My Account
An Auckland Council biosecurity officer has described efforts to rid Lake Tomarata of pest fish as ‘a race against time’.
Last month, Council, with assistance from the University of Waikato, made a second sweep of the lake pulling in nearly 300 fish.
Senior freshwater biosecurity advisor Belinda Studholme says Tomarata is the fastest declining lake in the Auckland region.
“We hope that by removing the pest fish, the lake will have a chance to recover,” she says.
“Unlike the nearby Slipper and Spectacle lakes, which are dominated by algae, there is still time to save Lake Tomarata.”
The pest fish are causing a decline in water quality and threatening native biodiversity, including unique submerged native plants, kākahi (freshwater mussels) and the threatened black mudfish, which live in the surrounding wetland.
Council first netted the lake in August last year, catching 800 fish over eight nights. Last month, the team netted over four nights catching 202 Rudd and 79 tench.
The process involves putting out a line of gill nets every 50 metres across the entire lake. The nets are three metres deep and are allowed to sink until they touch the bottom of the lake, which is about five metres deep.
“Tench are the trickiest to catch because they can hang out in the wetland area where we can’t net.
We’re really pleased with the results from last month though, as it appears we are reducing the biomass of fish.
“We’ll return in August and go through the process again, and then it will be a matter of doing the netting annually to keep on top of it.”
The fishing is unlikely to eradicate these pests, but the council is hopeful it will control fish to a level that will decrease pressure on native species. The native plants and kākahi will be monitored to assess their recovery.
Studholme says the rudd have completely devegetated the lake bed of native submerged plants. The reduction in rudd will reduce the pressure on the native charophytes, which are the native submerged plants.
“The submerged native plant communities are integral to the health of the lake, they create underwater meadows that bind the sediment to the lake bed and prevent mud and nutrients from being resuspended into the water column making the water turbid and causing algal blooms.”
The project is being funded by Auckland’s natural environment targeted rate, and the pest fish removed from the lake are being composted at Te Arai Organic.
“Dropping the fish off was a very smelly job,” Studholme concluded.
Help keep the lake clean
While Lake Tomarata is threatened by pest fish, it has so far remained free of invasive pest weeds. Biosecurity officer Belinda Studholme says that for this to continue, boat and watercraft owners must play their part by keeping their equipment, including trailers, clean. Moving boats between the sea and the lake is not a threat, but if boats have been in the Waikato or Bay of Plenty, then boat owners need to be vigilant.
