Reproductive strategy of spadenose shark, Scoliodon laticaudus Muller and Henle, 1839 along north-eastern Arabian Sea

Abstract

Scoliodon laticaudus constitute a major fishery along the north-west maritime states of India. Despite its contribution to the fishery, there is a dearth of information about the reproductive characteristics of the species in the region. The limited fecundity and its distribution in sensitive ecosystem could make it vulnerable to the impacts of targeted fishing and habitat degradation. Therefore, the present study was envisaged to collect information about the reproductive strategy of the shark which is essential for developing proper management measures for the sustainable exploitation of the resource. A total of 1,277 S. laticaudus specimens were studied to collect information about the maturity parameters, reproductive periodicity and reproductive potential of the species from the Gujarat coast of India. The length frequency distributions for both the sexes showed that mean and modal lengths of the exploited shark were 40.5 cm and 47.5 cm, respectively. Male and female sharks were found to mature at lengths of 33.8 cm and 35.8 cm, respectively which were lower compared to the predominantly targeted length group of the fishery. Though large and ripe ova were observed along with small developing ova throughout the year in the ovaries of the shark, significant increase (p ≤ 0.01) in mean ova diameter was observed during March and April followed by October and November which suggest the peak reproductive period of the shark. There was a significant relationship (p ≤ 0.01) between maternal body size and litter size where the larger females were recorded to produce more number of embryos compared to the smaller ones. The actual number of embryos carried by a single female ranged from a minimum 8 to a maximum of 19 embryos per pregnant female, with a mean embryo number of 10 per pregnant female. The higher mean size of embryos was recorded in August and September which coincided with the highest number of post-partum females and therefore, might be considered as the major parturition period. The length at birth (L0) was calculated to be 13.7 cm. The breeding behavior of the species appeared to be continuous as developed embryos were observed throughout the year. The present study provides vital information for deriving the appropriate size and time for the sustainable exploitation of the resource. Further study should be conducted to understand the relationship between spawning stock biomass and recruitment dynamics considering the lower reproductive potential of the species so that the optimum spawning biomass could be assessed to ensure sustainability of this resource.