Cetacean stranding

Cetacean stranding is a phenomenon in which cetaceans 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. Several explanations of the stranding have been proposed.

Every year, up to 2,000 animals beach themselves. Although the majority of strandings result in death, they pose no threat to any species as a whole. Only about 10 cetacean species frequently display mass beachings, with 10 more rarely doing so.

All frequently involved species are toothed whales (Odontoceti), rather than baleen whales (Mysticeti). These species share some characteristics which may explain why they beach.

Body size does not normally affect the frequency, but both the animals' normal habitat and social organization do appear to influence their chances of coming ashore in large numbers. Odontocetes that normally inhabit deep waters and live in large, tightly knit groups are the most susceptible. This includes the sperm whale, oceanic dolphins, usually pilot and killer whales, and a few beaked whale species.

Solitary species naturally do not strand en masse. Cetaceans that spend most of their time in shallow, coastal waters almost never mass strand.

Strandings can be grouped into several types. The most obvious distinctions are between single and multiple strandings. The carcasses of deceased cetaceans are likely to float to the surface at some point; during this time, currents or winds may carry them to a coastline. Since thousands of cetaceans die every year, many become stranded posthumously. Most carcasses never reach the coast and are scavenged or decomposed enough to sink to the ocean bottom, where the carcass forms the basis of a unique local ecosystem called whale fall. Single live strandings are often the result of illness or injury, which almost inevitably end in death in the absence of human intervention. Multiple strandings in one place are rare and often attract media coverage as well as rescue efforts. Even multiple offshore deaths are unlikely to lead to multiple strandings due to variable winds and currents.

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