12.07.2014

The Brutality of Nature

If there is intelligent design in nature, sea turtles are not it.

Tonight I watched female sea turtles on Heron Island haul their huge bodies up the beach, dig a huge hole (nest), lay eggs in it, and return to the sea, a process that takes upwards of three hours.

I learned from available literature on the island and a cute naturalist named Kate I met on the beach while turtle gazing that sea turtles will often lay over 100 eggs in these nests. They incubate for a few weeks and then some significant proportion, but not all, of these eggs hatch.

The hatchlings burrow out of the sand in the nest and make a run for the beach, a perilous and often lethal race. All but a tiny few, maybe three or four hatchlings, die. They are eaten by beach predators like birds and crabs, and by reef predators like big fish and sharks.

I feel kind of bad for the sea turtle mom. She herself won the evolutionary lottery (yea!), but it took her 20 years to reach sexual maturity and mate. She then instinctually returns to the same beach where she was born to lay her eggs. That actually makes a bit of Darwinian sense. From the mom's perspective, that beach resulted in at least one survivor hatchling (herself) in the past (though a lot can change in 20 years). By the time she lays her eggs, she is one bulky momma. These are not small beasties.

On Heron Island, most areas of the beach slope upward pretty substantially. While these turtles are designed for ocean swimming and do so gracefully, they are poorly designed for land. The mother propels herself over shoreline rocks and beach sands with her flippers and it looks like tiring work. She will typically do three or four strokes of her flippers at a time, moving perhaps a meter before she "sighs" (exhales) and takes a long rest. It can take a good 15 minutes or so for her to reach her nesting spot. Another hour or more is spent digging and laying the eggs. Then she sweeps the nest with sand for a while to putatively "camouflage" her work and she returns to the sea.

A weird thing happened with the turtle I saw when I was hanging out with Kate the naturalist. She got done laying eggs (the turtle...not Kate), and started to head back to the sea, but after she was about half way back down the beach, she seemed to have second thoughts when she hit the rock boundary with the sand.

She did an about face and climbed back up the beach even beyond the point of her first nest, presumably to fill a second nest with eggs. By then Kate was gone, so I could not ask her why a turtle might do this, or if it is common. It was late, so I left at that point.

The point is, it looks like hard work. But 160 million years of natural selection don't lie. It works for these turtles. They are pretty awesome.

Earlier in the day, I had seen a sea turtle while snorkeling and swam with it for a few seconds. That was cool.

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