Daniela Maldini, chief scientist with the Okeanis conservation group, said her group shot footage in September of a porpoise being fatally attacked by a group of dolphins, KTVU-TV, Oakland, Calif., reported.
"We saw severe beatings," Maldini said. "It was a mob of dolphins."
The severity of the wildlife attack would explain the broken bones and internal bleeding suffered by other dead porpoises found on the state's beaches in recent years.
A University of California, Santa Cruz, professor of ecology and evolutionary biology said while dolphins are traditionally seen as peaceful animals, the marine mammals can actually turn hostile in the wild.
"Everybody thinks Flipper is this nice, mellow animal," UC-Santa Cruz professor Dan Costa said. "In the wild, there's interactions that occur and not all of them are friendly."
KTVU said, according to scientists, nearly 74 dead porpoises were found in California in 2008 alone.