Pulling the plug on carp
Almost four tonnes of carp have been removed from two ponds that feed into Lake Tuggeranong.
Ecologists from the Conservation Research branch of the ACT Government removed 1.6 tonnes of carp from Isabella Pond and 2.2 tonnes from Upper Stranger Pond.
Both ponds were drained in preparation for major works on the weir and to build two new wetlands. It offered an opportunity not just to remove and study the carp but also to test the methodology behind estimating carp populations in waterways.
“Any future control plan will rely heavily on being able to accurately estimate the numbers – not just in terms of choosing the right approach but also in managing the clean-up,” said aquatic ecologist, Matt Beitzel, thigh deep in the mud and sediment that was left behind after the ponds were drained.
Carp is an invasive pest species introduced into Australia more than a century ago and now widespread throughout the Murray-Darling Basin. Highly adaptable and with destructive feeding habits, carp have a detrimental effect on native aquatic plants, animals and general river health.
Once the fish were euthanised, a team of volunteers from The Green Army and the Waterwatchers of Southern Murrumbidgee weighed and measured the fish and removed 100 heads for further research.
“Later in the lab the ear bone (or ‘otolith’) will be examined to gather a range of data, including the age of the fish. This type of life cycle information is really important to our understanding and management of carp,” said Matt.
Upper Stranger Pond will refill naturally and will be re-stocked with native fish. Isabella Pond will remain empty for 12-18 months while the weir is widened and the wetlands are constructed. It too will then be re-stocked with natives.
The twin wetlands in Isabella Pond are one of three projects planned for the ponds as part of ACT Healthy Waterways, a joint Australian and ACT government initiative to build water quality infrastructure on up to 25 sites around the ACT. Later in the year work will begin on the naturalisation of a concrete channel feeding Isabella Pond and a rain garden beside Upper Stranger Pond.
The three infrastructure projects, combined with the carp eradication program, will help to improve water quality in the ponds, in Lake Tuggeranong, downstream in the Murrumbidgee River system and in the wider Murray-Darling Basin.