Wairau hydro scheme would hasten terns' decline

28 June 2006 - Nelson

Contact: Forest & Bird Top of the South Island Field Officer Debs Martin, 03 545 8222, 027 684 0599

The number of black-fronted terns wintering in the Bay of Plenty has declined over the past 30 years according to regular winter counts, and building a hydro-electric power scheme on their breeding grounds on the Wairau River would hasten the species’ decline, Forest & Bird says.

Tauranga-based power company TrustPower proposes to divert most of the Wairau River flow into a 50km canal to develop a hydro scheme in Marlborough, destroying vital habitat where black-fronted terns and other endangered birdlife breed.

Black-fronted terns breed on South Island braided rivers like the Wairau, and fly to the coasts of the North and South Islands in the autumn to feed and winter over.

The Wairau is one of the most important breeding grounds for black-fronted terns, with 12% of their total population breeding there.

TrustPower’s own “backyard,” the Bay of Plenty, is a key North Island wintering location for black-fronted terns, and winter counts by Ornithological Society of New Zealand’s Paddy Latham between 1977 and 2002 show a marked decline in the numbers of black-fronted terns wintering there.

Mr Latham counted a maximum of 58 in the winter of 1978, but the maximum winter count numbers declined sharply through the 1990s to a low of seven in 1997 and 1999.  His last winter maximum count, in 2002, was of just 10 terns.  Although he has not conducted winter counts there since, Mr Latham does not expect numbers have recovered subsequently.

Recent winter maximum counts are far lower than winter maximum counts in the early 1950s which recorded numbers between 60 and 129 birds.

If winter maximum counts continue to fall at the rate they declined between 1981 and 2002, there would be no black-fronted terns wintering in the Bay of Plenty by 2010.

Maximum winter counts in the Bay of Plenty are an indicator of the terns’ overall population in the region. There are an estimated 5,000 black-fronted terns left in New Zealand and the species is listed as being in serious decline.

It is also included on the IUCN (World Conservation Union) 2006 “Red List” of Species Threatened with Extinction as Endangered, and the IUCN list notes rapid population decline in some wintering sites.

Forest & Bird Top of the South Island Field Officer Debs Martin says if the Wairau hydro scheme goes ahead it will further endanger the terns’ already precarious situation.

The scheme would cause smaller braids of the Wairau to dry up for much of the year, destroying important habitat for fish and water insects, and significantly reducing food supply for birds by an estimated 40%, and will increase access by predators to nest sites.

Sustained low flows may also increase summer water temperatures to levels that could kill fish and insects, further reducing birds’ food supply, Debs Martin says.

Forest & Bird is among more than 900 groups and individuals who have made submissions against the hydro scheme going ahead.

The importance of the Wairau as a breeding ground for black-fronted terns is one of the main reasons why Forest & Bird is also seeking international recognition for the Wairau under the Ramsar Convention on Wetlands.  

Maximum winter counts for black-fronted tern in the Bay of Plenty 1977-2002

SOURCE: “Black-fronted Terns Wintering in the Bay of Plenty”, Notornis 28: 221-239 (1981), P.C.M. Latham; and P.C.M. Latham, pers comm, 13/05/06.