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Clarification on the Fecundity of Rhinoptera bonasus (Mitchill)
Christian M. Jones and William B. Driggers III

Southeastern Naturalist, Volume 14, Issue 1 (2015): N16–N20

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2015 Southeastern Naturalist Notes Vol. 14, No. 1 N16 C.M. Jones and W.B. Driggers III Clarification on the Fecundity of Rhinoptera bonasus (Mitchill) Christian M. Jones1,* and William B. Driggers III1 Abstract - Accurate fecundity estimates are necessary for the proper assessment of fish stocks. Despite all recent investigations of the reproductive biology of Rhinoptera bonasus (Cownose Ray) indicating a maximum fecundity of 2 embryos per brood, maximum fecundity estimates of 6 per brood persist. All reports of 6 embryos per brood seem to stem from a single account. It is the purpose of this paper to present evidence indicating that the report of 6 embryos is based upon a misidentification in the field, and that maximum fecundity estimates for the Cownose Ray are therefore up to six-fold higher than actually observed. Rhinoptera bonasus (Mitchill) (Cownose Ray) inhabits coastal waters of the western Atlantic Ocean from the northern US to southern Brazil (Ebert and Stehmann 2013). The species is known to form large aggregations throughout its range (Clark 1963, Joseph 1961, Rogers et al. 1990) with a single aggregation observed in the Chesapeake Bay estimated to consist of 5,000,000 individuals (Blaylock 1989). Despite the relatively high rangewide abundance of Cownose Rays, the species is reported to have low reproductive potential, and brood sizes of 1–6 young are reported (Bigelow and Schroeder 1953). The inshore habitat, schooling behavior, and low fecundity of Cownose Rays led the International Union for the Conservation of Nature (IUCN) to categorize the species as near threatened and express concern that it would have limited ability to recover from overexploitation resulting from low reproductive potential (Barker 2006). However, this categorization may not accurately characterize the species’ vulnerability if the fecundity of Cownose Rays is lower than currently acknowledged. The congener R. brasiliensis Müller (Ticon Cownose Ray) was recently assessed as endangered by the IUCN (Vooren and Lamónaca 2004). This assessment was based upon the fact that high exploitation rates in its proposed native range and low fecundity of 1 embryo per brood make this species very susceptible to recruitment overfishing (Vooren and Lamónaca 2004). These factors, coupled with a lack of conservation actions, have likely already contributed to the species being extirpated from the southern portion of its range (Vooren and Lamónaca 2004). Fertility is among the most important vital rates in demographic models, so it is essential that accurate brood size data are available for such analyses. Recent investigations of the reproductive biology of Cownose Rays are dominated by reports of single-embryo broods (Fisher et al. 2013, Neer and Thompson 2005, Poulakis 2013) with exceptional reports of broods consisting of 2 embryos (Fisher et al. 2014, Poulakis 2013). Similarly, the congeners R. steindachneri Evermann and Jenkins (Golden Cownose Ray) and Ticon Cownose Ray both have reported fecundity estimates of 1 embryo per brood (Bizzarro et al. 2007, Vooren and Lamónaca, 2004). However, a maximum brood size of 6 is frequently reported in works summarizing the life history of Cownose Rays and is usually credited to Bigelow and Schroeder (1953), who reported an observation of 6 embryos in a single gravid female. As a result of the widespread reference to Bigelow and Schroeder’s (1953) work, brood size estimates of up to 6 embryos have persisted in the literature (Figueiredo 1977, McEachran