Two trouble-making sea lions who were sentenced to death for preying on endangered salmon have been given a reprieve by a Chicago aquarium.

The massive mammals — now named Biff and Otis — were rescued by the Shedd Aquarium in Chicago after being apprehended back in March, the Los Angeles Times reports. The sea lions were found at the Bonneville Dam between Washington and Oregon, where they were found feasting on Chinook salmon, a species wildlife officials spent decades and millions of dollars to protect. 

But it wasn’t the duo’s first infraction, so they faced the death penalty — until the aquarium stepped in. Now, they’re training to take part in a marine mammal show and are thriving.

Ironically, California sea lions were themselves overhunted, with their population falling to 10,000 in the 1950s. Today, some 300,000 populate the Pacific Coast between Mexico and Alaska.

By 2002, sea lions were preying on fish near the Bonneville, a 197-foot dam built in 1937 that was one of the first hydroelectric dams on the Columbia River. The dam attracts male sea lions from January to May, who arrive for the salmon spawning runs to fatten up; they return to their own breeding beaches in California and Mexico for their own mating season in June.

Biff and Otis were caught several times in recent years, as dam officials tried to chase off mammals by scaring them with boats, detonating underwater firecrackers and discharging rubber shotgun pellets. In 2008, federal authorities gave Oregon, Washington and Idaho permission to use lethal injections.

"This has been fairly controversial," said Craig Bartlett, spokesman for Washington’s Fish and Wildlife Department.

Luckily for Biff and Otis, Shedd has offered them a new lease on life. They are being tutored in the fine art of entertaining, and will soon become main-stage stars in a marine mammal show. Both sea lions have also slimmed down to about 650 pounds.

"They lived the life of Riley, catching fish at the dam," said Ken Ramirez, Shedd's vice president of animal collections. "But it was even easier to get fish from us, so they weren't upset at all to be hanging around with us."