When a whale lies on the beach, it's not sunbathing but is stranded.

Cetacean stranding, commonly known as beaching, is a phenomenon of dolphins and whales stranding themselves on beaches. There are around 2,000 strandings each year worldwide, according to Whales and Dolphins by Anthony R. Martin.

According to New Zealand Herald, a pod of pilot whales were found stranded on the beach of New Zealand's Farewell Spit from February 22 to 23, killing 19 of them. Meanwhile, 46 whales stranded on a beach on the Indonesian island of Madura died on February 19, according to Reuters.

Why do whales wash ashore and beach themselves?

There are many different factors that can cause a stranding. 

The beaching of a single whale is usually because of sickness and injury. Whales that are old, sick and those that die of natural causes are more likely to be washed up on the beach. Sometimes they rush up to the beach to avoid predators.

Human activities also have big impact on whale beachings. Underwater noise, sonar interference and water pollution interfere with the orientation function of the whale's echolocation system. And after years and months, its navigation system fails, causing it to get lost and be stranded on the beach. 

However, there are also cases of mass suicides, with groups of whales swimming to the beach, slapping, howling, and finally beaching and dying at low tide. This phenomenon is thought to be that whales are sociable animals that travel together in pods. They follow a leader, and die with their leader.

Though there are many theories and speculation within the biology community, the question still remains unresolved.

About The Blue World series:

The ocean covers more than 70 percent of the Earth. In this blue world, there are all kinds of marine life with surprising abilities we don't know about. In this series, CGTN guides you through the journey of exploring the amazing animals in the ocean. 

For more:

The Blue World: The mystery of the sex of green turtles

The Blue World: Brainless jellyfish

The Blue World: Half asleep, half awake dolphins

The Blue World: Never make a pufferfish angry

The Blue World: From round fish to flatfish

The Blue World: When a whale sinks into the sea

The Blue World: Sea otter's treasure chest

The Blue World: Mother octopuses' mission

The Blue World: When the beauty of coral fades

(All images via VCG)

(If you want to contribute and have specific expertise, please contact us at nature@cgtn.com.)