Tracking creatures through the trackless sea


1. Following fantastic fish

2. Turning turtle

3. To track, to conserve

A map of deep-sea longline fishing effort during 2000. Densest hook concentration shown in brown. Courtesy Lewison, Freeman & Crowder (see "Quantifying..." in the bibliography).

This fresh-tagged bluefin tuna looks ready to fly! A single bluefin netted $173,000 in Japan, and the species is severely depleted in the Atlantic. Through tagging, scientists are learning where bluefins go, which could lead to smarter management for the surviving bluefins. Photo: Jose Cort, NOAA.

Once you understand the movement of ocean animals, you can predict where they will hang out, feed and breed, and what migratory paths they will take.

To know, and then to act
Cutting through the researchers elated, "Gee-whiz, we can finally see where these animals live!" is an undertone of concern. Magnificent ocean creatures, like their counterparts on land, are under increasing threat. Among many causes is an ocean-ful of fishing hooks. Turtle researcher Larry Crowder says that in 2000, longline fishermen -- hunting tuna and a few other large, valuable species - set out almost 3.8 million hooks on the average night in the deep ocean.

Map shows fishing concentrated near equator.

That's a lot of hooks, but it's an underestimate because hooks set by illegal vessels were not counted.

Just as prosecutors occasionally convict the innocent, the global fish dragnet snares a lot of innocent bystanders in what is called "bycatch." A longline tuna boat may deploy thousands of hooks on a single, 40-kilometer line. When retrieved a day or so later, the line may contain tuna -- and sharks, birds and sea turtles. By the time they are hauled into the boat, many are dead.

A estimate of global bycatch, for all fisheries, reached 30 million tons -- about one -third of the total fishing haul.

South-seas supermarket
For conservation, the new animal-tracking projects highlight the importance of international cooperation, says Andrew Read, director of OBIS-SEAMAP, a large biological mapping project headquartered at Duke University. "Bluefin tuna are now known to move from North Carolina to the Mediterranean. How are we going to manage that? Wandering albatrosses might circumnavigate the Southern Ocean. How do we deal with the conservation of those animals?"

Man in boat throws silvery fish into air.

Another conclusion from the torrent of data on marine migration is that the ocean is not a uniform place. Marine conservationist Elliot Norse says the sea has cafeterias, bars and motels where organisms meet to eat, meet, greet and breed. "They commute among these places, behave almost as if are on a highway in the sea. If you want to do place-based conservation, you have to know the places where the large predatory species are."

(Why concentrate on big, showy species? First, they face the biggest threats. Second, they are big enough to carry tags. And third, if you save them, chances are good that you'll save other organisms that share their habitat.)

Although fishermen have long known of seasonal fish movements, only satellite-based data can supply broad, systematic coverage across the ocean. And that data can then be correlated with satellite information on ocean conditions -- sea surface temperature, winds and water chemistry.

Already, tracking devices from that large predators follow a characteristic pattern, Norse says. "They travel a fairly long distance in a straight line, at a good rate, and hit a certain patch, and then stop, go back and forth," indicating that they are feeding. Once it has cleaned out the food, or built up enough fat, the predator moves on.

A crowd of seals basks on beach.
The elephant seal dives 50 or 60 times a day to depths of 500 meters. Carrying a tag that measures pressure and temperature, a seal becomes an el-cheapo research sub. Photo: National Park Service.

Start making sense
After crunching oceans of data on animal movement and sea conditions, scientists should start to understand why creatures move as they do, Norse says, and "predict what places they will hang out, feed and breed, and the migratory path between them."

This richer understanding of ocean biology could set the stage for creating temporary, moving marine reserves in international water, hundreds of miles offshore. "Where the idea of 'place' is completely new, now we have the tools that allow us to start the process of identifying place," says Norse.

Soon, he predicts, it may be possible to predict that, in a certain month, at a certain location, an upwelling of nutrient-rich water will feed a bloom of plants and create abundant food. Based on historical data, and satellite sea-surface temperature measurements showing that the upwelling has begun, international fishing regulators may decide to protect a portion of open ocean, and broadcast a warning to nearby fishing boats.

globe, with yellow and red tracks along the northern half of the north american west coast
Map of the North Pacific Ocean shows tracks of male (red) and female (yellow) northern elephant seals. See "Foraging Ecology ..." in the bibliography. Courtesy University of California, Santa Cruz.

Something wrong with this picture?
It's a nice fantasy, but since nobody regulates fishing beyond each nation's 200-mile exclusive economic zone, it's not much more than a fantasy at this point. But regulation may be coming to the open ocean: In 1979, a sanctuary was established to limit (and since 1986 prohibit) whaling in the Indian Ocean. And as mentioned, the United States regulates U.S. fishing boats even beyond the 200-mile limit.

If marine animals continue to disappear at the present rate, regulation could start to make more political and economic sense.

Norse argues that open-ocean reserves already have some legal justification. "The [United Nations1982] Law of the Sea describes the high seas as the 'common heritage of humankind,' that means now that whoever gets there first gets the fish. But another way to look at it is that a person in Montana or Bolivia has as much to say about what happens to the fish as someone who is actively fishing on the ocean."

While Norse admits that the idea of temporary, open-ocean reserves faces "Challenges galore," he notes that some nations are already cooperating to conserve migratory animals on land. "We have been doing this with the whooping crane, shorebirds, ducks. We know that we can conserve the long-distance migrants by conserving the places that are crucial to them. In the open ocean, the places move, but now there are technologies for following the organisms, for observing the conditions they particularly like. That would allow us to quickly say, 'We need to protect these certain spots.' It's a revolutionary idea, protecting places in what previously seemed to be open ocean."

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