From Ed Yong:
In 1996, a loggerhead turtle called Adelita swam across 9,000 miles from Mexico to Japan, crossing the entire Pacific on her way. Wallace J. Nichols tracked this epic journey with a satellite tag. But Adelita herself had no such technology at her disposal. How did she steer a route across two oceans to find her destination?
Nathan Putman has the answer. By testing hatchling turtles in a special tank, he has found that they can use the Earth’s magnetic field as their own Global Positioning System (GPS). By sensing the field, they can work out both their latitude and longitude and head in the right direction.
By testing turtle hatchlings in a tank surrounded by magnets he could control, Putman showed turtles could sense it if he reversed the magnetic field around them and would begin heading in the opposite direction.
For more about the experiment—and how turtles can travel so far at such high stakes with just magnetism to guide them—check out the rest of Ed’s post at Not Exactly Rocket Science.
Not Exactly Rocket Science: Foxes use the Earth’s magnetic field as a targeting system
Not Exactly Rocket Science: Robins can literally see magnetic fields, but only if their vision is sharp
80beats: Did Earth’s Magnetic Field Have a Fast Flip-Flop?
Image: Wikimedia Commons
Leatherback turtles are the wandering type, undertaking far-flung ocean migrations of thousands of miles. What scientists who follow these long-lived creatures didn’t know, though, was just how many different routes they travel, and how far they journey before returning home. These are critical pieces of information for protecting the turtles, whose numbers are dropping. So Matthew Witt says he and his international team affixed trackers to the turtles and revealed the routes of their great sea voyages:
“What we’ve shown is that there are three clear migration routes as they head back to feeding grounds after breeding in Gabon, although the numbers adopting each strategy varied each year. We don’t know what influences that choice yet, but we do know these are truly remarkable journeys.” [The Guardian]
Gabon, in West Africa, is the home base for this largest breeding group of leatherbacks—it’s where they nest and lay their eggs. Witt’s team tracked 25 female turtles, all of whom followed one of those three general routes: out to the middle of the Atlantic and then back, down the African coast to the temperate South, or even all the way across the ocean to South America.
One female was tracked making a 7,563 kilometer (4,699 mile) journey traveling in a straight line across the South Atlantic from Africa to South America, said [Witt]. At a pace of 50 kilometers a day, that trip took about 150 days of consistent swimming, he said. [AP]
During the Pleistocene epoch animals thought big: It was the age of the megafauna, when creatures like the mammoth, an 8-foot-long beaver, and a hippopotamus-sized wombat walked the Earth. But these giants vanished one by one, and scientists have long wondered why.
Debate over what caused the megafauna to die out has raged for 150 years, since Darwin first spotted the remains of giant ground sloths in Chile. Possible causes have ranged from human influence to climate change in the past, even to a cataclysmic meteor strike. [BBC]
Now, a discovery on the South Pacific island nation of Vanuatu seems to have answered the question for at least one species. Researchers have turned up the bones of a giant land turtle in a dump used by the people who settled on the islands 3,000 years ago, and lead researcher Trevor Worthy says the evidence strongly suggests that the turtles were hunted into extinction.
In early July we brought you news of the Great Sea Turtle Relocation–an ambitious plan dreamed up by conservationists to scoop up some 70,000 sea turtle eggs from Gulf Coast beaches, to prevent the hatchlings from crawling straight into oil-fouled waters. The U.S. Fish and Wildlife Service noted that the plan carried considerable risks to the unborn turtles, but said it was the best chance of preventing the die-off an entire generation.
Now the update: Over the past week, the plan has gone into action, and baby turtles are now swimming free in the Atlantic Ocean. But some experts question whether the launched turtles have a chance.
On Alabama and Florida beaches workers are carefully digging up nests, marking the eggs with “this end up” symbols, and packing them in styrofoam coolers for the truck ride to a Kennedy Space Center warehouse. The eggs belong mostly to threatened loggerheads, along with some endangered green, leatherback, and Kemp’s ridley turtles.
Check out a photo gallery of the turtle rearing and release operations after the jump.
Things may be looking up, ever so slightly, for the Gulf of Mexico’s endangered sea turtles. A few days ago, environmental groups announced that they were suing BP and the Coast Guard over the “controlled burns” that were intended to burn off oil slicks in the water; the environmentalists said that sea turtles were getting caught in the infernos and burned alive. This morning a judge was prepared to hear arguments on a proposed injunction, but at the last minute the parties declared that they’ve reached a settlement.
The agreement comes in advance of an emergency court hearing set today in New Orleans federal court, where environmentalists sought to force BP to either stop controlled burns or place rescuers on the boats to scoop federally protected sea turtles out of floating sludge patches before the corralled oil is ignited [Bloomberg].
According to Sea Turtles Restoration Project, one of the plaintiffs in the case, BP and the Coast Guard have agreed to station a qualified biologist on every vessel involved in the burns, and to remove turtles from the burn area before setting the blaze. This is good news for the leatherbacks, loggerheads, and Kemps Ridley turtles that make their home in the Gulf. Of course, it would be better news if their home wasn’t saturated with oil and periodically set on fire, but we’ll take what we can get.
