409 Dive Log Australasia December 24

Notice the 9:2 dimensions on this very fat, pregnant female Bull shark

I have had the good fortune to swim with several types of whales. The 13.5 metre Southern Right whale I swam with had a diameter of 3 metres. I did not have my tape measure out but I could see that its enormous girth was about 3 metres. It is also true for big fish. Next time you see a big Dog Tooth tuna, notice its dimensions. The best shape Mother Nature could provide for these sleek underwater bullets is right there before your eyes. Some creatures have deliberately evolved a different shape suited to specific lifestyles. The short, round body of Porcupine fish is two to one and one to one when it ‘balls up’. It relies on its spines for defence and has sacrificed

the use of speed in the water. Moray eels have chosen a long shape of roughly 10 to one which suits their hunting lifestyle. Objects moving forward in the water create pressure waves. Energy is lost to the water. Fish and sharks have a lateral line which detects these vibrations in the water. If you try to grab a fish underwater, the very act of moving your hand creates a strong pressure wave. The fish is alerted long before your hand is anywhere near it and escapes easily. Pressure waves are energy. Humans are poorly designed for water movement. My head is a round block shape.

This Grey Nurse shark is banking to avoid collision with the photographer. (thankfully)

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DIVE LOG Australasia #409 - December ‘24

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