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Plight of the Bluefin Tuna

Image: Painting of bluefin tuna devouring mackerel

Bluefin tuna devouring mackerel (View larger version)

By Michael J. A. Butler

Published

The following text is republished from the August 1982 issue of National Geographic Magazine

With the roar of the diesel and the whine of a 15-gear transmission, the tractor trailer pulled away from St. Margarets Bay in Nova Scotia. Our cargo: seven six-foot-long ice-packed containers. Each held a giant bluefin tuna. I had joined them for an 8,000-mile journey from eastern Canada to Japan.

Thirty-one hours later the truck squealed to a stop at Japan Air Lines’ freight terminal in New York City. We took off into predawn skies: Niagara Falls . . . the Canadian Rockies . . . Anchorage. Over the Bering Sea, with the Aleutian Islands to the south and the Soviet Union’s Kamchatka Peninsula to the west, we crossed the date line, then set down at Tokyo’s new Narita Airport.

Through rush-hour traffic in Tokyo I accompanied the seven bluefin to the Tsukiji Market, one of the world’s largest. There a technician took their temperature, cut thin slices from tail and abdomen to judge fat content, flesh color, freshness. Muscle temperature was ideal—40 to 45°F; higher would indicate loss in flesh quality; lower, frozen outer layers—a bane to gourmets. These bluefin graded high, harvested in late October precisely when the flesh appeals most to the Japanese palate.

Three containers were repacked with ice and trucked out. Regional tastes dictate destinations: Kyoto prefers reddish meat; Yokohama, pink; Osaka, oily. Four bluefin were reserved for Tokyo, which favors meat of the brightest red.

Next morning, at 5:50, a bell summoned tuna brokers in numbered hats to a tiered stand. The auctioneer, hand raised for silence, exploded with a startling “kiai!” The bluefin averaged $6.80 a pound.

I followed one on its cart to a vendor, who carved it with a razor-sharp five-foot knife. Prime cuts, the muscle around the body cavity, now retailed for $17 a pound. I tracked ten pounds of it to a raw fish bar. Here connoisseurs paid $24 a pound.

How can one explain its appeal? Artist Stanley Meltzoff put it this way: “Fresh bluefin at the peak of their autumnal fattening, cut paper-thin and eaten raw, provide an experience for which the Japanese have a vocabulary of distinctions as exquisite as that of the French for Bordeaux wines.”

The traditional Japanese raw fish dish of sashimi, or sushi if it is combined with rice, is not just tuna. For many, late season jumbo maguro—the North American giant bluefin—is the ultimate epicurean delight. Regardless of one’s income, the Japanese New Year, a birthday, or a wedding is not complete without it.

I ordered a slice. It melted in my mouth. It was 10 a.m. Thursday. Five days earlier that mouthful had been part of a bluefin swimming in Nova Scotia waters, half a world away.

Delicious. But my curiosity about bluefin is not culinary, nor do I identify with sport fishermen, for whom landing this largest, speediest, most powerful of tunas is the peak of thrills. As a marine scientist enthralled for many years by these magnificent beasts, I am interested in their future well-being.

Novelist Zane Grey boated a 758-pound bluefin in Nova Scotia waters in 1924 that for a decade remained a world record. Nova Scotia in October 1979 also set the present record with a 1,496-pound bluefin about 32 years old. Because the bluefin keeps on growing, I can imagine 35-year-olds swimming out there that weigh a ton.

Among the largest of fish, the bluefin is also one of the fastest, capable of bursts up to 55 miles an hour. Three-quarters muscle, hydrodynamically superb, with a powerful heart, ramjet ventilation, heat exchangers, and other special adaptations, the bluefin is built for speed. No predators except the mako shark and the killer whale can catch it. Because of this remarkable speed, the Swedish naturalist Linnaeus gave the bluefin its scientific name, Thunnus thynnus, from thuno, the Greek verb meaning “rush.”

Scientists classify the bluefin and 12 other species of tuna, or tunny, as the tribe Thunnini within the family Scombridae. Tuna, the common name in North America, most probably originated with 19th-century immigrant fishermen in California. Of the world’s 20,000 fish species, the family Scombridae is among the most advanced, renowned for speed and endurance. The bluefin marks the zenith of this evolution.

