Why Are Killer Whales Harassing and Killing Porpoises Without Eating Them? | UC Davis
A pod of Southern Resident orcas
Photo: NOAA Fisheries.
The problem creationists have with trying to cling to a counter-factual superstition like theirs is that so many facts run counter to it. To normal people, that might be considered a good reason to reassess their opinions and drop those shown to be at odds with the facts and form some based on reality instead.
Not so creationists. To a creationist, the thought of being wrong is an existential threat which, if allowed to develop, would destroy their entire world view which has them at the centre of a specially created universe, the creator of which holds them in high regard. Dropping this childish belief would mean they don't feel as important as they think they are and would maybe have to think the unthinkable - a universe which doesn't have them at the centre of it and eventual oblivion in which the world continues to exist and function without them in it or able to observe it from a privileged position.
The Salish Sea. Location for the study.
Traditionally, creationists cite examples of how humans are unique, having characteristics shared by no other species - ignoring the fact that that pretty much defines a species and the same case can be made for every other species. One of these is of course another creationist sacred cow - humans have social ethics and a conscience, which creationist dogma asserts could only have come from their particular creator god - the same god whom they believe inflicted a mass genocide on Earth and creates parasites, apparently.
Explaining social ethics, or pr-social behaviour, and a conscience which motivates pro-social behaviour, rewarded by endorphins, is not difficult for science to explain as the result of gene-meme co-evolution in a cooperative species that could not survive as individuals without the support of a social group.
And, to reinforce that, we now have evidence of pro-social behaviour and human-like activities in another species - the orca or killer whale.
At least, that's the explanation for an observed change in behaviour of a pod of orca in the Salish Sea, described in a paper published, open access, in Marine Mammal Science. The investigating team was co-led by Deborah Giles of Wild Orca and Sarah Teman of the SeaDoc Society, a program of University of California Davis (UCDavis) School of Veterinary Medicine.
First a little background on the Southern Resident killer whales, the subject of the study:
What do you know about the Southern Resident killer whales (Orcinus orca)? The Southern Resident killer whales (Orcinus orca) are a distinct population of killer whales that inhabit the northeastern Pacific Ocean, primarily along the coast of Washington State in the United States and British Columbia in Canada. These killer whales are known for their unique social structure, vocalizations, and dietary preferences. Here are some key facts about the Southern Resident killer whales:
- Population and Status: The Southern Resident killer whale population consists of three distinct pods: J, K, and L pods. Each pod is made up of multiple family groups. As of my last knowledge update in September 2021, the population was critically endangered and faced significant challenges to its survival. Their numbers had declined to around 75 individuals, which was a significant decrease from historical levels.
- Social Structure: Southern Resident killer whales are highly social animals and live in matrilineal family groups. Each pod is led by an older female, known as the matriarch, who plays a crucial role in the social cohesion and hunting strategies of the group. These family groups can be seen traveling and hunting together.
- Vocalizations: These whales are known for their complex and distinctive vocalizations, which are often referred to as "whale songs." These vocalizations serve various purposes, including communication, navigation, and potentially hunting. Researchers have been studying these vocalizations to better understand their behavior and social interactions.
- Diet: Southern Resident killer whales primarily feed on Chinook salmon (Oncorhynchus tshawytscha), a type of salmon that is also in decline in the region. The dependence on Chinook salmon as their primary food source has made the Southern Residents vulnerable to changes in salmon populations due to factors such as overfishing, habitat degradation, and dam construction.
- Conservation Challenges: The Southern Resident killer whales face several significant threats to their survival, including food scarcity, environmental toxins (such as PCBs), vessel traffic, and noise pollution. The reduction in Chinook salmon populations, in particular, has been a major concern for their conservation.
- Conservation Efforts: Efforts to protect and conserve the Southern Resident killer whales have included measures to reduce vessel noise and disturbance, habitat restoration, and fisheries management to protect Chinook salmon. Various organizations, government agencies, and stakeholders have been working together to develop and implement conservation strategies to help this endangered population recover.
Please note that the status and specific details about the Southern Resident killer whales may have evolved since my last update in September 2021, so it's a good idea to consult more recent sources for the latest information on their conservation status and efforts.
The UCDavis news item by Justin Cox explains the study:
For decades, fish-eating killer whales in the Pacific Northwest have been observed harassing and even killing porpoises without consuming them — a perplexing behavior that has long intrigued scientists.
