The Tuna, Now Appearing in an Ocean Near You, Is Turning Out to be a High-Tech Creature That Never Stops to Rest : The Magnificent Machine of the Sea

Abruptly, the engines grind to a slow idle. The mound of foam seething at the stern sinks into the water’s surface, and the boat floats passively in the long, blue, indolent swells.

“Put on some weights! Let’s go down for ‘em!” yells the skipper from his station at the wheel. Yet, frustration and weariness make his voice droop, and everyone knows his command is actually an admission of defeat. With no sign of fish, throwing out bait at random on the open ocean is a blind gambit with roughly the same chance of success as winning the state lottery.

The men grumble among themselves.

“Come on, captain. I didn’t pay for no bottom fishing,” says one.

“Yeah,” says another, “The Whale-Watch Special.” He sticks his head out over the rail and stares with exaggerated, bug-eyed sarcasm into the water.

But they resign themselves to the fisherman’s fate and slowly add weights to their lines, bait their hooks with live anchovies and let their lines down.

The men lounge along the railing, holding their rods loosely. They have been at sea since 1 a.m., and now, at mid-afternoon, the day’s failure breeds exhaustion. They are doggedly using up the time they have purchased aboard the sport fisher. Some drowse as the boat rocks quietly in the swells.

Then it happens. A pole leaps forward in the hands of a napper. Only his reflex grip saves his gear from going over-board. He jerks awake, and as his senses light up, he emits a high-pitched whoop.

“Hoo-- HOOK UP!”

The line begins to scream off his reel. Men jump into action as though they’ve been plugged in. They bound from their bunks below deck, come scrambling up from the hold as if the engine were on fire, grapple for their rods in the holders along the cabin, and go stumbling over tackle boxes and lurching against the railing in their frantic haste to get bait in the water.

Screel! --another pole turns on. Then another, and another. Chaos erupts as man after man hooks into some powerful, incredibly fast creature rushing through the depths below his feet.

Just how fast and powerful soon becomes apparent to a boy of about 16 who has jumped into the fray unprepared, his reel fastened insecurely to his pole. A fish strikes his bait; the reel whines as the line melts off the spool. But his drag is set too tight, and suddenly the extra friction makes the mechanism jam. Something has to give. The reel wrenches free of the pole, jumps out of the boy’s hands and flies forward. It slams into the first eyelet on his rod and breaks it off, then--pop, pop, pop--breaks every eyelet in succession as it proceeds down the pole, snaps off the tip and disappears into the sea. Everything happens so fast that the boy simply stands at the rail staring at the remains of his stick.

What these men are encountering is a school of albacore tuna 40 miles out from San Diego. The albacore, along with five or six of its close relatives--tunas with such names as bluefin, yellowfin, skipjack, bigeye, bullet--pass through Southern California waters at various times between June and October on their migrations. Fishermen, of course, count the days until they appear; sushi sophisticates covet the red, succulent flesh, and the general public reveres tuna salad as a cultural tradition.

U.S. consumption of tuna has risen 1,300 % in the past 50 years; with modern fishing techniques, the worldwide catch stands at roughly 2.2 million tons annually. And, like all wildlife, tunas can be over-exploited if hunting is not controlled. These efficient new fishing methods have had a heavy impact on tunas in certain parts of the world. They have also created an international controversy over the netting--and killing--of dolphins that feed along with the tunas. Already this year, the U.S. tuna industry has nearly reached its limit on dolphin kills; when it does, the fleet will be ordered to discontinue all fishing on dolphin schools in the eastern Pacific. Protecting both the fish and the mammals from serious depletion requires a thorough understanding of their biological needs--what they eat; what kinds of temperatures, depths and oxygen concentrations they prefer; how they operate internally.

Imagine the surprise, then, when researchers working toward this end discovered that the lowly tuna is so different from other fish, so sophisticated, that it seems to belong in its own category. It was known decades ago that, unlike other fish, the tuna is warmblooded. But as our knowledge has increased, it has become apparent that the tuna has entered into a sort of devil’s pact with evolution: In order to keep its body temperature high, it must swim continuously. If it stops, it suffocates.

