Mollet et al,: Reproductive biology of Isurus oxynnchus 



307 



«=58) and mature females in the 

 range of 5.0-22.7 cm (mean 10.7, 

 SE 0.7, n=AA) (Fig. 2D). The uterus 

 widths of pregnant ( with egg cases or 

 embryos) and nonpregnant females 

 overlapped. 



The HSI of immature and mature 

 females in the TL range of 0.73-3.66 

 m varied from 1.2 to 17.9% and 

 the overall mean HSI of 6.7*7^ 

 (SE=0.25%, « = 161 ) was a little lower 

 than the HSI of near-term embryos 

 (see below). The large HSI range 

 of immature females (1.2-17.67f, 

 n = V25) was almost the same as 

 that of mature females (2.5-17.9'^^ , 

 «=36). 



Gestation and parturition 



The capture of two females with 

 litters containing 3.0- and 52-cm 

 embryos (Table 2, nos. 3 and 4) in 

 the same month (January ) and loca- 

 tion (Puerto Rico) suggested that 

 gestation is longer than one year. 

 Assuming a gestation in excess of 

 12 months, the mean embryo length 

 for 26 litters and the length for 

 188 age-0+ fish from both the North- 

 ern and Southern Hemisphere were 

 graphed against season of capture 

 (Fig. 3A). Based on the three 

 females caught in early pregnancy 

 (Table 2), ovulation takes place in 

 fall. Parturition occurs in late 

 winter to mid-spring at ca. 70 cm. 

 The length-at-capture data of the 

 age-0+ fish indicated a smooth con- 

 tinuation of the growth rate evident 

 in utero. 



The relationship between embryo 

 length and time of capture of all 

 western North Atlantic litters (n-1 . 

 slope=3.7 cm/month, SE=0.6 cm/mo., 

 P=0.002, r-=0.87) predicted a ges- 

 tation of 19 months. The combined 

 Northern Hemisphere data, which 

 include five mid-term litters, yielded 

 a gestation of 20 months (n = ll, 

 slope=3.4 cm/month, SE=0. 05 cm/mo., 

 P<0.001,r2=:0.84). 



There were no mid-term litters 

 from the Southern Hemisphere. If 

 the two females with recently fer- 



1/5 



o 



> 



o 



■a 



B 



AS „ „ 



o o 

 o 

 X ex XX eo o 



XX3 oxo o o 



XSCK O O 



o 

 X )«< x«o o o 



X . X W >KiS <: (XX)M IC C i< (X . XXK 



2 3 4 



Total length (m) 



Figure 2 



The relationsliips between four reproductive parameters and lengtli of female 

 hurus o.xyrinchus. (A) Natural logarithm (Ln) of gonadosomatic index (GSI) was 

 used. iB) Maximum ova diameter. Lack of, or very small oocytes, are indicated 

 by diameter. A = female with active ovary and 3-cm-TL embryos; + = diam- 

 eter of yolk sac of 3-cm-TL embryo; S = female with spent ovary and 52-cm-TL 

 embryos. (C) Oviducal gland diameter of western North Atlantic specimens. iDi 

 Uterus width. (■ = pregnant; 0=mature, not pregnant; X = immature and ado- 

 lescent; E=enibryos present; EC=egg cases with single ovum present, i 



