FISHES OF THE GULF OF MAINE 



341 



Tuna often break the surface when striking a 

 bait, or they may even leap clear then. But for 

 some reason they do not jump ordinarily after they 

 are hooked, but first make one or more swift 

 shallow runs and then tend to bore deep unless 

 in very shallow water. 



Tuna prey on smaller fishes, especially those of 

 the schooling kinds, the particular species depend- 

 ing on the local supply. In the Gulf of Maine 

 they destroy great numbers of herring, large and 

 small; also mackerel of which they are often full. 

 They have been reported as pursuing silver hake; 

 26 tuna contained these, out of 30, that were 

 examined by Crane at Portland, Maine, in July 

 1936. She also reports a rosefish (Sebastes) in one. 

 No doubt they take whatever small fishes are 

 available locally, and a tuna has been known to 

 swallow a whole dogfish as large as 8 pounds. 

 Southward from Cape Cod they prey on men- 

 haden, as predaceous fishes do in general. They 

 also eat squid: Crane found squid, in two, at 

 Portland, and quantities of euphausiid shrimps 

 (Meganyctiphanes) in two others. It is not unu- 

 sual for tuna to strand in pursuit of prey. But 

 this is a timid fish and easily frightened though 

 so voracious. 



Tuna have no serious enemies in the Gulf of 

 Maine, but killer whales take toll of them in 

 Newfoundland waters where, writes Wulff 3 "one 

 or more times annually, usually in September, 

 orcas will ravage the tuna schools in the bays they 

 frequent most." 



The tuna is a fish of at least moderately warm 

 seas. The smaller sizes seem rather closely 

 restricted to regions where the surface layer is 

 warmer than 60°-62°, and while large ones are 

 regular visitors in summer to the eastern side of our 

 Gulf where the water warms only to about 50°-54°, 

 this, seemingly, is about the lower limit to the 

 thermal range they favor. 4 Few tuna, for ex- 

 ample, whether large or small, are seen in the 

 Passamaquoddy region in most summers (p. 343) 

 though the multitudes of small herring there would 

 seem to offer ideal feeding conditions, but where 

 the temperature rises only to about 52°-54° even 

 by August, when it is highest. And seasonal 

 chilling is generally accepted as. the factor that 



» Internat. Game Fish Assoc. Yearbook, 1945, p. 65. 



* The tuna that visit the west coast of Newfoundland find summer temper- 

 tures as high as 59°-60° along the south coast of Newfoundland, and 55 -57 < ' 

 in Trinity and Conception Bays on the southeastern part of the Newfound- 

 land coast. 



drives them from our northern coasts in the 

 autumn. 



Tuna tolerate a wide range of salinity, and they 

 run well up into bays, and even into harbors in 

 pursuit of herring; the bays on the outer Nova 

 Scotian coast for example; Bras D'or "lake," 

 Cape Breton; Bonne Bay on the west coast of 

 Newfoundland; and Trinity and Conception Bays 

 on the southeastern coast of Newfoundland. But 

 we have never heard of one entering brackish 

 water. 



Tuna are as definitely migratory as the mackerel 

 is, those that visit our coasts working northward 

 in spring, to drop out of sight again late in the 

 autumn. 6 They are said to be around Jamaica 

 throughout the year, but most plentiful there in 

 March and April 6 Ordinarily they appear ear- 

 liest on the Bahaman side of the Straits of Florida 

 in the first or second week in May; next off New 

 Jersey, off Long Island, off southern New Eng- 

 land, and in Cape Cod Bay in June. But they 

 have been reported well within the Gulf of Maine 

 by the last week of May (p. 342), or nearly as early 

 as in Bahaman waters. This, with the added 

 fact that they are not known to approach the 

 American coast anywhere between the Bahama 

 Channel and North Carolina or Virginia 7 sug- 

 gests that we may have two separate populations, 

 a southern and a northern. 



They usually arrive in Bonne Bay, on the Gulf 

 of St. Lawrence coast of Newfoundland in late 

 June or in early July, and a week or two later 

 in Trinity and Conception Bays, on the south- 

 eastern part of the Newfoundland coast. 8 



Finally, we should point out that it is not 

 known yet whether the tuna populations of the 

 two sides of the Atlantic are entirely separate, one 

 from the other, or whether more or less inter- 

 change takes place between them. 



The vertical range of the tuna is from the 

 surface down to an indeterminate depth; the 

 only barriers likely to limit their descent are the 



• See Heldt (Bull. No. 5, Station Oceanographique de Salambo, 1926), and 

 Sella (Int. Rev. Hydrobiol., Hydrogr., vol. 24, 1930, p. 446) for accounts of the 

 migration and food of tuna in the Mediterranean and eastern Atlantic. 



• Information contributed by Capts. Eddie Wall and Walter Whiteman, 

 for which we are indebted to Frank Mather of the Woods Hole Oceano- 

 graphic Institution. 



7 Frank Mather of the Woods Hole Oceanographic Institution informs us 

 that a 600-pound tuna has been taken in a trap 200 miles south of Chincc- 

 teague, Md., and that small ones are taken off Chincoteague. "Tuna" are 

 reported from time to time off North Carolina, also. But it is not yet certain 

 whether these actually are "bluefins." 



« Wulff, Internat. Game Fish Assoc. Yearbook, 1943, p. 65. 



