Of the most commercially important tuna species – northern bluefin, southern bluefin, yellowfin, bigeye, albacore, and skipjack – Thunnus thynnus, the Atlantic bluefin tuna is king. Commercially its flesh commands the highest value per pound (or kilogram) and in terms of its growth weight, it is simply the largest. Prime bluefin demand the highest prices at Japan’s famous Tsukiji Central Fish Market and the first auction of 2001 proved that point. On January 5, 2001, a 444-pound bluefin sold for US$174,000 (20 million yen). That’s $395 per pound. A two-inch long, one inch wide slice of that tuna had an estimated retail price of $25 per sashimi-size bite. The previous record was $44,000 for a 250 pounder in 1996. (AP, 2001)

Tuna are ocean-dwelling members of the Scombridae or mackerel family. With their scientific name aptly derived from the Greek verb thuno or “rush,” their bodies are designed for long distance traveling at high speeds as well as sustained visits to the oceans’ most frigid climates. They are among the ocean’s greatest and swiftest travelers migrating logging thousands of miles along coastlines, around islands and across the high seas each year.

Perhaps it is a result of Nature’s prescience that the bluefin and tuna in general are as fertile a species as they are considering they are an acknowledged worldwide taste treat by their most effective predator, we humans. To keep up with our hunger for tuna, they are capable of producing millions of eggs per female. As would be expected, the mammoth bluefin are prodigiously fecund averaging 10-30 million eggs.

Tuna and swordfish are “non-guarder” parents, spewing eggs into the ocean’s currents where they are fair game for any marine life. By contrast, once the giant Atlantic bluefin arrives at its massive adult size, it enjoys a minimum of marine predator/prey relationships. Killer whales, pilot whales and mako sharks are the few marine predators fast enough to feed on giant bluefins. Skipjacks and bigeyes on the other hand, add other tunas and billfish to their list of personal predators.

The Atlantic bluefin is truly an example of Nature’s finest marine engineering. Their eggs are buoyed with a droplet of oil that keeps them just below the surface and help them, to an extent, escape a short but useful life as nourishment for other marine creatures including other bluefin. They quickly become larvae that embrace their genetic fast track growth process allowing them to bulk up to nine pounds in their first year.

Bluefin consume 3.93 times their body weight in food per year. For the first four to five years they double their body weight annually. The rapid growth period slows after the 12th year. By their 14th birthday, they can reach to 600 pounds or more. Males and females of equal length achieve comparable weights, but males tend to grow longer while females lead longer lives. (Dept. of Fisheries & Oceans, Canada)

With a life span known to reach age 40 and body bulk topping 1500 pounds, the king of tunas are put into growth classes depending on their weight. “Small school” tuna measure between 26 and 45 inches in length and weigh between 14 and 66 pounds. The “large school” category runs to 135 pounds. “Mediums” are distinguished between “small” (135-235 pounds) and “large” (235 to 310 pounds). At 310 pounds, a bluefin is deemed a “giant.”

Once they achieve “giant” status, Atlantic bluefin tunas add 100 to 200 pounds during their northern migrations (approximately 4.4 pounds or 2.2 kgs daily). Interestingly enough, though they are the original steel-hard bodies of the fish world, most of the added weight is fat. Unlike its effect on sluggish, couch potato human co-inhabitants of earth, fat for a giant bluefin is accumulated to enhance its never-ending athletic performance. (Butler, 1982)

Fat produces twice the energy by weight as protein or carbohydrates. It’s bluefin flight fuel that not only gives twice the fuel economy, but also helps increase buoyancy and dampens surface friction as the sleek bodied racehorse of the sea slices through the water, mouth constantly opened to allow volumes of water to be forced though the gills.

The feeding fury needed to acquire this great body mass occurs three times a day: at dawn, midday and dusk. Feeding is a sight to behold. Once suitable prey is located, the great fish peels from its schooling formation. The first dorsal fin retracts into grooves in its sides to reduce high-speed drag. Its body rigid, unlike the undulating bodies of most fish in flight, pectoral fins acting as hydrofoils, as its fierce acceleration rapidly increases via the powerful motion of its half-moon or sickle-shaped tail. Within reach, gill covers suddenly flare open and the unsuspecting morsels are literally sucked inside. Herring, mackerel, capelin, squid, cod, hake, and anchovies are all items on the bluefin diet.

Their violent table manners let in some frigid water temporarily lowering internal body temperature in their stomachs. Internal body heat is vitally important to the tuna. The bluefin’s exceptionally large heart, unique circulatory system that acts as a “heat exchanger” and high volume of blood are necessary for the maintenance of its internal temperature. The “heat exchange” effect comes from warmer arteries to cooler veins that run parallel with each other where the exchange is made as the blood flowing through the artery-vein system traveling in opposite directions keeps both at a fairly constant temperature.

