Limiting freshwater pests ongoing task

OTAGO is free of freshwater pests and rangers want to keep it that way.

It is good news for native fish and plants, which are affected by introduced species in rivers, lakes and wetlands.

The Department of Conservation (Doc) said people needed to help protect ‘‘special freshwater places’’, as once established, freshwater pests were difficult and costly to control.

A search of 31 sites by Doc rangers, on private and public land in the Otago region, found no signs of pest fish and no new aquatic weed infestations.

‘‘The pest fish we were looking for this summer were rudd, koi carp, gambusia, and catfish,’’ ranger Helen McCaughan said.

None were found, but natives including the common bully and freshwater crayfish were observed.

Doc looked for pest plants, particularly hornwort and lagarosiphon.

She said pest fish reduced water quality, increased competition with native fish for food sources, and ate native invertebrates, fish and their eggs.

Freshwater weeds could also have economic impacts, including clogging dams and drains, and reducing suitable habitat for eel and whitebait.

People could help prevent such pests spreading.

‘‘Pest fish are most often spread by people introducing them illegally [and] . . . weeds, fish and their eggs are spread by people moving equipment between waterways.’’

She said people should check, clean, and dry all gear, including fishing gear and boats, when moving.