and Fechhelm 1998). However, Bigelow and Schroeder (1953) did not clearly reference 1National Marine Fisheries Service, Southeast Fisheries Science Center, Mississippi Laboratories, PO Drawer 1207, Pascagoula, MS 39567. *Corresponding author - christian.jones@noaa.gov. Manuscript Editor: Marsha Williams Notes of the Southeastern Naturalist, Issue 14/1, 2015 N17 2015 Southeastern Naturalist Notes Vol. 14, No. 1 C.M. Jones and W.B. Driggers III Figure 1. Dorsal (A) and ventral (B) views of American Museum of Natural History specimen number I-3728. Photograph courtesy of the Department of Ichthyology, American Museum of Natural History, New York, NY. 2015 Southeastern Naturalist Notes Vol. 14, No. 1 N18 C.M. Jones and W.B. Driggers III the origin of the brood-size information they presented. Coles (1913) is the only author to clearly state that he personally observed a brood size of 6 in a Cownose Ray. Coles (1913) documented the collection of 2 female Cownose Rays off Cape Lookout, NC, in 1909 and 1913, and reported both specimens contained 6 embryos; he deposited a single embryo (AMNH I-3728) and uterus (AMNH I-3729) from the later collection in the American Museum of Natural History (AMNH, New York, NY). Based on notes provided to him by R.J. Coles, Gudger (1913) reiterated the exact details described in Coles (1913) (e.g., dates of collection, number of individuals examined); however, Gudger (1913) identified the specimens as Myliobatis freminvillei Lesueur (Bullnose Eagle Ray). We examined the embryo placed in the collection of the AMNH by R.J Coles (AMNH I-3728) and determined that the specimen is from a Bullnose Eagle Ray and not a Cownose Ray, as reported in Coles (1913). The specimen was clearly from the genus Myliobatis because there was no medial indention in the cephalic fin (Fig. 1A, B). Placement of the dorsal fin (Fig. 2) and distance between 5th branchial openings relative to distance between nostrils (Fig. 1B) verified the specimen was a Bullnose Eagle Ray as opposed to the sympatric congener M. goodei Garman (Southern Eagle Ray). In a subsequent publication, Coles (1915) indicated that the Bullnose Eagle Ray gives birth to 6 young but provided no fecundity information on Cownose Rays. It is clear that the misidentification of Bullnose Eagle Ray specimens as Cownose Rays reported in Coles (1913) was noticed by both Coles and Gudger and that both later correctly attributed the observed fecundity of 6 to a Bullnose Eagle Ray. However, to our knowledge, no official correction of this misidentification has been made, and the specimens in the AMNH collection remain labeled as Cownose Rays. As a result, the fecundity estimate of 6 embryos Figure 2. Pelvic region of American Museum of Natural History specimen number I-3728 in dorsal view showing the placement of the dorsal fin in relation to the posterior margin of the pelvic fins. Photograph courtesy of the Department of Ichthyology, American Museum of Natural History, New York, NY. N19 2015 Southeastern Naturalist Notes Vol. 14, No. 1 C.M. Jones and W.B. Driggers III for Cownose Rays persists in the literature (Barker 2006, Bigelow and Schroeder 1953, Figueiredo 1977, McEachran and Fechhelm 1998). Although the Cownose Ray is not currently an important commercial species in US waters, it has been suggested that if a fishery were established, it might partially mitigate the damage this species inflicts on commercial shellfish populations (Barker 2006). Should an official assessment of the stock become needed, accurate estimates of fecundity will be required. We believe evidence suggests that the maximum fecundity estimate of 6 for Cownose Rays stems from a single source (Coles 1913) and is therefore, based upon a misidentification. Fecundity for this species should therefore be r egarded as 1 or (rarely) 2. Acknowledgments. The authors wish to thank Barbara Brown and Radford Arrindell (AMNH) for providing the photographs of specimen AMNH I-3728. We would also like to thank Dean Grubbs (FSU) and Robert Fisher (VIMS) for their insi ghts. Literature Cited Barker, A.S. 2006. Rhinoptera bonasus. In, International Union for Conservation of Nature (IUCN) red list of threatened species. Version 2013.2. Available online at www.iucnredlist.org. Accessed 16 May 2014. Bigelow, H.B., and W.C. Schroeder. 