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Humans are often implicated in orca deaths. Now a team that looked at how orcas in the Pacific Ocean died has linked some deaths with human activity.
Despite commonly being called killer whales, orcas are actually dolphins. Stephen Raverty at the British Columbia Ministry of Agriculture in Canada and colleagues examined 53 orcas that washed up from the eastern Pacific Ocean between 2004 and 2013 to determine what led to their deaths. The team was able to identify the cause for 22 individuals.
One calf died of sepsis after swallowing a large fishhook that pierced its throat, while six of the animals were struck by ships before dying and a further three had traumatic injuries that couldn’t be traced. According to Raverty, in one case an animal was observed approaching a ship and died after being struck by the propeller.
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Some orcas in the study died from infections, parasites, congenital anomalies and reproductive disease. Malnutrition contributed to several of the orcas’ deaths, with many appearing very thin or emaciated and presenting with a condition called “peanut head”, where there is a loss of fat from around the back of the head.
Malnutrition could 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.
“With killer whales living in every ocean from Arctic to Antarctic waters, it is hard to generalise but we can say that the greatest threat to wild orca health is simply proximity to humans,” says Erich Hoyt, co-chair of the IUCN Marine Mammal Protected Areas Task Force.
Journal reference: PLoS One, DOI: 10.1371
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