The biology and population dynamics of the spadenose shark Scoliodon laticaudus in the coastal waters of Maharashtra State, India

Abstract

The study of the biology and dynamics of Scoliodon laticaudus indicates a fast growth of 21.8 cm, 54.5 cm and 65.5 cm, in the first, second, and third year respectively. The von Bertalanffy growth equation was fitted to the above values for which the parameters calculated (on an annual basis) were : K = 0.6812, L^ = 74.023 cm, T_ = 12 years and t„= -0.01 year. The maximum length of this shark in the Mumbai waters is about 66 cm (3.1 years). The weight growth parameters (on an annual basis) for sexes combined by the VBGF are K = 0.5823, W_ = 1756.93 g, t^ = 0.0032 year. The length at birth is 14 cm with a gestation period of 4 months. The ovarian and uterine cycles operate concurrently with broods being released once a month. The average fecundity was 11 embryos per female. The LJL^ was estimated to be 0.47 - 0.54. Scoliodon laticaudus is an active carnivore with a mixed diet composing of small sized teleosts, prawns, squilla and molluscs. There is no evidence of cannibalism. The study of the dynamics of Scoliodon laticaudus indicates that the stock is exploited at its optimum level. Therefore any increase in effort from the present level may not increase the yield and it is advisable to sustain the effort at the present level. For the sharks (all species combined) and the elasmobranchs there is still some scope for increasing the effort in order to reach the MSY level.