Studying these superfish underwater, swimming among them in scuba gear in St. Margarets Bay, I have come to feel a personal affinity with them. I admire the power in their streamlined bodies and the grace with which they soar and glide within waves, much as birds do in rising air. I recognize individuals by their behavior—even know some by nickname, such as the glutton Piggy. They are quite used to divers and shiver when touched. Still there is danger. To have a thousand pounds of bluefin suddenly come at you in the murky water gives you a gut feeling for its size and speed. A close turn by a feeding bluefin can hurl you backward in an avalanche of water. I worry about a second behemoth barreling through that curtain of bubbles and not seeing me.

Delicious and Valuable Resource

My scientific fascination with the bluefin has deep roots. Aristotle in his History of Animals recorded observations on age and growth of tuna by ancient Greek fishermen and speculated on their migrations. The Roman naturalist Pliny the Elder wrote that Alexander the Great’s fleet once met a school of bluefin so vast that the galleys had to advance in battle line to force their way through. Indeed, the tuna had caught man’s eye thousands of years earlier. A Spanish cave drawing above the Bay of Biscay depicts the fish—one of the few we know to be so honored during the Ice Age.

Only 3 percent of the world fish catch in weight, tuna yet constitute one of the sea’s most valuable living resources. Japan and the United States lead in catch of the principal market species, up almost sevenfold since 1948. Fishermen get $1,000 to $3,000 a ton for frozen tuna—the skipjack, yellowfin, albacore, and bigeye you find in cans in the supermarket. In Japan, fresh bluefin can command 10 to 15 times that price.

The bluefin frequents both the Atlantic and the Pacific. The Atlantic population spawns in the Gulf of Mexico and the Mediterranean and feeds as far north as the Arctic Circle, making it one of the long-distance champions among migratory fish. By the age of 15 a bluefin will have swum an estimated million miles. In fact it moves every minute of its life. Prevent it from swimming and it will soon die from lack of oxygen.

Depending on age, each female carries from one million to thirty million eggs. Blue fin spawn fractionally, not releasing all the eggs in one session. The translucent eggs, a millimeter in diameter, float a few feet below the surface. The larvae hatch and grow rapidly, preyed upon by many species including their own. Bluefin reach nine pounds the first year, 640 pounds the 14th, and mature in three to five years.

Since 1955, bluefin of all sizes have been tagged in the Atlantic and Mediterranean. The returned tags—more than 3,000—indicate migration patterns. Two small bluefin tagged off Martha’s Vineyard, Massachusetts, in 1954 and recaptured in the Bay of Biscay five years later provided the first proof of transatlantic migrations. There have since been at least 50 recorded.

Seven giant bluefin tagged in the Straits of Florida have been recaptured in Norwegian waters, lean in contrast to the resident giants, presumably from migrating across the relatively barren mid-Atlantic. The crossing takes two to four months; one tuna averaged 80 miles a day, a current-assisted cruising speed of three knots. To date only six small bluefin tagged in the eastern Atlantic have been recaptured in the west. Conclusion: The Atlantic bluefin population consists of separate eastern and western stocks with a small, variable interchange.

The predictability of the bluefin’s marathon migrations between spawning and feeding grounds has threatened its survival. Every year the fish must run a gantlet of fisheries: purse-seine and longline fleets, traps, and pole-and-line and sport fishermen.

Today purse seiners account for half the Atlantic and Mediterranean bluefin catch. In 1958 the U.S. purse seiner Silver Mink demonstrated that the use of newly developed nylon purse seines in combination with a hydraulic device to haul in the net made catching bluefin off New England commercially feasible. From Cape Cod Bay the fishery expanded southward within a hundred-mile coastal belt to Cape Charles, Virginia. Canadian vessels also began to seine there. When fishing was poor for tropical tuna in the eastern Pacific or eastern Atlantic, superseiners arrived from Puerto Rico as well as the California clipper fleet (formerly pole-and-line vessels), swelling the new fishery to 18 purse seiners by 1963.

