Orcas swim in New Zealand

Orca deaths are due to human activity

By Krista Charles

Orcas swim off the coast of New Zealand

Naturbildbibliothek / Alamy

Humans are often implicated in orca deaths. Now, a team studying how orcas died in the Pacific has linked some deaths to human activity.

Although orcas are commonly referred to as killer whales, they are actually dolphins. Stephen Raverty, of the British Columbia Department of Agriculture, and colleagues examined 53 orcas that washed up from the eastern Pacific between 2004 and 2013 to determine what led to their deaths. The team was able to identify the cause for 22 people.

One calf died of sepsis after swallowing a large fishhook that pierced its neck, while six of the animals were hit by ships prior to death and had three other traumatic injuries that could not be traced. According to Raverty, in one case an animal was seen approaching a ship and died after being hit by the propeller.


Some orcas in the study died from infections, parasites, congenital abnormalities, and reproductive diseases. Malnutrition has contributed to several orcas deaths, with many appearing very thin or emaciated and exhibiting a condition called “peanut head,” which involves loss of fat from the back of the head.

Malnutrition can be a result of human activity. Overfishing and climate change can reduce the amount of food orcas can access. Pollution can also build up in the orcas’ bodies and weaken their immune systems.

“It is difficult to generalize about killer whales, which live in all oceans from the Arctic to the Antarctic, but we can say that the greatest threat to the health of wild orcas is simply being close to humans,” says Erich Hoyt, Co- Chairman of the IUCN Marine Mammal Task Force Protected Areas.

Journal reference: PLoS One, DOI: 10.1371

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