Cetacean stranding, commonly known as beaching, is a phenomenon in which whales and dolphins strand themselves on land, usually on a beach. Beached whales often die due to dehydration, collapsing under their own weight, or drowning when high tide covers the blowhole. Cetacean stranding has occurred since before recorded history.
Several explanations for why cetaceans strand themselves have been proposed, including changes in water temperatures, peculiarities of whales' echolocation in certain surroundings, and geomagnetic disturbances, but none have so far been universally accepted as a definitive reason for the behavior. However, a link between the mass beaching of beaked whales and use of mid-frequency active sonar has been found.
Although a range of cetacean species regularly strand in groups, including beaked whales, pygmy sperm whales, false killer whales and common and bottlenose dolphins, pilot whales are the most common in New Zealand. These whales sometimes strand in pods of more than loo and, of the half a dozen sites around the coastline involving mass whale strandings, Golden Bay beachings are the most regular and involve the largest numbers. Other locations include Ninety Mile Beach, the coastline near Whangarei, the Mahia Peninsula, the east coast of the Coromandel Peninsula and the Chatham Islands.