Tuesdays with Turtles – Navigation

Byoliveridley

If you did not know already, sea turtles tend to nest on (or close to) the beaches they were born at. It is known that they use the Earth’s magnetic fields to navigate. Here’s an article on the navigational natations (I strain to alliterate at times, but natation means swimming!) of the Green Turtle.

ScienceDaily: How Do Marine Turtles Return To The Same Beach To Lay Their Eggs?

I flagged this article not because it tells us much new, but just adds some nuances to sea turtle navigation.

The study has shown that the marine turtles’ navigation system allows them to maintain their course towards the egg-laying site wherever they find themselves. It is almost as if they were equipped with a compass pointing towards the beach in question. So they can correct any deflection they are subject to: transport by boat, ocean currents… But, unlike human navigators, they are not able to correct for ocean drift in plotting their course. So the movements recorded by the satellite are a combination of deliberate action by the turtles and the effect of currents. So it appears that the turtles’ navigation system is relatively simple and may cause them to be wander at sea for long periods during adverse ocean conditions. One turtle released 250 km from its egg-laying site on Europa traveled more than 3 500 km in two months before returning there!

Well, that’s interesting, if not surprising. It’s one thing to have a magnetic bookmark of a destination in your head (pretty wonderful thing, I wish I had it!) and swim continually towards this destination. It’s quite another thing to keep track of complex parameters like ocean drift and keep correcting continuously.

In essence, what they’re saying is that turtles home in on their destinations, but don’t always take the shortest way in because they tend to drift and not correct for this drift dynamically. It is not evolutionarily necessary because turtles probably do not get thrown way of course often enough that evolving even more sophisticated navigational systems (Garmin?) would provide a significant enough survival advantage.

In the Mozambique Channel, between the east coast of Africa and Madagascar, on the beaches of the French Islands of Europa and Mayotte, they caught turtles at the beginning of their egg-laying cycle, so that the animals were strongly impelled to return to this area to complete their cycle. After having Argos transmitters fitted to their shells in order to satellite track their return journey to the beach, the animals were released in open sea, several hundred kilometers from the egg-laying site.

Now that’s just mean! Imagine being kidnapped, tagged and released many miles away from home, and having to find your way back. Apparently, these turtles did it. Man, that would be such a cool navigational aid to have, quite a party trick!

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    Where I’m a day late and a dollar short. It turns out that the Mediterranean sea is awash with plastic and most of the loggerheads there have swallowed plastic bags. So, the next time you’re out looking for loggerhead nests and find one in which all the eggs have been double bagged, do not be surprised! Now. if they start swallowing egg cartons…

    Mediterranean drowning in a hidden sea of plastic rubbish – Independent Online Edition > Europe

    A recent study of the endangered loggerhead turtle off Spain’s Mediterranean coast found that 75 per cent of them had swallowed plastic bags. Mr Rodriguez said: “We have to understand the sea is not a tip; it will constantly return to us what we throw in.”

    Seriously, plastic bags need to go away.

  • Tuesdays with Turtles – Green Turtles Deluged?

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    I mentioned recently that elevated temperatures from climate could skew sea turtle sex ratios towards females. The featured news article highlights research which speculates that storm surges caused by increased hurricane (they call them cyclones in Austraila and India) intensity from climate change might lead to the flooding of green turtle nests in Florida, hastening their extinction. Why only the greens? Because they nest later than the other turtles and tend to be around during the height of the Atlantic hurricane season.

    We know from previous research that loggerhead turtles have been nesting earlier because of elevated temperatures. Will the greens catch up. More pertinently, will there be enough survival of the early nesters of this generation to keep a viable population going while the whole population adapts? As with all climate change suspense thrillers, only time will tell… Depressing, at any rate.

    News in Science – Cyclones may blast turtles to extinction – 15/05/2007

    More severe tropical cyclones expected as a result of climate change may lead to the extinction of the green sea turtle in some areas within 100 years, researchers say.

    The cyclones are expected to threaten how well the turtles nest and hatch eggs, placing pressure on already endangered populations, some of which are also threatened by fish trawling.

    Researchers including PhD candidate David Pike, from the School of Biological Sciences at the University of Sydney, report their findings online in the journal Oecologia.

    The researchers studied more than 40,000 sea turtles nests on an uninhabited, 38 kilometre stretch of beach along the Atlantic coast of Florida from 1995 to the end of 2005.

