A paper published this summer looked into over 100 times humpbacks were observed disrupting orcas who are hunting, like these humpbacks trying to save a gray whale and calf. But why do they do it?
Scientists propose the whales either mob like this to save a fellow humpback then stick around to help whatever is being hunted, or they just hate orcas and love their fellow sea friends, formally known as "interspecies altruism." The study examined MEKWs, or mammal-eating killer whales:
More often though, humpbacks approached MEKWs that were attacking prey species that were clearly not humpbacks (e.g., a gray whale calf with its mother, a seal hauled out on an ice floe, a sunfish), and although the humpbacks faced little risk of serious injury, they also gained no obvious benefits for their time and energy spent. However, if the net effect for mobbing humpbacks was an increase in their individual or inclusive fitness through kin selection or reciprocity, then this behavior could persist even if it inadvertently benefitted other species sometimes.