Port Jackson Shark

Port Jackson Shark Egg Case  A Port Jackson Shark with an egg case in its mouth


The Mermaid’s Purse

The strange brown object with the spiral flanges in our picture, can be found washed up on beaches in South Australia during their winter months. It is leathery and very odd. Because of its unworldly appearance some people call it the ‘Mermaids purse’, however its origins are a little less fanciful than this but still quite strange: for it is the egg case of the Port Jackson Shark.

This shark found in the Southern waters of Australia, feeds by browsing along the sea bed on hard-shelled molluscs, crustaceans, sea urchins, and fish. It is nocturnal, living in rocky undersea locations such as caves and belongs to a group of sharks which lay eggs rather than give birth to live young.

It differs from almost all other shark species in its teeth and the way it cares for its eggs. The teeth are quite unlike the ones we expect from seeing the film ‘Jaws’. The front teeth are small and sharp and the back teeth flat and blunt, so it nibbles with the front teeth and breaks, crushes and grinds with the back. Browsing on the sea bottom they can sometimes pick up indigestible items but they can turn their stomachs inside out to cough out any unwanted contents.

 Another difference is that they can eat and breathe at the same time.  Most sharks need to swim with the mouth open to force water over their gills and thus breathe. These sharks, however, have a different gill system which allows them to stay motionless on the bottom for long periods of time.

Perhaps the most interesting difference is the way they treat their young. They lay eggs rather than live young and these eggs are contained in a spirally shaped egg case. Once the egg case is laid, while it is still soft, the shark takes it in her mouth, finds a crack in a nearby rock and pushes it in. Its auger like shape soon hardens and it is thus held ‘rock solid’ until the baby sharks ( two per case) emerge in 10-12 months.

Here we have a fascinating variant from other sharks. Only one other species behaves in this way and for the believer in evolution it provides a number of thorny problems. For example why did its teeth and method of breathing evolve in a form so different from most sharks, requiring it to change its diet. Also, when did the stomach on this creature develop its amazing ability to turn inside out. There is also the question of the sharks unusually shaped mouth, and its ‘instinct’ to use it to pick up and carry the egg case containing its young. If one allows for evolutionary theory, one must ask, how many thousands of years elapsed before the shark worked this out and managed to pass the information on to its progeny. Finally, how many different shapes of egg case ‘evolved’ before the perfect auger shape suitable for securing the egg cases came into being and what ‘instinct’ made the shark utilise this when it finally appeared. Surely the explanation of the slow evolution of this strange creature might appear to some to be pretty ‘fishy’. The believer in a God, however, Who created all the creatures of the world in one go and found them all ‘very good’ (Genesis 1:31), has no such problems. The LORD God found a need for a creature to browse the Ocean floor and keep the species in check and thus created the amazing Port Jackson Shark.

Psalm 104:24  O LORD, how manifold are thy works! in wisdom hast thou made them all: the earth is full of thy riches.

25  So is this great and wide sea, wherein are things creeping innumerable, both small and great beasts. 26  There go the ships: there is that leviathan, whom thou hast made to play therein. 27  These wait all upon thee; that thou mayest give them their meat in due season. 28  That thou givest them they gather: thou openest thine hand, they are filled with good. 29  Thou hidest thy face, they are troubled: thou takest away their breath, they die, and return to their dust. 30  Thou sendest forth thy spirit, they are created: and thou renewest the face of the earth.

The Port Jackson Shark is another example of God’s wisdom and the rich diversity of His Creation!

Acknowledgements: http://australianmuseum.net.au