    Each night during this period researchers surveyed the beach for turtles emerging to lay eggs, or for tracks of turtles that had already deposited eggs.

    The stretch of beach is home to the loggerhead, green, and leatherback sea turtles, which start nesting at the beginning in April and end in late September.

    This nesting season largely coincides with region’s tropical storm season, which runs from June to November.

    Leatherback turtles (Dermochelys coriacea) and, to a lesser degree, loggerhead turtles (Caretta caretta) get around this by nesting and hatching earlier.

    Only nests laid late in the season are inundated with seawater during storm surges.

    But green turtles (Chelonia mydas) nest last.

    Their entire nesting season occurs during Florida’s tropical cyclone season, which means their nests and developing eggs are extremely vulnerable to being washed away and killed.

    Researchers are concerned that increases in the severity of tropical cyclones in the future may cause green turtle nesting success to worsen.

  • Tuesdays with Turtles – Archie Carr Edition

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    Archie Carr is considered the father of modern sea turtle research. And now, there’s a book about him about to come out. It’s called “The Man who Saved Sea Turtles”.

    Well, I guess saved is going a little too far. I would have said “postponed the extinction of”, given the imminent extinction of the Pacific leatherback. But hey, forget about the title, I am sure it’s going to be a good book to read.

    Oxford University Press: The Man Who Saved Sea Turtles: Frederick R. Davis

    Archie Carr, one of the greatest biologists of the twentieth century, played a leading part in finding a new and critical role for natural history and systematics in a post-1950s world dominated by the glamorous science of molecular biology. With the rise of molecular biology came a growing popular awareness of species extinction. Carr championed endangered sea turtles, and his work reflects major shifts in the study of ecology and evolution. A gifted nature writer, his books on the natural history of sea turtles and their habitats in Florida, the Caribbean, and Africa entertained and educated a wide audience. Carr’s conservation ethic grew from his field work as well as his friendships with the fishermen who supplied him with many of the stories he retold so engagingly. With Archie Carr as the focus, The Man Who Saved Sea Turtles explores the evolution of the naturalist tradition, biology, and conservation during the twentieth century.

  • Robot sea turtles for ocean Safety

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    I have only one question: Will these cute robot turtles come up to shore every year to lay eggs that will turn into cute little robot turtle hatchlings?

    I have to remind myself sometimes that this blog is named after a sea turtle and that my turtle overlords demand a post or two once in a while that propitiates them.

    Robotic sea turtles, on the other hand, can do all sorts of things. They can find out where a pipeline or a ship hull is damaged. Or the extent of an oil spill, or locate bodies in the wake of a disaster.

    via Robot sea turtles could help keep the ocean safe and clean | Grist.

  • Sea Turtle News of the day, genocide edition

    Byoliveridley

    Depressing as always, but this is a yearly headline around turtle nesting season.

    1,000 Giant Turtles Wash Ashore in India, Bangladesh

    It’s nesting season for the sea turtles of Bangladesh and India, but this year the beaches where the animals lay their eggs are eerily still.

    Nearly a thousand dead turtles have washed ashore along the coasts of both countries in the past few weeks, conservation workers report.

    About 200 dead reptiles have appeared in the past week alone along a single stretch of beach, pictured here, in the Bangladeshi tourist town of Cox’s Bazar (see Bangladesh map).

    A team of scientists visiting the beach on Monday to investigate the mysterious mass deaths concluded that fishing nets were to blame.

    Sea turtles swarming the shores to nest are getting entangled in poorly laid nets and drowning, the experts told Bangladesh’s Financial Express.

    The survival rate of turtle hatchlings is estimated at anywhere between 0.1 and 1%. Assuming 0.5%, this represents 20000 hatchlings. Assuming a hatching success (not all eggs hatch successfully) of about 2/3rds, that is 30,000 eggs, or between 200-250 nests. In my two years of turtle conservation work on an approximately 3 mile stretch of beach, we relocated about a 100 nests. These aren’t the same turtles (they tend to come back to nest very close to where they hatched), but there’s my two seasons of work down the drain and then some!

    Turtle safe fishing is a well researched technology and is not expensive. As I have mentioned before in a similar context, the gaps between the availability of a certain technology and its actual adoption and use are depressingly huge.

    When it comes to serious problems like global warming, all the talk is going to be about the cool science and innovative solutions, but how the technology transfers to India and China, how it is implemented, and the nature of the interactions between the traditional powers and the emerging ones is going to be more critical than the science. Something to remember as a scientist!