IV. DISTRIBUTION AND FISHERIES 



Figure 1 1. Bluefin distribution (longline catches oft' southwestern Africa probably 

 consisted mainly of southern bluefin, Thumms maccoyii). 



90° 75" SO" 45" 30" 15* 



Figure 12. Bluefin regions of capture by seine, live bait, and trap 



15 



A. GENERAL DISTRIBUTION 



The bluefm tuna has been re- 

 ported at one season or another over 

 an extraordinarily large area of the 

 Atlantic and the adjacent seas, and in 

 a wide variety of water types (Fig- 

 ures 11 and 12) In recent years it 

 has ranged off the Atlantic coasts of 

 Fvurope and Africa, from the North 

 Cape, inside the Arctic Circle, to the 

 Cape of Good Hope, and off the 

 American coasts from Newfoundland 

 to 40°S latitude, and also in most of 

 the intervening oceanic areas. It also 

 has been present in most of the adja- 

 cent seas, the North, Mediterranean, 

 Black and Caribbean Seas, and the 

 Gulf of Mexico. 



The distribution of the bluefin 

 tuna has vaned greatly with the sea- 

 sons and with the size of fish (Fig- 

 ure 13) Seasonal variations are in- 

 fluenced by the requirements of 

 spawning and feeding, and by water 

 temperature. Tiews ( 1 963) concluded 

 that distribution was limited by the 

 \2°Q (surface temperature) isotherm. 

 Distributional changes with size of 

 fish are probably related to the change 

 from a planktonic diet to one of small 

 fishes during its first few months of 

 life, to its first spawning at 3 to 5 

 years of age, or, possibly, to the fijll 

 development of its swim bladder at 

 ages 8 to 10 years (Sella 1929b, Sara 

 1973) Year-to-year changes in dis- 

 tributional and migratory patterns are 

 frequent Variations in environmental 

 conditions and the availability of food 

 are regarded as the major causes of 

 these changes 



B. DEVELOPMENT OF THE 

 MAJOR FISHERIES 



Large scale fisheries for bluefin 

 tuna have existed in the Mediter- 

 ranean and its approaches for centu- 

 ries, but those in the remainder of 

 the Atlantic are of more recent ori- 

 gin Several methods and gears have 

 been used The oldest large scale 

 method is the tuna frap, which has 

 been used through most of the Chris- 

 tian era and perhaps much earlier 



