DIVE LOG Australasia

These female Port Jackson sharks have swum for hundreds of kilometres for the annual mating aggregation off Sydney.

The mating behaviour of what is probably one of the most successful life forms on the planet in terms of evolution after the Crocodile and the Turtles remains a mystery! Port Jackson sharks have remained virtually unchanged for tens of million of years. For an evolutionary biologist, this means that whatever environmental pressures that Port Jackson shark face, they have survived without the need to change and adapt. They are so well adapted that they have reached a pinnacle of perfection! No need to change and little environmental pressure. The humble Port Jackson shark is the ‘ideal’ in terms of its survival skills and its ability to find food and deal with predators. Do not be fooled by its low intelligence

and slow behaviour. They have been perfected in nature’s great scheme of life tens of millions of years ago and do not need any improvements for their lifestyle. HOW DO SHARKS MATE? As with all sharks and Rays, reproduction is strictly internal. Male sharks have a pair of intro-mittent organs called claspers. These are modified pelvic fins. The inner edge has developed a tubular structure and is able to transfer a sperm packet inside the female’s cloaca during intercourse. Claspers are not penises. The do not have any erectile tissue. Instead, they stand at right angles for copulation.

The tip of the clasper unfolds to reveal clasper spurs which help to prevent the clasper from coming out during intercourse. Water is a spermicide and has to be prevented from entering the cloaca so it does not destroy the sperm. x Here is an interesting point for you to consider. Shark skin is made of denticles and is used as sandpaper by some South Pacific Islanders. I have had a close look at shark’s claspers, usually when a wobbegong has its head stuck in a crevice and it cannot turn around. The Ornate Wobbegong seems to have rough shark skin on the lower half of its clasper along its entire

Female Leopard shark lays eggs which hatches after 28 to 30 weeks.

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DIVE LOG Australasia #408 - October ‘24

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