Maps of Bluefin Spawning Areas
in the Atlantic Ocean and Adjacent Seas
image of giant bluefin tuna
According to the world scientific community, as represented by ICCAT's scientific advisory committee, the North Atlantic bluefin tuna subspecies (Thunnus thynnus thynnus) is composed of two separate populations or "stocks." The western North Atlantic stock is found from the Gulf of Mexico to Newfoundland.  The eastern North Atlantic stock ranges from the Canary Islands to south of Iceland.  Each is considered a distinct breeding unit.

Their two spawning areas are widely separated.  As shown in the stylized figure to the right, the western stock spawns in the Gulf of Mexico (including the Straits of Florida), and the eastern stock spawns in the Mediterranean Sea (also see map, below).  Although they undertake long-range migrations (in one recorded case, 1670 n. mi. in 90 days), less than 10 percent of bluefin tagged on one side of the Atlantic have ever been found on the other side.  Some adults of the two stocks likely intermingle along the Gulf Stream in the mid-Atlantic at the northern end of their respective ranges during their fall feeding period.  But by spring, each stock appears to find its way back to its own ancestral spawning areas - "homing" just as salmon to their natal streams. 

That they are two different populations is underscored by the fact that members of the western stock grow to a much larger maximum size; moreover, they reach sexual maturity at an older age and at three times the weight as compared to members of the eastern stock.  The western stock reaches maturity at 12 years of age and a weight of about 620 pounds.  No tagged bluefin that entered the Gulf of Mexico to spawn has weighed less than 600 lbs. In contrast, the eastern stock matures at 4 to 5 years of age (and about 85 to 135 pounds).  (Source, 1998 SCRS Report to ICCAT)

This figure shows the areas of intense spawning activity (dark blue) during late spring, the areas of larval distribution (green), and primary migratory routes of the juveniles (green arrows) and adults (red arrows) within the Mediterranean Sea.  Adults migrate out of the Mediterranean and north to at least the south of the British Isles and formerly into the North Sea.
Map above taken from a great new book entitled "Close to the Surface"- a pictorial history of 50 years of big game fishing in the Azores.  Its author is Greet Wouters.

Worldwide Range of the Northern Bluefin Tuna (Thunnus thynnus)

Primary Ranges of the Western and Eastern North Atlantic Bluefin Tuna Populations


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Longliners fish most heavily during the periods when the moon is brightest. So, this real-time image of the moon phase shows when the kill of swordfish is greatest and least. It also shows when the kill of blue marlin, white marlin, sailfish, sharks, tunas, sea turtles, marine mammals and a host of other marine life is also greatest - even though they are not even targeted. For more, see link above.

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