07/14/2026
Fascinating cooperative interspecies hunting:
Northern resident killer whales off British Columbia stopped echolocating when dolphins showed up, went quiet, and listened to the dolphins' sonar instead. The dolphins were scanning for Chinook salmon across a wider area than the orcas could cover alone. When the dolphins found one, the orcas followed them down.
Sarah Fortune, a marine scientist at Dalhousie University and the study's lead author, published the findings in Scientific Reports in December 2025. Her team had been tagging northern resident orcas with suction-cup biologgers off Vancouver Island, each equipped with a forward-facing camera, a hydrophone, and motion sensors. The goal was to study how the whales hunted Chinook salmon, which is at risk of extinction and is virtually the only prey this orca population eats. The dolphins were not part of the plan.
Pacific white-sided dolphins kept appearing in the footage, swimming alongside the orcas, diving with them, surfacing with them, and the researchers had to decide whether they were watching interference or something else entirely.
It was something else. Over 25 documented encounters, the orcas oriented toward the dolphins and followed them to depth. At 197 feet below the surface, in near-total darkness, the two species stayed within meters of each other. The orcas' echolocation clicks, which normally pulse through the water continuously during a hunt, dropped off when dolphins were present. Andrew Trites, a co-author and marine mammal researcher at the University of British Columbia, described what the hydrophones recorded: the killer whale was going quiet, and it was listening to the pings from the Pacific white-sided dolphins.
The dolphins were scouting. They spread out and pinged through the water across a much broader area than the orcas could search on their own. Trites said the whales were listening. When a dolphin's echolocation pattern changed in a way that indicated it had located a large Chinook, the orca moved toward the signal.
The division makes sense because neither species can do what the other does. Adult Chinook salmon weigh 18 to 30 pounds. A Pacific white-sided dolphin can find one but cannot catch and swallow it whole. An orca can catch and eat it but cannot scan as wide an area as a group of dolphins fanning out across a strait. The dolphins locate what they cannot kill. The orcas kill what they cannot locate as efficiently alone. After the kill, the orca tears the salmon apart.
Fragments drift. The dolphins eat the scraps. Fortune described it as a relationship where both sides appear to benefit, though she was careful to note that proving deliberate cooperation from observational data is difficult. There was some organization to the chaos, she said.
Not everyone agrees it is cooperation. Brittany Visona-Kelly of Ocean Wise, who has studied interactions between these same species for years and was not involved in Fortune's study, said that in her experience, the dolphins initiated contact with the orcas, not the other way around. She suggested the orcas may have viewed the dolphins as an annoying pest that was easier to tolerate than chase off. The dolphins may have been exploiting the orcas rather than cooperating with them.
The reason the dolphins can approach northern resident orcas at all is that these orcas do not eat mammals. The northeastern Pacific has three distinct orca populations that do not interbreed and do not share diets. Transient orcas eat marine mammals, including dolphins and porpoises. Offshore orcas eat sharks. Northern residents eat fish, almost exclusively Chinook salmon. The dolphins apparently know the difference. They approach northern residents without hesitation and avoid transients entirely. The survival of a dolphin swimming beside an orca depends on identifying which kind of killer whale it is looking at. Getting it wrong is fatal.
Fortune said the cooperative behavior may not be a sign of abundance. Chinook salmon populations have declined sharply across the Pacific. If the orcas are recruiting dolphin sonar because they can no longer find enough salmon on their own, the partnership is not a celebration of interspecies intelligence. It is a sign that the food supply is running out and the largest predator in the ocean is improvising.
Source: Fortune et al. (2025), Scientific Reports / CBC News / National Geographic / CNN / UBC Institute for the Oceans and Fisheries.
