Sediment smothers homes of giant freshwater crayfish

Northern Tasmania’s giant crayfish are being smothered by a build-up of sediment in rivers and water catchments, a crayfish expert has told an inquiry into Australia’s extinction crisis.

METRES of sediment is smothering the rivers and water catchments that are home to Tasmania’s giant freshwater crayfish, an inquiry looking into Australia’s extinction crisis has heard.

Tasmanian crayfish expert Todd Walsh told the Senate inquiry the vulnerable species is struggling to survive because its habitat is being covered by volumes of fine sand.

Mr Walsh said an investigation was needed into Tasmania’s water catchments.

“One thing I’d like to see come out of this is an investigation into how bad Tasmanian rivers are health-wise, because they are terrible. The clean green image is a complete myth,” he said.

“There are major sediment issues in probably three-quarters of all the large catchments and rivers that this animal occurs in, and 95 per cent of the rivers in the North-East, to the point where you can’t see the river for fine sand,” he told the inquiry.

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The giant freshwater crayfish is the largest crayfish species in the world and found only in the rivers of northern Tasmania. Mr Walsh, who is an aquaculturist and works in freshwater ecology, told the committee about a recent survey of the Great Forester River, in the North-East.

“The sediment was sitting above the waterline. It’s like someone had taken a whole beach and dropped it in the river.

“It’s covered from one end to the other. That covers up all the larger rocks where these animals and everything else in the river hide.

“These rivers are basically stuffed in a lot of ways.”

He said the health of the crayfish was intrinsically linked to the health of the rivers, because rocks and crevices provided protection from prey for juvenile freshwater crayfish as well as habitat for smaller invertebrates which they feed on.

He said juvenile giant freshwater crayfish took about seven years to “get to the size of your hand”.

BREAKTHROUGH AS TASMANIAN GIANT LOBSTERS BRED IN CAPTIVITY

Tasmanian crayfish expert Todd Walsh told a Senate inquiry the vulnerable species is struggling to survive because its habitat is being covered by volumes of fine sand. Picture: SUPPLIED

“In those seven years they need to hide under rocks, because everything else in the river eats them… to take away the areas they live under and hide just exposes them.”

Mr Walsh said he believed the Tasmanian government’s management of forests and the habitat of the crayfish has been inadequate.

He said the animal was listed as a priority species under the Tasmanian Regional Forestry Agreement in 1997, but since then “not one hectare’s been specifically reserved for the animal”.

He said the forestry industry had “done some positive stuff” in creating buffer zones.

But he said there was little point protecting rivers downstream when habitat loss upstream, at higher altitudes, was causing the sediment build-up.

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