January 24, 2011

Circle of Life.

Recently, we had the incredible opportunity to watch a man-influenced miracle of nature. The birth of 76 green turtles on South Beach in Dar es Salaam.

This story begins a very, very long time ago. During the Cretaceous period between 135 – 70 million years ago, also known as the Age of Reptiles, the class Reptilia dominated the land and the sea. Today, only a few species of reptiles live in the sea, including snakes, crocodiles and turtles. All reptiles are cold-blooded and gain their heat from the sun, making the tropics a far more habitable and likely home for them.

Now here is where this story gets a little X-rated. Copulation takes place in the water, with the male mounting onto the female, gripping on to her shoulders with his front flippers, securing her posterior with his long tail. This position may last for over an hour during which time the female is the only one of the two who can actively swim and, from time to time, must carry both up to the surface to breathe. Occasionally, up to five males may climb on top of one female, although one the male on the bottom of the stack is actively mating. There is strength in numbers, I suppose.

A few weeks after mating, the female crawls up a sandy beach and digs a nest, into which she lays a clutch of eggs. Eggs are white, roundish, and smaller than a chicken's egg with a soft, leathery shell. The female excavates the nest with hind flippers, and covers the clutch with sand before returning to the sea. Some reptiles offer parental protection to the eggs and offspring, however turtles abandon their eggs once laid. This, of course, makes them highly vulnerable.

And here is where our involvement in this story begins. Between crawling out of the nest and reaching the sea, turtle hatchlings are vulnerable to predators such as birds and ghost crabs, as well as man. Once in the sea, turtles immediately aim for open waters, but even at sea most are eaten by fish and very few will survive. Only those that reach maturity (about 5% of any given hatch), which takes up to 30 years, return to land and complete their life cycle. Sea turtles have been exploited by man for thousands of years. Parts have been used to make combs and decorative ornaments. The eggs of turtles are a favorite food item, as is the flesh of adults. All turtle species are on the endangered species list, thus no international trade of turtles of their products is permitted. 

Given their precariously low survival rates, a local NGO - Sea Sense - conducts conservation activities (including paying local fishermen a small sum to identify and protect the clutch of eggs immediately after the female returns to the beach) to ensure that most of the sea turtles make it to the sea once they hatch, under normal circumstances 60% of the hatch would be eaten by predators on the beach. We ushered 100% of this hatch to safety, for the time being anyway...

Interestingly, the temperature of the nest determines the sex of the hatchlings. For example, in the nests of the green turtle, temperature above 27C result in females. Oh, also, the green turtle gets its name from the thin layer of mucus like fat that is between its shell and its body.

The limbs of sea turtles are flattened and modified into flippers, which needless to say are well adapted for swimming. Man, these little guys swam like hell once they reached the water from their hatching site. It was truly a site to behold.

No comments:

Post a Comment