Why whales strand and how to help them
Farewell Spit is the country's largest sandspit, stretching for 32km from the northwest tip of the South Island. It protects Golden Bay from swells.
It is a world renowned bird sanctuary, but it is a known whale trap, where strandings by pilot whales are common and unfortunate.
DO WE KNOW WHY WHALES STRAND?
According to the Department of Conservation stranding is natural but not fully understood. More than one factor could be involved in any particular stranding.
For instance, a pod may follow a leader that is sick or disoriented into the shallows. or pod members might go to the rescue of a young whale that gets stuck.
Gently sloping sand or mud shorelines can absorb the sonar signals whales use for navigation and that leads the whales to think they are in deeper water.
WHAT IS THE PROBLEM WITH FAREWELL SPIT?
Jochen Zaeschmar, a marine biologist and member of whale stranding response group Whale Rescue, said part of the problem is that Farewell Spit reached so far out into Cook Strait.
"Inside it you get these massive mudflats where the tide goes out for 5km," he said. "They're (whales) swimming along, then the next thing they know the water literally runs out from underneath them."
Pilot whales relied heavily on sonar for their navigation but the gradually shelving sandy and muddy beaches in Farewell Spit gave off poor echoes. As a result the whales still thought they were in deep water.
Pilot whales were highly sociable. "It only takes one to get into trouble, then the others all try to help," Zaeschmar said.
It wasn't clear why pilot whales ended up close to land, as they were an offshore species, however whale strandings are expected at Farewell Spit particularly at this time of year.
WHY THIS TIME OF YEAR?
Pilot whales seemed to be in coastal waters more at this time of year, Zaeschmar said.
Strandings happened all year round and were more common in the north in winter. "It seems they go further south as the water warms up, probably following their prey."
CAN ANYTHING BE DONE TO STOP WHALES STRANDING?
People had tried to use pingers, which send out signals, to try to warn the whales off but they didn't seem to work well.
The best thing was to have a good sighting network, enabling a quick response to any stranding.
WHAT HAPPENS TO WHALES WHEN THEY STRAND?
As the water ran out the whales often ended up lying on their sides, Zaeschmar said.
They could not right themselves until fully afloat. That meant that as the tide came back in they struggled to keep their blowholes above water to enable them to breath.
"They literally drown because they run out of their strength trying to breathe. It's a slow, painful death for them. It will take hours for them to run out of strength to move their body up to breath."
HOW DO PEOPLE HELP?
Pilot whales could stay alive on a beach for a few days.
They were at risk of overheating so the aim was to keep them cold and put water over them.
"They won't like it but it doesn't kill them," Zaeschmar said.
"Right them, put them on their belly so the blowhole is up and stable, and keep them cool."