Brian Williams
September 10, 2008
SCIENTISTS are trying to figure out why some turtles benefit from breathing through their bottoms and are investigating their diet and lifestyle.
The so-called bum breathers can breathe by absorbing air from water taken in through their cloaca.
James Cook University physiologist Suzy Munns and ecologist Ivan Lawler are investigating the turtles, in particular the Irwin’s turtle.
It was found by Bob Irwin and later named after his late Crocodile Hunter son Steve. It is known only in north Queensland’s Broken-Bowen River and the lower Burdekin.
With about 5000 left in the wild and proposals for the Urannah dam to be built on the river, the turtles’ future is bleak.
“We believe that one of the major benefits of cloacal breathing is the amount of energy spent on having to surface is reduced significantly simply because they can obtain their oxygen from the surrounding water and so don’t have to surface to breathe,” Dr Munns said.
“We have not yet established how widespread cloacal breathing is and what advantage it confers, if any.”
During digestion a turtle’s resting metabolic rate may increase by up to three to five times the resting level.
“This increase may consume up to 30 per cent of the energetic value of the meal,” Dr Lawler said.
“Couple that with the fact that many have to then haul their body weight to the surface to breathe and it’s a significant cost.”
Another mystery is why different species choose to live at different points in the river and rarely cohabit.
One theory is that because Irwin’s turtle does not need to use energy to surface, it can live in areas where food is scarce. The turtle does not have to compete with neighbouring species.
Last year University of Queensland scientist Natalie Mathie found the endangered Mary River turtle, also a bum breather, could stay submerged for at least three days, possibly up to a week.
This allowed the turtle to avoid predators such as birds and hide from fish or eels.
stevem