The tuna has evolved a kind of energy economics in which it consumes an enormous amount of food, but most of this “income” is spent meeting its metabolic needs. It’s not stretching things to see the tuna as a metaphor for Westernized energy use. As the fish roams the oceans from continent to continent, never pausing to rest, it is forced to use energy the way Western civilization uses oil, with enormous consumption rates, enormous costs, large profits and a kind of fast-lane desperation.

The Southwest Fisheries Center of the National Marine Fisheries Service, La Jolla Laboratory, sits on a cliff overlooking La Jolla Cove to the south and Black’s Beach to the north. There, a small corps of marine biologists investigates questions that relate to the tuna industry. Elizabeth Vetter is a member of this group, and her work, like so much tuna research, involves energy use.

A tall, enthusiastic woman, Vetter is using a method called mathematical modeling to get at the heart of the tuna-dolphin problem in the eastern tropical Pacific, where schools of yellowfin tunas often swim beneath schools of spotted dolphins. Commercial fishermen simply net the entire school, with the dolphins often getting tangled in the nets and drowning.

“My models might help us find a way to catch tunas without catching the dolphins,” Vetter says. “They could help identify places where the tunas don’t have to hang around with the dolphins in order to get enough food, and we could get them by themselves.”

Her theories have illuminated how energy use may bind the two species, and suggested that it is probably the tunas that follow the dolphins.

“When the fishermen find a school of dolphins and tuna,” she explains, “they throw speedboats in the water and chase the dolphins at 10 to 12 knots for about a half an hour until they (the dolphins) get tired of being chased. The thing that’s really remarkable is that chasing those dolphins for half an hour doesn’t cause the tuna-dolphin association to break up.”

According to Vetter’s equations, energy costs seem to be near the center of the schooling behavior. It turns out that tunas school up under dolphin calves, which are about their same length. This is important because tunas and dolphins of the same length have the same optimal swimming speed--the speed at which they can go the farthest with the least amount of energy. So energy economics dictate that the tunas and dolphins will swim at the same speed; it is the most energy-efficient rate to travel. But the question remains: Why should the tunas stay with the dolphins? What do they gain?

Again, the answer seems to involve energy in the form of food. Researchers believe that the dolphins, with their sophisticated sonar, may be better at locating bait schools. Since they need even more energy than tunas and are fast, ravenous eaters with four times the stomach capacity, they could decimate the food supply before tunas in the area could find it. So, reasons Vetter, if the dolphins are better at finding food, why not stick with them until they find prey, then join in the attack?

To put Vetter’s work in perspective, it is important to realize that the tuna lives in the open ocean, where food is scarce. Sardines, squid, mackerel and other bait species do occur in large, dense schools, but the schools are scattered, apparently at random, forcing the tunas to range through a mostly barren universe with no guarantee of finding enough to survive.

They have solved this problem with a strategy of eternal, high-speed foraging in which they spend a very large sum of energy covering long distances as rapidly as possible. The upshot is that tunas are “energy speculators,” and that by developing body warmth they have raised the energy stakes to the highest in the fish kingdom. No other fish except the great white shark and a few of its cousins have accomplished this. Each day they gamble that with their high-speed searching capacity they will find enough food to meet their operating costs.

Judging from the facts, tunas succeed extravagantly. The bluefin and the albacore swim continuously around the Pacific on annual migrations. The yellowfin and the skipjack travel the warmer waters of the eastern tropical Pacific. It is difficult to say how far they actually go, however, because tunas do not take straight routes. They swim back and forth across a region in their search for food, cutting and veering, crossing and crisscrossing the three-dimensional spaces of ocean.

These performances are not those of an ordinary fish. Even a strong swimmer such as a salmon would quickly be exhausted by what for a tuna is casual cruising. What, then, gives the tuna the endurance and speed to meet the demands of its instinctive journey?

The answer involves a radical remodeling of the basic fish--everything from the biochemistry of the muscle to the rerouting of the blood vessels to the details of the fin and body shape:

The tuna’s body seems to approach perfection in hydrodynamic design, for low drag and high speed. When cruising, the fins extend, and the fish is a craft capable of cutting, turning and maneuvering. When it is sprinting, the forward fins fold down into slots or grooves, converting the fish into a living missile blasting along a straight course.

