Why do whales strand?

This Saturday, about 55 False killer whales (Pseudorca crassidens) stranded on Long Beach, Kommetjie, in South Africa. Both adults and calves began to appear on the shore around 5.30 in the morning, perhaps as a result of the bad weather. This incident is the second large stranding in a short period of time; in March about 80 whales stranded in Hamelin Bay on Western Australia’s southern coast.

Massive whale strandings are however not new phenomenon; Long Beach was for instance the site of a heartbreaking stranding in 1928 when 103 whales beached on Christmas Eve. This was before marine experts and volunteers had figured out how to save stranded whales, so all 103 animals died in the scorching sun. This was also during a period when whales were chiefly seen as something that you hunted; not something worth saving.

So, why do whales beach? Scientists are still in the dark on when it comes to this bewildering question and no hypothesis has been confirmed yet. In his book “Whales and Dolphins of the Southern African Subregion”, whale researcher Peter Best lists a long row of hypotheses – all of the seemingly plausible – and also states that whale strandings may be due to a combination of several factors.

“It is very likely that no single cause is responsible and elements of some hypotheses may have to act in combination to produce the circumstances for a mass stranding to occur”, Best explains.

Here are some hypotheses put forward by marine scientists:

• Parasites infesting the middle ear can cause severe disorientation and make it difficult for whales to navigate. If one or several animals in a group develop middle-ear problems, the other ones might follow them due to their social bonding, even if it means stranding on a beach.
• An injured or sick whale may send out a distress call that the others follow all the way up on the beach.
• If cetaceans navigate using the earth’s geomagnetic field, geomagnetic disturbances could make them disorientated and, if they’re unlucky, even cause them to beach.
• Beachings may be a density-dependent response, where a population approaching its carrying capacity suffers increased natural mortality.
• Whales hunting for food close to the shoreline may accidently strand themselves in the pursuit.
• Whales might end up on beaches after getting caught in a rip current, getting their sonar confused. A rip current (also known as rip tide) is a strong surface flow of water returning seaward from near the shore.
• Beaked whales seem to be extra sensitive to mid-range sonar, so human activities may be to blame for the stranding of beaked whales.