Scientists are hoping to boost dwindling pigeon guillemot populations in Prince William Sound, the last species of seabird listed as "not recovering" after the Exxon Valdez oil spill, more than 20 years after the oil tanker dumped more than 10 million gallons of crude oil into the waters of Alaska's Prince William Sound.

In 2008, around 100 of the seabirds were estimated to inhabit a cluster of islands called the Naked Island group, the animal's primary breeding grounds in the Prince William Sound. That's a decline of 90 percent since 1989. Now, U.S. Fish and Wildlife hopes to locally eradicate one of the pigeon guillemot's top predators, the American mink, in order to help the population rebound.

The oil tanker Exxon Valdez ran aground March 24, 1989, an accident which spilled 10.8 million gallons of crude oil into Prince William Sound, causing widespread destruction to animals and the sound's habitat.

Somewhere between 2,000–6,000 pigeon guillemots died from "acute oiling" following the spill, according to the U.S. Fish and Wildlife Service. Long-term effects continued to reverberate well after the initial incident, and a decade later a study concluded that the seabirds were still being exposed to oil in the sound.

In 1991, the Exxon Valdez oil spill Trustee Council was formed between Exxon Mobil, the state of Alaska and the federal government, tasked with overseeing the ecosystem's restoration following a $900 million civil settlement.

Three years later the Council adopted a list of wildlife and habitat it is responsible for restoring. Today, the pigeon guillemot is the only remaining bird species listed as "not recovering" on the Trustee's Injured Resource list. The Pacific herring is the only other species also listed as "not recovering."

As time passes, distinguishing between effects of the oil spill and other causes contributing to a species' decline becomes more difficult, but that doesn't "negate the responsibility of the Trustee Council to pursue restoration of spill-affected resources," its website states.

By 2004, scientists concluded that the birds were no longer feeling the effects of the oil spill. However, pigeon guillemot were still on the decline due to mink predation.

While "it's difficult to know exactly what happened" to the pigeon guillemot's populations, the birds "certainly were affected by the oil spill," said David Irons, seabird coordinator with Fish and Wildlife.

Regardless of the reason behind the continued decline, it is still up to the trustees to restore the bird's populations, Irons said.

To "restore [the pigeon guillemot] by removing the mink -- that's still fair game."

In its draft environmental assessment, U.S. Fish and Wildlife proposes trapping or shooting the mink over a 5 year period, with monitoring to continue for a total of 15 years.

Mink would be removed from the Naked Island group, a cluster of three islands where pigeon guillemots gather in "incredibly high density," said Irons. The birds nest on the islands far more than any other locale in the Sound; in 1989 a quarter of all pigeon guillemots nested there.

Figuring out how many mink to remove is "the hard part," Irons said, as the exact number inhabiting the cluster of islands is unknown, although their numbers are estimated to range roughly from 200-300.

By removing the mink, several other species of birds that nest on the islands would benefit as well, Iron said. Parakeet auklets, tufted puffins and horned puffins have also been on the decline in the past decades, but those birds are not on the Trustee Council's list of affected animals.

"Right now Naked Island is a desert of birds -- it used to be a hot spot," Irons said, adding that the Prince William Sound used to be home to 700 parakeet auklets, whereas now only around 40 remain.

If pigeon guillemot populations can be brought to 1,000 birds, it will be considered a "recovered" species by the Trustee Council.

Estimated cost of the project is between $1.9–$2.2 million should it go forward, split roughly between the Trustee Council and the National Fish and Wildlife Foundation.

Public comment on the draft environmental assessment and proposed eradication of mink on the Naked Island group is open until Aug. 17.