Ocean News

Study Reveals the Extent of Killer Whale Attacks on Humpback Whales

Orcas (also known as killer whales) are apex predators in the marine environment, often feeding on large marine mammals including at least 20 different species of cetacean (whales, dolphins, and porpoises). However, the ecological role that killer whales have on the predation of one whale species, the humpback whale, has long been debated as attacks are rarely seen. But now, a new study published in Endangered Species Research has found that killer whale attacks on humpback whales may be increasing.

"Because the chances of observing rake marks on young, vulnerable whales increased in the last 20 years, we think that killer whale attacks on humpback whales may be more common now than they were in the past, perhaps due to the recovery of whale breeding stocks in the Southeast Pacific after hunting was prohibited," said Juan Capella, lead author and marine biologist from Whalesound Ltd. in Chile.

To assess how common killer whale attacks are on humpback whales, the researchers studied photos of whales living in the warm water breeding grounds surrounding South America and the cold-water feeding grounds just off the western Antarctic Peninsula. "We set out to discover where, when and at what age humpback whales in the South-eastern Pacific are attacked by orcas," said Hector M. Guzman, marine ecologist at the Smithsonian Tropical Research Institute.

By analyzing the battle scars associated with a killer whale attack, the team found that 11.5 percent of adult humpback whales and 19.5 percent of their calves carried scars. "The number of scars borne by an individual whale didn't seem to change from year to year, suggesting that orcas primarily attack calves during their first migration," said Fernando Felix, a marine biologist from the Pontifica Universidad Catolica and the Whale Museum in Ecuador. Interestingly, scarred female adults arrived at the breeding grounds with more calves than those who had no scars. The researchers believe that maybe these individuals were better at evading orcas because they have survived previous attacks. As regular prey of killer whales, cetaceans likely have developed behavioral strategies to reduce predation risk, such as becoming silent, moving to shallow waters, hiding behind boats, or escaping by fleeing from high altitude summering grounds to low-latitude wintering grounds, where killer whales are less abundant.

This research is an example of excellent collaborative effort between international institutions. Guzmán finished by saying “We want to underscore the importance of transnational studies to better our understanding of marine environments and their inhabitants as we recommend policies that work both for the health of the ocean and for the beneficiaries of its wealth."

By Ellis Moloney

Capella, J., Félix, F., Flórez-González, L., Gibbons, J., Haase, B. and Guzman, H. (2018). Geographic and temporal patterns of non-lethal attacks on humpback whales by killer whales in the eastern South Pacific and the Antarctic Peninsula. Endangered Species Research, 37, pp.207-218.

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