An off-leash dog killed a threatened Guadalupe fur seal pup Monday in Point Reyes National Seashore, 30 miles north of San Francisco.

The canine was in an area of the park where dogs are currently prohibited due to nesting snowy plover birds, another threatened species.

A park visitor saw the incident happen and called the Marine Mammal Center in Sausalito, but by the time wildlife experts arrived, the animal was dead. A necropsy confirmed the cause of death was the dog attack.

The dog and the dog's owner allegedly left the scene, and an investigation is underway.

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Guadalupe fur seals were hunted to near-extinction in the 1800s and the only known breeding colony is on Guadalupe Island off the coast of Baja California, according to the Marine Mammal Center. The species once bred as far north as Point Conception in central California but were hunted to extinction in California in 1825. Today, seals sometimes make the big swim to the Channel Islands off Ventura, but park spokesperson Jennifer Stock says they're "very rarely" seen in Point Reyes.

"It was one individual seal," Stock says. "It was skinny so it was probably lost and searching for food."

Guadalupe seals are considered a threatened species, with their population estimated at about 34,000. They are protected by law in the United States and Mexico, and Guadalupe Island has been designated a sanctuary.

Dogs on-leash are allowed in the park in marked areas, but they're prohibited on some trails to protect wildlife that become nervous around dogs. Stock says the rules are well-marked on trails and at beaches.

"This is an incredible park where there's a lot of habitat for animals to feed and rest," says Stock. "A dog off-leash is a real threat to wildlife and habitat."

Stock says if you see someone committing a national park violation, such as walking a dog off-leash, the best thing to do is quickly gather information and then tell a ranger by calling the park or going to the visitors' center.

Walking a dog in a closed area, or walking a dog off-leash in a leash-only area, is a Class B misdemeanor with the maximum punishment a fine up to $5,000 or six months in jail.

"For a dog walker who is walking their dog off leash in a closed area (no dogs) and the dog kills a protected species under the Marine Mammal Protection Act, this may result in additional civil penalties (on top of the Park Class B misdemeanor) up to $11,000 or criminal penalties up to $100,000 plus one year imprisonment," Stock wrote in an email to SFGATE.