Why were Mahia’s stranded dolphins euthanised?

Nearly half of a pod of dolphins had died while the rest were badly injured by the time they were stranded a second time near Mahia - making euthanisation a “welfare decision”.

The pod of around 40 false killer whales and bottlenose dolphins was first stranded early on Sunday afternoon but refloated with the high tide about 3pm.

They stranded themselves for the second time later that evening, this time on a remote and inaccessible reef point further south from Taylor’s Beach, and DoC made the decision to euthanise the pod.

Project Jonah New Zealand said in a statement on social media that DoC rangers who got to the reef found almost 40 per cent of the pod had perished while others were badly injured.

“This is a very sad outcome for what seemed hopeful throughout the day. Among the pod were some bottlenose dolphins. Scientists from False Killer Whales NZ are travelling to the site to hopefully learn more about the pod,” the statement said.

Project Jonah general manager Daren Grover told Hawke’s Bay Today those scientists were on the ground as of Monday and were involved in hui with DoC and iwi.

He said that Project Jonah had received reports that dolphins in the pod were “smashing themselves on the rocks” due to stress when they beached a second time.

“The tide was out and would not come back for another 10 hours. [Euthanising] was a welfare decision. They weren’t going to make it, or if they did it would be in a terrible condition,” Grover said.

He said he was not certain what would be done with the remains yet, but he believed they were in a good position to satisfy both mātauranga Māori and Western scientific perspectives.

Though not on this scale, dolphin and whale strandings are not new to Mahia Peninsula.

In 2021, a 10 to 12-metre sperm whale died after it was stranded, in 2020, a two to three-metre pygmy sperm whale died on Mahia Beach and, in 2017, an 18-metre sperm whale died after it was stranded at Mahia Beach.

Hawke’s Bay Today has seen a social media post that says a rāhui has been placed on the Te Hoe Mātaitai reserve of the peninsula as a result of the euthanisations — confirmation of this from authorities has yet to be received.

False killer whales are found globally, typically in deep offshore waters.

Research from Far Out Ocean Research Collective, a New Zealand-based collaborative open ocean research platform, suggests there is possibly a small local population of false killer whales off north-eastern New Zealand.

“False killer whales also appear to form a permanent association with oceanic common bottlenose dolphins in the study area,” the Far Out Ocean website said.

“The interspecific associations between these two species and with pilot whales are the subject of ongoing behavioural research.”

False killer whales are often confused with the more common pilot whales.

Common bottlenose dolphins are considered “Least Concern” by the International Union for Conservation of Nature on a global level.

According to DoC, bottlenose dolphin population sizes are largely unknown but this species is relatively common worldwide.

“Bottlenose dolphins are commonly associated with other cetaceans including pilot whales, rough-toothed and Risso’s dolphins, and humpback whales,” the DoC website said.

James Pocock joined Hawke’s Bay Today in 2021 and writes breaking news and features, with a focus on environment, local government and post-cyclone issues in the region. He has a keen interest in finding the bigger picture in research and making it more accessible to audiences. He lives in Napier. james.pocock@nzme.co.nz