PARSONS: REPRODUCTIVE BIOLOGY OF ATLANTIC SHARPNOSE SHARK 



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Figure 12. — Mating season of adult male Atlantic sharpnose 

 sharks as evidenced by the seasonal increase in gonadosomatic 

 index (GSI). The data suggest that male sharpnose sharks are 

 reproductively active during late spring and summer. The 

 closed circles represent mean values and the numbers indicate 

 sample sizes, N= 20. 



and no visible sperm or semen in the seminal 

 vesicles. In late April the GSI had risen to 0.51, 

 but there was little sperm present in the seminal 

 vesicles. During mid- to late May the GSI aver- 

 aged 0.47. All mature individuals had enlarged 

 testes, turgid seminal vesicles, and copious 

 amounts of sperm present in the claspers as evi- 

 denced by microscopic examination. This condi- 

 tion was found to persist through June and July 

 with GSI equalling 0.59 and 0.57, respectively. 

 Several adult males examined in August were 

 found to have large quantities of sperm in the 

 seminal vesicles. A single GSI determination in- 

 dicated a slight decline from previous months. 



The mating season in female sharpnose sharks 

 was evidenced by an increase in ovarian egg di- 

 ameter (Fig. 13). From August to December the 

 average egg diameter increased from ca. 3.0 to 

 4.2 mm. In almost every ovary examined during 

 November and December, a few eggs were be- 

 ginning to visually dominate the other oocytes. In 

 February, the mean oocyte diameter equalled 

 5.0 mm, with some eggs reaching 11 mm. In Feb- 

 ruary, all mature ovaries contained four to eight 

 oocytes that were noticeably larger than sur- 

 rounding eggs. From mid-February to late May 

 or June, there was a rapid increase in egg diame- 

 ter to about 20 mm at ovulation. 



The information indicates that the mating sea- 

 son for male and female sharpnose sharks in the 

 northern Gulf of Mexico coincides, although 

 male sharpnose sharks are reproductively active 



earlier in the year. Assuming that females do not 

 mate when gravid and that ovulations occur 

 after copulation, then the mating season must 

 occur between mid-May and mid-July. Most 

 adult females still carried near-term embryos in 

 mid-May, and by mid-July all females examined 

 had uterine eggs. Considering the peak of partu- 

 rition for gravid females (see Embryonic Growth 

 and Development section), the subsequent ap- 

 pearance of uterine eggs, and the occurrence of 

 the first detectable embryos, the peak of mating 

 most likely occurs from mid-June to mid-July. 



Embryonic Growth and Development 



Embryos representing various stages of devel- 

 opment were weighed, sexed, and measured in 

 total length. Conceptions were estimated to be at 

 a peak in early to mid-July. At this time several 

 sharpnose sharks that possessed recently ovu- 

 lated uterine eggs but no visible embryos were 

 examined. In late August, gravid females were 

 collected, and they contained embryos ranging 

 from about 4 to 11 cm TL. The smallest embryos 

 examined were still dependent upon the yolk sac. 

 They had prominent branchial gill filaments, 

 undeveloped fins, and the anterior end was en- 

 larged in relation to the rest of the body. Pratt 

 (1979) suggested that growth of embryonic Prio- 

 nace glauca is linear. Increase in length of sharp- 

 nose shark's embryos approximates a sigmoid 

 curve as evidenced by polynomial regression 



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Figure 13.— Mating season of adult female Atlantic sharpnose 

 sharks as evidenced by the seasonal increase in ovarian egg 

 diameter, N = 1,260. The data suggest that the mating season 

 for females occurs from mid-June to mid-July. 



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