Friday, 25 July 2014

Why Do Whales, Dolphins and Porpoises Beach or Strand Themselves?

Whales and their relatives are intelligent animals. Many use echolocation (the emission of sound waves and the analysis of the reflected sound) to enable them to navigate even when the visibility in the ocean is poor. It's therefore very puzzling that whales, dolphins and porpoises sometimes swim on to a beach and strand themselves. The urge to reach the beach is so strong that if the animals are moved into the water, they often head back to the beach to face almost certain death. Although cetaceans are mammals and breathe air like us, their bodies are damaged without the buoyancy of water to support them. Starvation and dehydration also contribute to their death on land.

A killer whale and a calf - photo by Christopher Michel,
CC BY-2.0 License

Beaching of cetaceans (whales, dolphins and porpoises) has occurred since at least the time of Aristotle, so it's probably a natural part of their biology. It's possible that human activity is increasing the incidence of beaching today, though, which is one reason why it's important to know the causes. It's heartrending to see sentient animals in distress and dying on a beach. In addition, if a large group of animals beach themselves, or if beaching occurs frequently, the animal's population size may be adversely affected.

Beaching of single animals is generally due to the fact that the animal is sick and can longer swim or because a baby has lost its mother and is too weak to fight ocean currents. Mass beachings or strandings are harder to explain.

In many cases today, investigators never discover why a group of cetaceans beach. Sometimes there are clues, however. Occasionally the animals' bodies show injuries that suggest that they have recently been attacked by sharks or other cetaceans. They may be trying to escape the danger. In other cases, tests show that the whales are infected by parasites or viruses, which may affect their navigation system and cause them to become disoriented, Many cetaceans are very social animals and have close bonds with other members of their group. If one or more animals in a group beach, the others may follow because they don't want to be separated from their companions or their leader.

Beached false killer whales - photo by Bahnfrend,
CC BY-SA 3.0 License
There have been suggestions that military sonar interferes with the navigation system of cetaceans and causes beaching. High intensity sonar has been found to cause bleeding in the brains of cetaceans. Another suggestion is that beached cetaceans have been confused by magnetic field anomolies. There is no direct evidence for this, but a substance called biomagnetite has been found in the brains of some whales. It's known that some animals use this substance to detect the Earth's magnetic field and to navigate. However, we have biomagnetite in our body, too. The role of biomagnetite in whales and in humans is far from clear.

If one cetacean beaches and if that animal is small or is a youngster of a big species, it may be possible to save the animal if a rescue facility is nearby. When a big animal or many animals are stranded, it's harder to help them. It's sometimes possible to move stranded animals back into the water if they're not too big, but they may beach themselves again. One argument against moving the animals into the water is that if they've beached themselves because they're sick, when they're back in the ocean they may infect other animals. We really need to discover the causes of beaching for the sake of the world's cetaceans.

No comments:

Post a Comment