Factual
River Monsters Freshwater Shark
No fish inspires the same kind of terror as the shark. But, instead of being confined to the ocean, it seems one species of shark has been trespassing from saltwater into freshwater rivers. Biologist and extreme angler Jeremy Wade looks at how this is possible and just how far inland they can survive.
Jeremy heads to Australia, to the scene of a brutal shark attack ten miles inland. In Queensland in 2002 two students went for a swim in Miami Lake when one of them, Beau Martin, vanished swimming across the 500 yard wide lake. His sudden disappearance had all the hallmarks of a shark attack, but it was an inland lake in an urbanised area.
Jeremy meets Vic Hislop, known in Australia as the Shark Man who explains: “We’ve got sharks in Australia that hit and hit hard. They don’t leave anything. They’re so good at what they do they pull somebody under, you don’t see anymore. Someone’s got to be looking at that exact spot to see it happen.”
Beau’s body was found three days later and the autopsy revealed that he had been struck three times by a bull shark, one devastating bite on his left thigh proving fatal.
Jeremy says: “Bull sharks constantly test the salt content of the water with tiny sensors mounted all over the body…Then a special organ, the rectal gland, acts like an on off valve, releasing or retaining salt as required. The bull shark is the only species of shark that can do this.”
Jeremy investigates how Beau’s killer could have got so far from the ocean and looks at the shark nets just off the main beach on the Gold Coast. He says: “I can see no reason why bull sharks wouldn’t easily go under it or around it and then head on relentlessly into the canals. After all, the net is only 200 yards long and just 20 feet high.”
Vic Hislop agrees: “Shark nets in Australia are a false sense of security for tourism. They kill everything we love out there. They kill dolphins, turtles, dugong. But more important, the big sharks have learned to feed off those nets.”
Miami Lake is ten miles from the sea, but Jeremy has heard of another attack 80 miles in land and goes to meet racehorse trainer Alan Treadwell near Brisbane.
In 2005, Alan was taking one of his most successful horses for exercise in the river when the horse struggled and Alan realised there was something hanging off the back of it, submerging the 1,000 pound horse. Alan was able to pull his horse to safety and the vet who treated him photographed the wound.
Jeremy shows the photograph to scientist Vic Peddamors who says: “I would definitely say it looks like a shark bite… This isn’t much of a crescent, which suggests that the jaw must have been fairly big.”
Vic concludes that the creature that attacked Alan Treadwell’s horse was a bull shark over eight feet long, but Jeremy can’t work out how a shark could have got through Mount Crosby Weir; a dam that has been in place for over 100 years just five miles down the river. The difference in height between the water on the ocean side and the upriver side is 12 feet.
But, looking through government archives, Jeremy discovers the Brisbane River has flooded repeatedly, with one extreme occurrence in 1974. As the flood subsided, a colony of bull sharks, some growing to over eight feet long, were locked in far upriver.
Jeremy decides he needs to try and catch one of these sharks and meets some local expert shark fishermen. He says: “By fishing at night, we’re choosing the most likely time for sharks to go hunting. It’s in the dark when the supersensory bull shark has the edge over fish that rely more on vision.”
But this time luck isn’t on Jeremy’s side, so the next day he drives 50 miles inland to try again. Finally, he catches a small bull shark and says: “This may be a small one, but for me this is, in some ways, more unsettling… This one didn’t swim all the way from the ocean. It was most likely born in brackish water just downstream. And while only 18 months old, it seems to be thriving in freshwater.
“This shark is three feet six inches long and 15 pounds in weight, but in 15 years it could triple in length and become 30 times heavier.”
Jeremy releases his shark back into the river and says: “I’ve discovered this river monster could be breeding up here and it might be here to stay.
Last edited: Tuesday, 8 December 2009
