Recovery of native fish in Zealandia

February 28, 2013

Another step on the way to restoring Wellington’s Zealandia, as closely as possible, to its pre-human state has been achieved with the eradication of introduced fish from its upper waterways.

“We’ve had great success in controlling pest mammals but this operation to restore our freshwater ecosystem had been on our wish-list for many years so we’re delighted with the results” says Zealandia’s Conservation Manager, Raewyn Empson.

The operation, begun in 2011 in collaboration with DOC, was designed to see if using a naturally-occurring chemical, called rotenone, in flowing water would completely remove introduced trout and improve native freshwater fauna populations.

“A spectacular recovery of native freshwater fauna and continued absence of trout is strong evidence that trout have been eradicated from the upper Karori reservoir and streams” says David Moss from the Department of Conservation (DOC).

“Before the operation there were a few big banded native kōkopu, very few whitebait and hundreds of trout in the streams,” said Mr Moss. Results from fish sampling since the operation in February 2011 confirm trout have been eradicated, and show a dramatic increase in the number of whitebait and now juvenile banded kōkopu and kōura (freshwater crayfish).

With the confirmed absence of trout, Zealandia can now plan to introduce other native fish species into the safer reservoir and streams.

“This breakthrough means we can now start planning to enhance the recovery of the upper reservoir and its tributaries by transfers of other native fish - such as the threatened giant kōkopu” says Empson.

Further information:

-The fish toxin rotenone has been used in New Zealand for a number of years to remove pest fish from lakes and ponds. Eradication of introduced fish from streams is a “first” for New Zealand.

- Brown trout were introduced into New Zealand in 1867 as a sports fish. They compete with adult banded kōkopu and eat the juvenile stage whitebait, as well as invertebrates like kōura.

ENDS

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