FISHES OF THE GULF OF MAINE 



33 



to 16 feet are usual; 78 the maximum length (tail 

 included) is about 20 feet. Threshers are so large- 

 ly tail that they are much lighter than many other 

 sharks, length for length. The few actually 

 weighed have ranged from about 300 to 320 

 pounds at about 10 feet, and 375 to 400 pounds at 

 about 13 feet, to about 500 pounds at about 14% 

 feet. Perhaps 1,000 pounds is about the maxi- 

 mum to be expected for a very large one. 



Habits. — The reports of threshers are mostly 

 based on ones seen at the surface or caught either 

 in nets set shoal, or in traps set close inshore. But 

 a thresher has been hooked as deep as 35 fathoms 

 in British waters. 77 



The thresher feeds chiefly if not exclusively on 

 small schooling fishes; in American waters mostly 

 on mackerel, menhaden, herring, and bluefish 

 (Pomalomus) ; also on bonito and on squid. A 

 pair of threshers often work in concert "herding" 

 a school of fish, and it is to frighten its prey together 

 that the enormously long, flail-like tail is em- 

 ployed. Allen 78 gives an interesting eyewitness 

 account of a thresher pursuing and striking a 

 single small fish with its tail. 



The tale that the thresher leagues with the 

 swordfish to attack whales is time honored, but 

 has long since been relegated to the category of 

 myth. And so weak toothed is this shark that the 

 second part of the story (it makes a meal of its 

 huge victim) is close to an impossibility. The 

 thresher, we may add, does not harm human 

 beings. 



In American waters it is probable that threshers 

 are born throughout its range, very small free 

 living specimens having been caught off New Eng- 

 land on the one hand, and off Florida on the other. 

 The embryos do not develop a placental attach- 

 ment with the mother, and either 2 or 4 have been 

 reported in gravid females. 



General range. — This is an oceanic shark of 

 temperate and subtropical seas. In the Atlantic 

 it is known from southern Ireland and the North 

 Sea to Madeira and the Mediterranean in the east, 

 and also from the Cape of Good Hope ; from Nova 

 Scotia and the Gulf of St. Lawrence to Cuba and 

 the northern part of the Gulf of Mexico in the 



Tfl Several of that size have been taken in the traps at Woods Hole. 



11 There is another group of species of the genus, with very large eyes, that 

 live at greiter depths; for discussion of these, see Bigelow and Schroeder 

 (Fish. Western North Atlantic, Pt. 1, 1948, pp. 162, 163). 



" Science. N. Ser., vol. 58, 19?3, pp. 31-32. 



west, and again from southern Brazil and northern 

 Argentina. Seemingly it does not occur in the 

 equatorial belt of the Atlantic. But it does in the 

 Pacific, where it is known from Oregon to Panama 

 and Chile. Threshers of this same type are also 

 found in the central and western Pacific and in 

 the Indian Ocean. Whether the thresher of the 

 eastern side of the Pacific is identical with that 

 of the Indian Ocean remains to be determined. 



Occurrence in the Gulf of Maine. — The thresher 

 has often been seen off the southern coast of New 

 England and in some numbers. Three about 16 

 feet long have been taken near Woods Hole, for 

 example, in one trap in a single morning, and it 

 has been classed as the commonest of the large 

 sharks off Block Island. Scattered specimens 

 also visit the Gulf of Maine in some years, though 

 perhaps none in others. Thus two have been 

 reported in print from Nantucket; we saw several 

 large ones in Pollock Rip, off the southern angle 

 of Cape Cod on August 4, 1913; it has been re- 

 ported repeatedly on the coast of Massachusetts, 

 as at Barnstable on Cape Cod Bay, where one 

 about 10 feet long was taken in a trap on October 

 21, 1949, and from various localities in Massa- 

 chusetts Bay (e. g. Boston Harbor and Nahant). 



Records for it along the coast of Maine include 

 the vicinity of Monhegan Island, east of Matinicus 

 Island, the offing of Penobscot Bay where one 

 weighing about 500 pounds (estimated) was 

 caught in 1911 and another seen in 1911, in the 

 vicinity of Eastport. It has also been taken in 

 the cold waters of Passamaquoddy Bay; one for 

 instance in a weir at Deer Island, August 28, 

 1936; 79 also in the Basin of Minas on the Nova 

 Scotian shore of the Bay of Fundy. Occasionally 

 a thresher is netted or seen off the outer coast of 

 Nova Scotia. The most northerly record for it 

 from our side of the Atlantic is for the Bay of 

 Chaleur in the southern side of the Gulf of St. 

 Lawrence. It is to be expected in Gulf of Maine 

 waters only during the warm half of the year, 

 perhaps May to October (April to late autumn for 

 Woods Hole); in the cold season it altogether 

 deserts our northern coasts for warmer seas. 



Importance. — The thresher is not common 

 enough in the Gulf of Maine to be of any impor- 

 tance to fishermen one way or another, or to play 



'» Reported by McKenzie, Proc. Nova Scotia Inst. Sci., vol. 20, 1939, p. 14. 



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