At least 12 killer whales were found dead amid rough conditions at sea along New Zealand’s North Island.

Axar.az reports, citing Radio New Zealand, that Joel Lauterbach, a conservation official, said they were notified of the stranding of 15 pygmy killer whales on Thursday, when they along with volunteers launched a rescue mission on Ninety Mile Beach in the Far North District.

The whales were scattered across several kilometers of the beach, but conditions at sea were tough with tides, waves and fading light challenging rescue efforts.

“Conditions remained challenging today,” said the official as the process for burial of the dead whales was underway.

Lauterbach said officials were working to gather information to “understand the full circumstances of the stranding” of the whales.

According to the report, a dozen of the rare whales were also stranded in 2018, eight of which were transported to calmer waters, but only one survived the refloating attempt.