Warmer seas could be behind New Zealand whale strandings, expert says

Raising water temperatures caused by the El Nino weather phenomenon could be responsible for a series of whale strandings in New Zealand, a marine scientist says.

More than 200 whales died in the six days to Friday in three different mass standings across the South Pacific country.

Marine mammal specialist Karen Stockin told Radio New Zealand late on Sunday that higher sea surface temperatures were changing the movement of the mammals’ prey, causing a knock-on effect for their predators.  

"You're going to see more frequent sightings of both strandings and live sightings of some of these marine mammal predators coming closer to shore," the Massey University lecturer added.

El Nino occurs every few years and involves fluctuations in ocean surface temperatures in the Pacific.

More than 145 pilot whales perished on a remote beach on Stewart Island on November 24, while four days later 12 pygmy wales were stranded on the North Island's 90 Miles Beach.

On Friday, about 90 pilot whales beached themselves in the Chatham Islands. Between 30 and 40 of them managed to refloat and returned to the sea, while 51 died.

There has also been an unprecedented number of blue whale sightings in the Hauraki Gulf off New Zealand’s North Island.

Whale strandings are relatively common in New Zealand, with the Department of Conservation responding to an average of 85 incidents each year. Most of these are single animals and not large pods.

Pilot whales are prolific stranders but such behaviour is not well understood. Factors may include sickness, navigational error, geographical features, a rapidly falling tide, being chased by a predator or extreme weather.

"The more this goes on, the more animals that are coming, the more we're starting to challenge if there is something going on more broadly that we're not yet aware of," Stockin said.