342 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



low temperatures they would encounter in regions 

 where there is a strong thermal gradient (the 

 Gulf of Maine is an example, p. 344), the increasing 

 scarcity of prey, and, perhaps, darkness. 



The breeding habits of the tuna remained a 

 mystery until recently. And while it is now 

 known that those that visit the Mediterranean 

 spawn in June and July, both the spawning 

 grounds of our American tuna and their spawn- 

 ing season are yet to be learned. 



The eggs (Mediterranean) are buoyant, small 

 for so large a fish (1.05-1.12 mm. in diameter) 

 with one oil globule of about 0.27 mm. 



The larval stages have also been recorded in the 

 Mediterranean in abundance; and the characters 

 determined by which they may be distinguished 

 from allied species. 9 Tuna fry of 3% inches (81 

 mm.) and about 6 inches (152 mm.) have also 

 been pictured and are described from the Gulf 

 of Mexico by Fowler. 10 



Rate of growth. — The rate of growth of so large 

 a fish is naturally a matter of much interest. 

 Young fry grow so rapidly that fish hatched in 

 June in the Mediterranean reach a weight of a 

 little less than % pound to a little more than 

 1 pound (300-500 grams) by September. Accord- 

 ing to studies by Sella, based on the number of 

 concentric rings in the vertebrae 11 for 1,500 in- 

 dividuals, Mediterranean tuna average about 10 

 pounds at 1 year of age, about 21 pounds at 2 

 years, about 35 to 36 pounds at 3 years, about 

 56 pounds at 4 years, about 88 pounds at 5 

 years, about 128 pounds at 6 years, about 170 

 pounds at 7 years, about 214 pounds at 8 years, 

 about 265 pounds at 9 years, about 320 pounds 

 at 10 years, about 375 pounds at 11 years, about 

 440 pounds at 12 years, about 517 pounds at 

 13 years, and 616 to 660 pounds at 14 years 

 of age. 



Average lengths of 20 to 24 inches in their 

 second summer of growth, 27 to 34 inches in the 

 third, 35 to 40 inches in the fourth, and 42 to 46 

 inches in the fifth, reported by Westman and 

 Gilbert 12 suggest about the same growth rate for 



•See Sella (Atti Reale accad. Lincei, Roma, Ser. 5, vol. 33, Fasc. 7-8, 

 semestr. 1, 1924, p. 300) and Sanzo (R. Comit. Talass. Ital. Mem., No. 189, 

 1932) for description of the larvae; Heldt (Bulls. 5 and 18, Station Oceano- 

 graphique Salambo, 1926 and 1930) for summaries of all previous observations 

 on the breeding habits and larval stages. 



» Monogr. 6, Acad. Nat. Sci. Philadelphia, 1944, pp. 261, 373. 



» Memoria No. 166, R. Comitato Thalassograflco Italiano, 1929, p. 10. 



13 Copeia, 1941, pp. 70-72, based on length frequencies for those up to 3 

 years of age and on scale studies for the older ones. 



the American tuna. Thus the giants of 800 

 pounds and heavier have reached a very respect- 

 able age. According to Sella 13 Mediterranean 

 tuna weighing only 35 pounds may already be 

 sexually mature. But nothing definite is known 

 about the American fish in this regard. 



General range. — Warmer parts of the Atlantic 

 (including the Mediterranean) , Pacific and Indian 

 Oceans; u north regularly to the western, southern 

 and southeast coasts of Newfoundland, 15 on the 

 western side of the Atlantic; to Iceland and 

 northern Norway (Lofoten Islands) on the 

 European side. 



Occurrence in the Gulf of Maine. — The tuna is a 

 yearly visitor to our Gulf. Every fisherman 

 knows the tuna or horse mackerel, as it used to be 

 called, and this great fish visits all parts of the 

 Gulf of Maine, but we do not understand its 

 comings and goings much better now than when 

 Storer called attention to its abundance about 

 Provincetown nearly a century ago. Scarcity is 

 not to blame for this (it is common enough) but 

 the fact that little attention was paid to it until 

 recently for want of market value. And while a 

 demand for tuna has developed of late, as is 

 reflected in the catches (p. 346), and while many 

 anglers now fish for them (p. 347), most of the 

 resulting information is confined to the few inshore 

 localities where they either seem to be the most 

 plentiful, or where they are caught most easily 

 from small craft, or incidentally in the fish traps. 



It is now known that tuna are to be found all 

 around the shores of the Gulf from Cape Cod to 

 eastern Maine; in the Bay of Fundy; also along 

 the west coast of Nova Scotia. And fishermen 

 often report them on Nantucket Shoals, Georges 

 Bank, and Browns. In ordinary years the first of 

 them are likely to be seen as early in the season 

 between Cape Ann and the Maine State line as 

 they are off Cape Cod. In 1950, for example, the 

 earliest report of them was off Hampton, N. H., 

 May 26; the next off Plum Island, Mass., on June 

 9; and it was not until about June 16 that word 

 came of one hooked in Cape Cod Bay, and of the 

 first fish (one of 462 pounds) harpooned off Plum 



» Memoria No. 156, R. Comitato Thalassographico Italiano, 1929, p. 6. 



» Sella's recent studies (Internat. Rev. Ges. Hydrobiol., Hydrogr., vol. 25, 

 1931, pp. 48-50) showed no characteristic differences between the bluefln 

 tuna of the two sides of the Atlantic, and those of different oceans appear, at 

 most, to represent races of a single wide-ranging species. 



" Vcsey- Fitzgerald and Lamonte (Game Fishes of the World, 1949, p. 183) 

 report tuna from Hamilton Inlet. 



