With the ever present and dramatically increasing threat of oil spills in BC waters, Raincoast decided to take a hard look at the worst-case scenario. What if we had an oil spill? What would that mean for the marine mammal species living along the coast of BC? Are some species inherently more at risk from oil spills than others?
The paper, Oil Spills and Marine Mammals in British Columbia, Canada: Development and Application of a Risk-Based Conceptual Framework, was published this month in the journal Archives of Environmental Contamination and Toxicology by Raincoast biologists and Dr. Peter Ross at the Ocean Wise Conservation Association. It examined 21 marine mammal species present in BC waters and ranked them according to the potential for deleterious consequences in the event of an oil spill.
From sea otters to sperm whales to harbour porpoises, the marine mammals of BC are a diverse group and although all must spend time at the surface to breathe, which inherently increases their likelihood of oil exposure, species have different characteristics that can change their risk of individual oil exposure and its consequences.
At especially high risk are the Northern and Southern Resident killer whales and sea otters, followed closely by Bigg’s (transient) killer whales and Steller sea lions
In our “what if” scenario, we looked at five pathways that marine mammals can be exposed to oil during a spill – contact with oil, oil adhesion to the body, inhalation of oil vapours, and ingestion of oil directly and through prey. We found that baleen whales were particularly at risk from oil exposure, as a result of surface feeding activities, baleen plate fouling, oil adhesion, and indirect oil consumption through invertebrate prey. Sea otters, as expected, ranked high on exposure risk due to their time spent on the surface grooming and diet of benthic prey. Unexpectedly, harbour porpoises were also found to be at higher risk of oil exposure than similar species as a result of their unique diet containing a high proportion of squid, which becomes readily contaminated during oil spills.
After looking at individual oil exposure, we also examined the likelihood that a population would experience a decline in the event of an oil spill. To do this, we examined numerous population parameters, including population size and trends, time spent in BC waters and presence of critical habitat, life history traits, and dietary preferences. We found a few populations to be at high risk of decline – Steller sea lions, whose small population, presence in large groups, and reliance on rookeries along coastal BC puts them at risk, as well as Resident and Bigg’s (transient) killer whales, whose small population size, limited reproductive turnover, dietary specialization, long lives, and complex social structure makes them extremely vulnerable, as found during the Exxon Valdez spill.
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To get a complete picture of what could happen in the event of an oil spill, we combined risk of individual exposure with the likelihood of population-level effects. In doing so, we found that the majority of BC marine mammals are at high risk of oil spill impacts. At especially high risk are the Northern and Southern Resident killer whales and sea otters, followed closely by Bigg’s (transient) killer whales and Steller sea lions. These species are also of high conservation concern and are legally listed under Canada’s Species at Risk Act. It could only take one incident to severely impact populations that are supposed to be protected from decline.
With recent headlines and rhetoric promising the construction of pipelines and a corresponding increase in oil tanker traffic in BC waters, it seems only too soon before a “what if” becomes a reality. This new paper has shown how much of an impact an oil spill event could potentially have. Help us stand up for the marine mammals of BC and keep this worst case scenario from happening.