September 2011: Baby Turtles in Shimoda

I’m really disappointed at failing my attempt to dive once a month following the cancellation of my September dives.  I’d been looking forward to joining my dive group in the crystal clear waters of Hachijojima, 12 hours south of Tokyo by ferry, but when an approaching typhoon forced the group to call off the trip, I knew that the right decision had been made, and that it was not worth taking any risks in the path of an oncoming storm.  To ease my disappointment, I joined some friends on the island of Kozushima, about 8 hours south of Tokyo, where we camped, snorkeled and swam under excellent weather.  However, we ended up heading to the mainland on our second day after discovering that the typhoon was heading our way, and spent a night camping in a popular area called Shimoda full of good beaches.  While hanging out on the beach that night, we saw some baby turtles heading out to sea.

Knowing how rare it is to witness this by chance, we were really moved with what we saw, and as I can’t write about diving this month, I decided to go online and find out more about these turtles instead.

To break open their shells, the hatchlings use a caruncle or temporary egg tooth, an extension of the upper jaw that falls off soon after birth.  They then take about three to seven days to head up to the surface.  Once there, they make a complete circle around their nest before instinct drives them towards the water.  They start crawling to the sea towards the brightest horizon and can apparently set an internal magnetic compass which is used for navigation away from the beach.  As they reach the water, they dive into the waves and are carried out into deeper waters.  They settle themselves in areas with floating seaweed where they can be camouflaged and find food.  The currents then carry them for years unless they are eaten by predators. They spend their first few years growing and eating in nearshore areas.  Once they reach adulthood, they then head to a new feeding ground.  The males never leave the water once they enter, but the female makes the long trip back to her natal beach to lay her eggs.  It was nice knowing that the turtles we saw will eventually return to Shimoda!

Some other interesting facts:  The sex of baby turtles depends on temperature.  If eggs are incubated at less than 28 degrees, all the hatchlings turn out to be male.  If they are incubated at 35 degrees or warmer, they are all female.  Any temperature between 28 degrees and 35 degrees produces both males and females.  They are also said to detect the angle and intensity of the Earth’s magnetic field and determine latitude and longitude once out at sea.

Seeing them has more than made up for this month’s lack of dives!

About Rising Bubbles

Bonnie Waycott is a dive master and writer focusing on Japan's scuba diving and aquaculture. She is currently taking an MSc in Sustainable Aquaculture at the University of St Andrews via distance learning and is due to graduate in December 2017. Her written work has been featured in Asian Diver, Scuba Diver AustralAsia, DIVE, Marine Biologist, The Fish Site, Fish Farmer, Hatchery International and Outdoor Japan Traveler, while for Japanese divers she writes about marine-related issues abroad for Japanese diving website Ocean+α. You can follow Bonnie on Twitter (@risingbubbles), Facebook (https://www.facebook.com/RisingBubblesNotesOfANewDiver/) and Instagram (@bonniewaycott).
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2 Responses to September 2011: Baby Turtles in Shimoda

  1. lee says:

    I did not know that about the temperature! How funny! Thanks for sharing!

    Like

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