yield for S. laticaudus could be obtained by increasing fishing effort by almost 2.4 times higher than the present level which would deplete the spawning stock biomass (SSB) to 20%. Maximum economic yield could be obtained by increasing the fishing effort by 1.8 times which would also decrease the SSB, but to a comparatively safer 26.5% level. Considering 30% SSB as a precautionary management reference point, the effort could be increased by 50% exclusively for the sharks to increase the yield and revenue from fishery while maintain SSB at a safer 30% level.