Port Jackson – A Family Secret
Ian travels to Jervis Bay, south of Sydney, for the Port Jackson shark breeding season where he hopes to clear up a long-held mystery surrounding their eggs. Do Port Jackson mums wedge their large, coil-shaped eggs into rock crevices to keep them safe? Ian plans to prove whether this scientific belief is true by spying on their underwater antics.
At about 3ft (0.9 metres) long the unusual looking Port Jackson is not the most dangerous shark in the ocean, but possibly one of the more fascinating.
Presenter Ian Gordon takes us to Jervis Bay Marine Park, on the New South Wales coast south of Sydney, for the Port Jackson shark breeding season where he hopes to clear up a mystery surrounding their eggs.
The unusually shaped eggs, known as ‘mermaid’s purses’, are protected inside springy coils. There is a widely held theory that Port Jackson mums wedge these eggs into rock crevices to keep them safe and secure.
Ian plans to find out if they do.
These harmless sharks are only found around Australia and spend the daytime resting on the sea bed, making them easy prey for Ian’s experiment.
He catches one and demonstrates the intense power of their jaws, designed to crush shellfish.
To determine whether these sharks are loyal to a home breeding ground Ian selects and tags a Flintstone foursome, Fred, Wilma, Barney and Betty, names well suited to the Port Jackson’s “prehistoric look”.
The Flintstones are taken from their home reef and released several miles (about 3 km) away.
Meanwhile, Ian dons special diving equipment for a long underwater wait to watch for female behaviour around the masses of eggs on the sea bed.
Scientists suspect male Port Jacksons hanging around the eggs may actually eat some of them.
Ian comes across about 40 adult Port Jacksons lying, stacked on top of each other, either sleeping or doing a spot of fin fondling, in caves on the sea bed.
About four miles (6.4 km) away we visit “the nursery” where the hatched young congregate to grow and play.
He then takes a night dive to observe adult behaviour where he interrupts some serious lovemaking!
No sign of intentional egg placement, but the Flintstones are returning home.
Ian is about to abandon the egg placement theory when he witnesses a female take a large egg in her mouth and seemingly hide it in the seaweed.
Was that mothering behaviour or an aborted egg attack? Ian decides that will remain a family secret, well kept by the Port Jackson shark!
