Swimmers beware !

The sharks most likely to attack humans are the Great White, Tiger shark and the Bull shark, but the most lethal is the Bull shark.  It has horizontally opposed teeth - much like the cutters on a chain saw - and when it bites it usually uses a vigorous shaking of it's head resulting in great chunks of flesh gouged out of the victim's body - and the severance  of arteries.  Most people die from blood loss.

In the ocean, the Bull shark's preferred habitat is near the entrance to the sea of rivers.  It is known that these animals can tolerate brackish water that would kill most salt water fish and they have been known to foray into fresh water for limited periods of time.  Scientists now believe that this is a stage of the evolutionary process and that the Bull shark is making the transition to a fresh water fish.

This has probably been helped by the popularity of " canal estates " which have been a big development on the Gold Coast.  Miles of man made waterways wind around luxury housing and most of these are infested with Bull sharks, despite salinity ranging widely.   This has been a factor in allowing this species to develop it ability to live in freshwater.

There have been strange happenings in Queensland's inland rivers.  A horse being exercised in water was attacked by an unknown creature and had a sizeable flesh wound gouged out of it's rump.  A vet examination clearly pronounced the wound a " juvenile shark bite ".   This probably explains the mysterious disappearance of sheep, family dogs and native animals from properties near rivers that has otherwise defied an explanation.

It seems that the Bull shark has crossed the fresh water frontier, and this probably occurred at the time of heavy flooding in Queensland.   Many inland cities and towns have damned rivers to create a recreational lake area and this dam isolates the raised water level from the rest of the river.   During floods, water cascades over this barrier and Bull sharks have penetrated inland.   When the flood recedes, the barrier stops their return to the lower river system -  and they have adapted to a fresh water life.    They are now breeding in our inland waterways.

Many scientists think that this is simply natural evolution .  Most of the world's great rivers have fresh water predators that harm humans - such as the Piranha and the Snakehead of South America.    Australia has been mercifully free, but this Bull Shark evolutionary phase is a world wide phenomenon - speeded up by our use of canals and the inland lake traps.

The intrusion of Bull sharks to our inland rivers is in it's infancy, but there is every prospect that our carefree days of swimming in fresh water may be over.  Just as the Saltwater Crocodile is moving south from it's Northern Territory haunt, so the shark species has crossed the salt barrier to infest inland fresh water.   The Bull shark grows to a length of nine feet - and it is a formidable predator.

It seems only a matter of time before headlines scream  "  Freshwater Shark attack  " !