At St. Andrews, New Brunswick, Capt. Matt Giacalone showed me around the 250-foot Zapata Pathfinder. The streamlined superseiner reminded me of a Greek shipping magnate’s yacht. Sophisticated in equipment—with a satellite navigation system and a helicopter to spot tuna—such a vessel would cost 10 to 15 million dollars today. The carpet pile thickened as we moved from the bridge, through the navigation room, to the captain’s spacious suite with its bar and lounge, king-size bed, and golden bathroom faucets. A 20-man Central American crew also was well accommodated.

Considered the elite of the fishing world, superseiner captains and crews are paid according to their catch. A skipper can earn $100,000 to $250,000 a year. One fleet manager told me, “If the captain’s earnings drop below my salary, I fire him.”

As a seiner approaches the fishing grounds, the mast man in the crow’s nest sweeps the water with swivel-mounted binoculars. Crewmen ready the seine skiff atop the stacked purse seine at the stern.

Some captains claim to have a sixth sense for the presence of tuna; tangible signs are concentrations of birds, whales or porpoises, and floating logs and garbage, which attract fish on which tuna prey.

A school is sighted! The helicopter lifts off. From it the captain will direct the setting of the seine. Over the side goes the seine skiff with the end of the net, and the purse seiner encircles the school at full throttle, 17 knots, paying out all 4,000 feet of cork-floated net, extending down about 330 feet. Explosives resound as men throw cherry bombs to prevent fish from escaping during encirclement.

The seiner winches in the purse line to close the seine’s bottom and trap the fish, then slowly hauls in the net with the overhead power block. Hoisted with dip nets into a hopper and sent by chutes to below-deck tanks, the catch is immersed in brine and frozen. The Zapata Pathfinder’s 20 wells can refrigerate 1,700 tons of tuna—one and a half times the total annual United States and Canadian bluefin catch before the Silver Mink’s demonstration cruise.

Fleet capacity now far exceeds the potential catch, and the fishery has fallen into erratic decline. The older fish have been depleted; one- to three-year-old bluefin predominate in contrast to the three- to six-year-olds prior to 1965.

Big Market for Young Tuna

Actually, the canneries prefer immature bluefin. Like other long-lived species, blue fin accumulate mercury with age; hence the larger fish generally exceed U.S. and Canadian legal maximums and must be mixed with younger tuna to reduce the mercury concentration, or be used as animal food. But the scarcity of medium bluefin does not augur well for the health of the fish population or the economic viability of the fishery.

Similarly, in the Mediterranean, purse seiners caught large numbers of small bluefin less than a year old (60,000 fish in one set off Sicily) prior to 1976. The Italian fleet, centered in the Tyrrhenian and Adriatic Seas, expanded rapidly in the 1970s, and together with the French fleet captured a peak of 13,000 tons of bluefin in 1976. Now their catch is little more than half that figure.

Asian longline fleets are another threat to the fragile bluefin population. In one year, 1962, Japanese fishermen set and reset 12 million nautical miles of longline—enough to girdle the globe more than 500 times. Their 400 million baited hooks brought in 400,000 tons of tuna—almost half the world catch. In 1980 the Japanese longline fleet in the Atlantic consisted of 300 vessels; they captured 4,000 tons of bluefin, 24 percent of that year’s Atlantic catch.

The longline, developed by the Japanese some 250 years ago, exploits the larger tuna at depths to 500 feet during their oceanic migrations. Fish find the bait rather than men finding the fish, as with purse seining.

Starting at dawn, men bait the hooks on drop lines and pay out the surface-floated and flagged longline from the stern while the boat moves at seven or eight knots. On completing the set—as much as 80 miles of line—they begin to haul in at midday, gaffing the fish and gutting the large ones before freezing. The crew will finish around midnight—an exhausting day’s work, particularly as longliners may stay at sea three months at a time. Unlike superseiners, quarters are cramped and Spartan.

Tuna’s Taste Long Treasured

Trap, or set net, fisheries go back 3,000 years to the Phoenicians, who trapped bluefin near the Strait of Gibraltar. The word almadraba, Moorish for “trap,” came into Spain with the eighth century A.D. conquest. Barrels of salted bluefin from traps granted by the crown fed the family fortune of the Duke of Medina-Sidonia, who led the Spanish Armada. Coins bore tuna images, as still does the Cádiz town hall facade.

