Description & Behavior
Atlantic bluefin tuna, Thunnus thynnus (Linnaeus, 1758), aka blue fin tuna, blue-fin tunny, bluefin tuna, horse mackerels, northern bluefin tuna, and squid hounds…, are regarded as one of the most highly evolved fish species and one of the most prized fish in danger of overfishing. Tuna, originating from the Greek word meaning “to rush,” usually swim at speeds of 1.5-4 knots, can maintain 8 knots for some time, and can break 20 knots for short periods. These are one of the most magnificent fishes in the sea. One fish can sell for hundreds of thousands of dollars. A 342 kg tuna sold at Tokyo’s Tsukiji fish market for 32.49 million yen ($396,700 US dollars), the highest price for a single fish since record-keeping began in 1999, that’s 95,000 yen ($1,157) per kg!
Atlantic bluefin tuna are the largest member of the Scombridae Family (albacores, bonitos, mackerels, tunas). They are one of the largest bony fishes and can reach lengths of up to 3 m, although they are more commonly found from 0.5-2 m in length. Adult weights range from 136-680 kg, although the upper weight range is rare, especially now. They can dive as deep as 914 m, and are known to swim long distances as they are a highly migratory species.
Atlantic bluefins are dark blue to black on their dorsal (upper) surface and silvery ventrally (underneath). Bluefins are known for their finlets that run down their dorsal (upper) and ventral (lower) sides toward their anal fin. There are 12-14 spines in their first dorsal fin and 13-15 rays in their second dorsal fin. Their anal fin has 11-15 rays. The average natural lifespan of bluefin tunas is 15-30 years.
Atlantic bluefins are homeothermic (“warm-blooded”) and are therefore able to thermoregulate keeping their body temperatures higher than the surrounding water, which is why they are so well adapted to colder waters.
World Range & Habitat
Atlantic bluefins live in subtropical and temperate waters of the North Atlantic Ocean, the Mediterranean, and Black Seas. Bluefins are highly migratory and limited numbers of individuals may cross the Atlantic in as little as 60 days and are widely distributed throughout the Atlantic and can be found from Newfoundland all the way to the coast of Brazil. They range in the eastern Atlantic as far north as Norway and down to northern West Africa. Bluefins tagged in the Bahamas have been captured in Norway as well as off the coast of Brazil. Bluefins in the South Atlantic belong to a distinct southern population, with known spawning areas south of Java, Indonesia. The bluefin is a pelagic, schooling fish. They tend to group together according to size.
Feeding Behavior (Ecology)
Although Atlantic bluefin are widely distributed and migrate thousands of kilometers, there are two confirmed spawning locations — the Gulf of Mexico in the western Atlantic and the Mediterranean Sea in the eastern Atlantic. Although many ecological and environmental variables undoubtedly affect both the location and productivity of spawning in these two areas, relatively little is known concerning why bluefin spawn where they do.
Spawning in the Gulf of Mexico occurs between mid-April and mid-June when females, which mature around age 8, release approximately 30 million eggs each. The highest density of bluefin larvae, the primary indicator of spawning, occurs in the northern Gulf of Mexico with lesser larval concentrations appearing off the Texas coast and in the Straits of Florida.
In the eastern Atlantic, spawning occurs exclusively in the Mediterranean and Adriatic Seas from June through August, with the highest larvae concentrations appearing around southern Italy. Although some fishery biologists believe that eastern Atlantic bluefin reach sexual maturity several years earlier than western Atlantic bluefin (possibly as young as ages 4-5), this understanding has been criticized.
Conservation Status & Comments
“A taxon is Endangered when the best available evidence indicates that it meets any of the criteria (A to E), and it is therefore considered to be facing a very high risk of extinction in the wild.”
International sport fishing for “giant” bluefin originated about 100 years ago, becoming popular domestically in the early 1900s. The Sharp Cup in Nova Scotia was a distinguished international bluefin tournament held from the early 1930s through the 1960s, with a peak landing of 1,760 fish in 1949. Many other tournaments existed throughout the Northeast United States until the mid-1960s, when giant bluefin abundance near tournament sites appeared to decline. Although studies have been inconclusive regarding these changes, suspected causes include changes in water temperature, oceanic currents, availability of food, and overfishing.
Prior to 1970, sport fishing was exclusively recreational, as giant bluefin tuna had a commercial value of only $.05 per pound. Giant trophy tuna that were not kept for personal display or consumption were sold to cat and dog food producers. With the development of the Japanese specialty market in the early 1970s, giant bluefin tuna suddenly represented big money to traditional sport fishermen. Perspectives on the fishery shifted, and the recreational character of the fishery was altered by economic opportunity. A giant 225 kg trophy fish was, by the late 1970s, a highly valued Japanese delicacy. Participation exploded and the giant bluefin fishery capitalized quickly.
Now many “recreational anglers” also obtain commercial permits, so that virtually all giant bluefin tuna currently caught are marketed commercially, except for a small scale catch-and-release sport fishery in the Bahamas. A substantial charter- or party-boat fishery for small bluefin tuna also exists from North Carolina to Massachusetts. Estimated at more than 15,000 recreational anglers annually, this is the only U.S. fishery allowed to catch bluefin smaller than the minimum commercial size (1.78 m from the tip of a fish’s snout to the fork of its tail).
References & Further Research
Atlantic Bluefin Tuna: International Management of a Shared Resource, Eugene H. Buck, CRS Report: 95-367
TUNA RESEARCH AND CONSERVATION CENTER – Hopkins Marine Station – Monterrey Bay Aquarium
Song for the Blue Ocean, Dr. Carl Safina
Migration study finds that sweeping management changes are needed to protect Atlantic bluefin tuna
Bluefin tuna protection system ‘full of holes’
Top-of-the-line tuna sells for $400,000 in Japan
Lutcavage, M.E, Brill, R.W., Goldstein, J.L., Skomal, G.B., Chase, B.C., and J. Tutein. 2000. Movements and behavior of adult North Atlantic bluefin tuna (Thunnus thynnus) in the northwest Atlantic determined using ultrasonic telemetry. Marine Biology 137:347-358.
Brill, R., Lutcavage, M., Metzger, G., Stallings, J., Bushnell, P, Arendt, M., Lucy, J., Watson, C., and D. Foley. 2002. Horizontal and vertical movements of juvenile North Atlantic Bluefin Tuna (Thunnus thynnus) in the western North Atlantic determined using ultrasonic telemetry, with reference to population assessment by aerial surveys. Fishery Bulletin 100:155-167.
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