Zimbabwe Faces Crayfish Crisis In Water Ecosystem
Feb 12, 9:12 AM EST
BY ANGUS SHAW
ASSOCIATED PRESS
HARARE, Zimbabwe (AP) — Scientists in Zimbabwe say a fresh water crayfish
brought from Australia is breeding out of control in the northern Lake
Kariba, devouring the food sources of other fish and putting the nation’s
entire aquatic ecosystem at risk.
Officials at the Zimbabwe University lakeshore research station say the red
claw crayfish, introduced a decade ago for a fish farming project, has no
natural predators in the wild – crocodiles don’t like them – and they
produce clusters of eggs up to half the size of a tennis ball that hatch
prolifically.
Baby crocodiles still feeding on insects have been observed eating the
crayfish, as have Lake Kariba’s piranha-like tiger fish, but they generally
thrive in deeper water than the crayfish.
Chief ecologist Crispen Phiri said the exploding, migrant crayfish
population is infesting rivers, dams, ponds and tanks much farther afield
where `’the scavenger eats everything -rotting vegetation, anything organic
and micro-organisms” that other aquatic life and fish need.
The red claw crayfish, scientifically Cherax Quadricarinatus and known
colloquially in Australia as the yabby, is robust and hardy and cannot be
poisoned without killing other natural species, Phiri said.
It survives and multiplies in virtually any fresh water supply and though
its flesh is high in protein it is not popular in the diet of ordinary
Zimbabweans, even those facing food shortages in the troubled economy.
Phiri said it is not clear whether the sister crayfish, or Cherax
Destructor, is infesting Lake Kariba, too. As its scientific name suggests,
it is a burrower which can cause structural damage to drainage and
hydroelectric installations in Kariba, one of the world’s largest manmade
lakes stretching about 300 kilometers (200 miles) on the Zambezi River along
the northern border with neighboring Zambia.
Like professionals in most Zimbabwean institutions, the scientists are
suffering acute shortages of funding. The station’s only research vessel has
been docked for more than five years awaiting cash for repairs. What the
ecologists do know is that the red claw migrates deep into river systems.
“We have to do a lot more work on the crayfish invasion,” Phiri told The
Associated Press.
`’We don’t know yet what will happen to the ecosystem. It is an omnivore and
eats detritus, rotting vegetation, dead fish, the eggs of bream and other
aquatic life as well as all the organisms that are crucial in the whole
ecological chain,” he said.
Nor is it known exactly how many crayfish are in Kariba lake. Phiri says
they are most visible breeding unchecked close to human settlements, harbors
and slipways for boats. Kariba’s “kapenta” fish, a tiny tropical whitebait
or sardine that has become a staple food, was also introduced into the lake
but does not migrate because it only lives in deep water lake conditions.
The red claw from Australia was first “farmed” in neighboring Zambia but has
already found its way deep into that country’s lake tributaries where its
worrying impact is also being urgently tracked.
The solution to the crayfish crisis, said Phiri, seems to lie in commercial
exploitation in traps similar to those used to catch marine lobster.
In stores in Harare, it sells for $9 a kilogram (2.2 pounds), $12 still
alive in fish shop aquariums, and far more in upmarket restaurants
patronized by the wealthy well-traveled elite and Zimbabwe’s growing Chinese
community.
Phiri said impoverished villagers capture the red claw and relocate to water
closer to urban markets in central Zimbabwe.
Neighboring South Africa has banned commercial operations and breeding of
the still water crustacean in Argentina, Mexico and Australia is strictly
controlled for environmental reasons.
`’We don’t have the resources on the ground to license or police
exploitation on the right scale at Kariba,” said Phiri. “The important thing
is we don’t want people to introduce it elsewhere.”