CSIRO PUBLISHING www.publish.csiro.au/journals/mfr Marine and Freshwater Research, 2008, 59, 575–586 Demography and elasticity of the diamond stingray, Dasyatis dipterura: parameter uncertainty and resilience to fishing pressure Wade D. Smith A,B,D , Gregor M. Cailliet A and Enric Cortés C A Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA. B Oregon State University, Department of Fisheries and Wildlife, 104 Nash Hall, Corvallis, OR 97331, USA. C National Marine Fisheries Service, Southeast Fisheries Science Center, Panama City Laboratory, 3500 Delwood Beach Road, Panama City, FL 32408, USA. D Corresponding author. Email: wade.smith@oregonstate.edu Abstract. Despite their abundance in near-shore tropical and subtropical marine environments, which support much of the world’s elasmobranch fisheries, population dynamics and impacts of fisheries on stingrays are poorly documented. Age-structured demographic models were developed using empirical estimates of fecundity, longevity and maturity to project population growth parameters and potential responses to fishing mortality of Dasyatis dipterura from the Bahía Magdalena lagoon complex, México. Monte Carlo simulation was incorporated to include uncertainty in life history parameters into model projections. Six models were developed using deterministic and probabilistic approaches under unexploited and exploited (fishing mortality = 0.05 year −1 ) conditions. Mean annual population growth rates (λ) of 1.05– 1.06 (5–6% increase), net reproductive rates of 2.3–2.4 and generation times of 14.9–16.5 years were projected from simulations. The introduction of a low fishing mortality into probabilistic models produced λ of 1.01 year −1 . Elasticity analysis indicated that population growth rates for D. dipterura are more strongly influenced by the survival of juvenile and adult stages than by survival of neonates or changes in fecundity. Demographic analyses indicated that D. dipterura has a low intrinsic growth potential and limited resilience to fishing pressure. Localised depletion or population collapses are therefore likely to occur through unrestricted, unmonitored fishing effort. Additional keywords: age-based models, Dasyatidae, demography, fisheries management, Mexico, population biology. Introduction Dasyatid stingrays are common benthic inhabitants of inshore tropical and subtropical waters but have also successfully expanded into continental slope (to at least 480 m), euryhaline, pelagic and freshwater environments (Compagno 1990). The success of dasyatid stingrays in warm, marine environments is illustrated by Bigelow and Schroeder’s (1953, p. 338) descrip- tion of their abundance: ‘... in suitable localities ... they occur in such great plenty that it may seem as though the bottom were paved with them’. Despite such perceptions, the structure and dynamics of ray populations have rarely been examined. Slow growth, long life spans, late ages of maturity, low fecundity and extended gestation periods are life history char- acteristics that are commonly exhibited among sharks and rays (Holden 1973; Hoenig and Gruber 1990). These com- bined attributes constrain productivity and resilience to fisheries exploitation (Stevens et al. 2000). The vulnerability of batoids (i.e. skates and rays) to fishing pressure was not fully recog- nised until Brander (1981) documented the localised extirpation of a once-common skate, Dipturus batis, as a result of by-catch overfishing.Although several publications have drawn increased attention to the contribution and vulnerability of rays to both directed and by-catch fisheries, these studies and reviews have primarily related to skate populations from northern latitudes (e.g. Walker and Hislop 1998; Dulvy et al. 2000). Despite their abundance within the tropical and subtropical environments that support much of the world’s elasmobranch (shark, skate, and ray) fisheries, the potential impacts of these fisheries on stingrays have been rarely considered. Thrush et al. (1991) determined that rays may regulate populations of benthic organisms through their feeding activities in near-shore envi- ronments. Additionally, rays modify and enhance soft-bottom habitats by creating large feeding and shelter pits (Probert 1984). As a result, declines of ray populations may have significant and unpredictable cascading effects on the diversity, structure and function of marine communities. Mexico’s elasmobranch fishery ranks among the largest in the Americas (Bonfil 1994; Vannuccini 1999). Small-scale, coastal artisanal fisheries account for ∼80% of the nation’s elasmo- branch landings (Castillo-Géniz et al. 1998). Although batoids © CSIRO 2008 10.1071/MF07020 1323-1650/08/070575