Tunas have two kinds of swimming muscle, red and white, which makes them both sprinter and marathoner. Red muscle is designed for endurance and long-distance cruising. White muscle cuts in when a burst of speed is needed.

A tuna’s circulatory system functions as a heat exchanger as well as a blood-circulating device. Unlike that of other fish, the tuna’s main blood supply runs under the skin (it runs under the backbone in other species). Cold blood flows in toward the body core, picks up heat from warm blood coming out and returns it to the body.

To meet the muscles’ great need for oxygen, tuna blood is much richer in hemoglobin than the blood of other fish--as rich as human blood. Tunas also have much more blood, up to 20% of its volume, contrasted with less than 10% in a human.

The key to the tuna’s breathing is “ram-gill ventilation.” Using the same principle as a ramjet, tunas swim with their mouths partly open so water is forced over the gills. There is a price, however. Tunas have lost the muscles to pump their gills the way most fish do, and they could not breathe if they stopped swimming.

All this is testimony to the fact that tunas are not the sluggish, coldblooded beings that most fish are. An albacore may have a core temperature of 93 to 95 degrees Fahrenheit while swimming in water of 60 degrees, and this gives a tremendous advantage to an active animal. Muscle contracts more quickly when warm, and an albacore can produce twice as much power as a truly coldblooded fish in the same water. Body warmth is thought to be the key factor in the tuna’s combination of speed, endurance and strength, unequaled in the fish kingdom.

Long-time fisherman Charlie Davis, a former sport-fishing skipper and author of the book “Hook Up,” says tunas are among “the toughest, most demanding fish in the ocean. When a big yellowfin is heading straight down and you’re standing at the rail, every time that big old rascal sweeps his tail, it lifts your heels right off the deck.” Battles of three to four hours with 200- to 300-pound yellowfin are common, and when the fight is over, “virtually every muscle in your body aches, except maybe your eyelids. The fatigue is unbelievable.”

The fatigue is even more unbelievable if one considers what the tuna is fighting in addition to the fisherman.

Water is 800 times denser than air, and swimming through it takes a lot of energy. Water resistance also rises dramatically the faster a fish swims--and yet tunas have been clocked at speeds of more than 40 m.p.h. for bursts of up to 20 seconds--up to 55 m.p.h. in the case of the giant bluefin tuna. Then there is the problem of heat loss. Water absorbs heat up to 50 times faster than air, and gills compound the problem by acting as radiators. Finally, water simply can’t hold much oxygen--often less than 2.5% of the amount in the air. To an animal with high metabolic needs, this is a severe limitation.

It’s impossible to understand the tuna without comprehending how its body burns fuel and maintains its elevated temperature, and this requires state-of-the-art laboratory equipment. But tunas do not take kindly to laboratories for the simple reason that they like to keep breathing. To do that, they require a lot of space to maintain the speed necessary for their gills to operate. Or, it takes an ingenious device to keep them in place like a man on a treadmill. At the Scripps Institution of Oceanography, down the hill from the Fisheries Center, physiologist Jeffrey B. Graham is building a “tuna treadmill.”

This device “will be about a 20-by-18-foot structure,” says Graham, “and weigh six, seven tons when it’s fully loaded with water, refrigeration and a pump.”

The entire invention will be hoisted aboard a research vessel and carried out to the fishing grounds, because the experiments must be done with freshly caught specimens. If you can’t bring the tuna to the laboratory, bring the laboratory to the tuna.

When fully operational, sometime this fall, the treadmill propeller will push water through an observation chamber where Graham and other researchers will place a fish and force it to swim in place. They will then measure the effect of different temperatures, oxygen concentrations and water speeds. Even this behemoth machine will not come close to pushing the tuna’s limits, but still, it should generate some fundamental data.

“We can’t go as fast as a tuna can swim,” Graham says, “but we can look at how, say, various muscle groups are different, and how they respond to work. Another thing we can look at will be oxygen consumption. It’s the same thing as miles per gallon at different speeds. Consumption goes up as speed goes up. It’s a question of looking at the whole spectrum of physiology variables of tunas in motion--it’s exciting!”

