Tasty Athletes of the Deep
BY AWAKE! CORRESPONDENT IN AUSTRALIA
WHAT falcons are to the skies, these superfish are to the seas. Fast and sleek, they slice through the depths like shimmering darts. They are forever on the move, forever on the prowl. Indeed, their scientific name, Thunnus thynnus, stems from a word meaning “rush.” Part of a prestigious family, their relatives include marlins, spearfish, and swordfish. Yes, these aquatic athletes, if you have not already guessed, are in the tuna family, which comprises 13 species.
Of this athletic family, the stars are the bluefins. Found south of the equator, the southern bluefin grows to at least six feet [200 cm] and weighs up to 450 pounds [200 kg]. The family heavyweights, however, are the giant northern bluefins, found, as their name suggests, in the Northern Hemisphere. At nine feet [270 cm] or more (rare nowadays because of overfishing), they can tip the scales at over 1,500 pounds [700 kg]—75 percent of which is powerful muscle. But size does not slow bluefins down. The big fellows, in fact, are the missiles of the pack, able to attain speeds of about 45 to 50 miles per hour [70-80 km/hr] for short bursts.
Built for the Sprint and the Marathon
How do bluefins manage to swim so fast? National Geographic magazine explains: “Three-quarters muscle, hydrodynamically superb, with a powerful heart, ramjet ventilation, heat exchangers, and other special adaptations, the bluefin is built for speed.” In fact, the bluefin’s mighty heart is several times bigger than the heart of other fish and is more like a mammal’s heart than that of a fish. What is more, its heart, unlike that of a typical cold-blooded fish, pumps relatively warm blood through its ingenious circulatory system. An 18-degree-Fahrenheit [10°C] rise in its blood temperature increases the bluefin’s muscle power some threefold, helping to make it a formidable predator as it sates its appetite on fish, squid, and krill.
When a bluefin spots a tasty meal—let’s say, a mackerel—its sickle-shaped tail blasts it up to attack-speed in a heartbeat or two. Pectoral and pelvic fins retract into special slots in the fish’s steel-hard body to reduce drag. Fast though the mackerel may be, it has little chance of escape, for the bluefin is also equipped with binocular vision, extremely sensitive hearing, and chemical detectors that sample the water. As the bluefin is about to strike, its fins extend again for critical, split-second directional control. Then, in the blink of an eye, its gill-covers and mouth open and the mackerel is gone—sucked in and swallowed.
Because of their powerful heart, relatively warm blood, and exceptionally large gills, tuna recover from such sprints about ten times faster than any other fish. Yet, even while ‘catching their breath’—as well as while sleeping—they continue swimming, for they are heavier than water, and they do not have the gill pumps that allow other fish to come to a complete rest. Thus, like sharks, tuna swim with their mouths partially open. A tuna’s epitaph might simply read: “From birth to death a marathon, punctuated only by frenzied sprints.”
The most beautiful members of the tuna family are the giant yellowfin tuna. Yellowfins grow to about six and a half feet [2 m] and sport a yellow stripe, yellow finlets, and exceptionally long, swept-back fins. When knifing through a wave, these magnificent fish shimmer like darts on fire, especially at night. In fact, the Hawaiians call them ahi, meaning “fire.”
Athletes in Deep Trouble
Its copious red, oily flesh also makes the tuna a superstar on the dining table. Gourmet Japanese dishes, such as sashimi and sushi, have put bluefin among the most sought-after and expensive foods on the Japanese market. Sushi-bar clients pay big money for small servings of tuna. If you were to hear buyers bid on just one bluefin at an auction, you could be excused for thinking that they were bidding on a new car. Figures like $11,000 or more are common. One 715-pound [324 kg] bluefin, in fact, sold for $67,500! “Big as a Porsche, fast as a Porsche, and as valuable as a Porsche,” said one conservationist.
In view of the demand for tuna, fish stocks are in sharp decline. They are “overfished, overexploited, [and] wasted to make money as if there were no tomorrow,” says the book Saltwater Gamefishing. Modern industrial ships equipped with the latest technology, including aerial surveillance, take huge catches. When a ship called a purse seiner, for example, spots a school of tuna, it lowers a skiff that pulls a curtain of netting, or a purse seine, around the fish, blocking their escape. Long-liners, on the other hand, have been known to drag a line up to 80 miles [130 km] long. Attached to this primary line are some 2,200 shorter lines, each bristling with baited hooks. The stuff of tuna nightmares! Large bluefins are such a prize that boats and spotter planes “may spend weeks hunting down just a few individuals,” says the World Wildlife Fund.
Some countries have set limits on catches permitted in their territorial waters, but how do you police catches of pelagic fish like tuna? (Tagged and released near Japan, one northern bluefin was later recaptured off Mexico—nearly 7,000 miles [11,000 km] away!) Thus far, the answer has been that you cannot. Organizations within the United Nations are attempting to promote sustainable harvests, but pitted against them are powerful vested interests. In fact, when some countries have attempted to police catches, they have ignited explosive incidents.
You might wonder why fishermen put the oceans’ bounty, and even their own future livelihood, at risk by continuing to exploit dangerously depleted stocks. Says National Geographic: “In the face of such declines [in fish stocks] neither traditional nor industrial fishermen can turn to voluntary conservation, because there’s no profit in it. It just gives the fish to someone less scrupulous. Instead, everyone fishes harder.”
Will Tagging and Farming Save the Tuna?
The southern bluefin has been the object of considerable research. Part of this research incorporates the use of sophisticated electronic tags that reveal vital data about the habits and health of tuna schools. This information will aid in regulating fishing quotas.
Meanwhile, fish farming, which includes tuna farming, is gaining popularity in some countries. As far as fertility is concerned, female bluefins have a lot to offer the fish farmer—they release up to 15 million eggs in one spawning season! If successful, farming may ease the pressure on dangerously low, noncaptive fish stocks. It would be a tragedy, indeed, to see the extinction of such magnificent aquatic athletes as the tuna and especially the superstars of the family, the bluefins—fish that delight not just the eye but the palate as well.
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Yellowfin tuna
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Bluefin tuna
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