Reproductive biology of the school shark, Galeorhinus galeus, off Argentina: support for a single south western Atlantic population with synchronized migratory movements

Abstract

synopsis We sampled school sharks, Galeorhinus galeus, in Anegada Bay, Argentina, to investigate reproductive ecology. Males dominated the catches in October and April, while females were more abundant than males from November to March. Males were estimated to mature at a smaller size (108-119 cm total length) than females (mean 125 mm total length). Differences between fecundity and fertility were not dependent on mother size. The largest embryos were found in late October and November, coinciding with ovulation. This indicates that gestation lasts about 12 months. Embryonic growth was best described by a Gompertz model. Four groups of females were recognized: (1) juveniles up to 129 cm TL, with translucent-to-white ovarian follicles; (2) mature, non-pregnant, pre-ovulatory females with yellow ovarian follicles and low gonadosomatic index (GSI); (3) mature non-pregnant ovulating females with large yellow ovarian follicles, high GSI; and (4) pregnant females carrying near term embryos, with minute ovarian follicles. These observations support a 3-year female reproductive cycle. The patterns of occurrence, reproductive condition, and embryonic growth of school sharks in northern Argentina are complementary to those from southern Brazil, supporting the hypothesis that there is a single large population of school sharks in the south western Atlantic.