A new scientific paper published just prior to the worldwide outbreak of Covid-19 explores the potential danger posed to the endangered population of orcas in the Pacific Northwest.

The Southern Resident killer whales are the most studied population of orcas on the planet. Over 40 years of study with photographs, video—and in recent years drone surveys—has captured important insights into the social and family structures of this unique population.

Cetacean Morbillivirus / Stephens et. al.

These studies have revealed that males always stay with their mother, and that the mother’s extended family form a tight bond for life. In addition, they are highly social with members of the other pods within their community. These close familial and cultural ties, together with their almost singular preference for Chinook salmon has always bound them to place, and to each other. Could this combination of associations now make them more susceptible to this virus?

Cetacean morbillivirus has been found in a number of species which are regularly found in the Salish Sea, such as harbor porpoise and Pacific white-sided dolphin. The virus is highly infectious, and can be passed between species.

Much of the work currently being undertaken on predicting the transmission of coronavirus is based on computer modelling, and computer models were also used in this orca study. Much like the human studies, it is not fully understood how long droplets of morbillivirus remain in the air to be potentially inhaled by others. Therefore, for the purpose of their models, the scientists chose to be conservative, and defined the time at which respiratory transmission is feasible, as only when orcas surfaced simultaneously, or where an orca surfaced within one body length of another, but before the previous individual was completely submerged.

Courtesy of Sara Shimazu

After analysis of documented evidence of each of these types of close encounter, and noting which pod members were present, the scientists then estimated the number of potential contacts over the course of an entire season. This then enabled them to model the probability of an infected individual orca creating a cluster of cases within their family, and then by examining their wider social network across pods, the likelihood of transmission across the entire community of whales. Unfortunately, but not surprisingly, this showed that the disease would likely infect 90% of the population, leading to a high number of deaths.

A vaccine is thought to be one of the best ways we can control the spread of coronavirus in humans, but clearly this is not such a viable option in a wild, wide-ranging species like orcas, but in any case, was deemed ineffective by the modelling due to the high number of whales that would need to be vaccinated.

Courtesy of Sara Shimazu

The scientists state that three factors make this unique population of orcas more susceptible to succumb to this morbillivirus— poor nutrition, exposure to toxins like PCBs, and inbreeding. We know that their most urgent and immediate need is access to an abundant supply of fatty Chinook salmon. Something which is in our control. As is shown in human populations, poor diet leads to poor health outcomes, and recovery from disease becomes far more challenging. Food must be a priority, as good nutrition leads to resilience against stressors such as pollutants and noise. Access to plentiful salmon also increases the chance of successful pregnancies— the only hope for a future for this population.

Allocating a portion of the annual Chinook catch to these whales—their original harvesters—is essential. Their continued absence from the inland waters this spring and summer clearly expresses the lack of wild salmon in their traditional fishing grounds. This is unsustainable but entirely fixable. We must act NOW!

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