Seasonal Reproductive Biology of the Bignose Fanskate Sympterygia acuta (Chondrichthyes, Rajidae)

Abstract

Most skates are adapted to shelf and slope environments experiencing less seasonal variation than coastal ecosystems. Here, we analyze the reproductive ecology of Sympterygia acuta. We hypothesize that, like its congener Sympterygia bonapartii, S. acuta has a seasonal reproductive cycle. To test this hypothesis, we examined multiple lines of evidence: (1) time of appearance of females carrying egg cases and wild neonates; (2) seasonal variation in gonadosomatic index and follicle diameter, as indicators of reproductive activity; and (3) egg-laying season, incubation time, and fecundity in captive individuals. A total of 351 specimens were examined. Size at 50 % maturity was 475 and 478 mm total length for males and females, respectively. A marked seasonal reproductive cycle was observed. Both gonadosomatic index and follicle diameter of wild adult females increased from winter to spring and reached their lowest value during summer. Fecundity was, on average, 52 eggs per female per laying season. Egg laying of captive females peaked between August and December; eggs hatched after 119–131 days. This schedule predicts the appearance of neonates in the wild by January through April. Accordingly, wild neonates and young-of-the-year were observed between January and May. Unlike most other skates, southwest Atlantic Sympterygia species are adapted to life in shallow, coastal waters, matching the seasonality of the coastal environment with egg-laying activity in spring and hatching in summer. These shallow coastal waters, which are important in the life cycle of Sympterygia spp., are threatened by human impacts.