Large whales that strand themselves should be killed, as any attempts to save them are probably futile and likely to cause more suffering, according to animal welfare specialists.

The results of a series of autopsies of beached whales carried out by the Zoological Society of London (ZSL) have led veterinarians to conclude that sperm whales and beaked whales have little chance of survival if they become stranded.

"Euthanasia can be a very emotive issue," says Adam Grogan of the UK's Royal Society for the Prevention of Cruelty to Animals (RSPCA), "but it is often in a stranded whale's best interests." It is normally carried out by lethal injection.

The statement, made by the Marine Animal Rescue Coalition, a group of organisations including the International Fund for Animal Welfare and the RSPCA, comes as rescuers were trying to save 90 long-finned pilot whales and bottlenose dolphins that had beached themselves on the west coast of Australia. At time of writing, only 10 of the animals were still alive.

Crushing weight

Stranded sperm and beaked whales have been well studied in recent years - in particular, several have become stranded while still alive, allowing biologists to obtain blood samples and piece together what led to the beachings.

Deep-diving species, such as sperm and beaked whales often get into trouble if they stray off-course and find themselves in waters where there is little food for them. Because they are unable to feed, they also do not take in water, and become dehydrated.

The ZSL vets say that this and the whales' large size makes them vulnerable to kidney failure if they beach themselves. Without the support of the surrounding seawater, their weight damages their muscles, releasing stores of damaging myoglobin into the bloodstream.

Myoglobin is a protein essential for oxygen transport while the whales are submerged, but it is also toxic to the kidneys.

According to the autopsy data from the ZSL, once the whales have been stranded for an hour, the renal damage is already irreversible. Attempting to refloat the whales at this point only makes the situation worse, as it allows their blood to circulate more freely, carrying even more myoglobin into the kidneys.

Rescuers have often struggled to save stranded whales. In 2002, a pod of pilot whales stranded themselves on Cape Cod in Massachusetts, - many were refloated, but proceeded to re-beach themselves, with fatal results.