A young seal recognized as a threatened species was killed in a Northern California national park when an off-leash dog attacked the pup that had come ashore, park officials say.

Authorities at Point Reyes National Seashore in Marin County are now seeking information to find the dog's owner after the attack left a Guadalupe fur seal dead.

The seal species is protected and listed as "threatened" under the Marine Mammal Protection Act and the Endangered Species Act. The attack also occurred in a bird nesting area, where dogs are not allowed, the National Park Service said.

"There are no areas in the park where dogs are allowed to be off leash. These rules keep wildlife and our pets safe," Point Reyes National Seashore wrote in a Facebook post.

The attack occurred April 22, and visitors tried to get the dog off the seal, park spokesperson Jennifer Stock told USA TODAY on Thursday.

"They tried to get the dog off the seal by kicking sand onto it," she said. Once the dog let go, the parkgoers called The Marine Mammal Center, Stock said. However, the seal was dead by the time rescuers reached it.

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A necropsy confirmed the dog attack killed the seal, and an investigation was still underway Thursday, park officials said.

The dog owner was described as a woman in her 50s who walked with a cane and had dark, wavy hair with some gray in it, Stock said. The dog's breed was unknown but described as medium-sized and with long black and white fur, she added.

Guadalupe fur seals were hunted to near extinction by the 1900s, according to the National Oceanic and Atmospheric Administration. In 1954, scientists found them in a cave on Guadalupe Island off the coast of Baja California in the Pacific Ocean.

Conservation efforts have boosted the species' numbers by 10% between 1955 and 2010, NOAA says, and an estimated 20,000 animals were alive in 2010.

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Stock said that parks rules are in place to protect all visitors, their pets and wild animals, but that this case especially hurts given that it was a threatened species.

"Every single one counts. It's a real bummer to lose one," Stock said.

The person responsible could face two misdemeanors and civil or criminal penalties because of the seal's protected status, she said.

Allowing the dog into the restricted area and having it off leash in the park each could result in an up to $5,000 fine or six months in jail, Stock said.

Civil fines related to the animal's protected status could be up to $11,000. A criminal charge could lead to a $100,000 fine and year in prison, Stock added.

Follow USA TODAY's Ryan Miller on Twitter @RyanW_Miller