Reproductive biology of the bigeye thresher, Alopias superciliosus, in the Tropical Eastern Pacific Ocean

The bigeye thresher, Alopias superciliosus, is a commercially important species caught as a target and bycatch in Ecuadorian fisheries by artisanal fleets. However, information on its biology and ecology in the Southeastern Pacific Ocean is scarce and regulatory measures are lacking. It is considered a vulnerable species with a decreasing population trend. In the present study, we report on the reproductive biology of A. superciliosus landed in the Ecuadorian Pacific Ocean. A total of 133 specimens (46% females and 54% males) were examined from October 2012 to September 2013. The size range of females and males was 119–402 cm total length (TL, x̄ = 280.7 ± 50.3) and 132–341 cm TL (x̄ = 277.3 ± 47.3), respectively. The sex ratio (0.9 F:1.0 M) was not significantly different from the expected ratio 1:1; the sex ratio in embryos was not different either (1 F:1.0 M). The mean size at maturity (L₅₀) was estimated at 315.7 cm TL for females and 275.2 cm TL for males. Gravid females were recorded from April–September 2013 and ranged between 322 and 361 cm TL (x̄ = 336.6 ± 13.7). Fecundity was two embryos for each female and one embryo per uterus, and the size at birth was 122 cm TL after a gestation of twelve months. The births probably occurred in August. A description of three stages of embryos is included. The present study provides biological information on Alopias superciliosus, which can help in the development of fishery management plans for the conservation of the species.