BC’s marine mammals vulnerable to oil spills – especially killer whales

Calculating risk requires understanding the probability of a spill along with the consequences. In Raincoast’s new paper, we focus on assessing those consequences for 21 species of BC marine mammals. We provide an example of risk, in its full sense, using Southern Resident killer whales.

A humpback whale slips into the water near the

A humpback whale on the waters of the Great Bear Rainforest, BC Canada. Photo by Andy Wright.

BC’s marine mammals are at high risk from oil spill impacts. Our understanding of this has been deepened by our newly published research paper that developed a framework to assess the impact of oil spills on marine mammals.

It’s known that marine mammals, in general, are inherently vulnerable to oil spills due to the extended time they spend at the water’s surface.

Not all marine mammals are impacted equally by an oil spill.

But our study examined specific traits and population considerations among BC’s marine mammals to determine differences. Given BC’s growing threat of increased oil tanker traffic, it’s imperative that we have a more nuanced understanding of the actual risks to marine mammals. Calculating this requires that we understand that not all marine mammals are impacted equally by an oil spill.

We found that of the 21 marine mammals examined, 18 are at high risk, with Northern and Southern Resident killer whales, Steller sea lions and sea otters considered as being at especially high risk from an oil spill event in BC waters.

Both killer whales and sea otters experienced high mortality following Alaska’s 1989 Exxon Valdez oil spill.

As my colleague and lead author on this paper Adrianne Jarvela Rosenberger, notes, “it’s important to understand that the populations deemed to be at greatest risk for oil spill exposure and consequence are also those with a high conservation concern based on their listing under Canada’s Species at Risk Act.”

Of the 21 marine mammals examined, 18 are at high risk from oil spills.  Tweet This!

Our research paper, Oil Spills and Marine Mammals in British Columbia, Canada: Development and Application of a Risk-Based Conceptual Framework was published in the journal Archives of Environmental Contamination and Toxicology by three Raincoast biologists (Adrianne, Andy and myself) and marine mammal toxicologist Dr. Peter Ross at the Ocean Wise Conservation Association.

First we examined exposure pathways for each species. Exposure pathways are ways in which spilled oil can impact an individual animal. This includes ingestion, inhalation, direct contact and ingestion via contaminated prey.

We then combined this with the likelihood of impacts to the whole population using factors like their conservation status, distribution, habitat use, reproduction, and their ability to switch to other prey. This gave us a way to compare the impacts across different marine mammal populations in BCs.

After combining the likelihood of individual oil exposure with the likelihood of population level impacts, we were able to rank BC’s marine mammals species according to their overall risk of suffering detrimental impacts as a result of an oil spill event.” – Jarvela Rosenberger

What we found

Figure 3: Likelihood of population level effects. and likelihood of exposure to oil.

Figure 3: Overall risk of marine mammal species to oil spills in British Columbia waters is depicted using species cumulative rankings for likelihood of individual exposure to oil (x-axis) and likelihood of population-level effects (y-axis) from an oil spill. This figure is broken into four categories. The green shaded area represents the lowest combined risk, followed by yellow (moderate), then amber (high), and then red is highest. See species codes below.

Of the 21 BC marine mammals we examined, only the sperm whale (SPW), Northern elephant seal (NES), and California sea lion (CSL) were found to have a moderate risk of experiencing population level effects from an oil spill.1 In addition to Resident killer whales and sea otters, transient (Bigg’s) killer whales and Steller sea lions were also found to be at especially high risk.

A map of a model of an oil spill and bitumen at Arachne Reef in Northern Haro Strait BC.

Figure 4: Probability of oil presence within the critical habitat of Southern Resident killer whales following a 15000 m3 release of diluted bitumen at Arachne Reef in Northern Haro Strait, BC.

In addition to the framework that assessed the vulnerability of marine mammals, our paper also examined the risk to the Southern Resident killer whales from an oil spill in Haro Strait. Risk, in its true sense, is determined by oil spill probability multiplied by the consequence. We found that between 22% and 80% of Southern Resident killer whale Critical Habitat would be affected by a spill in Haro Strait.

Culturally and scientifically, society has learned a lot about the irreversible repercussions of the Exxon Valdez oil spill on two populations of Alaskan killer whales. Given that knowledge, and this assessment, we are in a position to make a more informed choice about whether to increase the pressure on these endangered Southern Resident killer whales.

“Pressure” in this sense, means the risk of extinction.

Sea lions in the Great Bear Rainforest

Stellar Sea Lions on the waters of the Great Bear Rainforest. Photo by Andy Wright.

  1. HP harbour porpoise, DP Dall’s porpoise, PWS Pacific white-sided dolphin, NRKW Northern Resident killer whale, SRKW Southern Resident killer whale, TKW transient killer whale, OKW offshore killer whale, MW minke whale, HW humpback whale, GW grey whale, SW sei whale, FW fin whale, BW blue whale, NPRW North Pacific right whale, SPW sperm whale, HS harbour seal, NFS Northern fur seal, SSL Steller sea lion, CSL California sea lion, NES Northern elephant seal, SO sea otter.

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