FISHERY BULLETIN: VOL. 81. NO. 1 



analysis (Fig. 14). After conception there is a pe- 

 riod of rapid growth through the remainder of 

 the summer and fall. By November the embryos 

 have attained an average of 21.3 cm and appear 

 almost completely developed. There is a notice- 

 able inflection in the regression line in Novem- 

 ber. The increase in length declines through the 

 winter and spring months, although a slight in- 

 crease may occur just before parturition in May 

 or June. Pups are born at an average of about 32 

 cm TL. Skocik (1969) reported a total length of 25 

 cm for sharpnose shark at birth, and Bigelow 

 and Schroeder (1948) stated that newborn sharp- 

 nose sharks are generally about 275 to 400 mm 

 long. The largest embryo recorded during the 

 study period was 36 cm TL and the smallest free- 

 living specimen was 32 cm. 



Increases in weight of the sharpnose shark's 

 embryo differed from the increases in total 

 length (Fig. 15). Embryo weight increased slowly 

 during the period from estimated conception 

 (mid-July) to October. Thereafter, however, until 

 parturition in late May or June, an almost linear 

 increase of about 16 g/mo occurred. Parturition 

 occurs most likely between about 95 and 150 g. 



By using the above information, it was possible 

 to estimate the gestation period. Atlantic sharp- 

 nose shark's embryos require a 10 to 11 mo gesta- 

 tion period, beginning in July or August and 

 ending in May or June of the following year. 



Relationships Between Adult Females 

 and Embryos 



A significant relationship was observed be- 

 tween total length of the gravid female and the 

 number of offspring produced. This is note- 

 worthy since other works have failed to show 

 such a relationship among carcharhinids 

 (Springer 1960; Clark and von Schmidt 1965). 

 Figure 16 shows that the total length of the adult 

 is correlated with litter size ( ANOVA significant 

 at <0.01). There is a direct relationship between 

 fecundity and the size of the adult with the 

 largest individuals being the most fecund. Grav- 

 id females produce an average of 5 pups/litter 

 per year (one to seven), but in most cases either 

 four or six embryos will be present. 



It was anticipated that a relationship between 

 litter size and embryo size could be detected. An 

 optimal clutch size has been demonstrated in 

 some species of birds (Lack 1954, 1966, 1968). 

 Compared with small and large clutches, inter- 

 mediate-sized clutches leave proportionately 



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Figure 14.— Growth of embryonic Atlantic sharpnose shark. 

 Regression analysis shows the increase in embryo total length 

 from fertilization to parturition, N = 300. 



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Figure 15. — Growth of embryonic Atlantic sharpnose shark. 

 Regression analysis shows the increase in embryo weight from 

 fertilization to parturition, N = 300. 



more offspring that survive to maturity. Birds 

 from large clutches are smaller in size than birds 

 from intermediate-sized clutches. After evalu- 

 ating the data, an "optimal litter size" could not 

 be demonstrated for the Atlantic sharpnose 

 sharks. However, when the right and left uteri of 

 adults collected during a single sampling trip (to 

 cancel out seasonal differences) were treated 

 separately, an inverse relationship was observed 

 between the numbers of embryos per uterus and 



70 



