Tagging whitebait to help species' survival

Scientists about to embark on a two-year-long game of tag with a species of whitebait are hoping their research will save the delicacy from disappearing.

National Institute of Water and Atmospheric Research scientists are beginning a trial today which will see them introduce 30 fish, which have all been implanted with individual transponder tags, into the Nukumea Stream in Orewa.

Freshwater fisheries scientist Paul Franklin said the giant kokopu, which as juveniles make up part of the whitebait catch, had not been seen in the stream since 2002.

Their decline in that waterway was thought to have began after a culvert was raised above the water level, preventing young fish from getting into the stream.

Now that culvert had been moved, scientists hoped the introduction of the fish would allow the species to re-establish a population there, Dr Franklin said.

Each fish, which was about three years old and 20cm long, had been implanted under anaesthetic with a transponder tag about 23mm long.

At each end of a 200 metre section of the stream, two antenna had been erected to monitor the fish by picking up a signal from their transponder tags, as it was hoped that they would remain in that area.

''It is the first time we've controlled the fish in this way in a trial,'' he said.

If the fish re-established themselves in the stream, Dr Franklin said it would be possible to stock other streams with them.

However, he said that where fish had declined because of changes made to the environment, their natural habitat would also need to be restored or fixed to stop them from dying out again.

As well as monitoring the fish with the antenna, scientists will also visit the stream regularly to check up on them.

They fish were hatched and reared in tanks at the Mahurangi Technical Institute and special project manager David Cooper said that while most fish were bred for ornamental reasons, if the trial was successful, more natives could be bred for future conservation projects.

NIWA ecology team leader Dave Slaven said scientists would also monitor whether introducing the fish had any impact on other species living in the stream.

GIANT KOKOPU

One of five species of fish which, as juveniles, make up the whitebait catch.

Giant kokopu live to about 10 years old and grow to about 40 centimetres.

The fish breed in freshwater around autumn and females can spawn thousands of fish depending on the conditions.

After a few weeks their larvae drift out to sea, where they spend a couple of months before returning to rivers.

Whitebait are classified as ''nationally vulnerable'' by the Conservation Department.

Loss of habitat is a major cause of their decline.

The other four species are the banded kokopu, the short jaw kokopu, koaro and inanga.

- © Fairfax NZ News