Tracking creatures through the trackless sea

POSTED 26 FEB 2004
 

1. Following fantastic fish

2. Turning turtle

3. To track, to conserve

Hammerhead photo: NOAA

A large nursery for blue whales was just discovered in Chile. The movement of large sea animals is still an area of darkness, but new tracking systems are shedding light on their wanderings. NOAA

Tracks from Laysan (yellow) and black-footed (red) albatrosses criss-cross the North Pacific. Courtesy Scott Shaffer and TOPP

That's no backpack. The harness replaces glue, which won't hold a satellite tag to the leatherback's leathery shell. Here, scientists attach tags to sea turtles that visit Monterey Bay in August and September, looking for a mouthful of peanut-butter-and-jellyfish. Photo: Monterey Bay National Marine Sanctuary.

The vast majority of large sea animals are completely  invisible. With electronic tags, day by day, season by season, we see the whole pattern of their lives.

Finally, fish (and friends) found
hammerhead photo front 3/4 viewA tuna flies above the ocean and dives. A pod of whales surfaces, gulps air, and disappears. A sea turtle breaks through its egg, scrambles into the surf, and is gone. An albatross soars above the swells on a remote reach of the South Atlantic. Aloft, at sea, for 11 months a year, it circles Antarctica in its search for dinner.

How little do we know about marine life? Consider the discovery in Chile of a nursery for blue whales, the largest animal on Earth, just last year. Hunted by whalers almost to extinction, the blue whale is slowly recovering. About 1,400 live in the Southern Hemisphere.

The back of a blue whale breaks the surface.

Finding the nursery was a shock, ecologist Rodrigo Hucke-Gaete, of the Universidad Austral de Chile, told BBC News Online. "It was amazing to discover something like this in 2003. One thinks this is not an era of discovery, but we still have much to learn."

While earthbound ornithologists can espy their quarry with binoculars and track them with radar and leg bands, and mammologists travel to remotest Asia to study the residents of Earth's distant corners, marine scientists are still trying to answer one simple question: Where are the critters?

"Believe it or not, we don't know where they are, even in the 21st century," says Barbara Block of Stanford University. Traditionally reliant on eagle-eyed, sometimes seasick observers and numbered tags placed on a few animals, ocean biologists have seized high technology to answer basic questions about ocean animals.

Now, sophisticated electronic tags (Block calls the mix "fish and chips" for its hybrid of fish and microchips) have started spewing a flood of data on the lifestyle and migration habits of the obscure objects of marine biologists' desire.

Swirled migration paths on satellite map

Small tags. Big benefits.
Marine organisms, it turns out, tend to congregate and move much like terrestrial ones. Where there is food, there are grazers, and where there are grazers, there are predators. "It's comparable in terrestrial terms to the Serengeti watering holes," says Block.

Modern electronic tags, some no bigger than a pen, store data and broadcast it to satellites. On air-breathing animals, the tags send data when they are above water; fish tags eventually release themselves, rise to the surface, and dump data. Often, researchers try to remove tags if they cannot be designed to release themselves.

An elaborate electronic tag can store 2 to 32 megabytes of data on water pressure, light level, ocean temperature and body temperature. Water pressure reveals depth, while light levels are correlated with sun position and time of day to pinpoint location. "It gives a complete picture of behavior as the animal moves through the water column, give a picture of its interaction with the environment," Block says.

Crew of scientists grip a giant turtle.

Block is a leader of Tagging of Pacific Pelagics (TOPP) project, which is tracking 22 species of fish, mammals, birds and reptiles through the Pacific Ocean. TOPP is one of several pilot research projects under the Census of Marine Life, a decade-long, international collaboration to understand life in the oceans. (The census, which extends far beyond tracking, has recently compiled a list of 15,304 ocean fish species.)

Something fishy
The result is nothing short of a revolution in the science of finding fish -- and marine mammals, turtles and birds. "The vast majority, especially if they are submerged for most of their lives, are completely invisible," says Randall Kochevar, head of science communications at TOPP and at the Monterey Bay Aquarium. "With the electronic tags, we can get a real animal's eye view of what their life is like. Day by day, season by season, we can begin to see the whole pattern of their life."

The picture becomes more complete when position data are correlated with other information on ocean conditions, derived largely from satellite. Suddenly, it becomes possible to answer intriguing questions about not just where organisms go, but why they go there.

Graph shows sea turtle decline.
This graph shows crashing sea turtle populations on Costa Rica's most important nesting beaches, which are among the most important in the Pacific. The long-term nesting data from these beaches serves as an index for leatherback population trends throughout the Pacific. Courtesy Sea Turtle Restoration Project

The sea looks "featureless and trackless," says Elliot Norse, president of the Marine Conservation Biology Institute, but the new data show that "the ocean is anything but homogenous. The big organisms, the big fish, the billfish [swordfish and sailfish], the tuna, pelagic [open-water] sharks, the marine mammals, the great wandering birds, like albatrosses, key in on certain features in the oceans ...where masses of water come together and create conditions they especially like. They commute among these places, behave almost as if they are on highways in the sea."

Norse hopes the new information will be used to design temporary reserves, where endangered organisms would be protected -- but only when they need protection. Industrial fishing fleets, he says, have pushed one prized prey after another to the vanishing point.

Ready to track turtles across the open sea?

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Terry Devitt, editor; Sarah Goforth, project assistant; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

©2004, University of Wisconsin, Board of Regents.