the scalloped hammerhead is one of the most 

 valuable food resources in Taiwan, many facets of 

 its life history, particularly reproduction, are not 

 well known. This study provides information 

 about certain aspects of reproduction in the scal- 

 loped hammerhead in northeastern Taiwan 

 waters. 



Materials and Methods 



From September 1982 to June 1983 and from 

 December 1983 to September 1985, shark speci- 

 mens were examined and material collected 

 monthly at Nan Fan Ao Fish Market. These 

 sharks had been caught by drift longlines set near 

 the surface to around 100 m, or by surface har- 

 poon. A total of 674 scalloped hammerhead 

 sharks were examined at the fish market (Table 

 1). Data recorded included total length measured 

 from the tip of the snout to the tip of the upper 

 lobe of the caudal fin (straight line measure), 

 body weight, clasper length (measured from 

 cloaca to the tip of claspers), ovarian egg diameter 

 and number, and condition of the uteri. In addi- 

 tion, uterine embryos were counted, sexed, and 

 measured for total length. Counts of litter size 

 included any uterine eggs as well as embryos. 



Stages of maturity for both females and males 

 were categorized simply as "mature" or "imma- 

 ture". Females having threadlike uteri and tiny 

 ovarian eggs were called immature, while those 

 with eggs larger than 25 mm in diameter, with 

 uteri containing embryos or eggs or with empty 

 but expanded and flaccid uteri, were designated 

 as mature. Males with rigid claspers were classi- 

 fied as being mature. Clasper length relative to 

 total length also gave an indication of maturity. 



Table 1 . — The number of specimens examined in 

 this study. 



Results 



The reproductive organs of scalloped hammer- 

 head closely resemble those of the bonnethead 

 shark, S. tiburo (described by Schlernitzauer and 

 Gilbert 1966). 



As with the bonnethead shark, only the right 

 ovary of the scalloped hammerhead is functional, 

 supplying both oviducts. As the ovarian eggs ma- 

 ture (>25 mm diameter), they pass through the 

 common ostium into the oviducts, where they are 

 fertilized. The eggs then become encased in the 

 embryonic membrane as they pass through the 

 nidamental gland and descend into the uterus. In 

 the uterus, embryonic development proceeds, 

 nourished by a yolk sac. After a period, the uter- 

 ine compartments develop, which enclose the em- 

 bryo, and a yolk-sac placenta is implanted. After 

 the yolk is exhausted, the embryo is nourished 

 until birth by the placenta through the umbilical 

 stalk. 



Based on the condition of the uterus and ovary, 

 female scalloped hammerheads became mature 

 at a larger size, around 210 cm, than males. All 

 females over 230 cm were mature. 



Based on the rigidity of the claspers, male scal- 

 loped hammerheads reached their first maturity 

 at a total length of 198 cm, while all those over 

 210 cm were mature. 



The clasper length of males increases rapidly 

 relative to total length, until the sharks reach 

 around 200 cm, at which size the clasper length/ 

 total length relationship plateaus, suggesting 

 that sexual maturity has been attained (Fig. 

 2). Also, this size marked the approximate transi- 

 tion point from fiaccid to rigid claspers (Fig. 

 2). 



It takes roughly 10 months of development 

 from egg formation to ovulation (Fig. 3). In Octo- 

 ber and November, eggs were very small, measur- 

 ing about 2 mm in diameter. By July they had 

 increased in size to about 30-38 mm and num- 

 bered 40-50 per female, and by August and Sep- 

 tember they had grown to about 40-45 mm. In 

 one mature female, in September we counted 28 

 uterine eggs and 4 ovarian ones measuring 45 

 mm in diameter. This suggested that the 4 

 ovarian eggs were ready for ovulation. Because 

 ovarian eggs larger than 30 mm in diameter 

 seemed near ovulation, we concluded that ovula- 

 tion occurred between July and October. 



The parturition season lasts from May to July, 

 and the gestation period of this species was esti- 

 mated to be roughly 10 months (Fig. 4). No em- 



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