Reproductive biology of the Bigeye Thresher Shark, Alopias superciliosus (Lowe, 1939)

Abstract

More than 1000 specimens of Alopias superciliosus from fisheries exploited by the Spanish fishing fleet in the north-eastern Atlantic Ocean (from Cape SLo Vicente to the Ivory Coast) and in the western Mediterranean Sea (i.e. west of an imaginary line between Monaco and Algiers) were observed in discontinuous samples between 1981 and 1989. Ten gravid females, 20 fetuses and a large number of egg capsules were studied in detail. The embryo morphology provided evidence of ovophagy. Size at birth was probably at least 100 cm. Six males with total lengths of 400-410 cm exceeded the previously reported maximum length for this sex. The characteristics of the claspers and deferent ducts suggested a total length at maturity of about 276 cm for males. The smallest gravid female was 341 cm long. Also described are litter sizes, indications of reproductive seasonality, and the possible existence of a nursery area in waters off the south-western Iberian peninsula.