Reproduction and seasonal occurrence of the copper shark, Carcharhinus brachyurus, from north Patagonia, Argentina

Abstract

Abstract The copper shark, Carcharhinus brachyurus, is the only member of its genus with a preferred habitat in temperate waters, and it usually gives birth in the cooler extremes of its range. Maturation patterns, reproductive condition, monthly sex ratios, and seasonal occurrence of copper sharks were analysed, mostly from Anegada Bay (Argentina), a presumed nursery area for the species. Males mature between 200 and 220 cm total length (LT), with a 50% size at maturity (L50) of 216.18 cm LT. Females mature between 215 and 223 cm LT (with an L50 of 222.16 cm LT). Maturity off Argentina is at a slightly smaller size than off South Africa and Australia. There is no sexual dimorphism in size at maturity. Only two pregnant females, each carrying 16 advanced embryos, were caught. The hepatosomatic index (IH) of adult males showed significant monthly changes, related possibly to an increase in the gonadosomatic index (IG). IH and IG of adult females showed no significant trend throughout the fishing season. The IH of adult females was significantly correlated with maximum diameter of ovarian follicles. Small translucent ovarian follicles in two gravid females indicated that ovarian and gestation cycles run sequentially, with maturation of oocytes subsequent to parturition. Neither newborns nor significant numbers of females bearing term embryos were recorded, and there was no evidence of a copper shark primary nursery area in Anegada Bay. However, most copper sharks in Anegada Bay were large juveniles and sub-adults. The species is found off Argentina from October to late March, but they do not move southwards to Anegada Bay until December, and they leave the bay again by April. These movements appear to be related more to water temperature rather than to migration of potential prey. Monthly variation in sex ratios is associated mainly with fluctuations in the sex ratios of juveniles.