PARSONS: REPRODUCTIVE BIOLOGY OF ATLANTIC SHARPNOSE SHARK 



oz 4 



LU 



3 



2 



• MEAN 

 I RANGE 



N = 78 



85-90 90-95 95-100 100-105 105-110 

 ADULT TOTAL LENGTH (cm) 



Figure 16.— Relationship between adult total length and litter 

 size of the Atlantic sharpnose sharks. The plot indicates that 

 fecundity increases significantly as adult total length increases 

 (F = 9.216, P<0.00001). 



24.1 + 



22.9 



I 

 i- 

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z 



LU 



_l 



_l 



s 



2 1.7- 



*~ 20.4 - 



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CE 

 HI 



s 



LU 



19.2 



18. X 



• MEAN 

 1 RANGE 

 EH 95% CONFIDENCE INTERVAL 

 N = 300 



I 



3 4 



No. PER UTERUS 



Figure 17.— Relationship between numbers of embryos per 

 uterus and embryo total length of the Atlantic sharpnose 

 sharks. Embryo total length decreases significantly with in- 

 creasing number per uterus, AT = 89. 



embryo size (Fig. 17). The figure indicates that 

 at the 95% confidence limits significant differ- 

 ences exist between the total lengths of the em- 

 bryos. Embryos were found to be largest when 

 one or two are present per uterus. However, in 

 only one case was there a single embryo found 

 within a uterus. 



It is conceivable that mechanical "packing" 

 within the uterus causes "intra-uterine competi- 

 tion" for nutrients. As already discussed, in addi- 



tion to placentally derived nourishment, sharp- 

 nose shark embryos may be able to absorb 

 directly nutrients which are produced by the 

 uterine epithelium. An increase in the number of 

 embryos within the uterus above some optimal 

 value might result in competition for this "uter- 

 ine milk" and a decrease in embryo size. 



In sharpnose sharks, the parents that produce 

 what might be termed an "optimal" number of 

 embryos per uterus are producing the largest 

 embryos. If we assume that these size differences 

 are retained until birth, and thereafter, these 

 larger embryos will result in progeny of highest 

 individual fitness. Larger offspring cost more to 

 produce, but they are also worth more (Pianka 

 1978). 



It would be interesting to examine the repro- 

 ductive strategy of tropical sharpnose shark 

 populations, since these sharks have been report- 

 ed to have litters with as many as 12 embryos 

 (Bigelow and Schroeder 1948; Skocik 1969). 

 Based on this study, it would be a logical extra- 

 polation to predict that these litters would result 

 in smaller offspring. A litter of 12 must be 

 approaching maximum fecundity for sharpnose 

 sharks. 



Seasonal Distribution 



In this study it was determined that migratory 

 behavior of the Atlantic sharpnose shark is pri- 

 marily limited to an inshore-offshore movement. 

 From late April to September of 1979, 93 sharp- 

 nose sharks were collected from shallow inshore 

 waters. During the period from late October 

 1979 to April 1980, despite numerous attempts, 

 no sharpnose sharks were collected inshore. 

 Sharpnose sharks may be encountered offshore 

 year-round; however, the data indicate that the 

 concentration of sharks is greatest during the 

 fall and in particular, winter months. From Octo- 

 ber 1979 to February 1980, 59 sharpnose sharks 

 were collected during offshore longlining. Fig- 

 ure 18 shows that the number of sharpnose 

 sharks landed in deep water, as well as the catch 

 per unit effort (CUE), is low in spring and sum- 

 mer (CUE = 1.2 and 2.4, respectively) and in- 

 creases to a high in winter (CUE = 7.3). 



The above data suggest that the migration 

 from inshore to offshore begins around October 

 or November. Atlantic sharpnose sharks appar- 

 ently remain in deeper waters during the colder 

 months and return inshore again in April and 

 May. 



71 



