Fishing helps clear the murky depths at Lake Wainamu

26 March 2007

Better water clarity, lower exotic fish numbers and increased recovery of native fish in Lake Wainamu, Te Henga/Bethells are the results of an Auckland Regional Council exotic fishing programme carried out over the last three years.

Latest results indicate that the turbidity (clarity) in Lake Wainamu and submerged aquatic vegetation growth substantially improved when over 9000 exotic fish were removed from the lake, particularly perch, goldfish and rudd.

ARC Parks and Heritage Committee Chair Sandra Coney says that the decline of water clarity became a matter of public concern in 1996 and exotic fish were suspected of contributing to the decline.

“Lake Wainamu has high recreational use, particularly swimming. The local community has welcomed the ARC fishing effort and the improvement in water clarity,” she says.

“The success at Lake Wainamu has encouraged the Te Henga community to undertake a similar initiative at the neighbouring Lake Kawaupaka, which is on private land.

“A recently formed group has successfully obtained Environmental Initiatives Funding to commence fishing, with logistical support also provided by ARC staff,” Cr Coney says.

Grant Barnes, ARC Project Leader, Freshwater Ecology says the fishing programme aimed to test the hypothesis that exotic, coarse fish were contributing to water quality decline by accelerating the collapse of submerged plants and disrupting natural food webs.

“Aquatic plant abundance is now rising. Water clarity results obtained since the project commenced have been some of the highest since regular monitoring began in 1988. However, it is too early to attribute this directly to the fishing effort,” Grant Barnes says.

ARC’s Environmental Research, Biosecurity and Parks staff examined the role of exotic coarse fish in a joint fishing programme, which commenced in 2004 and has been undertaken twice yearly. To date the fishing effort equates to 1,630 net nights or over 25 kilometres of net set. The programme has cost less than $20,000 per annum over the three years.

Notes for Editors

Lake Wainamu is a dune lake located in the northern Waitakere Ranges at Te Henga/Bethells. The lake and part of its supporting dune system is owned by the Queen Elizabeth II National Trust and managed by the ARC under a management agreement.

The lake is one of two major dune lakes in the Te Henga-Wainamu area, the other being Lake Kauwaupaka. The area contains complex habitats of wetlands, dunes, lakes and native forest with a rich and diverse flora and fauna not found elsewhere in the region. The area is considered to be of national importance.

Lake Wainamu is a deep dune lake with a good diversity of freshwater wetland bird species, including Australasian bittern, North Island fernbird, claks shag and little black shag. Native freshwater fish present include banded kokopu, inanga, common smelt, common bully, grey mullet, longfinned eel and shortfinned eel.

The full Parks and Heritage Committee Lake Wainamu project report is on the March committee agenda, available at http://www.arc.govt.nz/arc/about-arc/agendas-minutes/

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