The incident happened this May when a woman saw the seal pup on a beach near Westport, Washington, and carried it away in a recyclable shopping tote, NOAA public affairs officer Michael Milstein told ABC News today.
"She then took it home and realized she really didn't know what to do for it or how to take care of it," he said. "She later called the local aquarium, Westport Aquarium, which is part of our network of volunteers."
The aquarium's director, Marc Myrsell, told ABC News today that when he saw the seal on the woman's deck, it was "alive but extremely lethargic."
"Usually these animals will snap and struggle to get away if you try to approach them, but this pup was so lethargic," Myrsell said. "Putting him in the carrier to take him to a center was like picking up a sleeping human baby."
He said he and officials with the Washington Department of Fish and Wildlife originally hoped to return the pup to the beach where the woman had found it. However, it was "unfortunately so unresponsive, and so much time had gone by" that they decided the most humane thing to do would be to euthanize it.
The Washington Department of Fish and Wildlife did not immediately respond to ABC News' requests for additional information.
Though the incident happened in May, the pup's tragic story only recently started getting attention after the NOAA issued a news release this week reminding local residents of an "increasing alarming spate of similar incidents," according to Milstein.
"The best thing people can do to help marine mammals on the beach is to leave them alone, staying 100 yards away, if possible," the NOAA said in the news release. "Disturbing, feeding or attempting to move young seals or other marine mammals is illegal because it can stress the animals, interfere with their natural behavior and cause adult seals to abandon their pups."
Milstein told ABC News today that typically "there are only about six to 10 illegal seal pickup cases a year in the Oregon-Washington area," but there have already been at least four known incidents this year.
"The decision to euthanize an animal is one that we do not take lightly at all," said Kristin Wilkinson, a regional stranding coordinator for the NOAA's West Coast Marine Mammal Stranding Network.
She said that in the case of this seal pup, it was in such bad condition that its chances of survival were extremely low.
She added that rehabilitation centers are often full and that wildlife officers have to make tough decisions about how many animals can be accepted. Typically, pups assessed to have a higher likelihood of survival are ones that are taken into rehab centers, she said.
"We're very passionate about marine mammals, so of course we all want to see them survive in the wild," Wilkinson said. "We only resort to euthanization if the situation becomes so dire that it would be the most humane thing to do."