ances to migration such as the contours of the 

 bottom offer to haddock and cod. Thus, it is quite 

 possible that the dogfish stocks on the whole eastern 

 coast of North American mingle sufficiently to con- 

 stitute a single population." 



He modified this somewhat later (1954) after 

 analyzing his tag return data. "The distant recap- 

 tures are also numerous enough, considering the 

 small number tagged, and occur in enough differ- 

 ent years to show that even if there is not indeed a 

 single population, there is at least a widespread 

 intermingling of the populations of adult female 

 Squabus aoanthias on the Atlantic Coast of North 

 America." 



Exploratory cruise data indicate that, rather 

 than being distributed relatively homogeneously 

 over large areas, dogfish congregate in dense, lo- 

 calized schools. Thus, high concentrations of dog- 

 fish at a given time and locality provide no 

 accurate indication of their overall abundance, as 

 they may be exceedingly scarce a few miles distant. 

 Large hauls of dogfish tend to be grouped within 

 a period of a few days, as the vessel fishes the same 

 general area during the interval. Similarly, con- 

 secutive tows at different depths may produce no 

 dogfish at one depth but numerous dogfish at only 

 slightly greater depths (table 4) . 



There is evidence that dogfish may vary in 

 availability, or abundance, from year to year as 

 well as from place to place. Data were analyzed 

 from survey cruises of the research vessels 

 Albatross III and Delaioare (table 5). The rela- 

 tive abundance of dogfish, expressed as catch per 

 30-minute tow, was high in 1948, 1949, and 1950. 

 Abundance declined markedly in 1955 and 1956 

 but was moderately high in 1958. In 1959, abun- 

 dance of spiny dogfish declined once more, but 

 during 1960-62 it reached a high level nearly on 

 a par with the peak in 1949. The changes in abun- 

 dance are also reflected in the commercial catch 

 of dogfish (see figs. 8 and 9). No explanation 

 exists for this apparent periodicity in abundance. 



POPULATION DYNAMICS 



The dynamics of the spiny dogfish population 

 would be difficult to study now to any fine degree 

 because much of the necessary information is lack- 

 ing or is imperfectly known. Perhaps the greatest 

 gap in our understanding of the species is a knowl- 

 edge of the nature of the population itself. 



Table 4. — Dogfish catches on Albatross III Cruise 126, by 

 depth, temperature, and sex along Middle Atlantic Coast, 

 January-February 1959 



Table 5. — Spiny dogfish catch on annual survey cruises, all 

 seasons, all grounds from Nova Scotia to Hudson Canyon, 

 1948-62 



The basic plus and minus factors of natality 

 and mortality lack adequate quantitative investi- 

 gation. There have been some studies, however, of 

 certain phases in the reproductive cycle, and these 

 are discussed below. 



REPRODUCTION 



Spiny dcgfish are ovoviviparous. The eggs in 

 the female are fertilized internally by means of the 



LIFE HISTORY OF SPINY DOGFISH 



539 



