DIVE LOG Australasia

Judging by the fact that some turtles reach adulthood fairly intact, the defensive armour must be very effective. Although, most do fall to predation especially when young; some adults carry war wounds. Newly hatched turtles have very soft leathery shells. Most are eaten whole by seagulls; Ghost crabs nab new borns on the beach or predatory fish gulp them down in the water. Turtles shells are more hydrodynamic than tortoises. The shell is designed for swimming; streamlining reduces water resistance and saves energy. The carapace is flatter and has a specially adapted hydrodynamic shape. I suspect that the shape of the turtle shell is a perfectly designed masterpiece of engineering; a gift from Mother Nature to enable great ocean swims that many undertake. They have a much shorter neck and they cannot pull their head in like tortoises can. Nostrils or nares are fully closed under the water to avoid water entering the respiratory system. BASIC PHYSIOLOGY They are a reptile and are Cold blooded or more accurately, ectothermic. ‘Ecto’ means external and ‘thermic’ means heat. They take on the same temperature as the water, having little control over their body temperature other than by behavioural means. The three chamber reptilian heart includes two atria and one ventricle which is a reptilian feature. Some turtles can tolerate extremely high levels of Lactic Acid that would be lethal for many other animals. Research into the shell suggests that chemicals are released to neutralized excess lactic acid. Salt balance is controlled using their Tear Ducts or Lachrymal glands. These excrete excess salt as well as

This juvenile Hawkesbill turtle Eretmochelys imbricata from Walindi PNG is resting on a soft coral.

urea. They have a good sense of smell and they can hear low frequency sounds. BREATHING REFLEX They can slow down their heartbeat when they dive deep. In addition, they can change to a much slower rate of oxygen consumption. They deal with cold water by swimming to warmer water or by going into a partial hibernation. In this sleeping state, they can rest for up to seven hours on one breath.

The very famous Digger from the Febrina could bring turtles to you at will. He was often described as ‘the world’s best dive guide’.

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DIVE LOG Australasia #408 - October ‘24

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