The incident occurred at 1:40 p.m. Saturday at Goff Cove Beach while Kelly's 18-year-old daughter was walking the 65-pound bulldog on a leash, KCBS-TV, Los Angeles, reported. The dog ran off and attacked the sea lion, the TV station said.
The video shows the teen screaming while the dog holds the sea lion by its neck. Two women tried to help the teen before Kelly arrived and forced the dog off the animal but the sea lion later died, KCBS-TV said.
Nathan, who declined to give the TV station his last name, was having lunch nearby and took the video of the attack. He said he didn't know the incident involved Kelly's family when he posted it online. Kelly is married to former U.S. Rep. Gabrielle Giffords, D-Ariz.
"It was pretty much just panic. People didn't know how to act when a dog of this size just locked down [and didn't let go]," Nathan said.