Nearby, the famous almadraba of Barbate consists of net walls anchored to the seafloor in a hundred feet of water two miles offshore. A pair of leaders, almost two miles long, guides migrating bluefin to four chambers. In the final death chamber, men raise the net floor, aptly termed “red matador,” twice a day. Crews maintain and operate the trap with ten types of vessels, installing it in April and dismantling it in October, a tremendous task.

That most productive trap in the Atlantic-Mediterranean system averaged 18,000 bluefin a year from 1929-1962, and peaked with 43,500 in 1949. But it has since fallen below 2,000. Similarly, the Italian tonnare, a hundred strong at the turn of the century, the best of which could catch 10,000 bluefin a season, were reduced to 30 active tonnare by 1950 with a total catch of only 20,000 fish. Last year the remaining five caught fewer than 500 giants.

Publicity, however, has focused on the sport fishery’s decline. Take Nova Scotia, where bluefin, the local “horse mackerel,” were first caught with a dory cod line about 1870. Teams from 19 nations—a who’s who of international sport fishermen—once competed in the annual International Tuna Cup Match, inaugurated in 1937. Then the bluefin departed. Only one was caught in 1975, none the following year. The match has not been held since.

Newfoundland’s rod-and-reel fishery, launched in 1956, peaked in 1966 with 388 giants. I first became involved with research on these magnificent beasts during that record season in Conception Bay. Newfoundland’s 1981 catch: three bluefin.

Today, North Lake, Prince Edward Island, operating some 50 boats during August and September, proclaims itself Tuna Capital of the World. From 578 giants in 1974 it dropped to a mere 55 fish last year.

Since the fleets that harvest the highly migratory tuna operate worldwide, conservation must be international. Concern over their decline led to the founding in 1966 of the International Commission for the Conservation of Atlantic Tunas (ICCAT).

The overfished bluefin had sent many warning signals. Among them were reduced catches of all size groups despite increased fishing, more recaptures of tagged bluefin, and a scarcity of new recruits to the medium and giant ranges.

In spite of ICCAT’s regulations, recent data reveal a continuing decline: a 63 percent drop-off in the Atlantic bluefin catch from 45,000 tons in 1964 to 16,500 tons in 1980. Last February ICCAT nations agreed to halt bluefin fishing in the western Atlantic for two years, except for a limited annual catch for scientific purposes—to monitor population strength. The United States’ share is 605 tons, Japan’s 305, and Canada’s 250, for a total of 1,160 tons.

Short Supply, Insatiable Demand

While scientists battle to conserve the bluefin, the market in Japan, where fish account for nearly half the nation’s protein intake, has undergone a far-reaching change.

With quality fresh tuna in short supply, catches from home waters declining, and more nations forbidding foreign fleets to fish within 200 miles of their coasts, the Japanese have resorted to purchases and joint ventures abroad. In the fall of 1971 they began to airlift chilled bluefin from Taiwan, Australia, Norway, the United States, and Canada. In 1972 North America exported 216 giants. In 1978 the number topped 3,000. Despite the wholesale price doubling in the past five years, the demand appears insatiable. Last January 1, a 352-pounder sold at Tokyo’s Tsukiji Market for a record wholesale price of $19.35 a pound.

Until the advent of Japanese interest in jumbo maguro in the 1970s, the North American giants were primarily a challenge to sport fishermen. Mercury regulations kept them off home markets. But the Japanese accepted the mercury risk and began an enterprise so lucrative that it turned sport fisheries commercial and put “tuna jacking” into the vocabulary. Sportsmen pay $150 a day to charter a tuna boat in Canada, but the catch belongs to the captain. A hooked bluefin is potentially worth $1,000 to $2,000 to him, so woe betide the angler who blunders.

A profitable enterprise, but also unpredictable. Bluefin fail to appear in some waters—or refuse the bait. The Japanese buyers are vulnerable too. Since sashimi cannot be stored and released at a rate to ensure maximum wholesale prices, as with frozen or processed products, an unexpected glut can depress the market. A revolutionary answer? Bluefin ranching.

St. Margarets Bay, 15 miles west of Halifax, has supported a mackerel-trap fishery for years. Second-run mackerel enter the bay in mid-June, followed as predictably by a major predator, the bluefin tuna—to be caught in the mackerel traps.

