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Wednesday, Aug. 13, 2008
As 'canaries of the oceans,' sea turtles' demise is their habitat's, too
By ROWAN HOOPER
It's often said what a privilege it is to attend a birth, and so it was in July that I felt lucky to witness the moments after the birth — by hatching — of a Green Turtle.
I'd been enjoying the simple pleasure of a moonlight stroll along a beach on the Pacific coast of Costa Rica in Central America, when my girlfriend spotted something scurrying in the sand. I turned on the flashlight. It was a tiny turtle, which must have just hatched and was hefting itself down the sand to the sea.
I turned off the flashlight, because turtle hatchlings orient themselves by the reflection of moonlight on the sea. We followed the turtle as it struggled to the surf — and as soon as the first wave washed over it, it swam fast and easy. Only then did we notice dozens of tiny flipper-print tracks leading down to the ocean: We must have just caught the last of a mass hatching.
The next day, out at sea, we saw that other critical part of the turtle life cycle: mating. A female was literally being ridden by a male, who was gripping her with his flippers. She was swimming for the both of them, while both were being pestered by a second male attempting to bite the flippers of the first male and dislodge him.
But back to the moonlit beach. It was amazing to think that this same beach might have been used by turtles for millions of years — and it was a worry to think what the lights from the new hotels being built just behind it will do to their orientation. Even shining my flashlight had made the newborn reptile turn and start heading up the beach, away from the sea.
With luck, it made it into the deeper ocean, and has so far escaped predation by hungry fish and sharks and seals. If "our" turtle (as we thought of it) is really lucky, it will also avoid being "harvested" by Nicaraguan fishermen, who take an estimated 11,000 Green Turtles a year for local consumption. The "local consumption" bit gets around the fact that international trade in Green Turtles is banned under CITES — the Convention on International Trade in Endangered Species.
Green Turtles are the only herbivorous sea turtles, and they cover great distances to feed on sea grass in Nicaragua. Although the turtles are protected in Costa Rican waters, they aren't once they cross into neighboring Nicaragua to the north.
Marine biologist Cathi Campbell, of the New York, Bronx Zoo-based Wildlife Conservation Society tagged turtles in Nicaragua and found that they have only little more than a 50 percent chance of surviving until the next year. Nicaraguan turtle-fishing is unregulated and unsustainable, she says, and the practice must stop.
"Green Turtles cannot take this relentless pounding by the Nicaraguan sea-turtle fishing industry," said Campbell. "Drastic reductions are needed in fishing levels, or both the turtles — and turtle fishers — will vanish within a matter of years."
That same warning applies equally to the Leatherback Turtle, which also breeds on Pacific beaches in Costa Rica. At up to 5 meters long, it's the largest reptile in the world. In their case it is accidental catching rather than deliberate fishing that is doing them in — their numbers have crashed by over 90 percent in the last 20 years.
The turtles get tangled in fishing nets, and drown. Or they get hooked by their flippers to longlines set to catch Bigeye and Yellowfin tuna. When they are reeled in, the fishermen often chop off the flipper and leave the turtle to bleed to death in the sea, rather than attempt the troublesome task of freeing the hook first. They don't want to cut the line, as they will lose their valuable hook.
Leatherbacks, if they avoid dangers such as these, then embark on an epic migration that has been going on for millions of years, and which until recently was shrouded in mystery.
Leaving Playa Grande beach in Costa Rica, a female having laid her eggs will head out across the ocean, past the Galapagos Islands and across the Equator into the South Pacific. Biologists have this year figured out how the migration takes place, in the hope that knowing the details could save the remaining turtles.
"Given that the turtles seem to move in a predictable way from the nesting beach through the equatorial region from roughly February through April, we could potentially suspend fishing in certain areas while the Leatherbacks are passing through that part of the eastern Pacific," said George Shillinger, a marine biologist at Stanford University's Hopkins Marine Station.
Shillinger is part of a team of biologists and oceanographers from more than 80 nations engaged in a 10-year scientific initiative to assess and explain the diversity, distribution and abundance of life in the oceans.
"I wouldn't write these turtles off. If we can inform and change fisheries practices with sound science and policy, then hopefully there will be a chance to conserve turtles and the ecosystems that they occupy," Shillinger said. "These turtles could be a really awesome flagship for conservation."
Sea turtles are often called the "canaries of the oceans," since — like the canary in the coal mine — they act as indicators of trouble. If the canaries die, it's definitely time to act — and turtles have been dying in large numbers for years now.
The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is "Hito wa Ima mo Shinka Shiteru (The Evolving Human: How New Biology Explains Your Journey Through Life)."