Researchers are delving into a baffling phenomenon observed in the Salish Sea: a killer whale attacking a porpoise, a behavior that has confounded scientists for years. This investigation is a collaboration between Wild Orca and the SeaDoc Society at UC Davis. Credit goes to Wild Orca.
Exploring a Mysterious Behavior
Scientists have long been mystified by the actions of the fish-eating killer whales in the Pacific Northwest, noted for attacking and occasionally killing porpoises but not consuming them.
The findings of a recent study, spearheaded by Deborah Giles of Wild Orca and Sarah Teman of the SeaDoc Society at UC Davis’ School of Veterinary Medicine, have been published in Marine Mammal Science. The research examines over six decades of interactions between Southern Resident killer whales and porpoises in the Salish Sea, aiming to shed light on this peculiar behavior.
The Southern Resident killer whales, an endangered group with only 75 individuals, rely heavily on the endangered Chinook salmon for survival. Their existence is threatened by the scarcity of this vital food source.
Giles often faces the question of why these whales don’t switch to eating seals or porpoises. She explains that fish-eating killer whales differ significantly in their ecology and culture from those that consume marine mammals, despite sharing the same habitat. Therefore, their interactions with porpoises are believed to serve some other purpose, which until now has been mere speculation.
Three Potential Reasons
Despite records of Southern Resident killer whales harassing porpoises dating back to 1962, the motive behind this behavior has remained elusive. Giles, Teman, and their team analyzed 78 documented instances of this harassment between 1962 and 2020. The study proposes three potential explanations:
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Social Interaction: The harassment might be a form of social interaction for the whales. Engaging in playful activities, like many intelligent species, could aid in bonding, communication, or enjoyment, enhancing group coordination and teamwork.
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Hunting Skills Development: It’s theorized that harassing porpoises could be a way for the whales to refine their salmon-hunting skills, using porpoises as moving targets for practice, even if they don’t intend to eat them.
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Caregiving Instinct: The whales might exhibit caregiving behaviors towards porpoises they perceive as vulnerable or sick. This behavior, known as mismothering or displaced epimeletic behavior, might stem from limited opportunities to care for their young, as Giles points out that nearly 70% of pregnancies in Southern Resident killer whales result in miscarriage or immediate postnatal death due to malnutrition.
Specialized Diet
Giles, Teman, and their colleagues acknowledge that the true reason behind the porpoise harassment may remain a mystery. However, it’s clear that porpoises are not part of the Southern Resident killer whale diet, which is highly specialized for salmon. The idea of these whales consuming porpoises is thus highly unlikely.
“Killer whales are incredibly complex and intelligent animals,” says Teman. “The behavior of harassing porpoises has been passed down through generations and across social groups, showcasing the rich culture of killer whales. Yet, we don’t anticipate Southern Resident killer whales shifting their diet to porpoises, as their salmon-eating culture is deeply ingrained.”
This research highlights the critical need to conserve salmon populations in the Salish Sea and beyond to ensure the survival and well-being of Southern Resident killer whales and the overall health of the ecosystem.
Playful Nature
Concurrently, a different population of killer whales in the Iberian Peninsula has made headlines for interacting with and, in some cases, sinking boats off Portugal and Spain. While the Southern Resident killer whales and the Iberian Peninsula orcas are distinct in population and culture, they may share a common trait in their playful behavior.
Reference: Giles, D.A., Teman, S.J., et al. (2023). “Harassment and killing of porpoises (‘phocoenacide’) by fish-eating Southern Resident killer whales (Orcinus orca)”. Marine Mammal Science, DOI: 10.1111/mms.13073.
The study was financed by Wild Orca and SeaDoc Society, with contributions from multiple institutions including the University of Exeter, Fisheries and Oceans Canada, and others.
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Frequently Asked Questions (FAQs) about Killer Whale Behavior
Why are killer whales in the Pacific Northwest attacking porpoises without eating them?
This perplexing behavior has been observed for years and is the focus of a study by scientists from Wild Orca and UC Davis’ SeaDoc Society. The research, spanning over 60 years, investigates the interactions between Southern Resident killer whales and porpoises in the Salish Sea to understand the reasons behind this behavior, which include potential social play, hunting practice, or mismothering behavior.
What are the possible reasons for killer whales harassing porpoises?
The study suggests three plausible reasons: social play, where the whales engage in playful activities for bonding and communication; hunting practice, using porpoises as moving targets to refine salmon-hunting skills; and mismothering behavior, where whales might attempt to care for porpoises they perceive as weaker or ill.
Are porpoises a part of the Southern Resident killer whale diet?
No, porpoises are not part of the Southern Resident killer whale diet. These whales have a diet highly specialized for salmon, making the consumption of porpoises highly unlikely. Their culture and ecology differ significantly from orcas that eat marine mammals.
What is the significance of the study on killer whale and porpoise interactions?
The study underscores the importance of conserving salmon populations in the Salish Sea for the survival of Southern Resident killer whales. It also sheds light on the complex and intelligent nature of killer whales, emphasizing their culture and social behaviors.
How does this study relate to other killer whale populations?
While focusing on the Southern Resident killer whales, the study briefly mentions another population of killer whales in the Iberian Peninsula, known for interacting with boats. Although these populations are distinct, they may share a common trait in their playful nature.
More about Killer Whale Behavior
- Wild Orca Organization
- UC Davis School of Veterinary Medicine
- Marine Mammal Science Journal
- SeaDoc Society at UC Davis
- Fisheries and Oceans Canada
- The Whale Museum
- National Oceanic and Atmospheric Administration (NOAA)
- Cascadia Research Collective
- Center for Whale Research
- Ocean Research College Academy (ORCA) at Everett Community College
- Bay Cetology
- North Gulf Oceanic Society
- George Mason University
- Marine-Med Research Initiative
