Tag Archives: sea turtle

Sea turtles are amazing navigators — but they only use crude maps

: A Green Turtle that was returning to sea, the morning after she laid her eggs on Ascension Island. They lay on average 120 eggs in a clutch and may lay 6 clutches in a season. Credit: Wikimedia Commons.

Sea turtles are migratory species from the moment they are ready to come into this world. After they’ve hatched out of their nesting grounds on the beaches of Florida, Yucatan, or other eastern coasts of the Americas, they immediately embark on a frenzied race towards the sea.

On their journeys, these younglings can end up traveling more than 10,000 miles across the entire North Atlantic, before returning to their original breeding grounds.

Clearly, sea turtles are amazing navigators, likely using the earth’s geomagnetic field to pinpoint their position and orientate. However, don’t imagine that their internal GPS is very accurate.

According to a new study, sea turtles often miss their mark, sometimes by hundreds of miles. This can add thousands of extra miles to their migrations as they take less straightforward paths to their destination. So, instead of Google Maps, think of the sea turtle’s positioning system more like a very crude map — it’s far from perfect, but it gets the job done.

“By satellite tracking turtles travelling to small, isolated oceanic islands, we show that turtles do not arrive at their targets with pinpoint accuracy,” says Graeme Hays of Australia’s Deakin University.

“While their navigation is not perfect, we showed that turtles can make course corrections in the open ocean when they are heading off-route. These findings support the suggestion, from previous laboratory work, that turtles use a crude true navigation system in the open ocean, possibly using the earth’s geomagnetic field.”

Hays and colleagues attached satellite tags to 33 nesting green turtles (Chelonia mydas). Originally, the researchers wanted to find out more about the extent of the animals’ movements in order to identify key areas for conservation efforts.

But as the researchers tracked the turtles, they noticed that they were traveling to isolated islands and submerged banks — and they did so rather awkwardly.

The turtles were tracked from the moment they left their nesting beaches on the island of Diego Garcia in the Indian Ocean, from which they embark on a journey towards their foraging grounds across the western Indian Ocean.

According to the satellite data, 28 out of 33 turtles didn’t reorient themselves daily or at a fine scale. As a result, the turtle would often travel hundreds of miles out of their way before correcting their course. This confusion most often occurred in the open ocean.

So, instead of reaching their small island destination with pinpoint accuracy, the turtles more often than not overshot their targets or wasted time searching for their favorite remote islands during the final stages of their migration.

“We were surprised that turtles had such difficulties in finding their way to small targets,” Hays says. “Often they swam well off course and sometimes they spent many weeks searching for isolated islands.

“We were also surprised at the distance that some turtles migrated. Six tracked turtles travelled more than 4,000 kilometers to the east African coast, from Mozambique in the south, to as far north as Somalia. So, these turtles complete round-trip migrations of more than 8,000 kilometers to and from their nesting beaches in the Chagos Archipelago.”

Although this study shows that highly accurate turtle navigation is a myth, the findings do not subtract from their impressive migrating abilities. After all, this is the first study that showed that sea turtles are capable of reorienting themselves in the open ocean, which implies they actually have a mental map of some sort.

The study also has important applications for sea turtle conservation. Once their nesting season is done, turtles travel extensively across the open ocean. As such, conservation efforts have to be coordinated across large spatial scales, covering many countries.

In the future, the researchers would like to employ novel tag technology that will enable them to not only determine their location but also the turtles’ compass heading.

“Then we can directly assess how ocean currents carry turtles off-course and gain further insight into the mechanisms that allow turtles to complete such prodigious feats of navigation,” Hays says.

The findings were reported in the journal Current Biology.

Sea turtles are attracted to the smell of plastic like it is food

Loggerhead turtles went to the water’s surface to sniff airborne odorants from biofouled plastic just as often as they did for the smell of their favorite food. Credit: Joseph Pfaller.

It has long been thought that sea turtles are attracted to plastic debris and ingest them because they mistake them for prey, such as jellyfish. But it actually seems to be a lot worse than that. A new study showed that the turtles are attracted to plastic debris not only by the way it looks, but by the way it smells too.