A study published today in Marine Mammal Science, co-led by Deborah Giles of Wild Orca and Sarah Teman of the SeaDoc Society, a program of the UC Davis School of Veterinary Medicine, looked at more than 60 years of recorded interactions between Southern Resident killer whales and porpoises in the Salish Sea to better understand why they exhibit this behavior.
Southern Resident killer whales are an endangered population, numbering only 75 individuals. Their survival is intimately tied to the fortunes of chinook salmon — also an endangered species. Without enough chinook salmon, these whales are in danger of extinction.
Three plausible explanationsI am frequently asked, why don’t the Southern Residents just eat seals or porpoises instead? It's because fish-eating killer whales have a completely different ecology and culture from orcas that eat marine mammals — even though the two populations live in the same waters. So we must conclude that their interactions with porpoises serve a different purpose, but this purpose has only been speculation until now.
Deborah A. Giles, co-led author
Wild Orca, Washington
While scientists have recorded instances of Southern Resident killer whales engaging in porpoise harassment as early as 1962, reasons for this behavior have long remained a mystery. Giles, Teman, and a team of collaborators analyzed 78 documented incidents of porpoise harassment from 1962 to 2020. The study suggests three plausible explanations:
- Social play: Porpoise harassment may be a form of social play for killer whales. Like many intelligent species, these whales sometimes engage in playful activities to bond, communicate, or simply enjoy themselves. This behavior might benefit group coordination and teamwork.
- Hunting practice: Another hypothesis suggests that porpoise harassment might hone their salmon-hunting skills. Southern Resident killer whales could view porpoises as moving targets to practice their hunting techniques, even if they do not intend to consume them.
- Mismothering behavior: This theory suggests that the whales may be attempting to provide care for porpoises they perceive as weaker or ill — a manifestation of their natural inclination to assist others in their group. Females have been witnessed carrying their deceased calves and have been seen similarly carrying porpoises.
Salmon specialistsMismothering behavior — also known as ‘displaced epimeletic behavior’ to scientists — might be due to their limited opportunities to care for young. Our research has shown that due to malnutrition, nearly 70% of Southern Resident killer whale pregnancies have resulted in miscarriages or calves that died right away after birth.
Deborah A. Giles
Despite these intriguing insights, Giles, Teman, and their collaborators acknowledge that the exact reason behind porpoise harassment may never be fully understood. What is clear, however, is that porpoises are not a part of the Southern Resident killer whale diet. Southern Resident killer whale diets are highly specialized for salmon, making the idea of eating porpoises highly unlikely.
This research underscores the importance of conserving salmon populations in the Salish Sea and throughout the whales’ entire range. Maintaining an adequate supply of salmon is vital for the survival and well-being of Southern Resident killer whales and the overall health of the Salish Sea ecosystem.Killer whales are incredibly complex and intelligent animals. We found that porpoise-harassing behavior has been passed on through generations and across social groupings. It’s an amazing example of killer whale culture. Still, we don’t expect the Southern Resident killer whales to start eating porpoises. The culture of eating salmon is deeply ingrained in Southern Resident society. These whales need healthy salmon populations to survive.
Sarah J. Teman, co-lead author
SeaDoc Society
University of California Davis
Affinity for play
This study comes at a time when a separate population of killer whales on the Iberian Peninsula has drawn international headlines for interacting with, and on three occasions, sinking boats off the coast of Portugal and Spain. Ultimately, the Southern Resident killer whales and the Iberian Peninsula orcas are two different populations with distinct cultures. One thing the two might have in common is their affinity for play behavior.
In addition to forming complex social groups and distinct cultures, just like humans, these killer whales also go in for group play and hunting practice, very reminiscent of human team sports. They may also have 'displaced epimeletic behaviour' very much like humans adopting and raising animals and babies of other species.
Of course, orcas, like humans are highly intelligent social animals which can only exist as a group, so it's not at all surprising to an evolutionary biologist that similar environmental pressures produce similar results.
However, this utterly destroys the daft notion that these traits are unique to humans, and so are evidence of special creation. Instead, they are evidence of gene-meme co-evolution. As with physical evolution, the general similarities and the specific differences are the expected result of the natural process of evolution and diversification over time.
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