The on-going drought in Australia is having at least one positive spin-off - fewer carp are being distributed through inland waterways.
NSW Department of Primary Industries’ (DPI) fisheries researchers at Narrandera are identifying carp ‘hot-spots’ in conjunction with the Invasive Animals Cooperative Research Centre (CRC).
Known as the vermin of inland waterways, carp became a major pest in Australia in the 1970’s and now make up 80 to 90% of the fish in inland NSW.
NSW DPI researchers are identifying what are believed to be a relatively small number of locations where huge numbers of carp breed.
Fisheries scientist Dean Gilligan said the carp are concentrated in these hot-spots, and at one site there were about 30,000 carp larvae per megalitre of water.
Ten hot-spots have been identified, and four of these are internationally recognised wetlands - the Gwydir wetlands, Namoi wetlands, Barmah-Millewa forest and the Macquarie Marshes.
The researchers estimate there are around 20 major carp breeding hot-spots within the Murray Darling Basin.
They have found that carp like to breed in shallow, swampy areas that are regularly inundated by water - heavy rain and floods enable the carp to disperse into adjoining river channels.
The results support the larval drift theory, indicating the carp’s need for high water flow events to disperse their larvae.
The drought initially hindered this research, because the lack of water flow meant carp movements could not be tracked.
However, the researchers then used NSW DPI’s records of freshwater fish to map the distribution of baby carp over the last 13 years.
It is expected that targeted carp control at these major breeding locations will have a huge impact on massively reducing carp numbers in regional waterways.
The CRC is currently investigating a range of promising control measures, including techniques designed to trap carp but not native fish, and also methods to sabotage carp breeding.