Mollet et al : Reproductive biology of Isurus oxynnchus 



311 



e 

 "a 



o 

 U 



00 



the sandtiger shark, the blastodisc 

 capsules contain up to 14 blasto- 

 disc ova, but only one egg develops 

 and absorbed material and other 

 encapsulated ova contribute more 

 to initial development than does 

 the yolk sac (Gilmore et al., 1983). 

 A possible early-term great white 

 shark had a total of 192 egg cases 

 of three types of different size and 

 mass in the left uterus, but the 

 size and number of the ova were 

 not reported (Uchida et al., 1987). 



We obsei-ved 3-cm-TL shortfin 

 mako embryos still attached to 

 a relatively large yolk sac and 

 inside egg cases (Fig. lA). It is 

 not clear at what size the embryos 

 hatch from the egg cases, possibly 

 5-6 cm, the size at which porbea- 

 gle (Lamna nasus) and sandtiger 

 sharks hatch (Swenander, 1907; 

 Gilmore et al., 1983). This esti- 

 mate agrees with an estimate of 

 the embryo TL calculated from the 

 diameter of the blastodisc ovum 

 (Mollet, unpubl. data). Bigeye thresher embryos 

 hatch at a slightly larger size (7-8 cm FL) because 

 their yolk sac diameter (11 mm) is greater than 

 that of porbeage and sandtiger sharks (Chen et al., 

 1997). 



During the oophagous embryonic phase, lamnids 

 develop huge yolk-filled stomachs, sandtiger sharks 

 develop large yolk-filled stomachs, and alopiids 

 develop only slightly extended yolk-filled stomachs 

 according to photographs and our calculated condi- 

 tion factors (Nakamura, 1935; Gilmore et al., 1983; 

 Moreno and Moron, 1992; our Fig. 6 for lamnids and 

 alopiids). The condition factors of the shortfin mako 

 (our data and references in Table 1), the porbeagle 

 (Templeman, 1963; Francis^), the salmon shark, 

 Lamna ditropis (Lohberger, 1910; Otake, 1990), and 

 the great white shark (Norman and Fraser, 1938) 

 reach a maximum between 20 and 35 kg/m'^ when the 

 embryos are midterm. The condition factor decreases 

 in the last third of gestation and approaches values 

 similar to those of postnatal lamnids (our data for 

 the shortfin mako; Francis and Stevens (2000) for 

 the porbeagle; Uchida et al., 1996; Francis, 1996 

 for the great white shark). The yolk-stomach in the 

 sandtiger shark reaches its largest size between 33.4 



0.25 0,50 0.75 



Total length (m) 



1 00 



1.25 



1 50 



Figure 6 



The relationship between condition factor (M/TL^) and TL of lamnid and alopiid 

 embryos. Error bars give ±2 SE of mean, if available.  = Isurus oxyrinchus; O = 

 Lamna spp.; x =Carcharodoii carchanas; D = Alopias spp. See Table 1 for sources 

 of/, oxyrinchus data. Lamna spp. data from Lohberger! 1910); Templeman 1 1963); 

 Otake (1990); Francis;" Otake"'. Carcharodon carchanas data from Norman and 

 Fraser (1938, NandF); combined Francis ( 1996) and Uchida et al. (1996). Alopias 

 spp. data from Joseph (1954); Cadenat (1956); Gubanov (1972); Hixon (1979); 

 Gilmore ( 1983 ); Moreno and Moron ( 1992 ); Otake (1990 ). 



and 80 cm TL, but no embryo masses were reported 

 by Gilmore et al. (1983) and therefore the condition 

 factor could not be calculated. The condition factors 

 of thresher shark embryos are much smaller if TL 

 rather than PCL is used as the length parameter. 

 However, if the alopiids were to develop a large yolk- 

 filled stomach, then the condition factor of mid-term 

 embryos would be considerably larger compared with 

 that of early- and near-term embryos, which is not 

 the case (Fig. 6). The embryonic development of alo- 

 piids proceeds at a steady rate without development 

 of a large yolk-filled stomach and we expect ovula- 

 tion of nutritive ova right up to parturition. Francis 

 and Stevens (2000) have suggested that the puzzling 

 gross abdominal distention observed in porbeagle 

 embryos (and other lamnids) is energetically ineffi- 

 cient for the pregnant female. 



The HSIs of shortfin mako embryos from a full- 

 term litter were between 5*^ and 8 % and the yolk- 

 stomach constituted 3-15% of body mass. These 

 combined nutrient reserves may provide neonates 

 with nutrition while they improve their hunting 

 ability. From the metabolic rate of a shortfin mako 

 pup reported by Graham et al. (1990) (1.5% of 

 bodymass/d), we estimated that a 20% reserve would 

 enable pups to survive for about 20-30 days. This 



^ Francis, M. P. 1997. National Institute of Water and Atmo- 

 spheric Research (NIWA), P.O. Box 14-901, Wellington, New- 

 Zealand. Personal commun. 



' Otake, T. 1998. Mie University, 1515 Kamihama. Tsu, Mie 

 514. Japan. Personal commun. 



