HONOLULU -- A 78-year-old Kauai man on Friday admitted in court to killing a pregnant monk seal on Kauai.

Even though he said it was an accident, Charles Vidinha was immediately sent to prison.

Vidinha said he was preparing remote Pilaa Beach for campers when a monk seal he thought was eating fish from his nets beached itself. He pulled out a .22-caliber rifle.

"He shot his rifle from his hip so he didn't have really good aim and all he was trying to do was hit in the sand to get the seal away," defense attorney Alexander Silvert said.

Vidinha told the judge, "I shot at it to scare it away. It was a horrible mistake. I apologize."

"This is not who he is. This is not what he intended. It's really unfortunate that it happened," Silvert said.

Under a plea agreement, Vidinha was found unable to pay a fine. The judge sentenced him to 90 days in federal jail.

"He's very happy that he admitted it and he could come clean and tell his story that he did not intend to kill this seal," Silvert said.

One investigator still doubts Vidinha's story because the seal had two fatal wounds.

"One was in the heart and lung area and one was in the abdomen that entered the placenta near the near-term monk seal pup," National Oceanic and Atmospheric Administration marine animal expert David Schofield said.

Prosecutors said they did not have enough evidence to prove it was not an accident. They said if they did, they would not have agreed to the 90-day sentence. The maximum possible for intentionally killing a monk seal is one year.

"We of course don't want to see anyone go to jail, but we are happy that there were some consequences because you just can't kill an endangered species that's against the law," Schofield said.