DOC's Wairau predator trapping hasn't worked
November 17, 2006
by Ross McCullough
A Department of Conservation predator control programme on the Wairau River is proving ineffective for the endangered black fronted tern, a resource consents hearing in Blenheim heard yesterday.
DOC biodiversity assets programme manager Steven Cranwell told the hearing into TrustPower's proposed $280 million Wairau hydro scheme yesterday that the current level of predator control had not increased black fronted tern breeding success.
Started during the breeding season of 2004-05, one aim of the programme was to reduce key introduced species like cats, mustelids and rats, to improve the terns' breeding success.
Approximately 10 to 15 percent of the world's remaining black fronted terns breed on the Wairau.
As part of adaptive management, TrustPower has proposed a predator control programme to address concerns for the black fronted terns, should its scheme become operative.
Mr Cranwell said seven of 16 black fronted tern colonies in the area from Renwick Bridge to Rainbow Valley had been targetted for predators, with unsatisfying results.
"All results to date have demonstrated that DOC's trapping programme has failed to sufficiently increase hatching and fledgling success, in comparison to untrapped colonies," Mr Cranwell said.
The cost of the programme at the end of this breeding season was estimated to reach $133,000, but only 30 predators had been caught.
Mr Cranwell said despite no definitive evidence that trapping improved breeding success in colonies isolated by water, there had been fewer predators present on the islands than on the mainland.
"While predators can still get to islands, the amount of damage they do as opposed to mainland colonies is much less."
Ecologist James Jolly, who gave some rebuttal evidence for TrustPower, said without a long-term study into black fronted terns, which currently did not exist, it was not known how adult terns survived. "One needs a strong body of data to assess properly how they survive."
However, he said lowered flows resulting from TrustPower's scheme would have little effect on predator access to nesting colonies when compared to existing flows.
He said TrustPower proposed to undertake a study looking into what food chicks eat and the relationships between nesting success on and off islands, together with predator trapping.
Vern Harris of Property and Land Management Services Ltd (PALMS), which negotiated landowner access and set up meetings over the scheme for TrustPower, hit back at submitters who had accused it of blurring its role.
Mr Harris refuted claims various tactics were employed to persuade land owners to sign up to easements. He told the hearing neither he nor his colleague had any reason, need or desire to engage in the type of behaviour they had been accused of.
On the issue of land values decreasing if the scheme was to proceed, he said TrustPower had agreed to top up the sale price or purchase property based on valuation prior to the canal's existence, if that was what people wanted.
A previous map produced by PALMS showing the canal line and property titles it was proposed to cross had been "sanitised" due to confidential discussions taking place with land owners," Mr Harris said.
Commissioner Tony Willy made a request that an updated version be provided with the appropriate details included.
The hearing has adjourned and will resume on November 27 when TrustPower counsel Christian Whata will present its closing submissions.
