Watch orcas and dolphins team up to hunt—a possible scientific first
Researchers in Canada mounted cameras on orcas to spy on their behaviors and were amazed by what they saw.
With all the splashing, it was hard to tell what was happening under water. As the orcas surfaced to take a breath, dolphins were darting around their heads, but the water was so murky that the scientists didn’t have any idea what the animals were doing.
Using drones and cameras attached to the orcas, scientist have finally been able to learn something about the interaction between these two species that astonished them: the northern resident killer whales, also known as orcas, and Pacific white-sided dolphins seemed to be hunting together.
Researchers in British Columbia recorded 25 occasions where orcas followed dolphins diving down to find food. The authors think this is the first record of orcas and white-sided dolphins collaborating to hunt. The encounters were documented in a new study, published in Scientific Reports.
In one instance, the dolphins got involved after the orcas had caught a salmon. “As they were chomping down, there'd be bits of fish that would escape the [killer] whale’s mouth—like, a cloud of blood and scales,” says study author Sarah Fortune, assistant professor in the oceanography department at Dalhousie University in Nova Scotia, Canada. “And then we'd see dolphins coming around near the head to go after those fragments.”
It’s unclear if this is a new behavior or something the two species have always done. The finding may have resulted from improved technology like drones and lightweight underwater cameras that give scientists a better look at the animals’ lives. But some experts worry it’s a sign of a sparse food supply.
Fish-eating killer whales
There are three distinct orca populations—called ecotypes—in the northeastern Pacific, each with a different appearance, habitat, and diet.
“We have the transients, which are mammal hunters—[they eat] seals, sea lions, dolphins, porpoises and large whales,” says Josh McInnes, a marine ecologist with the Oceanic Research Alliance in California who wasn’t involved in the study. “Then we have offshore killer whales, which are much more rare… they eat sharks and fish.”
This study focused on resident killer whales, the third ecotype, which eat fish.
“They've evolved to feed almost exclusively on one species of salmon: the adult Chinook salmon,” says Fortune, who is also the Canadian Wildlife Federation Chair in Large Whale Conservation.
This salmon species is at risk of extinction, so the researchers wanted to know if the northern residents had enough to eat.
They attached suction cup tags—that popped off a few hours later—to individuals off Vancouver Island in British Columbia. The tags had forward-facing video cameras to capture an orca’s-eye-view, while drones analyzed the orca’s body condition from above.
Collaborating to hunt
The researchers noticed that “the killer whales were orienting towards the dolphins who were going after the salmon,” Fortune says. The two species weren’t just hunting the same prey at the same time—they were collaborating. “There was some organization to the chaos.”
The animals even stayed together at around 197 feet deep, cloaked in almost total darkness. “You could still occasionally see the silhouettes of several dolphins near the head of the killer whale,” she says.
Underwater sound recordings showed they were both echolocating, taking turns to vocalize clicks to locate prey. “This might suggest that the dolphins and the killer whales are eavesdropping on each other,” says Fortune.
Perceiving each other’s clicks means “they'd be reading each other’s sonar,” says McInnes.
Although more research is needed to confirm this is an example of cross-species communication, it “would be really fascinating if it is true,” he says.
Advantages of hunting together
The researchers don’t know why the orcas and white-sided dolphins are hunting together, but they think there must be some advantage for both species.
“In nature, mutualism—where both parties benefit—is the most likely reason that you would have two disparate groups coming together,” says Ari Friedlaender, professor of ocean sciences at UC Santa Cruz, who wasn’t involved in the study.
Northern resident orcas specialize in hunting salmon, while white-sided dolphins eat small fish, such as herring and anchovy. McInnes wonders if the killer whales can more easily locate salmon when hunting with a larger group of dolphins.
Meanwhile, the salmon “are too large for the dolphins to eat,” he says, but they can feed on scraps left by the orcas.
This teamwork might be more necessary if food is scarce. “The more eyes looking out for food, the better,” says Friedlaender. “By working together, you can increase the amount of food that each individual gets.”
Spying on the underwater world
Northern resident orcas had previously been observed with Pacific white-sided dolphins, but it was difficult for scientists to determine the nature of their interaction from the boat. “You see them for one second. They surface, they dive, they're gone for minutes,” says McInnes. “Cold, temperate water is very green. We can't really see a lot.”
One theory has been that the dolphins feel protected from predators—like mammal-eating transient orcas—with the fish-eating residents nearby. McInnes had wondered if the dolphins were “like pesky little teenagers bugging somebody,” but the study authors saw no evidence of antagonization, such as charging, biting, or swimming away.
The study’s use of orca-mounted tags now reveals the association might be because of feeding opportunities. This use of technology to see below the surface “is a game changer,” he says. It also eliminates bias because researchers don’t need to speculate what’s happening out of sight.
The authors of this new study want to do more research to determine how common this behavior is, whether residents catch more salmon when hunting with dolphins, and if this affects their health and reproduction.
Conserving Chinook salmon
If these collaborations are new, it could be a warning sign. “What's happening to the environment that’s necessitating this novel behavior?” says Friedlaender. “Are they coming about because of a pressure that's being exerted on those animals?”
Chinook salmon are threatened by warming temperatures and receding water levels in their spawning rivers as well as overfishing. The ripple effect of a dwindling population would be felt through the food web.
If future studies show orcas and dolphins foraging together more often when food is scarce, it could suggest a need for stricter conservation to protect salmon stocks and the marine animals that rely on them.
“We already know that those salmon are very limited,” says Friedlaender. “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.”
