Biologists say the images have revealed ingested hooks, weights and swivels inside the large fish that can live up to 100 years. Idaho fishing regulations require anglers to release sturgeon unharmed.

Some of the gear found inside the fish, officials said, is for catching steelhead, bass or crappie. The study has found that only a tiny percentage of the hundreds of X-rayed sturgeon were deeply hooked.

During the survey, crews have been sampling sturgeon each week from June to October in a 140-mile stretch of the Snake River and 23 miles of the lower Salmon River, Idaho Power spokesman Brad Bowlin said.