Reproductive biology of the cownose ray Rhinoptera bonasus (Elasmobranchii) in the Southeastern Gulf of Mexico

Abstract

The cownose ray Rhinoptera bonasus is one of the most abundant batoid species in southeastern Gulf of Mexico, where it is occasionally caught and salt-dried for human consumption. To date, there are no estimates of the reproductive parameters which are needed to assess the dynamics of the local population of this species, and its vulnerability to fisheries. The analysis of 136 females with a size range of 43-106 cm disc width (DW) and 56 males with a size range of 43-93 cm DW, allowed to estimate that the lengths at maturity (DW50%) are 89.1 cm DW and 76.4 cm DW for females and for males, respectively. The female reproductive cycle is apparently biennial. The gestation lasts close to 12 months, gestation and vitellogenesis are consecutive, and ovulation and parturition occur from mid-March to mid-June. The results indicate a brood size of one and the lengths at birth ranged between 37.5 and 43 cm DW. Apparently, the sizes at maturity estimated for the southeastern and the northern Gulf of Mexico are different, because the data for the northern Gulf of Mexico indicate DW values of 65.3 and 64.2 cm for females and males, respectively. The biennial reproductive cycle of the southeastern Gulf of Mexico population seems different from that of the northwestern Atlantic, which is apparently annual.