ACT News

Scientists break into circle to find Lake Burley Griffin carp's vulnerability

Looking for a chink in European carp's armour, Dr Danswell Starrs is focusing on an annual social circle among the feral fish.

Each spring the carp, an unstoppable scourge of Lake Burley Griffin, begin the unusual ritual says Dr Starrs, an Upper Murrumbidgee scientific officer.

"It is almost a social behaviour that carp exhibit where they form a nice, neat circle on the surface of the water, with all the mouths in the middle. It is peculiar behaviour, but regularly seen in Sullivans Creek at the ANU and Jerrabomberra wetlands," Dr Starrs said.

"We don't know why the carp do it, it has been observed in South Australia regularly, it seems like it is come sort of carp communication that is going on, a carp conference," Dr Starrs says.

"A gab fest," says Woo O'Reilly, an ACT Waterwatch spokeswoman.

They believe Lake Burley Griffin holds many tonnes of carp. "If the Coarse Fishing Club can catch three-and-a-half-tonnes of carp in a weekend, we are looking at tens of tonnes, potentially more," Dr Starrs says.

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Water ecologists are asking for the public's help to uncover where carp are breeding in Canberra's lakes and streams. Dr Starrs says when the water warms up to about 17 to 24 degrees celsius carp begin to spawn. They congregate over good vegetation, aquatic plants and tree roots to spread their eggs. Male carp chase females around, splashing across the water surface.

During this distinctive behaviour they are laying and fertilising their eggs. Scientists want a more accurate picture of where and when this activity is happening. If you have seen a carp circle, don't assume everyone else has seen it too. The Waterwatch Group wants you to go on-line to www.feralfishscan.org.au and report carp sightings.

Breeding hotspots are suspected to be at Sullivans Creek, where Dr Starrs has seen large numbers of eggs deposited and larval fish, and Jerrabomberra Wetlands' man-made channels.

When congregating carp can be seen in their hundreds and possibly thousands. A female carp lays anything from one million to eight million eggs, although the actual numbers are hard to count. In warmer parts of Australia they can spawn multiple times in a year, says Dr Starrs.

Dr Starrs says there is a great deal scientists don't know about carp and how they grow their population. "We need to know where and how they do this. The more detail and specific information we have, the more targeted can be our control and more cost-effective it can be." 

Ms O'Reilly says over the longer term, if  a biological control is developed it can be targeted at known breeding areas with a more successful outcome. Citizen scientists who report sightings can win a table and other prizes.

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