26 BULLETIN OF THE BUREAU OF FISHERIES 



from various localities within Massachusetts Bay, and even from as far north as St. 

 Andrews in the Bay of Fundy, where one was caught in July, 1913, it occurs only 

 as a southern straggler in the Gulf of Maine, and that so rarely that neither of the 

 authors has ever seen it north of Cape Cod. So far as known its occasional incur- 

 sions into the Gulf are sporadic — at least they have not been correlated with unusu- 

 ally warm summers or with the presence of other southern fishes. 



On the outer part of the continental shelf Nantucket Shoals must be regarded 

 as the easterly limit of its regular occurrence, for it is not recorded nor reported 

 by fishermen from either Georges or Browns Banks, nor was it detected there by 

 the representatives of the Bureau of Fisheries during the trawhng investigations of 

 the years 1912 and 1913 (p. 9). 



The smooth dog is most familiar as a shore fish and a bottom swimmer, com- 

 monly entering shoal harbors and bays, nor is it known to descend to any consider- 

 able depth. 



Food. — The food of the smooth dog consists chiefly of the larger Crustacea, and 

 it is perhaps the most relentless enemy of the lobster, which had been eaten by no 

 less than 16 per cent of the fish examined by Field (1907). Large crabs are like- 

 wise an important article in its diet, as are the smaller fishes. Field estimated that 

 in Buzzards Bay 100,000 smooth dogfish would annually devour over 600,000 

 lobsters, 90,000 to 100,000 fish of one kind or another (menhaden and tautog are the 

 species most often found in dogfish stomachs), and a couple of million crabs. While 

 these figures are to be taken only as broadly suggestive, they are based on a suf- 

 ficient number of observations of the stomach contents to serve as a general indi- 

 cation of the destructiveness of dogfish. They also feed on squid, especially in 

 spring, and while they do not regularly take mollusks, razor clams have been found 

 in the stomachs of several at Woods Hole. When kept in oaptivity they are con- 

 stantly on the move, searching the bottom for food, which they find chiefly by the 

 sense of smell though their sight is also keen. 18 Any crab that may be offered is soon 

 found, seized, shaken to and fro, and eaten, and with packs of these sea hounds 

 hunting over every square foot of our southern bays and sounds it is a wonder any 

 of the larger Crustacea escape when dogfish are abundant. Field also made the 

 interesting observation that the smooth dogs never molested healthy and active 

 menhaden but soon devoured any sick or injured fish that might be in the same 

 tank with them. 



Breeding habits. — Not being a characteristic Gulf of Maine fish we need merely 

 note of its breeding habits that it is viviparous, 18 giving birth to from 4 to 12 young 

 at a litter, the pups being about a foot long and practically of adult form when born ; 

 and that in the Woods Hole region females containing eggs and embryos at various 

 stages in development are to be found throughout the summer. How many litters 

 of young are produced by any one female during a year is still to be learned. 



'" The senses of this shark have been studied by Parker (Bulletin, U. S. Bureau of Fisheries, Vol. XXIX, 1909 (1911), pp. 

 43-57) and by Sheldon (Journal of Comparative Neurology and Psychology, vol. 19, 1909, No. 3, p. 273). 



>> In the report of the Massachusetts Commissioners of Fish and Game for 1905 it is erroneously said to be oviparous, 

 apparently being confused with the European dogfish, ScyUium canicula. 



