The Southern Resident killer whales are declining toward extinction in plain sight, so say the authors of a new study. They found that “the threat with the greatest impact on their population growth is the availability of Chinook salmon.” Yet, they noted, Chinooks’ ability to “support survival, let alone recovery of the Southern Resident killer whales, has been in question for over two decades.”
Therefore, NOAA’s 2008 Southern Resident killer whale recovery plan—to sustain 2.3% growth—must also be in question, as this new study predicts an annual population decline of 1%. In fact, the authors caution that this figure might be optimistic, given that “many threats are expected to worsen in future.”
Thankfully, they conclude that with appropriate and timely actions, preventing their extinction is still possible but “will require greater sacrifices than would have been the case had threats been mitigated even a decade earlier.”
What was the study?
Scientists created a “population viability analysis” model using demographics from 1976 to 2022. These included factors such as gender, reproductive success, longevity, age at death, and cause of death, if known.
With this model, they could simulate possible futures by manipulating changes in survival rates and numbers of successful births. Then, they could model the impacts of three critical threats: insufficient Chinook salmon, vessel noise and foraging disruption, and the role of PCBs and other harmful contaminants.
They also modeled climate change impacts, and with likely increases in shipping through the Salish Sea, they assessed oil spill risks. Finally, they analyzed the consequences of implementing successful management measures to mitigate human-caused impacts such as overfishing and environmental pollution.
What did they find?
They found that “Protecting Southern Resident killer whales appears to be impossible without restoring diminished populations of Chinook salmon, which in turn requires effective implementation of conservation and precautionary resource management measures.”
Modeling showed that moving fisheries from salmon rearing and migration routes would immediately increase the number of Chinook—by up to 25%—in the whales’ foraging areas. Allowing more older female Chinook to reach their spawning grounds would increase size by up to 40% over the next 50 years.
They found that while “no salmon recovery scenario alone resulted in a fully recovered population,” modeling showed that it was essential to include “some ambitious salmon recovery scenarios” such as those mentioned above. They also noted, “It may be necessary to consider ocean noise budgets, caps, or limits that allow killer whales to hunt scarce prey efficiently.”
While such proposals are likely to be unpopular, this is sadly the consequence of decades of inaction to save these killer whales and their vital Chinook prey. The authors noted, “Eleventh-hour rescues carry higher environmental and societal costs than earlier actions might have.”
The model showed that a single birth or death increases or decreases this endangered population by 1.4%. Simply put, we need more births and fewer deaths. The authors noted, “The continued loss of genetic diversity will likely hamper the population’s ability to adapt to an ever-evolving threatscape.”
They proposed that appropriate veterinary interventions might be necessary, such as preventing premature deaths by administering treatment for diseases or parasites or implementing preventative measures such as vaccinations for the deadly cetacean morbillivirus.
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While these may seem extreme measures, they noted that it “is critical to strike a balance between risk and reward of any particular intervention.” They proposed that with a combination of approaches, “concerted efforts can reverse the decline and possibly reach 1% annual recovery.”
As killer whales have long lifespans, the success of mitigation efforts may be slow to appear. Hence, the study suggests using short-term metrics such as body condition, growth rate, pregnancy, and behavior to track signs of recovery that would lead to population growth.
Wild Orca’s health monitoring program tracks pregnancies, nutritional stress, and contaminant levels; we also record their behavior. We will make our data available to management agencies so they can take the most appropriate actions to secure a healthy future for this unique killer whale culture while time is still on our side.