Literally junk food

Loggerhead turtles often ingest plastic debris such as handbags or bottle caps, causing them to become ill or stranded on the beach with their digestive system full or partially blocked.

In order to study the behavior of sea turtles around marine plastic debris, researchers at the University of North Carolina at Chapel Hill and the University of Florida compared how 15 young, captive-reared loggerheads (Caretta caretta) reacted to the odors of turtle food, ocean-soaked plastic, clean plastic, and deionized water.

According to the results of an experiment performed in a laboratory setting, the turtles ignored the scents of clean plastic and water. However, when exposed to the smell of food and soaked plastics, the turtles became attracted to the scents and began exhibiting foraging behaviors. This included poking their noses out of the water, a sign that they were trying to identify the food source. They also became more physically active as they searched for food.

Biofouled plastics build a coating of algae, plants, plankton, and microorganisms, which may explain why the turtles mistake them for food. However, the scientists were extremely surprised to find that the marine creatures responded to the odors of biofouled plastic with the same intensity as they would to the smell of fish and shrimp, their favorite food. Compared to water and clean plastic, the turtles kept their noses out of the water more than three times longer.

“We expected them to respond to both to a greater extent than the control treatments, but the turtles know the smell of their food since they’ve been smelling and eating it in captivity for 5 months. I expected their responses to food to be stronger,” Joseph Pfaller of the University of Florida, Gainesville said in a statement.

No turtle involved in the study was allowed to ingest plastic and were later released into the ocean after the research was over.

These findings help to explain why turtles, especially very young turtles that tend to swim closer to the surface than older turtles, are so affected by marine pollution.

“The plastic problem in the ocean is more complex than plastic bags that look like jellyfish or the errant straw stuck in a turtle’s nose,” Pfaller said. “These are important and troubling pieces to the puzzle, and all plastics pose dangers to turtles.”

Nearly all species of sea turtle are classified as Endangered, and plastic is doing more than its share of damage.

Globally it’s estimated that approximately 52% of all sea turtles have eaten plastic. In 2018, researchers at Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) estimated that 90% of juvenile green sea turtles off the coast of Brazil have ingested plastic. They also found that once a turtle had ingested 14 plastic itemts, there was a 50% likelihood that it would die.

According to a study undertaken by the World Economic Forum, the Ellen MacArthur Foundation, and McKinsey and Company, 32% of the 78 million tons of plastic packaging produced annually winds up in the ocean — that’s equivalent of pouring one garbage truck of plastic into the ocean every minute.

“In parts of the Pacific Ocean there are huge areas covered with floating plastic debris,” said Kenneth J. Lohmann, a professor of biology at the University of North Carolina. “One concern this study raises is that dense concentrations of plastics may make turtles – or other species – think the area is an abundant source of food. These areas may draw in marine mammals, fish and birds because the area smells like a good foraging ground. Once these plastics are in the ocean, we don’t have a good way to remove them or prevent them from smelling like food. The best thing we can do is to keep plastic from getting into the ocean at all.”

The findings appeared in the journal Current Biology.

Credit: Pixabay.

Just a few pieces of plastic are enough to kill sea turtles

Credit: Pixabay.

Credit: Pixabay.

Scientists estimate that more than half of all sea turtles have eaten plastic debris in some proportion. The rubbish, which was once in the hand of a human before it made its way into the world’s oceans, comes in all shapes and sizes, from microscopic pebbles to jellyfish-like undulating plastic bags.

A recently published study cataloged the damage done to sea turtles by plastic pollution. The findings suggest that just 14 pieces of plastic are enough to significantly increase the animals’ risk of death. If an animal had ingested more than 200 pieces of plastic, death was inevitable. In some cases, a single piece of plastic was deadly.

The international team of researchers wanted to investigate the inflection point where the ingested plastic reaches a lethal level. To this aim, they examined the necropsies of 246 sea turtles, as well as 706 records from a national stranding database relating to sea turtles in Queensland, Australia.

The researchers found that the animals that died for reasons unrelated to eating plastic had less plastic in their gut than sea turtles that died of unknown causes or direct ingestion of plastic.

