Jeffrey Short has been asking the same question for nearly three decades: What happened to the herring?

After the 1989 Exxon-Valdez oil spill off Alaska’s southern coast, the fish ― a vital link in the food chain and resource for the local economy ― began disappearing. Yet Short, a scientist stationed in Alaska for the National Oceanic and Atmospheric Administration, struggled to connect the dots between the spill and the herring population crash.

Now his latest study ― one of two published this month examining how the 2010 Deepwater Horizon disaster affects animal and plant life in Gulf of Mexico ― offers some clues. The spill, caused by a BP oil well that blew out and gushed /www.popularmechanics.com/science/energy/a6032/bp-oil-spill-statistics/"}}" data-beacon-parsed="true">200 million gallons of crude for 87 days straight, killed thousands of mammals and sea turtles and more than 1 million birds.

Without those predators, schools of fish rapidly multiplied, straining an ecosystem not designed to handle populations of that size. The number of menhaden, a species of fish in the herring family known colloquially as bunker or pogies, roughly doubled in a year.

SAUL LOEB via Getty Images Oil-covered brown pelicans found off the Louisiana coast after the BP Deepwater Horizon oil spill in the Gulf of Mexico wait in a holding pen for cleaning in June, 2010.

“It’s an astonishingly huge effect,” Short, who now runs his own environmental consultancy in Juneau, Alaska, told HuffPost. “The result of doubling that population put enormous stress on the rest of the food web because Gulf menhaden were already at carrying capacity of that habitat.”

As a result, the fish put pressure on their planktonic prey and began to starve, in turn becoming less nutritious to the remaining seabirds and other fish that rely on them as food.

“The seabirds, were they alive, would eat enormous numbers of juvenile menhaden,” Short said. “Instead they were dead, and didn’t eat them, accounting for a classic example of a population explosion by release from predation.”

The study, published in the journal Archives of Environmental Contamination and Toxicology, combined a review on fish numbers after the Deepwater Horizon spill with two studies the researchers published in 2014 on bird populations following the disaster.

The findings also could explain why the herring population never fully bounced back after the California-bound Exxon-Valdez tanker struck a reef in Prince William Sound and leaked 10.8 million gallons of crude. Up to 690,000 birds died as a result of the spill, according to a 1996 study by the American Fisheries Society. The herring population was near capacity in 1989, Short said. After the spill, the fish became hyper-abundant, leaving them malnourished and susceptible to disease, he theorized.

Julie Dermansky via Getty Images One of the fish kills in Louisiana following the 2010 BP oil spill in the Gulf of Mexico.

“We suspect this may be the answer to the herring question,” Short said. “Diseases caused the population to crash and they never recovered. We think this is a pretty big deal.”

The ecosystem in the Gulf of Mexico also may never recover, Short said.

“So far, it looks like the Gulf menhaden population is permanently in what I’d call a hyper-abundant state, which means they’re continuing to be chronically under-nourished and consume a lot of the productivity in the ecosystem,” he said. “It’s not impossible, but it may be an irreversible effect.”

He added: “We think it’s by far the biggest ecological effect, on the surface at least, of the Deepwater Horizon … This is something that happens across many thousands of square kilometers, from Alabama almost to Texas.”

Another study released in July suggests the effects of the BP spill are taking a worse toll on shore than previously thought. After the spill, oil seeped into the Louisiana wetlands and became buried under plants. Now, researchers at the American Society of Agronomy found that the oil slows the intake of oxygen through the plant roots, according to their study published in the Social Science Society of America Journal.

“This delay in oxygen availability caused by oil can increase stress on wetland plants, unable to supply enough oxygen to their root system,” the researchers wrote in a press release. “This stress can contribute to accelerated loss of marsh area through erosion in a region where marshes are already rapidly disappearing″ due to a rise in sea levels.

The new research comes amid a push by President Donald Trump and Interior Secretary Ryan Zinke to boost offshore oil and gas drilling and reverse rules made after 2010 to prevent similar disasters.

The administration “is proposing to weaken drilling safety standards and dramatically expand offshore drilling, threatening the beaches of the Atlantic, the Pacific, the Arctic, all while we’re still feeling the impacts” of the BP spill, Alex Taurel, the deputy legislative director at League of Conservation Voters, told HuffPost.

At the same time, BP is doubling down on offshore drilling, investing tens of billions of dollars to try to make it cheaper.