Reproductive parameters of blue shark, Prionace glauca, and other sharks in the Gulf of Guinea

Abstract

In total, 1967 pelagic sharks of eight different species were sampled in waters of the Gulf of Guinea between June and August 1993 by commercial longline gear. Catches of Prionace glauca and Sphyma zygaena included a large number of pregnant females, making it possible to calculate some of their reproductive parameters. In total, 419 gravid females of P. glauca were caught, ranging in size from 170 to 260 cm fork length. The size at which 50% of females have embryos was determined to be 180 cm FL. Examination of the uteri from 128 of these females showed a higher number of embryos (59-60%) in the right uterus. The mean number of embryos was 37. Data on embryo size suggests that P. glauca may have a west-east migration to give birth along the Atlantic equatorial line. The embryonic sex ratio was 1 : 1. In the same catch there were 21 gravid females of S. zygaena. No difference in the number of embryos between uteri was found in this species. Mean embryo number was 33.5 and embryonic sex ratio was 1 : 1.