Beyond Predation - Killer Whales Mysterious Treatment of Porpoises
Author: Kyra Zimnik
Beyond predation: killer whales' mysterious treatment of porpoises
In a baffling twist of marine behaviour, endangered Southern Resident killer whales are attacking and killing porpoises without consuming them. This strange phenomenon has stumped scientists for decades, and a new study dives deep into the mystery, exploring whether these acts are playful antics, hunting practice, or something even more complex.
For the past 45 years, Southern Resident killer whales have puzzled scientists with their strange habit of harassing and killing porpoises without eating them. These whales have been seen pushing, carrying, launching, and ramming porpoises, often causing them to drown. Surprisingly, they don't eat the porpoises afterward. This behaviour continues to mystify researchers and highlights the complex social lives of these marine mammals.
A closer look
The endangered Southern Resident killer whales have been observed partaking in the harassment and killing of Harbor- and Dall’s Porpoises despite having a fairly strict fish based diet. To delve deeper into this phenomenon, a study led by Giles et al. (2023) analysed historical data from three well-established families, also known as pods, of Southern Resident killer whales. Deborah Giles and her colleagues examined the age and sex demographics of both the killer whales and their porpoise victims, as well as the generational patterns of porpoise harassment within different killer whale families. These patterns reveal how specific behaviours are passed down from one generation to the next, indicating the role of family dynamics in shaping such interactions.
Insights from the study
The study by Giles and her colleagues suggests several possible reasons for the harassment of porpoises by Southern Resident killer whales. These include playful tendencies, hunting practice, or even displays of displaced maternal behaviour among females of reproductive age. Displaced maternal behaviour occurs when female whales show nurturing and protective actions toward non-offspring, possibly due to hormonal influences or social bonding needs. The notable fact that these killer whales refrain from consuming the porpoises suggests a deep-seated cultural preference for fish in their diet, indicating that this behaviour is not predatory in nature.
Previous studies have observed young killer whales engaging in various playful and “trendy” behaviours, such as wearing salmon heads on their noses and colliding with boats in the Gibraltar Strait. The transmission of such behaviours within killer whale pods highlights the importance of social learning in these communities. Social learning involves the transfer of behaviours and skills from one individual to another, ensuring that cultural traits and practices are maintained across generations.
While this study offers intriguing theories about non-prey harassment and killing behaviours in killer whales, the true motivations remain a mystery. The enigmatic conduct of these intelligent and beautiful creatures continues to fascinate researchers, as the whales themselves hold the secrets to their mysterious actions.