MAF and iwi to check effectiveness of sea squirt removal

Friday 18 March 2011

The Ministry of Agriculture and Forestry (MAF) and Northland iwi are back on the coastline next week to measure the effectiveness of last year’s trial removal of an invasive sea squirt from some Far North shorelines.

MAF Senior Marine Adviser Kathy Walls says the sea squirt /Pyura praeputialis/ (known simply as Pyura) has been an aggressive invader of rocky shorelines where it has established outside of its native Australian habitat.

It was first detected at the remote Twilight Beach near Cape Maria van Diemen and MAF surveys have since found Pyura to be widely distributed around the Far North coastline.

Because of the species’ ability to impact on other marine organisms on the shore, including green shell mussels, and local concern about it, a decision was made to test the effectiveness of removal techniques through a three stage pilot treatment programme.

“While we’ve already determined that fully eradicating this well established sea squirt is not feasible, there is a high level of interest in the local community and we decided that trying to remove the species from some sites where population numbers are relatively low had merit. This programme will tell us whether it’s worthwhile attempting to manage Pyura at other places where numbers are low.”

Last August a team of local people teamed up with MAF and marine scientists and spent several days manually removing the sea squirts from the rocks at the Bluff at 90 Mile Beach and Whareana Bay. At the same time, a scientific control trial was carried out on a population at the entrance to Parengarenga Harbour, where one marked area was treated and one left alone to compare results.

Now it’s time to revisit the areas to check how effective the treatment has been and see if reinvasion into the cleared areas has occurred. Any Pyura found will once again be removed. The team will start at the Bluff on Sunday afternoon, 20th March, and it’s hoped the work will be completed at all three sites on Wednesday 23 March.

Kathy Walls says the plan is to undertake a third stage to the trial in six months to further evaluate the removal success. If, however, the Pyura is found to have returned with a vengeance (over more than 80% f the trial areas) MAF may have to re-evaluate the trial’s continuation.

“Ultimately it will be up to communities involved to determine if they wish to continue with management of this sea squirt after the trial period,” Ms Walls says.

“This teamwork is an exciting development which supports MAF’s goal of enabling communities to lead the long-term management of pest incursions, raises local awareness of biosecurity issues and prepares communities ahead of any future marine biosecurity events,” she says.

ENDS

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