Reproductive biology of the smooth butterfly ray Gymnura micrura

Abstract

This study provides the first detailed information on the reproductive biology of the smooth butterfly ray Gymnura micrura. A total of 905 individuals were sampled, 377 of which were used for the reproductive study. Juveniles accounted for 75% of the sample, but all life cycle stages were present in the study area. The disc width at which 50% were mature (W(D50))was estimated at 269 and 405 mm for males and females, respectively. The W(D50V) (based on the onset of vitellogenesis) was estimated at 359 mm. Uterine fecundity (mean ±s.d. = 3·8 ± 1·3; range: 1-6) was positively correlated with female size. A 3564% gain in mean wet mass was observed from egg to full-term embryo in utero. Size at birth ranged from 135 to 175 mm W(D) (19·5 to 55·0 g), with a mean of 165·1 mm W(D) (43·3 g). The embryo sex ratio was not significantly different from 1:1. The ovaries of pregnant females were undergoing vitellogenesis during gestation, with females ready to ovulate soon after parturition. Gymnura micrura may have an asynchronous reproductive cycle, with females reproducing continuously throughout the year.

Reproductive biology of the stingrays, Myliobatis goodei and Myliobatis ridens (Chondrichthyes: Myliobatidae), in southern Brazil

“…As observed in several Chondrichthyes species, the males attain smaller sizes than females, e.g. Myliobatis californica Gill 1865 (Martin & Cailliet, ; Villavicencio‐Garayzar, ), Myliobatis aquila (L. 1758) (Capapé et al ., ), Myliobatis longirostris Applegate & Fitch 1964 (Villavicencio‐Garayzar, ), Urolophus bucculentus Macleay 1884 (Trinnie et al ., ) and Gymnura micrura (Bloch & Schneider 1801) (Yokota et al ., ).…”

“…Pregnant females of Gymnura altavela (L. 1758) were also actively vitellogenetic, such that oocytes increase in correlation with the growth of the embryos until they become ready to be ovulated, after giving birth (Capapé et al ., ). In north‐eastern Brazil, pregnant G. micrura , Dasyatis guttata Bloch & Schneider 1801 and Dasyatis marianae Gomes, Rosa & Gadig 2000 females are actively vitellogenic too (Yokota & Lessa, ; Yokota et al ., ), as is Rhinoptera bonasus (Mitchill 1815) in Florida (Poulakis, ).…”

First description of the embryos of the stingray Gymnura altavela (Linnaeus, 1758) (Myliobatiformes: Gymnuridae), a species at risk of extinction

“…However, this study is over 60 years old. For the southern Atlantic Ocean there are no data for G. altavela , only for its congener Gymnura micrura , with an estimated birth size between 13.5–17.5 cm (Yokota, Goitein, GianetI, & Lessa, ). These data indicate that the GA49 ray embryos were closer to parturition than the GA24 embryo.…”

Diet and feeding strategy of smooth butterfly rayGymnura micrurain northeastern Brazil

“…For comparison purposes, the daily feeding rate for sharks in captivity fed to satiation rarely exceeded 3% of body mass (Wetherbee and Cortés, :Table 8.1). The significantly lower RI values for spring‐summer are probably related to a lower condition factor in these seasons, a consequence of some competition pressure caused by a greater relative abundance of juveniles (Yokota et al., ).…”

“…When the difference was significant, multiple comparisons of mean ranks were performed. Lifecycle stages (or maturity stages) defined based onYokota et al (2012). Mann-Whitney U-test compared Repletion Index between sexes.…”