1953. Part Two: sawfishes, guitarfishes, skates and rays, and chimaeroids. Pp. 515–562, In J. Tee-Van, C.M. Breder, A.E. Parr, W.C. Schroeder, and L.P. Schultz (Eds.). Fishes of the Western North Atlantic. Sears Foundation for Marine Research, Yale University, New Haven, CT. 589 pp. Bizzarro, J.J., W.D. Smith, J.F. Márquez-Farías, and R.E. Hueter. 2007. Artisinal fisheries and reproductive biology of the Golden Cownose Ray, Rhinoptera steindachneri Evermann and Jenkins, 1891, in the northern Mexican Pacific. Fisheries Research 84:137 –146. Blaylock, R.A. 1989. A massive school of Cownose Rays, Rhinoptera bonasus (Rhinopteridae), in lower Chesapeake Bay, Virginia. Copeia 1989:744–748. Clark, E. 1963. Massive aggregations of large rays and sharks in and near Sarasota, Florida. Zoologica 48:61–64. Coles, R.J. 1913. Notes on the embryos of several species of rays, with remarks on the northward summer migration of certain tropical forms observed on the coast of North Carolina. Bulletin of the American Museum of Natural History 32:29–35. Coles, R.J. 1915. Notes on the sharks and rays of Cape Lookout, NC. Proceedings of the Biological Society of Washington 28:89–94. Ebert, D.A., and M.F.W. Stehmann. 2013. Sharks, batoids, and chimaeras of the North Atlantic. Food and Agriculture Association of the United Nations (FAO) Species Catalogue for Fishery Purposes, No. 7. FAO, Rome, Italy. 523 pp. Figueiredo, J.D. 1977. Manual de peixes marinhos do sudeste do Brasil. I. Introdução. Cações, raias, e quimeras. Museu de Zoologia, Universidade de São Paulo, Brasi l. 104 pp. Fisher, R.A., G.C. Call, and R.D. Grubbs. 2013. Age, growth, and reproductive biology of Cownose Rays in Chesapeake Bay. Marine and Coastal Fisheries 5: 224–235. Fisher, R.A., G.C. Call, J.R. and McDowell. 2014. Reproductive variations in Cownose Rays (Rhinoptera bonasus) from Chesapeake Bay. Environmental Biology of Fishes 97:1031–1038. Gudger, E.W. 1913. Natural history notes on some Beaufort, NC, fishes: 1912. Proceedings of the Biological Society of Washington 26:97–110. Joseph, E.B. 1961. An albino Cownose Ray, Rhinoptera bonasus (Mitchill) from Chesapeake Bay. Copeia 1961:482–483 McEachran, J.D., and J.D. Fechhelm. 1998. Fishes of the Gulf of Mexico, Vol. 1: Myxiniformes to Gasterosteiformes. University of Texas Press, Austin, TX. 1120 pp. Neer, J.A., and B.A. Thompson. 2005. Life history of the Cownose Ray, Rhinoptera bonasus, in the northern Gulf of Mexico, with comments on geographic variability in life-history traits. Environmental Biology of Fishes 73:321–331. 2015 Southeastern Naturalist Notes Vol. 14, No. 1 N20 C.M. Jones and W.B. Driggers III Poulakis, G.R. 2013. Reproductive biology of the Cownose Ray in the Charlotte Harbor estuarine system, Florida. Marine and Coastal Fisheries 5:159–173. Rogers, C., C. Roden, R. Lohoefener, K. Mullin, and W. Hoggard. 1990. Behavior, distribution, and relative abundance of Cownose Ray, Rhinoptera bonasus, schools in the northern Gulf of Mexico. Northeast Gulf Science 11:69–76. Vooren, C.M., and A.F. Lamónaca. 2004. Rhinoptera brasiliensis. In, International Union for Conservation of Nature (IUCN) red list of threatened species. Version 2014.2. Available online at www. iucnredlist.org. Accessed 3 November 2014.