Why Do Whales And Dolphins Beach?

Jan 27, 2012 By Deepa Gopal
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Farewell Spit, New Zealand: The shallow, sandy waters off New Zealand's South Island lie in the migration path of whales. On Monday, a pod of 99 pilot whales were found stranded on the beach, prompting a huge rescue operation. With 36 dead, volunteers were working round-the-clock caring for the remaining -- keeping them cool and wet, and nudging them towards the open sea during high tide. 

While seventeen made it back out at the first high tide on Monday night, multiple attempts were made to re-float the remaining whales. The disoriented mammals beached themselves again within a few hours. The beached whales have died or have been put to sleep (euthanized) by New Zealand officials.

Cape Cod, Massachusetts: A pod of 85 dolphins beached themselves off the north-east coast of United States this past week. The cape's U-shape and shallow water inlets can be confusing to dolphins. With over fifty dead, rescuers were able to re-float the remaining dolphins. So far the signs are encouraging, and the dolphins have been spotted in deep waters off the coast of Maine.

Why do dolphins and their whale cousins beach themselves in such large numbers? 

A misguided leader?

Whales and dolphins travel in groups, called pods. While some species of dolphins may migrate as they follow warm ocean currents and food, whales are the long-distance travelers. Every winter they travel to warm Equatorial waters to give birth to their young. And every spring with their young ones in tow, they travel back to the cold Arctic waters to feed on krill and other food that is in abundant supply. 

Scientists believe there is a social structure in the whale and dolphin family --  a dominant mammal who leads the pod. One theory is that when the leader gets sick or disoriented and heads into shallow waters, the group follows his distress signals, leading to mass beaching. Or perhaps the leader may come too close to the shore while following a school of fish or to escape predators such as killer whales.

Is our Earth playing havoc?

Weather may play a part, as the El Nino cycle (described here) causes changes in the water temperature that could affect the food supply. Changes in our Earth's magnetic field as a result of earthquakes or volcanoes may also disrupt a whale's sense of direction -- animals as you know are the first to sense the slightest disturbances. The recent solar storm that plummeted the Earth last Tuesday may have discharged enough radiation to cause the recent beaching as well.

There are other theories -- algal blooms that cause poisonous red tides (read here), diseases such as pneumonia, and man-made pollution from large shipping vessels and underwater exercises by the Navy (read here).

Mass beachings such as these have been recorded in history. Pliny the Elder, a Roman Historian in first century A.D, recorded that the "receding tide had left behind 300 beasts of marvelous size" in south of France. However, with so many species of whales on the endangered list, it is sad to see these huge mammals meet their end on our beaches.

Courtesy Scientific American, Discovery News