Oil Spills and marine mammals: development and application of a risk-based conceptual framework

New research paper identifies elevated risk to marine mammals in BC, Canada.

Whales eating close to the shore on the North Coast of the Great Bear Rainforest.

Baleen whales were found to be highly vulnerable due to blowhole breathing, surface filter feeding, and invertebrate prey. Photo by A.S. Wright.

Biologists at Raincoast, along with Ocean Wise research scientist Peter Ross, have published a new paper in the Journal Archives of Environmental Contamination and Toxicology.  We developed a conceptual framework to evaluate the impacts of potential oil exposure on marine mammals and applied it to 21 species inhabiting coastal BC.  Oil spill vulnerability was determined by first examining the vulnerability of each species being exposed to spilled oil, and then the consequent likelihood of population-level effects.

Abstract

Marine mammals are inherently vulnerable to oil spills. We developed a conceptual framework to evaluate the impacts of potential oil exposure on marine mammals and applied it to 21 species inhabiting coastal British Columbia (BC), Canada. Oil spill vulnerability was determined by examining both the likelihood of species-specific (individual) oil exposure and the consequent likelihood of population-level effects. Oil exposure pathways, ecology, and physiological characteristics were first used to assign species—specific vulnerability rankings. Baleen whales were found to be highly vulnerable due to blowhole breathing, surface filter feeding, and invertebrate prey.

Sea otters (Enhydra lutris) were ranked as highly vulnerable due to their time spent at the ocean surface, dense pelage, and benthic feeding techniques. Species-specific vulnerabilities were considered to estimate the likelihood of population-level effects occurring after oil exposure. Killer whale (Orcinus orca) populations were deemed at highest risk due to small population sizes, complex social structure, long lives, slow reproductive turnover, and dietary specialisation. Finally, we related the species–specific and population-level vulnerabilities. In BC, vulnerability was deemed highest for Northern and Southern Resident killer whales and sea otters, followed by Bigg’s killer whales and Steller sea lions (Eumetopias jubatus)

Our findings challenge the typical ‘‘indicator species’’ approach routinely used and underscore the need to examine marine mammals at a species and population level for risk-based oil spill predictions. This conceptual framework can be combined with spill probabilities and volumes to develop more robust risk assessments and may be applied elsewhere to identify vulnerability themes for marine mammals.

Citation

Jarvela Rosenberger, Adrianne L.1, Misty MacDuffee1, Andrew G. J. Rosenberger1 and Peter S. Ross2 2017. Oil Spills and Marine Mammals in British Columbia, Canada: Development and Application of a Risk-Based Conceptual Framework. Archives of Environmental Contamination and Toxicology (2017) 73: 131. https://doi.org/10.1007/s00244-017-0408-7

Affiliation

  1. Raincoast Conservation Foundation
  2. Ocean Wise Conservation Association (formerly known as Vancouver Aquarium)

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Oil spills and marine mammals risk based conceptual framework (PDF)

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Figure 2

Likelihood of population level effects (ranked)

Figure 2: Likelihood of population level effects (ranked).

Likelihood of population-level effects is depicted here in the event of an oil spill for marine mammals in BC ranked. Four categories are scored as low, moderate, high, and highest using equal intervals from the minimum possible cumulative score to the maximum possible cumulative score as follows: (min/max score (8/24), with bins for low (8–11), moderate (12–15), high (16–20) and highest (21–24). Purple: dolphins, porpoises: HP harbour porpoise, DP Dall’s porpoise, PWS Pacific white-sided dolphin; green: killer whales: NRKW Northern Resident killer whale, SRKW Southern Resident killer whale, TKW transient killer whale, OKW offshore killer whale; blue: baleen whales: MW minke whale, HW humpback whale, GW grey whale, SW sei whale, FW fin whale, BW blue whale, NPRW North Pacific right whale; light blue: SPW sperm whale; red: pinnipeds: HS harbour seal, NFS Northern fur seal, SSL Steller sea lion, CSL California sea lion, NES Northern elephant seal; orange: SO sea otter.

Figure 3

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

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

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. 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.

Figure 4

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 following a 15000 m3 release of diluted bitumen at Arachne Reef in Northern Haro Straight, BC.

Black to grey shading indicates the probability of oil presence 15 days following a 15,000 m3 fall release of diluted bitumen at Arachne Reef in northern Haro Strait, BC. The modelled probabilities of oil presence (EBA 2013) are overlaid with the Critical Habitat of Southern Resident killer whales in Canada and the United States.

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