Deep-diving whales may get into trouble when they stray off-course and find themselves in a region with too little food to feed upon. Lack of food means they get too little fresh water and become dehydrated. When their kidneys start to fail, the whales throw themselves on the shore.

Once out of water, the great weight damages the whale’s body, releasing into the bloodstream stores of protein myoglobin. This protein is essential for oxygen transportation under the pressure in the depth, but in large quantities it damages kidneys even more. After about an hour on the beach, a whale’s health is beyond recovery, and even if refloated, myoglobin will just run faster to kill the animal quicker, ZSL specialists say.

“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.”