734 



Fishery Bulletin 100(4) 



that mating had taken place but that ova were not 

 yet fertilized. On the basis of the occurrence of early- 

 stage gravid females, the ripe condition of the males, 

 and the presence of recent mating scars, we concluded 

 that most mating occurs from late September through 

 November. Mature males with copious amounts of 

 spermatophores and mature females were captured 

 on the same gear numerous times during the fall. 



The right uterus of the one gravid female observed 

 during late September had one single ovum capsule 

 with no visible embryos, along with several blastodisc 

 or nutritive capsules, whereas the contents of other 

 uterus appeared to have been aborted. This was the 

 only recently mated female observed in September. 

 Some gravid females in October and November con- 

 tained capsules with a single ovum, 6-7 mm diameter, 

 in addition to varying numbers of empty, blastodisc, or 

 nutritive capsules. These single ovum blastodisc cap- 

 sules (usually two per uteri) were considered to be the 

 annual developing embryos, their single ovum larger 

 than those of the aggregate blastodisc or nutritive 

 capsules. Gravid females examined during October had 

 either single ovum capsules or embryos 0.9-6.8 cm TL^ 

 (0.6-5.3 cm FL), and those seen in November had a de- 

 crease in occurrence of single-ovum capsules, and embryos 

 ranged from 1.1 to 37.8 cm TL^ (0.7-31.2 FL). No gravid 

 females with single ovum capsules were seen during De- 

 cember, and embryos ranged from 2.3 to 43.1 cm FL (Fig. 

 10). Only one nearterm, gravid porbeagle, caught in mid- 

 April, was examined in our study. This shark had three 

 embryos ranging in size from 59 to 72 cm TL^ (50-59 cm 

 FL). The considerable variation in embryo length among 

 litters during early gestation indicates a protracted mat- 

 ing season. 



Postpartum females were observed from the first week 

 of May to the first week of June. Our data from these fe- 

 males suggested that parturition extends from early April 

 through early June. The presence of postpartum females 

 in May-June after the September-November mating in- 

 dicates a gestation period of about 8-9 months. 



Although numerous gravid females are present from 

 late September through December on the Scotian shelf 

 and Grand Banks region, mature gravid or nongravid fe- 

 male sharks are seldom seen from January through June 

 in the Canadian fishery. Gravid females were caught be- 

 tween Georges Bank and the Grand Banks (Fig. 11). 



Fecundity 



Embryos were found to be at the same developmental 

 stage in each female, although embryo size varied as much 

 as 14.6 cm in one litter Runts were encountered in five 

 females and although clearly developing, were consider- 

 ably smaller than the coexisting embryos. Fecundity was 

 calculated by using all embryos. The average number of 

 embryos per porbeagle was 4.0 (304 embryos from 76 lit- 

 ters) although litters ranged from 3 to 6. In 66 litters there 

 were two embryos per uterus. The sex ratio of 202 embryos 

 (99 male and 103 female) was not significantly different 

 from one (;t:2=0.08, P>0.1). 



Figure 8 



Photograph of an ovary and open uterus of a gravid porbeagle 

 showing a developing embryo amid ova capsules. 



In the uteri of six females, fertilized ova were found in 

 the same ova capsule with one to three late developing 

 yolksac embryos. Some of these fertilized ova appeared 

 to be decomposing. These capsules were in the same uteri 

 as a larger, developing litter, but the size of the embryos 

 associated with the capsules (averaging 4-20% of the aver- 

 age size of the developing litter) were smaller than runts 

 (runts averaged 24-43% of the average size of siblings) or 

 the main litter. Because of their small size in relation to the 

 developing litter, and their appearance of decomposition, it 

 was presumed that they were ova that had been fertilized 

 late by remaining sperm and that had probably not contin- 

 ued to develop. However, this is not to rule out the possibil- 

 ity that some of these embryos could have developed into 

 runts or be consumed when littermates initiated feeding 

 on egg capsules. Further research is being conducted on 

 this subject and will be reported at a later date. 



Embryonic development and growth 



Newly fertilized ova, without visible embryos, were 6-7 

 mm in diameter As the embryo developed, their yolk sacs 

 decreased in size, and by the time the embryos were 

 between 4.2 and 9.2 cm TLs (3.3-4.5 cm FL), the yolk sacs 

 were tiny, white, ovoid structures attached to the embryo by 

 a short stalk. Embryos were found in capsules up to 4-^.2 

 cm TLj, (3.1-3.3 cm FL). The smallest posthatch embryos 

 were 3.2^.2 cm TL, (2.5-3.3 cm FL). The abdomens of 

 posthatch embryos between 4.7 and 5.1 cm TL^, (3.7 and 4.0 

 cm FL) were slightly swollen. Functional embryonic denti- 

 tion appeared in embryos at 12 cm TL^ (9.8 cm FL). As the 

 embryo continues to grow, the yolk stomach increases in size 

 as a result of in utero consumption of ova capsules by the 

 embryo. The stomach becomes grossly distended by the time 

 the embryo reaches 27-13 cm TL J 23-36 cm FL). The large 

 amounts of yolk material in the stomachs of these embryos 

 was characteristic of oophagy. Frequently, parts of ova cap- 

 sules, parts of, or whole, ova, and white flocculent material 

 were observed in the clear intrauterine fluid surround- 