Elsewhere in turtle news, conservationists are preparing to collect 70,000 turtle eggs from Alabama and Florida beaches. The ambitious scheme, coordinated by the U.S. Fish and Wildlife Service, is seen as the best chance of preventing a massive die-off of the threatened creatures.
We already knew that great numbers of sea turtles are killed when they’re caught up in the nets used by fishing operations around the world. But according to a study in Conservation Letters, the actual number of turtles accidentally killed over the last two decades has been vastly underestimated: Rather than counting in tens of thousands, study author Bryan Wallace argues, commercial fishing has probably killed sea turtles in the millions.
The official records show about 85,000 turtles killed by fishing operations from 1990 to 2008. But Wallace, the science adviser for Conservation International’s sea turtle program, says that’s deceptively small accounting. “Because the reports we reviewed typically covered less than 1% of all fleets, with little or no information from small-scale fisheries around the world, we conservatively estimate that the true total is probably not in tens of thousands, but in the millions of turtles taken as bycatch in the past two decades,” said Dr Wallace [BBC News]. Six of the seven sea turtle species are presently listed as in danger. They include loggerheads, leatherbacks, hawksbills, Olive Ridleys, Kemp’s Ridleys and green sea turtles; the flatback, an endemic to Australia, is currently categorized as Data Deficient [CNN].
Of all vertebrate animals, turtles have one of the stranger body plans. Unlike all other four-limbed critters, which have their shoulder blades riding on the outside of their ribs, the turtle’s ribs are outside of its shoulder blades. This allows turtles to make their shell out of fused bones–the only animal to do so [ScienceNOW Daily News]. Now, scientists have determined that embryonic turtles develop this set-up through a neat bit of origami.
Researchers compared the developing embryos of turtles, chickens, and mice to watch for the point at which turtle development diverged. At first a turtle embryo grows much like a chicken or mouse. But then the developing body wall makes a critical fold, and the usual body plan starts to become an unusual turtle…. The developing muscle tissue that would lie along adult ribs in a standard amniote began to fold underneath itself in the turtle. This tissue tucked inward, bending up to lie below the developing ribs. On this kinked-under section, the shoulder blades, or scapulas, formed [Science News].
The surprising find of a freshwater, tropical turtle fossil in Arctic Canada suggests that the first turtles to migrate from Asia to North America may have taken the most direct route, swimming and island hopping straight through the Arctic Ocean. This was possible, researchers say, because the Arctic was warmer and ice-free 90 million years ago, when carbon dioxide levels were extraordinarily high. “The fossil record is giving us more and more information about how ancient animals responded to a warming world,” [says] geophysicist John Tarduno…. “They moved toward the poles” [Wired News].
The freshwater turtle was able to survive in the ocean, Tarduno says, because of a floating freshwater highway that led from Russia to Canada. Numerous rivers from the adjacent continents would have poured fresh water into the ancient Arctic sea…. Fresh water, which is lighter than marine water, may have rested on top of the salty ocean water allowing animals such as the turtle to migrate with relative ease [Telegraph].
The oceans are getting noisier, and that’s bad news for whales, dolphins, and sea turtles who use sound to communicate and navigate, researchers declared at a United Nations wildlife conference. Rumbling ship engines, seismic surveys by oil and gas companies, and intrusive military sonars are triggering an “acoustic fog and cacophony of sounds” underwater, scaring marine animals and affecting their behavior. “There is now evidence linking loud underwater noises with some major strandings of marine mammals, especially deep diving beaked whales” [Reuters], says Mark Simmonds of the Whale and Dolphin Conservation Society.
Researchers have long worried that high-powered sonar pulses confuse whales and dolphins and may cause the animals to beach themselves. Marine mammals are turning up on the world’s beaches with tissue damage similar to that found in divers suffering from decompression sickness. The condition, known as the bends, causes gas bubbles to form in the bloodstream upon surfacing too quickly. Scientists say the use of military sonar or seismic testing may have scared the animals into diving and surfacing beyond their physical limits, Simmonds said [AP]. He points to two recent strandings as possible results of the noisy waters (although a link has not been proved): the 100 melon-headed whales that were found on a Madagascar beach, and the two dozen dolphins that got stranded in southern England.
It’s a question that has fascinated scientists for decades: When sea turtles and salmon decides to give up the freedom of the open ocean and head back to their birthplaces to breed, how do they find their way back? Some species of sea turtle migrate thousands of miles across entire oceans back to their birthplaces after leaving more than 10 years earlier. And after hatching in rivers, salmon travel hundreds of miles out to sea before returning home to spawn years later [Press Association]. Now one researcher thinks he has the answer. Marine biologist Kenneth Lohmann believes that these marine animals can detect the distinctive magnetic fields of different spots and use them to navigate.
“What we’re proposing is the sea turtles and salmon, when they begin life, basically learn or imprint on the magnetic field that marks their home area,” he said. “They retain this information. And years later, when it is time for them to return, they are able to exploit this information in navigating back to their home area” [National Geographic News]. Lohman says this doesn’t contradict the existing theory that when salmon reach coastal waters, chemical scents guide them upriver to the particular stream where they were born; those olfactory cues probably have a limited range, he says, and couldn’t extend thousands of miles into the ocean to guide the salmon all the way home.