The most vulnerable group are juveniles — half of which are expected to die if they ingest 17 pieces of plastic of more. A sea turtle typically lives to be 80 years old but a juvenile, which is too young to reproduce, can range from 20 to 30 years of age. The authors estimate that 90% of juvenile green sea turtles off the coast of Brazil have ingested plastic.

“Young small turtles actually drift and float with the ocean currents as does much of the buoyant, small lightweight plastic,” Dr. Britta Denise Hardesty from Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO), told BBC News.

“We think that small turtles are less selective in what they eat than large adults who eat sea grass and crustaceans, the young turtles are out in the oceanic area offshore and the older animals are feeding in closer to shore.”

It’s difficult to pin the cause of death of a turtle to plastic except for in cases where the damage is self-evident. However, the work quantifies the toll of plastic pollution on sea turtle health and provides a measurable yardstick for future research.

In one case, researchers found as many as 329 pieces of plastic in the gut of a sea turtle. On the opposite end, a deceased turtle was found with its digestive tract blocked by a single item — a soft piece of plastic. In another turtle, its intestines were perforated by a sharp plastic debris.

The authors of the study write that even though plastic might not kill all turtles, its presence will certainly weaken the animals by impending their normal digestion.

The next step in the research is to establish whether plastic pollution in the oceans is causing a population decline. In some places, the problem is worse than in others. For instance, the Mediterranean and the southern Atlantic Ocean are so riddled with debris that it’s almost impossible for turtles to avoid the debris.

More research will hopefully paint a clearer picture of the damage — done not just to sea turtles, but other animals as well. Previously, a study found plastic debris in the guts of 90% of seabirds.

The authors say that it’s possible to reduce plastic exposure by banning certain high-impact items, such as straws or coffee pods. 

The findings appeared in the journal Scientific Reports.

Sea turtles use magnetic fields to navigate the world

Turtles seem to “imprint” the magnetic field of the beach they were born, returning to it decades later to hatch the new generation. However, researchers report, this strategy sometimes tricks turtles into navigating to a beach that has a similar magnetic field to the one they were looking for.

Loggerhead sea turtles are a strange bunch. Facing an extremely dangerous beach run to the sea, and then daring the ocean on their own, they still somehow remember their birthplace, returning to it years and years later to lay their own eggs.

“Loggerhead sea turtles are fascinating creatures that begin their lives by migrating alone across the Atlantic Ocean and back. Eventually they return to nest on the beach where they hatched – or else, as it turns out, on a beach with a very similar magnetic field,” said Kenneth Lohmann, professor of biology in the College of Arts and Sciences at University of North Carolina (UNC).

UNC biologists Kenneth Lohmann and Roger Brothers already had some proof that adult loggerhead sea turtles use magnetic fields to find their way back to the beach where they themselves hatched. In a new study, the two scientists report that magnetic fields are the strongest predictor of genetic similarity among nesting loggerhead sea turtles, which adds new evidence to their magnetic imprint theory.

Traditionally, scientists have thought that animals that live close to each other are more likely to be similar genetically. This might also be the case because animals living in similar environments tend to develop similar adaptations. But for the loggerheads, proximity isn’t a predictor of genetical similarity — bug magnetic field is. In other words, turtles which lay eggs on a particular beach are more similar to other turtles which lay eggs on a beach with a similar magnetic field — even if that beach is much farther away, like on the opposite coast of Florida. Actually, researchers report, turtles sometimes mistake their beach for a different beach with a similar magnetic field.

Turtles aren’t the only ones to use magnetic fields to navigate across great distances, and researchers say this new finding could be extremely important for the conservation of these species.

“This is an important new insight into how sea turtles navigate during their long-distance migrations. It might have important applications for the conservation of sea turtles, as well as other migratory animals such as salmon, sharks and certain birds.”

Journal Reference: J. Roger Brothers, Kenneth J. Lohmann. Evidence that Magnetic Navigation and Geomagnetic Imprinting Shape Spatial Genetic Variation in Sea Turtles.