The Japanese knew of this resource, but those early-run bluefin, without the desired fat that late-run giants accumulate in northern feeding grounds, fetched only a tenth of the price. Then in 1974 Janel Fisheries brought to Nova Scotia waters the feedlot technique familiar to cattlemen. Two huge impoundment nets, suspended by buoys and cork floats and anchored to the seafloor, were placed in 90 feet of water next to one of the mackerel traps.

Fifty bluefin were impounded the first year, pursed from that trap or towed in a cage from distant ones. In 1976 nine impoundments were constructed and 300 bluefin fattened for market. The following year the operation doubled to 18 impoundments holding 948 giants, employing a hundred people, and shipping three-quarters of a million pounds of dressed tuna to Japan at a freight rate alone of a dollar a pound. In 1978 530 bluefin were fattened in 23 impoundments. The decline in catch had begun. Last year only 116 tuna were trapped in St. Margarets Bay.

Scientists Study Bluefin Behavior

Our team from the St. Andrews Biological Station, eager to study the bluefin under confined but relatively natural conditions, began scientific work at St. Margarets Bay in 1975. The ranch owners subsequently installed an additional impoundment specifically for research and invited scientists to undertake a number of projects.

We tagged bluefin with external ultrasonic transmitters and fed them others concealed in food fish to monitor water, muscle, and stomach temperatures, swimming depth and speed, and tail beat. Picked up by a hydrophone, the signals went via underwater cable to shore-based receiving, decoding, and recording equipment.

We even undertook to weigh a live giant, anesthetized with a harpoon-borne syringe and winched out on a tubular metal stretcher. Knowing the precise weight at the beginning and end of residence at the “Bluefin Motel” would enable us to calculate how efficiently the bluefin processes its food.

Giants gain 100 to 200 pounds during their northern feeding migration, most of it in fat. Producing twice as much energy by weight as protein or carbohydrate, fat is the logical fuel for migratory fish, the equivalent of high-octane gasoline. The bluefin’s fuel economy is about twice that of an equivalent-size mammal. Fat also adds to the bluefin’s buoyancy and, sandwiched between layers of connective tissue underlying the skin, acts as a turbulence damper to reduce surface friction.

Bluefin eat most vigorously at dawn, midday, and dusk. Impoundment fish, fed to satiation, can consume 8 to 10 percent of their body weight in food daily. General belief had it that bluefin do not feed at night because they rely on vision rather than smell or hearing when closing on prey. My observations showed, however, that bioluminescent plankton can provide sufficient light for night foraging—the prey fish disturb the plankton, which respond by greater light production, a fatal revelation. Bluefin exhibit no pecking order, select mackerel from different food species offered, and complete digestion in about 20 hours. Perhaps they convey well-fed contentment to other tuna. Once “wild” bluefin were observed trying to get into the impoundment.

Bluefin tissues were analyzed for mercury and other contaminants, and the sexes were successfully distinguished, in the absence of external characteristics, by hormonal analysis of blood samples.

How did we estimate a fish’s age? By microscopic study of growth rings—layers of calcium carbonate laid down at alternating fast (summer) and slow (winter) rates—in vertebrae and in otoliths, small bones in the inner ear.

“A Specially Remarkable Species”

From such studies and underwater observations emerges a physiological and behavioral profile of our superfish: Sighting food, a bluefin breaks formation and accelerates toward it, powered by rapid beats of the large lunate tail fin, with no waves of flexure passing down its steel-hard body as in most fish. The large flexible first dorsal fin and the paired pectoral and pelvic fins quickly retract into slots to reduce drag at high speed. The smallness of its gas bladder increases vertical mobility, with its pectoral fins acting as hydrofoils to compensate for the negative buoyancy of the fish.

Just prior to impact, the retracted fins extend for directional control, the gill covers suddenly open wide, and the prey is sucked in. Ultrasonic telemetry indicates that some water is swallowed with the food rather than going out over the gills, causing a sudden drop in stomach temperature.

The bluefin swims with its mouth partly open, relying on ramjet ventilation, unlike slower fish, which rhythmically force water through their gills to remove oxygen and release carbon dioxide. Seawater contains only about 2.5 percent as much oxygen as in the air we breathe. To get the oxygen it needs from the volume of water flowing through its mouth, the bluefin has proportionately one of the largest gill areas of any fish.

