male's claspers, and the young are born alive. The 

 period of fetal development is lengthy, perhaps 

 up to 2 years. The number of young produced at 

 each delivery by a female dogfish is small. 

 Sex Ratio 



During development in the females, and pre- 

 sumably at birth, the sex ratio of the pups is very 

 nearly 1 : 1. Ford (1921) collected 2,720 embryos 

 at the fish market in Plymouth, England, and 

 found 1,377 were males and 1,343 were females. 

 Temple.man (1944) counted 933 males and 931 

 female embryos in the uteri of 492 females col- 

 lected in July-November 1942, off St. John's, New- 

 foundland. For dogfish in the Pacific, Bonham et 

 al. (1949) report, "Males and females occur in 

 equal numbers among the embryos." Aasen 

 (1964b) examined the pups in a sample of 41 fe- 

 males collected in November 1958 about 100 miles 

 west of the Orkney Islands. There were 126 males 

 and 130 females. Our observations for dogfish in 

 the Gulf of Maine agree with those from other 

 waters. In July-August 1961 on a cruise of the 

 Delaware in Ipswich Bay, 234 female dogfish were 

 examined. Fifty-three contained pups, of which 

 155 were males and 140 were females. 



From the time of birth to the time of attaining 

 sexual maturity, the young dogfish tend to school 

 together, but the mature adults tend to school by 

 sex. Ford (1921) classified the schools, or shoals, 

 as follows: (1) Shoals of large fish consisting 

 exclusively of females, the majority in the pregnant 

 condition; (2) shoals of medium-sized fish exclu- 

 sively males in the mature condition; (3) shoals 

 of medium-sized fish of which the majority were 

 immature females; and (4) shoals of immature 

 fish in which the males and females were equal in 

 number. 



Sex-size segregated schools are also reported by 

 Hickling (1930) around Ireland, Temple.man 

 (1944) off Newfoundland, and Bigelow and Sch- 

 roeder (1953) in the Gulf of Maine. In the eastern 

 Pacific, however, Quigley (1928b) observed that 

 t he schools contained both sexes, and the data listed 

 by Bonham (1954) for the same general area sup- 

 port this statement, although in individual catches 

 the percentage of males varied as much as from 

 35 to 76 percent. In the western Pacific, however, 

 Kaganovskaia (1933) observed the schools of dog- 

 fish to be segregated by sex, size, age, and depth. 

 She notes, ". . . the shore-set nets caught mainly 



immature sharks from 4 to 8 years of age, the bot- 

 tom-set nets older fish, from 10 to 18 years, mainly 

 males — (July-October) ; the drift pelagic nets — 

 chiefly mature females." Thus, her observations 

 agree in general with those reported from other 

 parts of the world. I suspect that the dogfish in 

 the eastern Pacific also school by sex despite the 

 reports to the contrary by Quigley (1928b) and 

 the data presented by Bonham (1954) . 



On the basis of the reports from areas that in- 

 clude the known range of the spiny dogfish, it is 

 difficult, therefore, to determine the sex ratio of the 

 adults because of the manner in which they school. 

 Size at Sexual Maturity 



Sexual maturity in male dogfish is attained at a 

 smaller size than in females, and reported studies 

 indicate that the larger the maximum size of fish 

 in a population, the larger the size at maturity. 

 Table 6 lists the data extracted from reports that 

 specifically mention average size at first maturity 

 for the spiny dogfish. 



Table 6. — Maximum size and size at first maturity of spiny 

 dogfish from several areas 



' Sex not specified, probably a female. 



Because of the age determination problem dis- 

 cussed earlier, it is difficult to assign an age value 

 to the time of first maturity. Templeman (1944), 

 however, suggests that, ". . . it takes the average 

 female dogfish 9 or 10 years from the fertilized egg 

 or 7 or 8 years after birth to reach sexual matur- 

 ity." Based on the spine readings of Bonham et 

 al. (1949), the data indicate 11 years for males 

 and 19 to 20 years for females as the age of first 

 maturity for spiny dogfish in waters off Wash- 

 ington. Kaganovskaia (1937) did not discover 

 mature females less than 19 years old or less than 

 1,000 mm. long. It seems incredible that dogfish 

 mature at such a late age, but a critical examina- 

 tion of the evidence offers support for Bonham's 

 data and Kajmnovskaia's statement. 



r,4n 



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