Journal of Fish Biology (2012) 80, 1246–1266 doi:10.1111/j.1095-8649.2012.03237.x, available online at wileyonlinelibrary.com Reproductive variables of Urotrygon rogersi (Batoidea: Urotrygonidae): a species with a triannual reproductive cycle in the eastern tropical Pacific Ocean P. A. Mejía-Falla*†‡, A. F. Navia* and E. Cort´ es§ *Fundaci´ on Colombiana para la Investigaci´ on y Conservaci´ on de Tiburones y Rayas, SQUALUS, Carrera 79 No 6-37, Cali, Colombia, †Grupo de Investigaci´ on en Ecología de Arrecifes coralinos, Departamento de Biología, Universidad del Valle. A.A. 25360, Cali, Colombia and §National Marine Fisheries Service, Panama City Laboratory, Panama City, FL 32408, U.S.A. Reproductive aspects of the round ray Urotrygon rogersi were studied based on 2005 specimens obtained in the artisanal shrimp fishery operating on the Colombian Pacific coast. Females reached greater maximum total length (L T ), disc width (W D ) and mass (M) (38·0 cm, 19·9 cm and 348 g) than males (32·5 cm, 17·0 cm and 165 g). Sex ratio of juveniles and adults was 1:1. Clasper length increased rapidly between 10·0 and 12·5 cm W D . The smallest mature male measured 10·5 cm W D and the largest immature individual 13·7 cm W D . Male first maturity was reached at 61·8% of maxi- mum W D , and estimated W D50 was between 11·5 and 11·8 cm. The smallest mature female measured 10·5 cm W D ; the size at first maturity was 52·8% of maximum W D , and estimated W D50 was between 11·8 and 12·3 cm. Embryos were found in females ≥10·5 cm W D and maximum fecundity was three embryos per female (mode = 1) and varied with maternal size. Embryos were found in all months, but three birthing peaks per year were identified and a gestation period of 4–5 months estimated. Based on ovulation time, embryonic growth and parturition dates, a triannual reproductive cycle was inferred for this species, with overlapping ovarian and uterine cycles. These results suggest that U. rogersi has a reproductive strategy based on low fecundity, a rapid reproductive cycle (short ovulation and gestation time), three birth peaks per year and large embryos. This strategy probably allows U. rogersi to withstand the fishing pressure they are subject to on the Colombian Pacific coast. The results also suggest that the study area is an important nursery and reproductive area for this species.  2012 The Authors Journal of Fish Biology  2012 The Fisheries Society of the British Isles Key words: birth size; elasmobranch; fecundity; gestation; maternity; size at maturity. INTRODUCTION Elasmobranchs possess biological characteristics, such as longevity, low fecundity, slow population growth and late maturation, exemplifying an ‘equilibrium’ (K -selected) life-history strategy that makes them inherently more susceptible to overfishing than teleosts and invertebrates (Holden, 1974; Cort´ es, 2000, 2004, 2008; Frisk et al., 2001, 2005). Since reproductive, growth and age variables differ among species and even populations (Casey & Myers, 1998; Walter & Hislop, 1998; Stevens, ‡Author to whom correspondence should be addressed. Tel.: +57 2 3705589; email: pmejia@squalus.org 1246  2012 The Authors Journal of Fish Biology  2012 The Fisheries Society of the British Isles