Seasonal reproductive biology of the bignose fanskate Sympterygia acuta (Chondrichthyes, Rajidae)

EZEQUIEL MABRAGAÑA; LUIS O. LUCIFORA; MARÍA DE L. CORBO; JUAN M. DÍAZ DE ASTARLOA

ESTUARIES AND COASTS

SPRINGER

Año: 2015 vol. 38 p. 1466 - 1476

1559-2723

Most skates are adapted to shelf and slope environ- ments experiencing less seasonal variation than coastal eco- systems. 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 ac- tivity; and (3) egg-laying season, incubation time, and fecun- dity 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 sum- mer. 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 sched- ule 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 sea- sonality 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.