Tuesdays with Turtles – Hiatus Edition

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!

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!

Where I shamelessly defer to the experts, just listen to the podcast from the folks at seaturtle.org and their blog, twist (this week in sea turtles).
This Week in Sea Turtles

Meanwhile, in the great turtle race, my pick billie’s back in first, chased by the Stephen Colburtle…

Great Turtle Race

Follow eleven turtles as they sprint from Costa Rica to near the Galapagos. Each of them has a corporate sponsor, and at 20 miles an hour, they will get there in a couple of weeks! I think Billie’s going to win, but the leatherback turtle is in bad shape, endangered due to poaching, adult mortality and habitat loss. They may be gone very soon.

Here’s the flickr page for the race, some beautiful pictures already.

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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Tags: SSTCN, Olive Ridley, Sea Turtles, Chennai