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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    Sea Turtle News o' the day – Global warming edition

    Byoliveridley

    ScienceDaily: Scientists Warn Of Climate Change Risk To Marine Turtles

    North American marine turtles are at risk if global warming occurs at predicted levels, according to scientists from the University of Exeter. An increase in temperatures of just one degree Celsius could completely eliminate the birth of male turtles from some beaches. A rise of three degrees Celsius would lead to extreme levels of infant mortality and declines in nesting beaches across the USA.

    Here’s the paper.

    Like a lot of other reptiles, the sex of the hatchling is dependent on nest temperature. Warmer temperatures make female turtles (my mnemonic was hot females!), and even warmer temperatures just kill the eggs. But, I wonder if the turtles would adapt by nesting a little earlier. I don’t think it is yet clear when turtles decide to nest. If it is based on sea temperature, then they would eventually figure it out. This paper from 2004 appears to conclude that loggerheads in Florida do nest earlier than before, so there is hope.

    John F. Weishampel, Dean A. Bagley, Llewellyn M. Ehrhart (2004) Earlier nesting by loggerhead sea turtles following sea surface warming Global Change Biology 10 (8), 1424–1427

    The onset of spring, noted by the timing of wildlife migratory and breeding behaviors, has been occurring earlier over the past few decades. Here, we examine 15 years of loggerhead sea turtle, Caretta caretta, nesting patterns along a 40.5 km beach on Florida’s Atlantic coast. This small section of beach is considered to be the most important nesting area for this threatened species in the western hemisphere. From 1989 to 2003, the annual number of nests fluctuated between 13 000 and 25 000 without a conspicuous trend; however, based on a regression analysis, the median nesting date became earlier by roughly 10 days. The Julian day of median nesting was significantly correlated with near-shore, May sea surface temperatures that warmed an average of 0.8°C over this period. This marine example from warm temperate/subtropical waters represents another response of nature to recent climate trends.

    So the truth lies somewhere between easy adaptation and giant swarms of frustrated female turtles!

  • Casuarina plantations and the Olive Ridley

    Byoliveridley

    The Students’ Sea Turtle Conservation Network was featured in the Hindu today.

    Sea turtle lovers are concerned at the disturbance caused to turtle nesting habitats along the Tamil Nadu coastline, where casuarinas have been raised by the State Forest Department.The sea turtle’s egg-laying season began a month ago. Volunteers of the Chennai-based Students’ Sea Turtle Conservation Network (SSTCN) had written to the World Bank stating that the Forest Department should reverse the damage done.The SSTCN also wanted the Bank to provide funds for taking up transplantation work.Akila Balu, co-ordinator, SSTCN, said after the tsunami, the World Bank funded an Emergency Tsunami Reconstruction Project (ETRP) in Tamil Nadu.Under this programme, the State Forest Department had taken up the work of raising casuarina plantations to act as a bio-shield on the coastline. The casuarina saplings were planted right up to the high-tide line. In the process, it eliminated large stretches of sea turtle nesting habitat.Department’s defenceA senior Forest Department official said casuarinas had not been raised all along the State coastline.Adequate space had been provided between each sapling through which the turtles could enter the sand and lay eggs.The ETRP is a conservation-oriented programme, and so far the department has not received any complaints that the casuarina plantation had affected egg-laying of the Olive Ridleys, the official said.“In most of the areas, the saplings are not touching the high-tide line. If we plant closer to the line, the saplings will not survive. On the whole, the plantation will surely not affect the egg-laying turtles,” the official added.

    The Hindu : Tamil Nadu / Chennai News : “Casuarina plantations affecting turtle nesting habitats”

    To find out more, visit the SSTCN website.

    cross-posted at the Students’ Sea Turtle Conservation Network

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  • Tuesdays with Turtles – Gahirmatha Arrribada Hatchings

    Byoliveridley

    In case I forgot to mention, the Olive Ridley arribada started during the 2nd week of February, so about 50 days later, here they are, the “millions” of hatchlings.

    The Hindu News Update Service

    Olive Ridley hatchlings emerge in Gahirmatha

    Kendrapara (Orissa), April 10. (PTI): Millions of tiny olive ridley sea turtle hatchlings are now emerging out of nests at the Gahirmatha beach in Orissa’s Kendrapara district, wildlife officials said on Monday.

    The eggs laid by thousands of adult females in the Nasi-2 and Babubali islands in the Gahirmatha marine sanctuary have began to hatch over the last two days, they said.

    Wildlife officials stationed at the nesting grounds were witness to the phenomenon, but tourists and researchers were not allowed into the unmanned territory close to the Wheeler’s island where a defence test range is located.

    India’s intermediate range nuclear-capable missile Agni III is likely to be test fired from there some time this week, defence sources said.

    You know what, the fact that this area is under close military supervision because of India’s grandiose missile dreams may not be sucha bad thing (sacrilege!!!). The area is under so much development pressure that even military operations are better than the alternative.

    For more about the Gahirmatha area, visit the official website. At this point in time, the Arribada is very tourist unfriendly, and there are few, if any volunteering opportunities. I will keep any eye open for changes

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  • Tuesdays with Turtles -Thursday Edition – Pacific Leatherbacks in Trouble

    Byoliveridley

    Personal Note
    I swear, this blog has gone to pot. Either I’ve been too busy at work (yes, that does not explain everything), or I have not been thinking enough. I started this blog so that when I saw something interesting, I would have to think a little bit, and gather some information to write about what I saw/read. Apparently, I don’t read/see any more (which is not true), I don’t think any more (possible), or I am too lazy to spend enough time thinking to throw a coherent blog post together.

    This has got to stop, and it stops right now!!
    End Personal Note
    Back to the topic on hand…

    The Pacific Leatherback is in serious trouble and is slated to go extinct soon.

    ENN News Network

    Experts at the Bellagio Sea Turtle Conservation Initiative have just concluded a conference to save the imperiled Pacific leatherback sea turtle from extinction. The International Union for the Conservation of Nature and Natural Resources (IUCN) has classified Pacific leatherbacks as critically endangered.

    The meeting convened an internationally diverse group of scientists, conservationists, economists, fund-raisers and policy makers. One focus was the development of immediate actions to boost hatchling production of the Western Pacific nesting populations by protecting nests from predation, beach erosion and human consumption on the beaches of Indonesia, Papua New Guinea, Solomon Islands, Vanuatu, Vietnam and Malaysia. Although there are still hundreds of turtles nesting, with 75 percent in one area on the north coast of Papua (Indonesia), researchers are concerned by new information indicating that the majority of nests laid are not producing hatchlings. Some simple procedures have been developed to improve hatch success, and applying these techniques now may ensure the populations are sustained in the future.

    Some radical measures have been suggested, including cloning. Well, highly unlikely. Jurassic Park horrors and ethical dilemmas aside, cloning reptiles ain’t so easy.

    What ails the Pacific Leatherback? Their numbers have dropped from 115000 reproductive females to less than 3000. This news release from a 2004 conference has more. But the usual suspects are destruction of nesting habitats, long line fishing, egg poaching, and to a more uncertain degree, climate change.

    It’s depressing, I’ve never seen a leatherback, I guess I need to get on the case and see one before they disappear for ever.

  • Tuesdays with Turtles – Archie Carr Edition

    Byoliveridley

    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.