A unique circulatory system, with an exceptionally muscular heart, large volume of blood, and high concentration of oxygen-carrying hemoglobin, transports the oxygen under high pressure to the tissues. Unlike a vast majority of fish, which are cold-blooded and dissipate heat (a by-product of metabolism) through the gills, the bluefin conserves and regulates heat, enabling it to feed in northern seas as cold as 40°F and to spawn in tropical waters as warm as 85°F. Bluefin muscle temperature of 88°F has been recorded in water less than 50°F. Paired arteries and veins with opposite directions of flow act as heat exchangers and as a thermal barrier to block heat loss.

The bluefin’s elevated body temperature speeds up transmission of nerve impulses, muscle contraction and relaxation (muscle power increases threefold with an 18°F rise), digestion and assimilation, compensating for its remarkably small stomach.

Indeed, as Pliny the Elder noted 20 centuries ago: “We are dealing with . . . a specially remarkable species.”

We’ve felt a sense of urgency about the research program in St. Margarets Bay, a unique but transient opportunity. The bluefin could suddenly shun these waters, and a failing fishery would attract fewer government research funds and fewer scientists.

Also, the Japanese are making great strides in “domesticating” the bluefin. A 1978 conference cosponsored by the Japanese at the University of Languedoc in southern France considered bluefin aquaculture in the Mediterranean and the possibility of supplementing wild stocks of bluefin with hatchery-reared fish, much like our salmon enhancement schemes. Restocking the oceans, no less!

Spawning fish captured by French and Italian purse seiners and tonnare can be stripped of eggs and milt, as with salmon and trout. Zooplankton from Mediterranean lagoons can provide food for the larvae and juveniles. An assured supply of fertilized eggs to laboratories in interested countries may turn the bluefin’s fortunes.

Is the Bluefin’s Future in Captivity?

“Once we overcome technical problems of supply of eggs and rearing of larvae, bluefin aquaculture will become more profitable than our long-established yellowtail culture,” Dr. Yutaka Hirasawa told me at the Tokyo University of Fisheries. Yellowtail culture currently contributes 150,000 tons to the Japanese market, raised from 75 million fingerlings.

Cultured bluefin convert food into weight more efficiently than the yellowtail and grow five times as fast. They also command a market price even higher than wild fish because of higher fat content.

Boarding the “bullet train” from Tokyo, I raced by fields of rice, tea bushes, and ripening persimmons to Shimizu on the shores of Suruga Bay. There longliners crowded the docks, and the freezer carrier Choshu Maru No. 21 was unloading 300 tons of frozen bluefin caught by Spain’s Barbate trap and the Norwegian purse-seine fleet. At the Far Seas Fisheries Research Laboratory, Dr. Shoji Ueyanagi outlined its two major programs of tuna-aquaculture research, which began in 1970: to collect and artificially fertilize eggs from ripe yellowfin tuna and rear the resulting larvae, and to capture young bluefin and develop techniques to rear them in captivity. A breakthrough came when six research installations overwintered bluefin in net cages.

One of the most successful programs is run by Kinki University at its Kushimoto and Shirahama Laboratories farther southwest on Honshu. With the director, Dr. Teruo Harada, I inspected five circular floating cages of wire netting 90 feet in diameter, 25 feet deep, anchored offshore in the shelter of an island. Each holds a different age group, 5,000 bluefin in all. Less than half a pound when caught in 1974, and fed twice daily, the bluefin weighed 100 to 150 pounds four years later. Summer growth is particularly rapid, the very small bluefin increasing their weight tenfold in four months.

Despite high mortality during capture and transfer to the cages, and the necessity to develop an alternate food since humans consume the abundant fish species in Japan, I am convinced of the ability of Japanese scientists to domesticate the bluefin. Three years ago the fish added their vote of confidence when Dr. Harada’s oldest bluefin, in captivity a record five years, spawned for the first time in captivity.

Juveniles from thousands of its fertilized eggs are now being reared—an exciting scientific challenge.

For the sake of the bluefin, good luck!

2 comments
John Lewis
John Lewis

We as consumers of the water ways of the earth must do what is right for all to survive! So that the next generation can exsperance the same as we did in life.