Reproductive strategy of the Pacific cownose ray Rhinoptera steindachneri in the southern Gulf of California

Abstract

Rhinoptera steindachneri is one of the most common batoid species in the artisanal gill net fishery of the Gulf of California. In this study we investigated its reproductive biology based on 317 specimens caught in Bahía de la Paz, Mexico. Females measured up to 94.2-cm disc width (DW) and males reached 82.5cm DW; there were no significant differences in size or weight between sexes. The median size at maturity was estimated at 68.5cm DW for males and 71.8cm DW for females, and the median size at pregnancy was 84.3cm DW. Only the left ovary and uterus were functional; a maximum of six preovulatory vitellogenic follicles per female was recorded, although uterine fecundity was one embryo per female. Ovulation and birth occurred in May, June and July, with birth sizes ranging from 38.1 to 42cm DW. R. steindachneri in Bahía de la Paz exhibited low fecundity, large size at maturity and birth and a continuous and synchronous annual reproductive cycle.