Photograph by Mark Ralston/AFP, Getty Images
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Smoke envelops Mondos Beach near Ventura, California, in 2017. Dolphins and porpoises that swim just offshore are particularly vulnerable to breathing in smoke.

Photograph by Mark Ralston/AFP, Getty Images

Wildfire smoke may harm whales and dolphins: Here’s what we know

As North America's West Coast burns, scientists are concerned marine mammals will be harmed by smoke inhalation, an unstudied phenomenon.

Little research has been done on how marine mammals are affected by prolonged exposure to the smoke and chemicals released during wildfires, but if the aftermath of the Deepwater Horizon oil rig explosion in the Gulf of Mexico is any indicator, they could face serious health effects in the years to come.

Ten years ago, as a first responder in New Orleans, veterinarian Cara Field saw for herself how the worst oil spill in U.S. history affected the region’s wildlife. The spill released 200 million gallons of oil into the ocean, much of which rose to the surface. As part of the cleanup, crews burned it off into the atmosphere. But research just five years later showed bottlenose dolphins that breathed the chemical-laden smoke developed severe lung diseases, were more prone to infections, and their offspring died at higher rates.

Field, now the medical director at the Marine Mammal Center, a conservation nonprofit in Sausalito, California, fears that marine mammals along the western coast of North America could be facing a similar fate, during a season of disastrous wildfires that have destroyed more than seven million acres.

Wildfire smoke is made up of a range of gases, including carbon monoxide; nitrogen dioxide; polycyclic aromatic hydrocarbons, or PAHs; and hazardous particulate matter, which has been shown to increase risks of respiratory and cardiovascular illnesses in humans.

Because whales, dolphins, porpoises, and other marine mammals are adapted to life at sea, where there are fewer air pollutants than on land, they “would be expected to be more susceptible to injury from inhaled particulates,” Field says. That could have grave consequences for species such as sea otters and orcas, or killer whales, which are already in decline in the region. (Read how the Exxon Valdez spill devastated orcas.)

Because the effects of wildfire smoke on marine mammals aren’t well understood and the potential threat is high, Field is urging scientists along the West Coast to begin collecting data now on marine mammal health in areas affected by wildfires. Though there have not been reports of stranded marine mammals suffering from smoke inhalation this fire season, it’s still possible, Field says.

“Now is the time to get our baseline, pick what samples to look for, and start identifying species or populations that would be potential candidates to study,” she says.

Vulnerable anatomy

The anatomy of whales, dolphins, and porpoises makes them more vulnerable to the harmful effects of wildfire smoke, Field says. Because they exchange big gulps of air rapidly through their blowholes, they can easily inhale airborne smoke particles.

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A Guadalupe fur seal swims in a pen amid smoky air from the recent California wildfires at the Marine Mammal Centre in Sausalito. The animal was rescued before the blazes began.

They also lack sinuses and other nasal structures found in land animals—physical barriers that trap particles in mucus and allow animals to sneeze or cough them out, so that fewer particles reach the lungs, says Stephen Raverty, a veterinary pathologist at the Ministry of Agriculture in British Columbia.

“With a more rapid inhalation and exhalation, lack of these protective structures, and large volume of lung exchange with each breath, whales, dolphins, and porpoises are at an increased risk” of smoke exposure, he says.

Necropsies of the 46 dolphins that washed ashore dead following the BP oil spill also offer some insight into how wildfire smoke injures marine mammals, Field says. (Read how the BP oil spill is affecting wildlife, 10 years later.)

The dead dolphins had severe lung disease and degenerated adrenal glands—organs that regulate hormones, the immune system, responses to stress, and more. Scientists concluded this could have been caused by exposure to hydrocarbons from the smoke, because, in lab animals, exposure to PAHs can lead to similar adrenal atrophy and harm their reproductive systems. In humans and animals alike, the chemicals have been linked to various forms of cancer.

Smoke signals

It’s impossible to tell what most hurt the dolphins in the Gulf: breathing in the smoke when the spilled oil was burned off, ingesting oil through the food chain, or a combination of both, Field says.

Regardless, dolphins and porpoises are more likely to experience irritation of their airways and absorb more hydrocarbons than whales, as they tend to stay closer to shore and breathe more frequently than deep-diving mammals.

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“Given that we know dolphin airways are probably more susceptible…to inhaling these particulates, it’s very likely that inhaling ash and particulates is going to cause damage,” she says.

Scientists have also looked at the impact of smoke and chemicals on sea otters, an endangered species in California.

A 2014 study of 39 California sea otters found that exposure to wildfire smoke and runoff—a toxic mix of sediment, metals, and chemicals that flows into water bodies adjacent to forest fires—weakened their immune systems. A follow-up study showed that 15 months later, the otters’ immune systems seemed to have recovered.

But the number of animals in the study was small, Field says, and the long-term impacts to the species remain unknown. (Learn how nature can bounce back from an oil spill.)

Research challenges

Conducting research on this topic is difficult, for the obvious reason that scientists can’t easily study live animals while a wildfire is raging, Raverty says.

“We can’t go out and live-capture animals for a variety of ethical and logistical reasons, so we rely on dead, stranded animals,” he says. For instance, scientists in British Columbia have examined more than 6,000 stranded marine mammals over a decade as part of a long-term project that has yielded data about the animals’ overall health, such as the levels and types of pollutants found in an animal’s tissue. (Learn how new diseases and toxins are harming marine life.)

Due to climate change, wildfire seasons in the western U.S. will only grow more extreme, and Raverty expects scientists will launch similar studies to investigate how wildfire smoke affects marine mammals.

The key, Field says, is following the animals—many of which are long-lived species—for decades.

“Effects of wildfires are often cumulative,” she says. “Things may not be obvious for years, so you have to have the longevity to keep those studies going.”