20 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



twice from Casco Bay, and once from St. Andrews, 

 New Brunswick, near the mouth of the Bay of 

 Fundy, its most northerly known outpost, where 

 one was taken in a weir in 1913. 



In New England waters the sand shark occurs 

 only as a summer visitor. The winter home of 

 those that summer along the northeastern United 

 States is not known, nor has any increase been 

 noted in Florida waters (where they are taken at 

 all times of year) coincident with their winter dis- 

 appearance from the northern part of their range. 

 Like various bony fishes they may move offshore, 

 and perhaps southward, to escape winter chilling. 



Importance. — There were commercial fisheries 

 for the sand shark around Nantucket during the 

 first quarter of the present century, but these were 

 short lived, reputedly because of exhaustion of the 



local stock. And the sand shark is of no commer- 

 cial importance on the New England coast at 

 present. Westward from Cape Cod it is of some 

 interest to anglers, who catch considerable num- 

 bers, both as objects of special pursuit, for it takes 

 almost any natural bait readily, or incidentally 

 while surf casting for better fish. But it is not 

 plentiful enough in the Gulf of Maine to be worth 

 fishing for. 



There is no record of attacks by sand sharks on 

 human beings in North American waters, though 

 bathers often come close to them. Our own experi- 

 ence bears this out; in fact, it is looked upon as a 

 harmless nuisance on the New England coast 

 wherever it is plentiful enough to be familiar. 

 But its relative (or relatives) of East Indian waters 

 have a more sinister reputation. 



MACKEREL SHARKS. FAMILY ISURIDAE 



Sharks of this family are easily recognizable 

 by the very firm half-moon-shaped (technically 

 lunate) caudal fin, with lower lobe but little shorter 

 than the upper, in combination with large awl-like 

 or blade-shaped teeth, and with gill openings 

 larger than any other Gulf of Maine shark except 

 the basking shark. Their tail fins, in fact, recall 

 the tails of such bony fishes as the mackerel tribe 

 or the swordfish, in outline, likewise in firm tex- 

 ture, hence their common name. The basking 

 shark also has a caudal fin and peduncle of this 

 same sort, but its teeth are minute and very 

 numerous, and its gill openings are so long that 

 those of the two sides nearly meet on the lower 

 surface of the throat. 



Other diagnostic features are that they have an 

 anal fin ; that their caudal peduncle is expanded as 

 a prominent longitudinal keel on either side; that 

 their dorsal fins are not preceded by spines; and 

 that the inner margins of their gill arches do not 

 have horny gill rakers. 



Mackerel shark Lamna nasus (Bonnaterre) 1788 



Porbeagle; Blue dog (in Gulf of Maine) 



Bigelow and Schroeder, 1948, p. 112. 



Garman, 1911, pi. 6, figs. 4-6 (as Isurus ■punctatus). 



This is a stout, heavy-shouldered shark, tapering 

 in front to a pointed conical snout and behind to 

 a very slim tail root. Its dorsal and pectoral fins 

 are large; the former, originating a little rearward 



of the armpits of the pectorals, is triangular and 

 about as high as it is long; the pectoral fins are 

 only half as broad as long. The second dorsal and 

 anal fins are very small indeed, and the pelvics 

 but little larger. The second dorsal fin stands 

 over the anal. There is a conspicuous transverse 

 furrow or pit on the upper surface of the root of the 

 tail, also one on the lower surface close in front of 

 the origin of the caudal fin. The lower lobe of the 

 caudal fin is two-thirds to three-fourths as long 

 as the upper lobe, and there is a small secondary 

 keel on the base of the caudal fin on either side, 

 below and behind the rear end of the primary 

 keel formed by the sidewise expansion of the 

 caudal peduncle. 



The teeth of the porbeagle are alike in the two 

 jaws, slender, pointed, smooth-edged, and with a 

 sharp denticle near the base on each side (young 

 fish may not have these) which the mako lacks 

 (P- 23). 



The only Gulf of Maine sharks with which the 

 porbeagle might be confused are the maneater 

 (p. 25), or the mako (p. 23). And it is easily 

 told from the former by its slender, smooth-edged 

 teeth, as well as by the position of its second 

 dorsal fin directly over the anal; from the mako 

 by the shape of its teeth (cf. fig. 5 with fig. 6), 

 each usually with a small basal denticle on either 

 side, which the mako lacks; also by its stouter 

 body and by the presence of the secondary 

 longitudinal keel on the anterior part of its 

 caudal fin. 



