For the first time ever, a unique cooperative hunting arrangement between dolphins and orcas has been documented. Researchers believe killer whales find salmon by tailing dolphins, who in turn benefit from bite-sized fish pieces.
The elaborate hunting strategies of orcas are nearly legendary in the animal kingdom. They've been observed creating ocean waves that tip seals off ice floes; herding herring into tight balls that they stun with tail slaps; and expertly stranding sea lions on beaches without getting stuck on the sand themselves. And that's just to name a few of the strategies we've actually seen. Orcas are such adept hunters, in fact, that they've even been spotted taking down the whale shark, the world's largest fish, as well as great whites.
Now, a team of international researchers led by Dalhousie University (DU) in Canada has uncovered another hunting strategy of killer whales off the coast of British Columbia by using aerial drones, underwater video feeds, acoustic recordings, and, for the first time on a resident killer whale population, suction-cup movement trackers called Customized Animal Tracking Solutions Tags (CATS).
The multi-media data they gathered allowed the researchers to discover orcas turning down their own echolocation sounds when they encountered a pod of Pacific white-sided dolphins. This, the researchers believe, let them better hear and track the dolphins who were on their way to a group of large Chinook salmon.
The salmon are too large for the dolphins themselves to eat, but the researchers found that once the dolphins led the orcas to the schools of fish, the whales herded them to the surface where the rest of the pod gobbled them up. This left behind bite-sized pieces that the dolphins could then scavenge. Because no antagonistic behavior was observed between the dolphins and the whales, the researchers have concluded that the entire endeavor is an example of cooperative foraging in which both species benefit. They also say that by using the dolphins to lead them to the fish, the orcas are likely cutting down on their own echolocation times.
You can hear more about the research and watch the behavior in the following video:
"The strategic alliance we observed between the dolphins and killer whales is extraordinary," says study co-author Andrew Trites, director of the Marine Mammal Research Unit at the University of British Columbia's Institute for the Oceans and Fisheries.
"By working together, killer whales can conserve energy and use the dolphins as radar-equipped scouts to increase their chances of finding large Chinook salmon at deeper depths. In return, the dolphins gain predator protection and access to scraps from one of the ocean's most prized fish. It's a win-win for everyone involved."
As Trite mentions, the researchers say that feeding might only be one of the benefits in the dolphin/orca relationship. Another might be that dolphins hang out with a resident pod of orcas for protection from transient orcas, some groups of which predate on dolphins. Additionally, the dolphins may also be associating with non-dolphin-eating orcas to learn to distinguish their sounds from those of the threatening mammal-eating killer whales. They say that further research is needed to untangle the relationship between the dolphins and orcas.
"We need to figure out how prevalent co-operative foraging is and whether there might be benefits to the population," says study first author Sarah Fortune from DU. "Do killer whales that forage with dolphins have better success catching salmon? Is their body condition better than those that hunt alone? These are the kinds of metrics we can use to figure out whether this is a mutually beneficial interaction."
Source: Dalhousie University
