Hakai Magazine

Coastal science and societies

Southern resident killer whales
Measurements of polycyclic aromatic hydrocarbons (PAHs) taken from Salish Sea killer whales’ feces suggest a US law regulating how close boats can approach is helping. Photo by Richard Ellis/Alamy Stock Photo

Sucking Gas

Killer whales take in fewer hydrocarbons following tougher restrictions on vessel distances.

Authored by

by Larry Pynn

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When the BP Deepwater Horizon drilling platform exploded in 2010 and spewed an estimated four million barrels of oil into the Gulf of Mexico, scientists realized how little they knew about hydrocarbon pollution levels in marine life.

Without data on the hydrocarbon status quo, it’s difficult to determine the environmental impact of an oil spill or the success of cleanup efforts. It’s also hard to distinguish the effects of a spill from the effects of pollution from other more common coastal sources, such as urban runoff or industrial activities.

Since the Deepwater Horizon disaster, researchers across North America have been working to gather this baseline data. They’re collecting the feces of marine mammals and analyzing them for the presence of polycyclic aromatic hydrocarbons (PAHs), which are ranked as one of the top 10 most hazardous substances by the US Agency for Toxic Substances and Disease Registry.

Oil pollution from vessel traffic is a major concern in the Salish Sea, which straddles the Washington-British Columbia border and is home to the endangered southern resident killer whales. Canada’s controversial planned Trans Mountain Pipeline expansion—approved by the federal government in 2019 but still subject to legal challenges—would result in a sevenfold increase in oil tanker traffic through the killer whales’ critical habitat.

Researchers’ quest to establish baseline data on PAHs in these whales has produced a completely unexpected finding. The study suggests that tougher rules on whale watching vessels are having positive effects on the health of these iconic marine mammals.

Implemented in 2011 in the United States, the law doubled the distance boaters must keep from killer whales, extending it from 100 to 200 yards (91 to 183 meters).

According to the new study, in which researchers used dogs trained to sniff out killer whale feces floating on the ocean surface, killer whales in the Salish Sea showed “negligible” contamination with PAHs. Of 70 fecal samples collected off San Juan Island, Washington, from 2010 to 2013 and analyzed, most had concentrations below 10 parts per billion.

Of key importance, however, were four samples collected in 2010—one year before the tougher regulations came into force—that had significantly higher PAH levels, ranging from 11 to 104 parts per billion. That suggests that the levels of hydrocarbons in whales were considerably higher when the old boating rules were in place.

The year-to-year change in PAH levels came as a surprise to researchers. “It was an interesting finding,” confirms Gina Ylitalo, an environmental chemist at the Northwest Fisheries Science Center in Seattle, Washington. “That wasn’t the reason for doing what we were doing. It was just … happenstance.”

One of those four samples had the signature of crude or refined oil, suggesting a spill or fuel leak as the contamination source. The other three showed evidence of fuel combustion, consistent with the engines of smaller vessels, such as those used by whale watching tour operators.

PAHs do not accumulate up the food chain like some other contaminants, such as PCBs, though they do tend to linger in the environment for much longer than other hydrocarbon compounds such as benzene, which is quick to evaporate after a spill.

For marine mammals, exposure to oil has been linked to adrenal, reproductive, and immune problems; lung and heart disease; gastric lesions; and population declines. Killer whales are considered especially vulnerable; when they come to the surface to breathe, they can inhale, swallow, or even absorb PAHs through their skin.

Whale watching in the Salish Sea is a popular activity with the potential to negatively impact the killer whales. In a separate 2018 report, researchers with Soundwatch, a nonprofit organization that tracks and educates boaters in the San Juan Islands, documented more than 600 potential violations of whale watching regulations, about one-third of them occurring within the 200-yard no-go zone. Recreational boaters accounted for 90 percent of incidents last year.

In May this year, the Canadian government announced an interim order expanding the distance vessels must keep from whales even farther. The new rule prohibits vessels from approaching within 400 meters of killer whales within the southern residents’ critical habitat. Commercial whale watching operators and ecotourism companies may apply to approach 200 meters.

Joe Gaydos, science director for the SeaDoc Society who was not associated with the study, says that governments in Washington State and British Columbia already have concerns about ship strikes and the impacts of vessel noise on the southern resident killer whales. But this latest study shows that the debate must be broadened to also include hydrocarbon contamination, he argues.

The hydrocarbon study recommends ongoing sampling of killer whale feces for PAHs and observes there is no substitute for preventive action to reduce the risk of an oil spill. With the number of southern residents down to just 73 individuals, there is little room for error.