Two distinct species of bluefin, the Northern bluefin (Thunnus thynnus) and the Southern bluefin (Thunnus maccoyii), are divided into three populations. Northern bluefin are found in the northern sections of the Atlantic and Pacific Oceans with traditional Atlantic breeding grounds thought to be in the Gulf of Mexico and the Mediterranean. They school on occasions with albacore, yellowfin, bigeye, skipjack and frigate tunas in the Atlantic and with bonito and yellowtail amberjack in the Pacific. Pacific spawning grounds are northeast of the Philippines. Western Atlantic northern bluefins range from Labrador and Newfoundland south to the Gulf of Mexico, the Caribbean, Venezuela and Brazil. Eastern Northern bluefin extend from the Canary Islands and the Mediterranean in the south to the Lofoten Islands off Norway. A small population resides off South Africa. Pacific northern bluefins range from the Gulf of Alaska to southern and Baja California in the East to the Sakhalin Island in the southern Sea of Okhotsk to the northern Philippines.

As its name indicates, the Southern bluefin prefers the southern sections of the Atlantic and Pacific Oceans and is also found in the Indian Ocean. Spawning is in the warm tropical waters off the west coast of Australia. Southern bluefins have half the life-span of their Northern relatives, eat half as much, and reach a maximum weight barely a fifth of their weightier brethren. But, they are no less controversial serving as a constant source of Japan bashing by Australians who, ironically, vie with Japanese fishermen for the lucrative Japanese market.

While environmental groups and special interests from “western cultures” enjoy characterizing the Japanese as “environmental predators” the Japanese did lead the worldwide effort to decrease both commercial tuna fleets and to close global markets to rogue fishing vessels flying “flags of convenience” indicating vessel registry in one country while the true ownership rests in another. FoC fishing craft seen throughout the commercial fishing world as honoring no international or national regulations governing the conservation of hard pressed fish stocks.

The skipjack (Katsuwonus pelamis) is the most abundant tuna worldwide and accounts for nearly 50 percent of the world tuna catch. Skipjack tuna can top out at 72-76 pounds but average 18-20 pounds. Their range is a band as wide as the length of Africa encircling the planet’s circumference. Skipjacks spawn throughout the year in equatorial waters, from spring to early fall in subtropical waters. Opportunistic feeders, skipjack school in association with birds, drifting objects, sharks, whales and other tunas near the ocean’s surface. No skipjack stock is considered over fished. (ICFA, 1998)

Thunnus albacares, the yellowfin tuna is the second most abundant tuna at 35 percent of the world catch. They are found globally throughout tropical and subtropical waters with the exception of the Mediterranean Sea. Known as Ahi, yellowfin tuna are greatly admired for their deep coloration (intense blue-black sides, bright yellow fins, and a golden stripe the length of their bodies. Yellowfin demand oxygen levels more dense than 2ml/l and therefore are found only in the upper 100 meters of the water column (FAO, 2000) Yellowfin can grow to lengths of six to nine feet and can weigh up to 450 pounds. In the eastern Pacific, larger yellowfin (those with fork lengths greater than 85 cm) school with porpoises. Spawning occurs throughout the year with peaks during the summer months in both hemispheres.

Bigeye tuna, Thunnus obesus, enjoys the distinction as the tuna whose flesh is nearly as prized by sushi and sashimi connoisseurs as that of bluefin. A world traveler as with most tuna, the bigeye has many similarities to bluefin that probably account for their equation with the great tuna’s gourmet factor, namely, their penchant for colder, deeper waters (17ºC to 22ºC) resulting in their physical adaptation of greater hemoglobin and subcutaneous fat. Bigeye are a large species weighing anywhere from 279 to 460 pounds. Bigeye accounts for less than10 percent of the world tuna catch, yet its highly desirable flesh brings the total value of the commercial harvest to an amount greater than any other tuna. Juveniles and small adults enjoy schooling near the surface either in exclusively bigeye packs or together with yellowfin and/or skipjack tunas. (FAO 2000)

Both its taxonomic and common names are used by French and Spanish speaking people to refer to yellowfin and Chileans associate the name with swordfish, still, albacore tuna (Thunnus alalunga) is sought as an important commercial species by 15 nations around the world. (FAO, 2000) Albacore is the only tuna legally entitled to the descriptor “white meat.” They are often distinguished by their very long pectoral fins. Bigeye, also sport long pectoral fins but differ in that their fin tips are rounded.

Albacore are the swiftest of tunas having been clocked at speeds in excess of 70 mph. They are somewhat smallish averaging 20 to 40 pounds with some as large as five feet in length and about 80 pounds in heft. Albacore follow the richness of the oceans’ oxygen more so than rich foraging waters, preferring “thermal discontinuities” such as the Transition Zone in the north Pacific and Kuroshio Front east of Japan over cooler upwelling waters with greater forage populations. Alabacore appear to adopt migrating patterns based on its various life stages. It is thought that at least two distinct stocks, with equally distinct spawning areas and seasons, exist in the Pacific and Atlantic Oceans each. Pacific stocks range from the surface to depths of at least 380 meters while in the Atlantic the depth limit appears to hit 600 meters. Similar to other tuna, smaller albacore appear to favor larger schools while larger albacore travel with fewer companions. Their range is worldwide including the Mediterranean.