Reproductive Biology of the Pacific Spadenose Shark Scoliodon Macrorhynchos, a Heavily Exploited Species in the Southern Taiwan Strait

Abstract

The reproductive biology of the heavily exploited Pacific Spadenose Shark Scoliodon macrorhynchos was studied by examining 246 males and 197 females, including 64 gestational individuals, caught by semi-industrial fisheries using demersal trawling in the southern Taiwan Strait. Total length (L_T) at 50% maturity (L₅₀) was estimated at 464 mm L_T for males and 429 mm L_T for females. The annual reproductive cycle was determined based on the percentage of pregnant mature females and the concurrent vitellogenesis with embryonic development. Mating occurred from August to December, as evidenced by the presence of females with fresh mating injuries on their body surface and spermatozoa in the cloaca and uteri. The monthly change of embryo size indicated that parturition occurred between June and August after 5–6 months of gestation, with an L_T of 190–218 mm at birth. The litter size, which ranged from 1 to 20 pups with a mean ± SD of 9.4 ± 3.9 pups (n = 64), was positively correlated with the maternal L_T. Altogether, these findings provide valuable information that is needed for the adequate management and conservation of Pacific Spadenose Sharks in the southern Taiwan Strait and adjacent waters.