FISHERY BULLETIN: VOL. 84, NO. 4 



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EMBRYO DISC WIDTH (mm) 



Figure 4.— Relationship of yolk-sac volume (mL) to disc width (mm) for Rhinoptera 

 bonasus embryos collected in late summer and fall. 



favorite prey (Darnell 1958; Budker 1971) are abun- 

 dant seaward of the Virginia capes during summer 

 (Lawler 1976), but generally only the sandbar shark, 

 Carcharhinus plumbeus, and the bull shark, C. 

 leucas, frequent the Chesapeake Bay proper 

 (Schwartz 1960; Musick 1972). Although gravid 

 female sandbar sharks utilize the eastern shore of 

 the Chesapeake Bay (Lawler 1976), they may not 

 pose a threat to cownose rays, since the female sand- 

 bar sharks generally abstain from feeding while on 

 their pupping grounds and males tend to avoid such 

 areas (Springer 1960). Bull sharks (Schwartz 1959) 

 may represent the only major predators of rays in 

 Chesapeake Bay during summer. 



ACKNOWLEDGMENTS 



We thank J. A. Musick, G. R. Huntsman, A. B. 

 Powell, W. R. Nicholson, J. Colvocoresses, and two 

 anonymous reviewers for their comments and 

 critical review of the various drafts of this manu- 

 script. Numerous students and staff at Virginia In- 

 stitute of Marine Science lent valuable assistance 

 during various phases of this study, especially J. 

 Gourley, R. Lambert, R. K. Dias, E. F. Lawler, R. 

 J. Orth, and C. E. Richards. Captains Buddy Pon- 

 ton, George Ross, Benny Belvin, and Herman 

 Greene kindly provided "stingers" from their com- 

 mercial catches. W. S. Otwell and F. J. Schwartz 

 generously shared their life history notes on the 

 cownose ray. 



Support for the study was provided by the Sea 

 Grant program of the Virginia Institute of Marine 



Science (Grant Nos. 04-6-158-44-047 and 04-7-158- 

 44-109). Additional financial assistance was provided 

 by the Gulf and South Atlantic Fisheries Develop- 

 ment Foundation, Inc., Tampa, FL. 



LITERATURE CITED 



Babel, J. S. 



1967. Reproduction, life history, and ecology of the round 

 stingray, Urolvphus halleri Cooper. Calif. Dep. Fish Game, 

 Fish Bull. 137:1-104. 

 Bearden, C. M. 



1965. Elasmobranch fishes of South Carolina. Contrib. 

 Bears Bluff Lab. 42:1-19. 

 BlGELOW, H. B., AND W. C. SCHROEDER. 



1953. Fishes of the Western North Atlantic. Pt. 2. Sawfishes, 

 guitarfishes, skates, rays, and chimaeroids. Mem. Sears 

 Found. Mar. Res., Yale Univ. 1:1-588. 

 Budker, P. 



1971. The life of sharks. Columbia Univ. Press, N.Y., 222 p. 

 Clark, E., and K. von Schmidt. 



1965. Sharks of the central Gulf Coast of Florida. Bull. Mar. 

 Sci. 15:13-83. 

 Daiber, F. C, and R. A. Booth. 



1960. Notes on the biology of the butterfly rays, Gymnura 

 altavela and Gymnura micrura. Copeia 1960:137-139. 

 Darnell, R. M. 



1958. Food habits of fishes and larger invertebrates of Lake 

 Pontchartrain, Louisiana, an estuarine community. Publ. 

 Inst. Mar. Sci. Univ. Tex. 5:353-416. 

 Gilbert, P. W., and G. W. Heath. 



1972. The clasper-siphon sac mechanism in Squalus acanthias 

 and Mustelus canis. Comp. Biochem. Physiol. A Comp. 

 Physiol. 42:97-119. 



Gudger, E. W. 



1910. Notes on some Beaufort fishes-1909. Am. Nat. 44: 

 395-403. 



1912. Natural history notes on some Beaufort, N.C., fishes, 

 1910-11. No. I. Elasmobranchii— with special reference to 

 utero-gestation. Proc. Biol. Soc. Wash. 25:141-156. 



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