What’s in the news?

• Two people were rescued after a group of orcas, also known as killer whales, sank their 15-metre-long sailing yacht in the Strait of Gibraltar.

About

• Orcas (also known as killer whales) are marine mammals. 
• They belong to the sub-order of toothed whales (known as odontocetes) but are also the largest member of the dolphin family.
• Orcas are highly intelligent and social animals, spending their lives in groups or pods where they hunt together and share responsibility for raising young and taking care of the sick or injured.
• Orcas only allow one half of their brains to sleep at a time. The other half stays alert enabling them to continue breathing whilst looking out for dangers in the environment. They only close one eye when they sleep. The left eye will be closed when the right half of the brain sleeps, and vice versa. This type of sleep is known as unihemispheric sleep as only one brain hemisphere sleeps at a time. Orcas periodically alternate which side is sleeping so that they can get the rest they need without ever losing consciousness. 

Physical Appearance

• Adult orcas have shiny black backs, white chests and patches of white above and behind their eyes. 
• They have paddle-shaped pectoral fins and tall triangular dorsal fins. 
• Orcas vary in size depending on where they live. Adult males are larger than adult females, with males reaching 32 feet (10 meters) in length and females growing to 28 feet (8.5 meters).

Location and Types

• Orcas are likely the second most widely distributed mammal in the world, next to humans and are found in every ocean on the planet. 
• There are three distinct types of orcas recognized in the eastern North Pacific Ocean—transient, resident, and offshore. 
  • Residents live close to shore in large pods of about 10 to 20 individuals and feed primarily on fish. 
  • Offshore orcas are similar to residents, but are distinguished by their smaller overall size and rounded, nicked fins. 
  • Transient orcas live in smaller groups of about three to seven individuals and spend their lives out at sea where they prey on seals, sea lions, and other dolphins. 

• All three types of orca have genetic differences and do not mingle or interbreed.

Natural Predators

• Killer whales have no known natural predators except possibly other killer whales. 

Conservation status

• Killer whales were actively hunted in Norway, Japan, the Soviet Union and the Antarctic through until the 1980’s, but are now only taken in small numbers for food (or as a population control measure) in coastal fisheries in Japan, Greenland, Indonesia, and the Caribbean islands15. 
• Killer whales are considered Data Deficient on the IUCN Red List of Threatened species16.  

Sources

• https://indianexpress.com/article/explained/explained-sci-tech/orcas-sinking-boats-9335819/
• https://iwc.int/about-whales/whale-species/killer-whale
• https://www.nwf.org/Educational-Resources/Wildlife-Guide/Mammals/Orca