Tracking creatures through the trackless sea

 

1. Following fantastic fish

2. Turning turtle

3. To track, to conserve

250,000 loggerhead sea turtles get snagged in fishing gear each year, and 30 percent to 50 percent die. Could information on loggerhead movement reduce the toll to this endangered animal?

The tracks of two loggerhead sea turtles, released in September, 2002, against a map of sea surface temperature for February, 2003. Both turtles traveled along the edge of the Gulf Stream before spending months in eddies (large whirlpools). Turtle researchers are still getting data from #37200 as she heads back toward North Carolina, more than 500 days later. Graph: Catherine McClellan and Andrew Read, Duke University.

In these rich fishing grounds, American swordfishing boats face restrictions designed to prevent bycatch of sea turtles. Boats from other nations, however, fish here without restriction. Original map: NASA

See sea turtles!
Scuba diver watches turtle on sea floor.As with many large sea critters, the study of sea turtles suffers from the now-you-see-them, now-you-don't problem. After a turtle hatches on a beach, it may not be seen by humans until it returns 10 to 30 years later to lay its own eggs. A male turtle may never reappear, even if it survives what some researchers call the "gauntlet of hooks" in the deep ocean.

An admiring diver ogles a loggerhead sea turtle. Loggerheads have a suicidal tendency to swallow hooks set for tuna and swordfish. As new electronic tagging projects answer questions about the movement of loggerheads and other long-distance swimmers, could they help preserve vanishing marine creatures? Photo: NOAA.

In the meantime, a sea turtle may migrate half-way across the ocean, or get hooked or netted.

Those lines and nets cause a lot of death. Larry Crowder, professor of marine biology at Duke University, estimates that 250,000 loggerheads get caught in fishing gear each year, and 30 percent to 50 percent die. Number-crunching, he says, suggests "the Pacific loggerhead has a 50 percent chance of extinction in two generations," and that a similar fate awaits Pacific leatherbacks, about 60,000 of which get snagged each year.

So what if these turtles go extinct? Consider that the leatherback:

hung out with dinosaurs (the turtle's evolutionary history stretches back 100-million years).

holds the sea-turtle deep diving record, more than one-half mile.

is the only sea turtle without a hard shell.

is warmer than the average reptile. "They aren't cold blooded in the sense that most reptiles are," Crowder says. "Because of their activity level and size, the temperature runs higher than background."

Tracks run from North Carolina to Europe. One comes partway back.

Conservation conundrum
As marine biologists learn more about the movement of endangered and threatened ocean species, they are finding a predictable overlap with marketable species. Predators, not surprisingly, concentrate near prey, making it tough to sort plate-bound predators from endangered ones.

In the Atlantic, for example, loggerhead turtles move northeast from the Carolinas along the Gulf Stream, toward the once-plentiful fisheries south and east of Nova Scotia. Here, at the junction between the warm Gulf Stream and colder, southbound currents, nutrient-rich bottom water feeds blooms of plankton, starting a rich food chain that attracts many large predators. The edge of the Gulf Stream, turtle-tracker Andrew Read says, "is extraordinarily rich with many large pelagic [open-ocean] organisms, swordfish, tuna, sea turtles and marine mammals."

map of north america pinpoints Geoges and Grand Banks between Cape Cod and Newfoundland

For centuries, fishermen have fished such hotspots as the Flemish Cap, the Grand Banks, and Georges Bank, and that has played havoc with the population of such large predators as tuna and sea turtles. The population crash of sea turtles, says Read, has impacted the American (but not international) swordfishing industry. "The Grand Banks was extremely important for sea turtles, and it was closed to American swordfishermen because of bycatch of sea turtle."

Array of tagging instruments.
A: A pop-up satellite archival tag on a pole used to attach it to a fish. Pop-up tags release from the animal, pop to the surface, and send stored data to a satellite.
B: Two small archival tags.
C: A pop-up satellite tag rigged to a shark harness.
D: Small plastic tags, once the mainstay of fish tagging, are still handy for some research.

Photo: NOAA.

Could technology come to the rescue? Already, shrimp boats in the Gulf of Mexico use turtle-excluder devices to prevent sea turtles from drowning in their nets. Knowledge of turtle behavior derived from satellite tagging could spawn other techniques for sparing sea turtles. For example, it's now known that sea turtles spend 90 percent of their time in the top 40 meters of water. If fish hooks are placed below that level, turtle bycatch should decline.

Could the new understanding also hatch a revolutionary conservation technique?

backmore
The Why Files (home)

There are 1 2 3 pages in this feature.
Bibliography | Credits | Feedback | Search

©2004, University of Wisconsin, Board of Regents.