The results of laboratory work have made it clear that tunas are precision machines. Each species seems designed to operate in a different combination of temperature, oxygen concentration and pressure where its finely tuned physiology gives maximum performance. That is why the albacore appear first in the season; they prefer the coldest temperatures. Then come the skipjack and yellowfin and bigeye, which dwell mainly in tropical waters and arrive only in warm years--the skipjack specializing in the upper layers, the yellowfin the middle layers and the bigeye lurking as far down as 1,500 feet.

Few things intrigue tuna eco logists more than what tunas do in the dark, unbearably heavy depths where they spend much of their lives. Fish that can rocket away like meteors in the water may as well be flying in outer space. In an attempt to study them in something close to their natural element, the Fisheries Service has built several large pools next to the sea at its Honolulu laboratory. Here, scientists have been able to watch tunas such as Big Boy, a large yellowfin tuna, over the course of several years.

“He was one of my fish,” explains Kim Holland, a biologist from the University of Hawaii who collaborates with biologists from the Southwest Fisheries Center, Honolulu Laboratory. “He was about four pounds when I got him and ended up around 150.”

The fish had been left over from a previous experiment, and the staff grew somewhat attached to him. Since no one had ever had a pet tuna, what they learned was completely original.

“Tuna change colors when they get aroused,” Holland says, “and that arousal can be because they’re fighting for their lives at the back of a boat, or mating, or eating. When they become ‘house trained,’ so to speak, they learn to associate things with food, and they start flashing their feeding colors as people arrive around their tank.

“Big Boy was amazing. You could take a piece of food and throw it 20, 30 feet in the air, across the tank, and that fish would track it under water--you could see him sprinting across the tank at the same time the food was still 30 feet above him--and he’d intercept it just as it hit the water!”

Unfortunately, Big Boy came to a mysterious and sad end. When the staff arrived for work one morning they found him next to the tank, dead. The official conclusion was that he had become too aroused and leaped up into the unknown. But speculation persists that the real reason he ended up on land was that some boys got into the compound during the night with fishing gear, but were unable to lug him away.

Nevertheless, work goes on at the Honolulu facilities, and Holland is perfecting ultrasonic telemetry, a method in which he attaches transmitters to freshly caught tunas, then returns them to the sea. The device gives information on depth as well as direction, and Holland calls it “our window into their world.” As a result, Holland says, “we now have insights literally from second to second on their swimming patterns, and we’re starting to see behaviors we had no idea were occurring. We tracked one bigeye tuna that dove 750 feet in less than a minute, and it was down deep to begin with.

“Another thing we’ve found is that they can swim a lot slower than we predicted from captive animals and from theoretical modeling. They have techniques like turning over on their sides at about a 45-degree angle and using their entire body as a hydrofoil,” Holland says.

(Before this discovery, it was thought that tunas spent most of their lives cruising with their pectoral fins extended, literally flying through the water. Being denser than water, they would otherwise sink.)

“We’ve also seen a lot of what we call ‘fly-glide behavior.’ It’s similar to the behavior of certain birds that fly and then glide, fly and glide. It may be a way for fish that are heavier than water to conserve energy.”

The next few years promise to be landmarks for tuna research. Holland and his colleagues have plans for the next generation of transmitters, which will actually take readings inside the tuna’s muscle.

“This will give us a more direct measure of how much energy the fish is using,” Holland says. “When we see the fly-glide pattern, we’ll also be able to see if the fish uses a number of tail beats to make the climb, and then stops beating while it glides.”

Eventually, work like this will help assemble a scientific image of how these masters of the water are able to cope so dramatically with a universe we can barely begin to imagine. We will then understand how it is that a creature is able to rocket 50 m.p.h. through a medium that will stop a bullet within several feet, dive within minutes to depths that could crush a conventional submarine, extract enough oxygen to keep its body near the temperature of a human and come slashing up from nowhere to stun, thrill and frustrate a boatload of fishermen. William Hamner, a marine biologist at UCLA, tells a story that sums up the tuna.

He and his wife were diving near Palau in Micronesia, when, without warning, they were engulfed in a school of skipjack.

“It was like being inside a drum,” he says. “There was this pounding vibration all around us. You could feel the power in your guts. It was their tails--that short, explosive stroke. They came rocketing right at us. But at the last second they would veer off and shoot by, an inch away, without touching.

“Then, just like that, they were gone.”