FISHERY BULLETIN: VOL. 84, NO. 4 



3) mature - ovary with large yellowish ova >1 cm 

 diameter; uterus well-developed and rich in tropho- 

 nemata, generally >1 cm long. 



Uteri and oviducts were opened and inspected for 

 ova or embryos. Embryos were weighed and mea- 

 sured for disc width (mm). Yolk-sac volume (mL) was 

 measured by volumetric displacement in a graduated 

 cylinder. 



RESULTS AND DISCUSSION 



Like many other elasmobranch populations which 

 occur along the east coast of the United States, cow- 

 nose rays are highly migratory and exhibit a north- 

 ward coastal migration in spring and a southward 

 movement in fall (Schwartz 1965; Smith 1980). Our 

 earliest spring collection of adult rays occurred dur- 

 ing 2-5 May 1977 on the North Carolina Outer 

 Banks. Our latest fall collection of adult males was 

 on 7 September 1978 in the lower York River, while 

 the latest fall collection of adult females occurred 

 on 12 October 1977 near Cape Henry, VA, at the 

 mouth of the Chesapeake Bay. Adult rays were 

 absent from pound net catches in the lower bay after 

 mid-October; furthermore, they were unavailable to 

 us until the following spring when they migrated 

 back into Chesapeake Bay. 



Size at Maturity 



At the onset of sexual maturity, terminal cartilage 

 elements develop distally on the claspers of male 

 elasmobranchs (Bigelow and Schroeder 1953), and 

 the allometric growth of these appendages has been 

 used to determine the attainment of sexual matur- 

 ity in various elasmobranchs (e.g., Clark and Von 

 Schmidt 1965; Struhsaker 1969; Gilbert and Heath 

 1972). In male cownose rays the ratio of clasper 

 length to disc width increases slightly at 75-85 cm 

 DW suggesting the onset of sexual maturity (Fig. 

 1). Males <75 cm (n = 68) appear immature; their 

 testes are thin, white and ribbonlike and their 

 claspers are narrow and flexible. Males ranging 

 80-98 cm (x = 89.8 cm; n = 115) appear mature; 

 their testes are pinkish white in color and greatly 

 swollen, and their claspers are rigid and well-cal- 

 cified. Based on clasper length to disc width ratio 

 and cursory observations of the testes, we estimated 

 that male cownose rays begin sexual maturation at 

 about 80 cm and most are probably mature at disc 

 widths >84 cm. 



Considerable discrepancies exist in the literature 

 concerning size of female cownose rays at sexual 



maturity. Gudger (1910) claimed a female about 60 

 cm wide gave birth to a pair of young. Bearden 

 (1965) reported four premature young from a female 

 measuring 712 mm (disc width?) taken in South 

 Carolina. Joseph (1961) and Orth (1975) collected 

 gravid females in Chesapeake Bay of 89 and 90 cm, 

 respectively. We classified females <84 cm (n = 86) 

 as immature (immature ovaries are thin and flac- 

 cid, and immature uteri are thin and elongate). 

 Females that we judged as mature ranged 84.5-100 

 cm (x = 96 cm; n = 117). Mature ovaries possess 

 yellowish ova >1 cm in diameter; the left uterus of 

 mature females is well-developed and rich in tropho- 

 nemata (uterine villi), which are generally >1 cm 

 long, red in color, and spatulate distally. We clas- 

 sified eight specimens (range: 84-92 cm) as matur- 

 ing females. Although ova <1 cm in diameter are 

 visible in the ovary, the left uterus is not well- 

 developed and the trophonemata are generally <0.5 

 cm long. The smallest gravid female measured 87 

 cm. Based on these observations we estimated 

 that female cownose rays begin sexual maturation 

 at 85-90 cm and are mature at disc widths >90 

 cm. 



Only the left reproductive tract appears functional 

 in female cownose rays. There is no macroscopic 

 evidence of follicular development in the right ovary. 

 The right uterus in mature specimens shows some 

 distension (ca. 3 cm wide), but does not exceed the 

 breadth of the left uterus. Embryos and ova occur 

 only in the left uterus, although we found an empty 

 shell capsule in the right uterus of several gravid 

 females. Nonfunctional right reproductive tracts 

 have been reported in the roughtail stingray, Dasya- 

 tis centroura, (Struhsaker 1969) and the bluntnose 

 stingray, D. sayi (Gudger 1912; Hamilton and Smith 

 1941; Hess 1959). 



Reproductive Cycle 



Numerous literature accounts reported on the cap- 

 ture of singular gravid cownose rays (Smith 1907; 

 Gudger 1910; Bigelow and Schroeder 1953; Joesph 

 1961; Hoese 1962; Bearden 1965; Orth 1975) and 

 these provided fragmentary information on the ray's 

 gestation cycle. Schwartz's (1967) abstract defined 

 June through October as the breeding cycle and 

 closely parallels our results, although we disagreed 

 on size at parturition. We collected 67 embryos 

 (range: 18-440 mm; sex undetermined for 3 speci- 

 mens) from the lower Chesapeake Bay and vicinity. 

 Data for 19 embryos (all specimens sexed, length 

 undetermined for 8 specimens) taken in April 1978 

 near Cape Lookout, NC, were provided to us by W. 



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