The Cownose Ray Rhinoptera bonasus is an opportunistic predator of benthic invertebrates and has had a long history of negative interactions with commercial shellfish industries. Most recently, Cownose Rays have been implicated in negatively affecting the recovery of bay scallop Argopecten irradians stocks in North Carolina and oyster restoration and commercial aquaculture efforts in Chesapeake Bay. A mitigation attempt to decrease predation on shellfish has resulted in an unregulated fishery for Cownose Rays. Cownose Ray life history suggests that they are highly susceptible to overexploitation. We determined age, growth, and size at maturity for Cownose Rays collected in Chesapeake Bay. In total, 694 rays were used for the study: 246 males ranging in size from 30.0 to 98.0 cm disc width (DW) and 448 females ranging from 30.0 to 110.5 cm DW. The oldest individual observed was a female (107 cm DW) estimated at age 21. Our data suggested that Cownose Rays grow considerably faster during the first few years than has been previously reported, thus producing higher estimates of the growth coefficient k. The best‐fit growth models (three‐parameter von Bertalanffy models) estimated k‐values of 0.2741 for males and 0.1931 for females. The large sample size and inclusion of many older animals (n = 119 rays over age 10) resulted in theoretical maximum size estimates that matched the observed sizes well. The median size at 50% maturity was 85–86 cm DW for males and females (corresponding to ages of ∼6–7 for males and ∼7–8 for females). Fecundity in Cownose Rays was typically one embryo per mature female, with a gestation period of 11–12 months. Our study confirms that the Cownose Ray is a K‐selected species with late maturity, long gestation, and low reproductive potential, indicating that it could be highly susceptible to overexploitation. Received February 28, 2013; accepted June 3, 2013

The purpose of this study was to determine the ability of the cownose ray, Rhinoptera bonasus (Mitchill, 1815), to manipulate oysters and clams, to test for relative prey preference, and to investigate whether susceptibility to cownose ray predation changes with bivalve ontogeny. We investigated patterns of predation for captive adult and young-of-year cownose rays on 4 species of bivalves, including Crassostrea virginica (Gmelin, 1791), Crassostrea ariakensis (Fujita, 1913), Mercenaria mercenaria (Linnaeus, 1758), and Mya arenaria Linnaeus, 1758. In oyster (C. virginica) trials, predation probabilities by adult rays were highest at shell heights of 30-70 mm and shell depths of 8-22 mm. The rates of predation by adult rays in trials in which samesize oysters were used were higher than rates in most comingled trials. Adult rays showed no differences in predation between native oysters (C. virginica) and nonnative oysters (C. ariakensis; P > 0.05). Adult rays selected hard-and soft-shell clams (Manly-Chesson index M. mercenaria, a ¼ 0.736 ± 0.002, electivity ¼ 0.473 ± 0.007; M. arenaria, a ¼ 0.742 ± 0.003, electivity ¼ 0.485 ± 0.013) over oysters (C. virginica, a ¼ 0.263 ± 0.002, electivity ¼-0.473 ± 0.007; a ¼ 0.257 ± 0.003, electivity ¼-0.485 ± 0.003). In young-of-year feeding trials, oysters with a shell height of 10-35 mm and a shell depth of 3-12 mm had the highest probability of predation. Native oyster and hard clam peak force or load crush tests resulted in forces of 200-1,500 N and 400-1,400 N across shell depths of 10-35 mm and 21-34 mm, respectively, before valve failure. The results of this study indicate that cownose ray predation on shellfish is limited by shell size and is likely related to ray jaw gape and bite force.

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