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I wrote a little bit about the red crabs in my last post so this seems like a good time to post couple of photos related to the same topic. I think I mentioned that we did not travel for the main crab migration but we did see the baby crabs returning to shore and that is what I wanted to show you today. These are two different perspectives taken of the same path where millions of baby crabs were making their way from the sea back onto the island. The babies were about as big as a fingernail (maybe even smaller) and the leaf that you see prominently in both photos was about fifteen centimetres long. I hope that can help you to visualise the scale of this phenomenon.
The main red crab migration starts with the first rainfall of the wet season, usually in October or November. The exact timing and speed of the migration is determined by the phase of the moon. Red crabs always spawn before dawn on a receding high-tide during the last quarter of the moon. Red crabs all over the island leave their homes at the same time and start marching towards the ocean to mate and spawn. Male crabs lead the migration and are joined by females along the way. When the moon reaches its last quarter, the females will go out to sea to release their eggs in the water.
About a month afterwards babies start to emerge back onto the shores. However, the vast majority of larvae never make it out of the water. Instead they are eaten by fish, manta rays, and the enormous whale sharks that visit Christmas Island to take advantage of this annual feast. Most years, no or very few baby crabs will emerge from the sea at all. But once or twice a decade, a huge number will survive, which is enough to maintain the island’s large red crab population. For the first three years of their lives, babies will hide in rocky crevices and amongst the forest floor debris until they grow large enough to relatively safely venture outside. I think we must have encountered one of the large number events as we saw many many baby crabs in different parts of the island. There was a number of road closures in place as well to protect the tiny ones to ensure that they make it safely to their new homes.
I hope you find the photos and the description interesting. It is also an opportunity for me to post something different. I quoted the Christmas Island National Park website for the above information.
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