A population of about 200 killer whales is believed to live in the North Atlantic, primarily around the areas of Newfoundland and Labrador in Canada. Compared to the well-studied orca populations of the Pacific Ocean, little is known about these Atlantic residents. Interested to learn more, a graduate student at the University of Rhode Island is the first to investigate the whales' ecology. The findings of her study revealed minke whales are the killer whales' prey of choice, which could prove useful for animal conservation.
"We had no idea what they were even feeding on in the Atlantic, but eventually it has become more and more clear that minke whales are the predominant prey source for certain killer whales in our area," Tara Stevens, who will earn her doctorate at the University of Rhode Island Graduate School of Oceanography later this year, explained in a news release. "Their strategy is to drown the animal. We would see sometimes 10 or 20 killer whales jumping on a minke to force it under water to drown it."
Due to the remoteness of the whales' Canadian range, Stevens conducted a series of field observations, and gathered sighting reports from fishermen and tour boat captains to ensure she wasn't missing anything. The data collected indicates killer whales also prey on dolphins, porpoises, seals and other small prey. However, it is difficult to determine if or what kind of fish the whales eat because that takes place entirely under the water and out of sight.
Comparatively, it is well-known that Pacific Northwest killer whales mostly prefer feasting on Chinook salmon.
While it is unknown whether killer whales in the North Atlantic are prey specialists, as they are in the Pacific, Stevens believes the whales' distribution and migration patterns are directly linked to those of their prey. For example, those that remain in Newfoundland and Labrador year-round have been seen lingering around pack ice, feeding on breeding seals.
In an effort to better track their movements and social interactions, Stevens plans to next catalog photographs of North Atlantic killer whales. She has also collected DNA from some animals for analysis.
"The population dynamics seem to be similar to those of the transients in the Pacific," Stevens said. "They seem to roam around in groups of five or six individuals and don't have strong fidelity to any particular site. They don't spend long periods of time in the same area like resident populations do out west [U.S.]."
Their social groups also tend to be quite variable -- similar to Pacific transient whales, which are characterized by a broader range more variable social groupings than residents, which remain in stable social groups for life.
Additional groups of killer whales have also been spotted around the British Isles, Norway and the Arctic Canadian islands, so Stevens is interested in whether those animals occasionally interact with the Newfoundland whales. Since so there are so many questions left to be answered, the next phase of research may involve tagging a few individuals. Stevens recently presented the results of her study at the 2016 biennial Ocean Sciences meeting in New Orleans.
Killer whales have suffered dramatic population declines. While they are not listed on the Endangered Species List, due to a lack of "sufficient data," they are vulnerable to a series of environmental risks, including climate change, overhunting, prey and habitat loss, and excessive noise, to name a few. With a better understanding of their Atlantic Ocean range and food preference, conservation efforts can be targeted to better protect the iconic species.
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