GILMORE ET AL.: REPRODUCTION AND EMBRYO DEVELOPMENT OF SAND TIGER SHARKS 



because cellular differentiation and organ formation 

 were still in a primitive phase of development. When 

 they have developed sufficiently to consume external 

 food, larger early embryos (20-63 mm) may consume 

 other ova contained within their own capsule. 

 Therefore, following the consumption of internal, en- 

 docoelomic yolk, the embryo may enter another nu- 

 tritional phase while still encapsulated. These obser- 

 vations suggest that initial internal coelomic yolk 

 supplies and other encapsulated ova and albumin 

 contribute more to initial embryonic growth and dif- 

 ferentiation in embryos 49-57 mm TL than does the 

 yolk of their own yolk sac. Although several blas- 

 todiscs and ova are observed in a single capsule, only 

 one embryo develops indicating that the activity of 

 one blastodisc somehow reduces or arrests the activi- 

 ty of other blastodiscs. 



After developing functional teeth and hatching at 

 49-63 mm, the embryo may utilize a variety of nutri- 

 tive sources. It is possible that intrauterine fluid, as 

 well as the yolk remaining in the yolk sac, may be a 

 food source. The 62 and 63 mm specimens still 

 possessed a 5.5 mm diameter yolk sac and well- 

 developed branchial filaments. Uterine fluid was 

 found to increase in volume after hatched embryos 

 were found. It is possible that this fluid may be ab- 

 sorbed through the extensive branchial filaments 

 found in these embryos. However, these filaments 

 also may have a respiratory function. Of the many 

 anatomical features observed in the developing em- 

 bryos, the presence of a filament attached to the cor- 

 nea of the 57 mm embryo was among the most in- 

 teresting. Its presence on the cornea suggests a res- 

 piratory rather than a nutritive function. The normal- 

 ly high metabolic demand of retinal tissue suggests 

 that there may be a need for such a filament. 



After the embryo hatches, the yolk sac eventually 

 declines in size demonstrating the utilization of this 

 nutritive source. Uterine fluids were observed to in- 

 crease in volume when newly hatched embryos were 

 present. This fluid could also be consumed by the 

 embryo. Activity of the hatched embryo within the 

 uterus may cause uterine hormones to induce in- 

 creased ovarian activity, since ovulation rates and 

 uterine yolk capsules increase after the first embryo 

 hatches. Other embryos also developing in some of 

 these capsules were not attacked when hatched em- 

 bryos were only 17-40 mm larger than encapsulated 

 embryos. The size advantage of a hatched 63 mm em- 

 bryo over a 46 mm encapsulated embryo may not be 

 great enough for an active attack, even though the 

 potential prey is restricted in movement due to its en- 

 capsulation. The first embryo to hatch apparently 

 does not begin to hunt for and detect other encap- 



sulated embryos until it reaches about 100 mm in 

 length. Initially only those capsules containing em- 

 bryos are attacked, while up to 81 capsules without 

 embryos are undamaged. Attacks are made by 

 puncturing and cutting the capsule membrane with 

 teeth. These attacks may also puncture and tear the 

 embryo within the capsule, as we found punctured, 

 dead embryos still encapsulated. The encapsulated 

 embryo that was attacked is probably consumed 

 later after the capsule is eventually opened by 

 repeated attacks from the larger embryo. 



It is apparent from these data that the first embryo 

 to hatch and reach a length approximating 100 mm 

 would be most likely to survive. By the time the em- 

 bryo reaches a length of 227-340 mm, during August 

 and September, it will have consumed its in- 

 trauterine competitors. If the embryo first to develop 

 dies in utero before consuming all other embryos, the 

 next largest embryo will probably become the domi- 

 nant predator and continue the developmental pat- 

 tern. The two 320 and 334 mm embryos from 5 

 August 1976 had consumed other embryos and also 

 contained 7.5-9.0 g of yolk in their stomachs. After 

 reaching 300-400 mm and having consumed all 

 smaller embryos, the embryo begins attacking egg 

 capsules which contain 7-23 unfertilized ova. In most 

 cases the capsules were not consumed but were torn 

 open near the posterior portion of the capsule and the 

 ova or gelatinous material had been removed. Em- 

 bryos 131 mm or greater in length were found to con- 

 tain varying quantities of yolk in both their stomachs 

 and valvular intestines. 



The embryo increases significantly in size (i.e., from 

 334 to 1 ,060 mm) by consuming uterine yolk supplies 

 and uterine fluid. After the embryos reach a length of 

 about 1.0 m and weights of 3.8-10.0 kg, parental 

 ovarian activity is reduced, stomach yolk content of 

 the embryo declines, and its liver increases in size. 

 After 9-12 mo of gestation, birth occurs. 



Teeth in the newborn 0. taurus are well developed, 

 extending beyond the gums (Fig. 17B). The teeth in 

 the newborn 91 cm female pup we examined had 

 well-developed lateral tooth denticles typical of 

 adult specimens. However, Taniuchi(1970) reported 

 no O. taurus <100 cm with lateral tooth denticles. 



Although only two young are produced at the end of 

 a lengthy gestation period, they have several selec- 

 tive advantages as top predators in marine food 

 webs. The newborn sand tiger sharks are large at 

 birth and are comparable in size to many common 

 adult neritic predators (e.g., scombrids and caran- 

 gids). They are also larger than the young of most 

 other galeoid sharks (45-60 cm, Wourms 1977). 

 Their larger size as a top predator also allows a 



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