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

Abstract

This study, carried out between spring 2012 and winter 2014, characterized the sexual development and reproductive cycle of Myliobatis goodei and Myliobatis ridens in the extreme south of Brazil to support future management and conservation plans. Ninety-five specimens of M. goodei (24 males and 71 females) and 175 M. ridens (24 males and 151 females) were sampled. Female M. goodei attained disc-width-at-50% maturity (WD50 ) at 683 mm. Uterine fecundity was four to five embryos. The largest male recorded, a mature individual, had a disc width of 650 mm. In M. ridens, WD50 was 662 mm. Uterine fecundity varied from one to eight embryos. The largest male on record was a maturing 590 mm WD individual. The hepato-somatic index was higher in autumn in females of M. goodei, and in the summer in M. ridens. The gonado-somatic index and the largest vitellogenic follicle diameter were higher in spring in both species. Pregnant females of both species were recorded during spring, although for M. ridens, these females also occurred in summer. Embryos had WD of 61-218 and 40-236 mm for M. goodei and M. ridens, respectively. The incidence of pregnant females in southern Brazil in spring-summer coincides with the small-scale beach artisanal fisheries season peak, when M. goodei and M. ridens suffer fishing mortality, while using the coastal shallow areas in the warmer periods (spring-summer) to give birth.