THE AUSTRALIAN (Sydney, Australia) 11 April 08 Tortoises under threat from sea worm (Andrew McGarry)
Photo at URL below: A tortoise whose shell has been infested by the bristle worm
A new threat is emerging to marine life at the bottom end of the Murray River, with increasing numbers of freshwater tortoises falling victim to sea worms attracted by the saline waters.
An unknown number of tortoises have died at the Lower Lakes of the Murray and near the mouth of the river in South Australia, while one volunteer group has taken 150 injured tortoises into its care.
"We got our first call in mid-March, but we didn't think much of it," said Native Animal Network volunteer Deanne Smith. "We had two calls in two weeks, but then it just snowballed."
The tortoises are turning up on river and lake shores or stuck in mud banks, after being paralysed by the predatory bristle worms.
The worms attach themselves to the tortoises and infest their shells with their castings so theyare unable to swim or walk.
"They (bristle worms) don't normally turn up in fresh water, but now they are able to live in the lakes," Ms Smith said.
"The more castings that are attached, the heavier it makes the tortoise. In the worst cases,they look like rocks."
The infestation can mean a slow death for the river creatures.
"They can't get away from predators, and some of them are being found with rat bites," Ms Smith said.
"They also move their limbs to aid breathing, so if they can't move, they find it hard to breathe."
The lakes and the bottom end of the river are heavily saline, and without solid rainfall or fresh water to flush out the system, the prognosis does not look good for the tortoises and other freshwater marine life.
Members of the public are being asked to alert authorities if they find an injured tortoise.
Yesterday, Murray-Darling Basin Commission chief executive Wendy Craik warned of harsh consequences for the bottom end of the river if inflows remained low for five years.
"Clearly, there wouldn't be enough fresh water for the Lower Lakes if these conditions we've had the last year or two continue," she said. "It's hard to see where you would get water for the Lower Lakes."
Waters in the lakes are already 0.4m below sea level and falling.
They are under threat of being poisoned by acid-sulphate soils if lake beds are further exposed.
Dr Craik acknowledged that one option was to let sea water in, turning the lakes saline and killing off existing marine life.
"Letting in the sea might be a less worst-case option than having acid-sulphate soils on the Lower Lakes, but that would have to be a last resort, probably," she said.
Dr Craik also warned that drastic falls in water flows on the Victorian section of the Murray had already equalled the CSIRO's most extreme climate change predictions for 50 years from now.
"The average inflow for the last decade crosses the CSIRO's extreme climate change scenario for the Victorian Murray in 2055," she said.
"So what we've been experiencing is what we thought we might get in 2055."
Tortoises under threat from sea worm