PORTLAND, Ore. -- Six sea lions found dead at Bonneville Dam on Sunday weren't shot to death, officials said Wednesday.

The cause of death remains unknown, according to the NOAA's Fisheries Service. Earlier this week, there were widespread reports that the sea lions died of gunshot wounds.

Necropsies identified numerous shallow puncture wounds in one animal that were consistent with sea lion bite marks.

X-Ray exams conducted Tuesday revealed metal fragments in the neck of two animals. A metal slug was also found in the blubber of one animal.

However, officials said, the fragments and slug didn't cause death and they may be associated with old wounds.

The National Oceanic and Atmospheric Administration said it would continue its investigation to determine how the animals died and how the sea lion traps were closed.

Anyone with information is asked to call the NOAA Enforcement Hotline at 1-800-853-1964.

Officials: Cause Of Sea Lion Deaths Unknown