Watch These Orcas Follow Dolphins to Snag a Salmon Feast. - see Video at Bottom of Blog

 

Off the coast of British Columbia, killer whales are tailing dolphins, and both seem to be rewarded with fishy meals. But not everyone is convinced it’s teamwork—and the behavior may hint at other ocean stressors

Sara Hashemi - Daily Correspondent - Smithsonian

Orcas and dolphins are often seen sharing the waters off the coast of British Columbia. Sometimes, the creatures swim mere feet away from one another. Now, multiple observations of orcas, also called killer whales, trailing behind dolphins on salmon hunts suggest that the two predators sometimes team up to capture meals.

The findings were published in the journal Scientific Reports on December 11.

“These whales are top salmon hunting specialists. They’re highly specialized and highly skilled predators. To see them following dolphins as though they were leaders was really counterintuitive—and really exciting,” study co-author Sarah Fortune, a marine scientist at Dalhousie University in Canada, tells Leyland Cecco at the Guardian.

Fortune and her colleagues wanted to investigate why the whales and dolphins hang out together so much. So, in August 2020, the team tracked nine northern resident orcas (Orcinus orca) and observed how they interacted with Pacific white-sided dolphins (Lagenorhynchus obliquidens) during hunts for Chinook salmon around Vancouver Island. While the whales are top predators of this type of salmon, these fish are generally too big for the dolphins to catch and eat on their own.

Data trackers attached to the orcas with suction cups recorded the times and depths of dives, as well as underwater audio and video. Aerial videos filmed with a drone also helped the researchers monitor the animals’ behaviors.

Overall, the researchers identified 258 instances of orcas actively foraging while tailing dolphins on a salmon hunt. The two species often coordinated their movements with one another, and orcas dove deeper in the presence of dolphins compared with when they weren’t there. Orcas also reduced their echolocation and rolling movements when traveling with dolphins, hinting that the whales might eavesdrop on the dolphins as they locate fish. On one occasion, an orca munched on a fish while dolphins scavenged for scraps from the messy affair.

The team suspects that whales and dolphins were working together because they weren’t acting aggressively or avoiding each other. But some experts are doubtful.

“I’m not completely convinced that what we’re seeing here is cooperative; it seems clear that the dolphins can benefit from reduced predation risk and scrounging from killer whale kills, but I think more work needs to be done to demonstrate a benefit to the whales,” says Michael Weiss, a marine mammal biologist and research director of the Center for Whale Research who was not involved in the work, in an email to Live Science.

Jared Towers, an ecologist and executive director of the conservation organization Bay Cetology who also wasn’t involved in the study, tells the outlet that the behavior may instead be an example of kleptoparasitism, where an animal steals food from another.

But “if the dolphins were parasites, just there for a free lunch, the whales might act aggressively toward them to get them to leave—or the killer whales themselves might leave and go feed in adjacent areas,” Fortune tells the Guardian. “We really didn’t see evidence of antagonistic behaviors between species. And that really surprised us.

Even if the reason behind this species pairing is unclear, studies like this one illuminate how animals coexist in complex ecosystems, Erin Ashe, a marine conservation scientist at the nonprofit Oceans Initiative who was not involved with the study, tells the New York Times’ Alexa Robles-Gil.

“It could be that the dolphins are having some sort of refuge with the fish-eating killer whales,” Ashe says to the outlet. “The refuge might allow dolphins to get close to killer whales that don’t pose a threat. They can sort of size up their predator on some level.”

The researchers will conduct further studies to understand how common this cooperation between the two species truly is, per National Geographic’s Melissa Hobson. If this is a new strategy, it could be a bad sign for Chinook salmon, which are vulnerable to climate change and overfishing.

“What’s happening to the environment that’s necessitating this novel behavior?” says Ari Friedlaender, an ecologist at the University of California, Santa Cruz who wasn’t involved in the study, to the outlet.

“We already know that those salmon are very limited,” he adds. “If there’s now two populations of animals that rely on them instead of one, that could signal a requirement for even tighter legislation or restrictions.”

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