Dolphins cooperate with orcas in unique hunting behaviour
A pod of Pacific white-sided dolphins off the coast of British Columbia has been observed cooperating with orcas, an unexpected alliance given that orcas are typically known for preying on dolphin species, reports BritPanorama.
Scientists documented the dolphins working alongside a local population of killer whales, known as Northern Resident orcas, to hunt salmon. While other groups of orcas are known to hunt dolphins, the Northern Residents have not previously been seen participating in such cooperative behaviour with them. This marks the first documented instance of this type of interaction between the two species, according to the researchers.
“Seeing them dive and hunt in sync with dolphins completely changes our understanding of what those encounters mean,” said Sarah Fortune, Canadian Wildlife Federation chair in large whale conservation and an assistant professor at Dalhousie University’s oceanography department. Fortune led the study published Thursday in the journal Scientific Reports.
To capture the interactions, researchers utilised drone footage and underwater video, attaching suction tags with cameras to the orcas. The footage revealed killer whales following dolphins both at the surface and during dives of up to 60 meters (197 feet) as they targeted Chinook salmon. Despite low light levels at these depths, the cameras recorded orcas catching salmon, with evidence of their kills evident through blood clouds in the water.
The study detailed 258 instances of interaction between the dolphins and orcas recorded between August 15 and 30, 2020. Each interaction revealed that the orcas were engaged in hunting behaviour, suggesting they were utilising the dolphins to improve their foraging efficiency.
Fortune explained that hunting with echolocating dolphins would expand the orcas’ acoustic range, increasing their ability to detect salmon hiding in depths to evade predators. This strategy would also help conserve energy as salmon often seek lower depths to avoid larger predators.
Interestingly, while the orcas benefit from hunting success, the dolphins are believed to gain protection from potential threats posed by transient killer whales that prey on their kind. The footage collected indicated that once orcas caught fish, the dolphins quickly took advantage of the leftovers.
In addition to the Northern Residents, the coastal region also hosts a distinct type of orca known as Bigg’s or transient killer whales that primarily prey on marine mammals. The unique interactions between Northern Resident orcas and dolphins have been noted for over three decades off northeastern Vancouver Island, according to Brittany Visona-Kelly, a senior manager at Canadian conservation group Ocean Wise’s Whales Initiative, who has studied these interspecies relationships.
Visona-Kelly, who was not involved in the current research, expressed skepticism about the cooperative nature of these interactions, suggesting that the dolphins may have initiated contact with the orcas. She posited that the orcas might see the dolphins as an irritation rather than active partners in hunting.
Nevertheless, Fortune argued that her study contradicts this perspective. She dismisses the notion that dolphins merely benefit from scraps and asserts that both species engage meaningfully with one another, claiming no evidence of antagonistic behaviour from the orcas towards the dolphins has been found.
This research marks a significant stride in understanding interspecies cooperation, particularly among mammals. While cooperative behaviours are common in nature, occurrences that involve predators are typically rare, according to Judith Bronstein, a professor at the University of Arizona who studies interspecies cooperation.
As scientists continue to investigate these interactions, the research underscores a complex relationship between dolphins and orcas that may redefine how interspecies dynamics are perceived within marine ecosystems.
