On March 24, 1989, the Exxon Valdez oil tanker collided with the Blight Reef in Alaska, spilling at least 11 million gallons of crude oil into Prince William Sound. Some estimates put the number as high as 38 million gallons. The spill was on record as the largest in US waters until the BP Deepwater Horizon disaster in 2010, and the immediate aftermath was devastating. 250,000 seabirds died and billions of fish eggs were destroyed, crashing the marine food web.
Now, 26 years later, scientists have found that the spill was even more ecologically catastrophic than originally predicted. In a study published this morning in Scientific Reports, researchers led by NOAA toxicologist John Incardona show that even very low levels of oil contamination can disrupt normal development in salmon and herring.
Incardona and his colleagues exposed Alaskan-sourced salmon and herring embryos to varying degrees of crude oil contamination, ranging from a low dose of .023 parts per billion (ppb) to a high dose of 45 ppb. In the months after the fish hatched, the team observed a sliding scale of growth problems and heart defects in them, proportional to the oil exposure level.
This is because oil literally gets under the skin of these developing fish through absorption during the pivotal embryonic stage. Even the lowest doses prevented a healthy population from emerging. Given that there are still about 21,000 gallons of oil dispersed throughout Alaska's Prince William Sound—and lingering contamination hundreds of miles beyond it—it's no wonder that salmon and herring populations have not significantly recovered.
"These juvenile fish on the outside look completely normal, but their hearts are not functioning properly and that translates directly into reduced swimming ability and reduced survival," said Incardona in a statement. "In terms of impacts to shore-spawning fish, the oil spill likely had a much bigger footprint than anyone realized."
Exxon has repeatedly dodged the charge that Prince William Sound is suffering long-term consequences from the spill, taking the depressingly predictable approach of science denialism.
"We've done 350 peer-reviewed studies of Prince William Sound, and those studies conclude that Prince William Sound has recovered," said Exxon spokesman Mark Boudreaux in 2006.
"It's healthy and it's thriving."
While some species have recovered to their pre-spill numbers, the overall health of the region is still dire over a quarter century after the disaster. If there's one silver lining to this grimy oil slick, it's that scientists have a much more accurate picture of the consequences of oil contamination, and can effectively shut down claims that ecosystems are "healthy and thriving" in their wake.
Hopefully this will lead to better regulation in the oil industry—and harsher reprisals when spills occur. If the Exxon Valdez disaster is still preventing fish from recovering in Prince William Sound, imagine how much worse the situation will be for the Gulf of Mexico after Deepwater Horizon, which spilt an insane 168 million gallons of oil into the ocean.
"Our findings are changing the picture in terms of assessing the risk and the potential impacts of oil spills," said study co-author and ecotoxicologist Nat Scholz in a statement. "We now know the developing fish heart is exquisitely sensitive to crude oil toxicity, and that subtle changes in heart formation can have delayed but important consequences for first-year survival, which in turn determines the long-term abundance of wild fish populations."
As much as the petroleum industry would like to shrug these ecological catastrophes off as short-term inconveniences, oil spills can clearly devastate biodiversity for decades—even centuries—after the event itself. We cannot afford to wait and see where the next worst disaster in US ecological history will take place.