Mollet et al : Reproductive biology of Isurus oxyrinchus 



305 



Table 2 



Details for pregnant hunts oxyrinchus. i 1-3) Females in very early pregnancy with blastodisc and nutritive egg cases. Observa- 

 tions appear in proposed chronological order. (4-6) Females with well-developed embryos. (L=left; R=right.) GSI = gonadosomatic 

 index; HSI = hematosomatic index. 



No. TL(m) Date 



Location 



Observations 



1 2.92 19 Mar. 1987 KwaZulu-Natal 



2 2.88 10 June 1986 KwaZulu-Natal 



3 3.09 9 Jan. 1993 Puerto Rico 



4 3.25 15 Jan. 1992 Puerto Rico 



5 3.34 27 Aug. 1997 KwaZulu-Natal 



6 3.14 15 Aug. 1997 South Pacific 



6(L)-f5(R) egg cases with single egg; no blastodisc observed; 4(L)-i-8(R) 

 nutritive egg cases with numerous burst eggs; capsule being formed in left 

 oviducal gland; GSI = 1.13%, HSI = 10.6%; mating bites. 



7{L)-f7(R) egg cases wdth single egg ( some blastodisc); 12( L+R) nutritive egg 

 cases with up to 14 eggs of 4 mm diameter; several ova being encapsulated 

 in right oviducal gland; GSI = 1.219?. HSI = 10.3'7f ; mating bites. 



7(L) empty egg cases; 4(Li blastodisc egg cases at least, with one embryo 

 each (-3.0 cm TL, badly disintegrated when measured); 5(R) blastodisc egg 

 cases ( 3x 10 cm ) with one embryo each ( 2.6, 2.9, 3.0, 3.0, & 3.3 cm TL ); 43( L) 

 + 42(R) nutritive egg cases (3x5 cm) with 16-20 eggs per capsule, 7-9 g 

 each capsule, 334 g total (R); 2(L) egg cases in lower oviduct; GSI -5'5 

 (estimate from ovary dimensions 44x27 cm). 



7(L) embryos (1 female, 5 males, and 1 lost). 51.0-54.0 cm, 1.660-2.300 

 kg; 8(R) embryos (4 females), 50.5-53.8 cm, 1.435-2.370 kg; mean length 

 and mass of 14 embryos 52.0 cm (SE 0.4) and 2.000 kg (SE 0.071); uteri 

 dimensions 103x22 cm (L), 111x22 cm iR); GSI -0.3% (estimate from ovary 

 dimensions 27x9 cm), spent ovary. 



9(L-i-R) embryos (5 females), 56.8-62.0 cm (mean 59.9 cm, SE 0.6), 

 2.100-2.800 kg (mean 2.416 kg, SE 0.094); embryo stomachs with 551-846 

 gyolk, 26.2-32.0% of total embryo mass (;!=4); embryo livers 75-110 g, HSI 

 range 3.4-4.1% {n=4); GSI = 0.185% (spent ovary), HSI = 2.465%. 



13 (L+R) embr>'os (6 females), 64.6-70.7 cm (mean 68.8 cm, SE 0.5); 

 2.300-3.125 kg (mean 2.830 kg, SD 0.062); embryo stomachs with 73-478 

 g yolk, 2.6-15.3% of embryo mass; embryo spiral valve with 68-88 g .yolk, 

 2.4-3. 37t of embryo mass (mean 2.9% ); embryo livers 146-234 g, HSI range 

 5.2-8.0% (mean 7.0%, SE 0.2); GSI and HSI of female not available. 



Litter size ( LS) increased with maternal TL accord- 

 ing to 



LS=0.810 rL2 3-16 



(n=24,P=0.013, /■2=0.25) 



and fell within the band of a model calculation 

 (LS=(0.26 to 0.46) TL'^^"^). The model was derived 

 from the maternal mass-length relationship (M= 

 7.658 rL3 10; Stevens, 1983) by postulating that the 

 litter mass is a constant fraction of the pregnant 

 female mass (10-15%, based on available data) and 

 by using an estimate of the embryo mass at birth 

 (2.5-3.0 kg, based on available data). The power 

 regression was still significant (P=0.029) if the small- 

 est litter of four (an outlier) and the largest litter of 

 27.5 were excluded. 



There were no significant differences between the 

 mean litter size of Northern ( 14.0, n = 13} and South- 

 ern Hemisphere females (11.1, n= 17, ANOVA,P=0.09) 

 or between western North Atlantic (12.8, n=8} and 

 Southern Hemisphere females (ANOVA, P=0.28). 



Indicators of sexual maturity 



The size of reproductive organs increased as the 

 shortfin mako approached maturity (Fig. 2). A loga- 

 arithmic scale was necessary to present the large 

 GSI range between 0.00044% and -5.0% (Fig. 2A), 

 reflecting ovaries weighing less than 10 g in imma- 

 ture sharks smaller than 2.4 m, up to an estimated 

 11.3-13.5 kg in a female in early pregnancy (no. 3 in 

 Table 2). There was considerable overlap in the GSI 

 of adolescent females (range: 0.005-0.28%, a; =28) 

 and that of mature, nonpregnant females with inac- 

 tive ovaries (range: 0.08-0.81%, n=38) or pregnant 

 females with near-term embryos and spent ovaries 

 (GSI=0.185% and -0.3%, n=2). The GSI (1.1%) of 

 recently fertilized females with egg cases and the 

 GSI ( -5% ) of the female with the 3-cm embryos were 

 the largest observed (Fig. 2A). 



Oocytes of noticeable size (1 mm) appeared in 

 maturing females larger than 2.4 m (Fig. 2B). The 

 MOD of immature fish ranged from 1.0 to 4.0 mm 



