The reported sizes of spiny dogfish at time of 

 first maturity are about 72 percent (range 68-80 

 percent) of the reported maximum sizes for the 

 species. This is in general agreement with similar 

 data reported by Bigelow and Schroeder (1953) 

 for nine species of sharks from the Gulf of Maine 

 where the sizes at first maturity are about 62 per- 

 cent (range 52-75 percent) of the maximum sizes. 

 If we assume (1) that the maximum age (sexes 

 combined) of the spiny dogfish is 25 to 30 years, 

 (2) that we can equate length with age, and (3) 

 that the largest individuals are females, then the 

 age at first maturity of the females is about 72 per- 

 cent of the maximum or about 18 to 21 years. 



Mating 



Although there are no recorded observations of 

 the actual mating of spiny dogfish and no con- 

 clusive data to confirm the season of year when it 

 takes place, the evidence presented by most au- 

 thorities suggests that mating takes place during 

 months when the water temperatures are low. 

 Ford (1921) found newly formed embryos at 

 Plymouth during November to May. Templeman 

 (1944) concludes that the eggs are fertilized and 

 pass into the uteri in February and March, but 

 more generally in March. He cautions, however, 

 that his lack of information about the spring tem- 

 peratures when the eggs are developing may vary 

 the dates a month in either direction. An exami- 

 nation of dogfish captured in the Woods Hole area 

 suggests that ovulation probably occurs in Feb- 

 ruary or March (Hisaw and Albert, 1947) and 

 perhaps we can infer that mating and fertilization 

 of the eggs take place soon after. Bigelow and 

 Schroeder (1948) believe that in the Atlantic 

 Ocean, mating probably takes place shortly after 

 the young are born, although no definite informa- 

 tion is available. 



Reports on mating of the spiny dogfish in the 

 Pacific Ocean tend to be contradictory, but in gen- 

 eral support the hypothesis that mating takes place 

 in the cold months, as in the Atlantic Ocean. 

 Quigley (1928b) examined slightly over 200 dog- 

 fish collected in June, July, and August and found 

 embryos that ranged in size from the smallest to 

 those with the umbilical scar completely healed and 

 apparently ready for birth. These observations 

 suggested that ". . . in the vicinity of Nanaimo, 

 Squalm sucklli breeds at all times of the year." 

 We know now, of course, that what she had seen 



LIFE HISTORY OF SPINY DOGFISH 

 795-358 O — 66 2 



were the two broods of young that are typical of 

 the species. Hart (1942) on the other hand, re- 

 porting the work of Lucus, concluded that breed- 

 ing takes place during the winter and that, 

 ". . . fertilization by the male takes place soon 

 after the birth of the young . . ." Bonham et al. 

 (1949) admitted that the season at which mature 

 dogfish mate is not known, but regards as a popular 

 misconception the belief that dogfish breed and 

 bear young at all times of the year. Sato (1935) 

 concluded, without much firm basis for the state- 

 ment, that dogfish breed throughout the year 

 around Hokkaido. 



Fecundity 



As might be expected for a live-bearer, the 

 number of young produced per female spiny 

 dogfish is small and the period of development 

 within the mother is long, lasting nearly 2 

 years. The eggs are large and contain a great 

 deal of yolk and have been well described by Tem- 

 pleman ( 1944) . Following fertilization, and dur- 

 ing early development of the fetus, the eggs (figs. 

 6 and 7) are contained in a horny capsule ("can- 

 dle") that later breaks down leaving the embryos 

 free in the enlarged part of the oviduct (termed 

 the "uterus"). There is no placental attachment 

 (Bigelow and Schroeder, 1953) as with some other 

 species of sharks, but additional material (at least 

 water) is obtained from the uterine wall (Temple- 

 man, 1944). The reported number of pups per 

 female probably should be considered a minimal 

 figure. The observations were made of fish 

 caught by otter trawls or other fishing gear and 

 examined on board the vessel or in the market. 

 I have seen pups that were apparently near term 

 prematurely delivered when the females were 

 landed on the deck of our research vessel. It seems 

 reasonable to assume that this also happened in 

 the studies reported in the literature. Fortu- 

 nately, the number of premature pups was never 

 very great so that the reported data may be ac- 

 cepted with a fair degree of confidence. 



The greatest number of pups per female was 

 reported by Kaganovskaia (1937) who recorded 5 

 to 19, with an average of 11, for the spiny dogfish 

 near Sakhalin. The least number of pups per 

 female was reported by Templeman (1944) who 

 recorded 1 to 7, with an average of 4, for the dog- 

 fish near Newfoundland. Ford (1921) reported 1 

 to 11, mostly 2 to 4, from England, while from the 



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