Taranaki seabed mining raises whales concerns

The protection afforded to blue whales in New Zealand waters may need to be increased, now a study has found they may be more regular visitors to the South Taranaki Bight than previously thought.

The whales had been thought to pass through the bight while migrating to and from summer feeding grounds in Antarctica.

But a study by the National Institute for Water and Atmospheric Research (Niwa) of whale sightings between 1979 and 1999, and two surveys in 2011, show the whales are a regular presence.

Blue whales are the giants of the ocean, growing more than 20m in length and weighing more than 100 tonnes. They feed on huge amounts of plankton.

Jim Campbell, biodiversity manager for the Department of Conservation in Wanganui, said the presence of blue whales in the bight was food related.

"There are all these nutrients that come up from Cook Strait, and they meet other currents, and it's just a really fertile feeding ground for them," Mr Campbell said. Recordings of blue whale sightings from the Wanganui coast were virtually non-existent because they did not come close to shore, he said. "Blue whales are usually spotted from the Taranaki oil rigs, or from fishing boats, a long way out to sea."

However, two years ago a dead pygmy blue whale - a smaller subspecies of the blue whale - washed up on Wainui Beach. It was more than 22m long and took two diggers to bury it.

Mr Campbell said in the 19th and early 20th centuries blue whales had been hunted nearly to extinction, and their slow calving rates did not help.

"They appear to have shown an improvement in numbers recently, but it's really slow."

And now blue whales could be under threat again - but this time from mining.

Niwa marine ecologist Leigh Torres said more work was needed to determine the scale and significance of the South Taranaki Bight foraging ground.

"The South Taranaki Bight is the largest offshore natural gas and oil exploration area in New Zealand, with seven production platforms, considerable seafloor pipelines, and significant plans for expansion in the near future.

"Shipping traffic and seabed mining activities have been shown to impact blue whales directly - altering their behaviour and degrading their habitat through acoustic disturbance and ship strikes. We need to gain a better understanding of how and when blue whales forage here so that possible impacts can be avoided."

Dr Torres said the blue whale was classified as a migrant species, meaning they were not afforded the same level of protection as other large whales in New Zealand coastal waters.