CASCADE LOCKS, Ore. -- Biologists are unsure how six trapped sea lions died on the Columbia River, NOAA's Fisheries Services said Wednesday.

AP photo

Six sea lions were found dead in the traps near Bonneville Dam Sunday.

It was originally thought they had been shot, but accordoing to NOAA Fisheries the preliminary examinations found no evidence of recent gunshot wounds.

When biologists first found the dead animals, it was assumed they were shot because a once-closed trap had an open door, and the floor of it was covered in blood.

X-rays did show metal fragments in the neck area of two of the sea lions. A metal slug was also in another, but scientists said the metal did not appear to cause the deaths, and could have been old puncture wounds common in sea lions.

"The investigation continues" into what NOAA spokesman Brian Gorman called the "mysterious" deaths. Gorman said they were conducting toxicity tests on the animals that otherwise appeared to have been in good health.

Biologists were still examining a seventh dead sea lion.

The animals are federally protected by the Marine Mammal Protection Act. Oregon and Washington state were granted the rights to trap the animals to keep them from eating salmon.

A court ruling Tuesday put the trapping is now on hold until next spring after a threatened suit by the Humane Society of the U.S.

"We're just anxiously awaiting the results," of the investigation Kelly Peterson of HSUS said. "They were left vulnerable in government traps without proper monitoring."

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