Orcas and dolphins were recorded hunting salmon together off British Columbia

Off the coast of British Columbia, Canada, killer whales and Pacific white-sided dolphins have been recorded hunting together, sharing food, and working as a unit rather than competing for the same catch. The observations come from a paper titled Cooperative foraging between dolphins and fish-eating killer whales, led by Sarah M. E. Fortune and her colleagues and published in Scientific Reports. The fieldwork took place in the North Island waters of Vancouver Island, British Columbia, including Johnstone Strait, Queen Charlotte Strait and Queen Charlotte Sound, between August 15 and 30, 2020. The researchers tagged nine northern resident killer whales, four of which were later recorded interacting with Pacific white-sided dolphins over four days. The team behind the findings says the observations are among the first recorded examples of this kind of joint hunting between the two species.

The new research offers a different explanation, with observations showing the dolphins and orcas sometimes diving and foraging together in deeper water. To study these encounters, the scientists combined aerial drone footage with biologging tags attached to the whales, which recorded underwater video, sounds and dive movements. Four of the tagged orcas were recorded diving with the dolphins to depths of around 60 metres while pursuing Chinook salmon, also known as king salmon, which can shelter among rocks and crevices.

The footage suggested a working partnership rather than a chance encounter. According to the paper, the orcas appeared to orient themselves towards the dolphins while diving, potentially monitoring their movements rather than hunting alone. Dolphins use echolocation, a form of biological sonar that helps them locate prey even in murky, low-light water. The authors propose that the orcas may have reduced their own noise to better detect these signals, potentially helping them locate salmon in deeper water.


How the two species shared the catch

Chinook salmon are large fish, often too big for a dolphin to swallow whole. The observations suggest that killer whales processed the fish by biting them apart, while dolphins took advantage of pieces left behind. In one prey-capture event involving a confirmed adult Chinook salmon, dolphins were observed scavenging on the remains as the killer whale consumed the fish, with researchers reporting no signs of aggression or avoidance between the two species. The researchers also documented dolphins scavenging during prey-sharing events between killer whales, while noting that the dolphins could not dismember large Chinook themselves.

The researchers describe the relationship as opportunistic cooperative foraging, rather than presenting the prey sharing as proof of a deliberate reciprocal arrangement. They suggest the killer whales may benefit from the dolphins' echolocation while the dolphins gain access to salmon scraps, but they also emphasise that the extent of these benefits remains uncertain and requires further study.

Why this discovery matters

This kind of coordinated foraging between different predator species is unusual and difficult to observe directly. In this study, the underwater recordings showed the killer whales changing their direction to follow dolphins and engaging in foraging behaviour while the dolphins were present. The researchers propose that the dolphins may help the whales detect Chinook salmon at depth, while the dolphins can benefit by accessing pieces of fish processed by the killer whales.

The combination of drone footage, underwater video, acoustic recordings and dive data provided evidence of coordinated interactions that would have been difficult to interpret from surface observations alone. The paper notes that further tagging studies are needed to determine how much these interactions actually improve foraging success and whether the behaviour occurs more widely or at other times of year.