Tuna are among the most economically important creatures in the sea. Worldwide, the tuna fishing and processing industry amounts to some $3 billion annually. In the United States, people consume more than 900 million pounds of canned tuna a year. It troubles experts that so little is known about the behavior of tuna, never mind less commercially valuable creatures. “We can go to Mars and the Moon,” Block says, “but we haven’t had a way to see where the ocean animals go.”
Tuna draw heat from the action of their own muscles. That gives the fish more power, according to Block’s laboratory experiments, but it also means they need lots of oxygen: water must flow ceaselessly through their gills. If they don’t swim, they die. In the wild, a bluefin grows rapidly. If it lives long enough, it might top 1,000 pounds. Yet it’s a marvel of hydrodynamics, says Randy Kochevar, a biologist at the Monterey tuna center and a colleague of Block’s. Abluefin can sprint 40 miles an hour and cruise 150 miles a day. The giant Atlantic bluefin, which Block has studied even more extensively than the Pacific variety, may survive 25 years or longer and reach 1,500 pounds.
The Pacific bluefin is one of the world’s most prized fishes. Sushi lovers pay a premium for its fatty meat. At Tokyo auctions, dealers routinely spend $10,000 for a fish. Though bluefin are caught with hook and line, in commercial operations they are typically captured with a purse seine, an enormous net that encircles a school and entraps the fish when cinched at the bottom. A large school in the eastern Pacific can consist of 2,000 fish.
Unlike other tuna species, the Pacific bluefin appears to be holding its own in the face of fishing pressure, although population data from the Pacific, which Block calls “that big blank slate,” are limited. As Chuck Farwell, codirec-tor of the Monterey tuna center, remarked, “If there were a problem, we wouldn’t know it.”
In the Atlantic Ocean, the problem is worse, but the data, thanks largely to Block and coworkers, are better. Each winter since 1996 she has chartered fishing boats to survey tuna off the North Carolina coast. She follows the animals with satellite tags or another type of sensor, known to the scientists as an archival tag, which she sews into the abdomen of a large tuna. It, too, records the fish’s movements and the ocean temperatures and depths, but furnishes researchers with more data—provided that whoever catches the fish is willing to return the device to the researchers for decoding. (It’s plastered with a return address and the promise of a $1,000 reward.)
Sitting in her office at the tuna research center, a joint venture between Stanford University and the Monterey Bay Aquarium, Block, a Stanford professor of biological sciences, pushed an archival tag across her desk. It looks like a metal cigarette lighter with a short probe and is surgically implanted in a fish’s belly. The probe pierces the skin and measures the water temperature and pressure every two minutes. The pressure indicates the depth at which the tuna is swimming. A clock and a light-sensitive diode establish the time of the setting and rising sun, which can be converted to latitude and longitude. Thus, the scientists can reckon a tuna’s position on the globe once a day within 60 miles.
Block took out a map showing the distribution of plankton in the North Pacific. Plankton, a general term for tiny drifting plant and animal life, are at or near the bottom of the food chain, and all sorts of marine creatures flourish where plankton abound. “In the center of all oceans are empty gyres— ‘deserts’ with low chlorophyll and plankton—across which the animal migrates to get to ‘hot’ zones off the continents,” she said. Color-coded, the hot zones were strips of reddish yellow and the desert a yawning blue. “If you’re a tuna, why do you risk your life crossing the desert? You wake up in the Coral Sea, and you swim to the other side. That’s a journey of 6,000 kilometers [3,720 miles]. Why? We think they somehow know the food is better that particular year in the zone of rich upwelling off Baja California, for instance.” She glanced at the ocean outside her window. “We can’t tell you where the most lucrative animal in the sea feeds or breeds,” she said, shaking her head.
The idea for the census of marine life originated with Jesse Ausubel, a program officer at the Alfred P. Sloan Foundation. Based in New York City, the foundation sponsors research and helps launch new scientific programs. In 1997, following a National Academy of Sciences report calling for increasing research on marine biodiversity, the foundation proposed a sweeping tally to be called the Census of the Fishes. But counting even a fraction of the fish in the sea, scientists hastened to point out in several brainstorming sessions, would be impossible. After all, scientists estimate there are 20,000 kinds of marine fish—including perhaps 5,000 yet to be discovered.
Sloan Foundation advisers, led by Frederick Grassle of Rutgers University, scaled back the plan, deciding to hunt for some new species and assess others. The project shifted focus again after biologists studying marine mammals and other non-fish creatures said they wanted in on the action too. So it was renamed the Census of Marine Life. All told, the enterprise will consist of 30 to 40 separate field studies, at $5 million to $25 million apiece, with the money coming largely from the U.S. and foreign governments.
The census’s senior scientist, Ronald O’Dor, a marine biologist at Dalhousie University in Halifax, Nova Scotia, who is now based at the Consortium for Oceanographic Research and Education in Washington, D.C., says the virtue of the approach is that the animals lead the way. “They cover more area than an expensive, traditional research cruise can,” he says. “You let the animals choose your sites.”