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Grass Carp Unlikely to Save Lake Omapere

9 April 2001 - Wellington


Grass Carp Unlikely to Save Lake Omapere

Forest and Bird is concerned that grass carp won’t save Lake Omapere. The underlying cause of the problems with Northland’s largest lake – agricultural practices in the catchment - has been overlooked in the current controversy about the lake.

“Forest and Bird shares Ngapuhi’s concern about the state of their taonga, Lake Omapere”, said Forest and Bird’s Conservation Manager, Eric Pyle. “What has happened to the lake is a tragedy. But the real cause of the problem is farm runoff and grass carp won’t fix that”.

“Use of grass carp for weed control in the lake is an experiment and a risk to Northland’s biodiversity. Furthermore, it does not address the underlying problems”, said Mr Pyle.

Forest and Bird is concerned that it will not be possible to remove the grass carp from the lake and they could be spread to other parts of Northland. “We already have enough problems with introduced species in our environment. We shouldn’t create any more”, said Mr Pyle.

For several years now Forest and Bird has unsuccessfully sought to have a catchment plan for the lake developed. “The problem is catchment management. A catchment plan is urgently needed to develop a long term solution to this problem”, said Mr Pyle.

Little has been done to address the management of the lake’s catchment to minimise nutrient run-off. In 1997, the Far North District Council sanctioned the clearance of approximately 50 hectares of the last remaining lakeside wetland, which is critical to removing nutrients and maintaining the health of the lake. Stock still have access to the lake and inappropriate cowshed effluent disposal systems are being used in the catchment.

“The release of grass carp into the lake would be dealing with the symptom, not the cause of the problem. Farming practices in the catchment are the cause and need to be cleaned up” said Mr Pyle. “Grass carp are not a long term solution and pose an unacceptable risk to Northland’s waterways”.

Notes for editors

Lake Omapere is shallow and vulnerable to eutrophication (weed growth and algal blooms).

Efforts by the Far North Branch of the Forest and Bird Protection Society to have a special catchment management plan for the lake as part of the regional Water and Soil Plan were rejected several years ago. The catchment is relatively small (1700 hectares) and a catchment management plan could easily be developed.

Grass carp have never been used for weed control in such a large lake in New Zealand. Efforts to remove grass carp from much smaller lakes have failed. Once the grass carp are released into Lake Omapere they are likely to be there forever.

Forest and Bird is opposed to the release of grass carp into New Zealand’s waterways. Although used for weed control, the fish are known to favour native species, and weeds are generally eaten only after more palatable vegetation has been exhausted. Lake Omapere is the only site in Northland of the fern ally Isoetes aff. kirkii, which is of restricted distribution in the North Island, with this being the only remaining site north of Rotorua. The plant was only recently rediscovered in the lake and appears to be very rare, classified as being Critically Endangered - Taxonomically Indeterminate. The native plant is a small sedge that grows in shallow water and would be vulnerable to grass carp.

Forest and Bird is concerned that fish would be illegally taken and released into waterways of high ecological value where they could destroy native aquatic plant communities, some of which are already threatened. In Northland, there are many small, highly vulnerable lakes and streams. Because Lake Omapere is such a large lake, bordered by many properties, the security of any fish released there is doubtful. Forest and Bird knows of situations where private landowners have discovered people at their farm ponds trying to capture grass carp.

Claims that the grass carp will not breed need to be carefully scrutinised. Conditions in Northland’s Northern Wairoa River could provide suitable breeding areas, and with global warming there is no certainty that breeding will not occur here.

Contact: Eric Pyle– phone 04 385 7374 work; 04 233 3993 home, 025 227 8420

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