LOS ANGELES, Feb. 4 (UPI) -- A population explosion among California's elephant seals is creating headaches for motorists who drive the state's scenic coastal highway.

Officials say in recent weeks at least four of the 5,000-pound animals from the Piedras Blancas birthing area have gotten past fences designed to protect them and made their way onto Highway 1 near Hearst Castle, The Los Angeles Times reported Monday.

"When a 4,700-pound pickup truck meets a 5,000-pound seal, they both lose," says Ken Cummings, a docent with Friends of the Elephant Seal.

Biologist Brian Hatfield of the U.S. Geological Survey, says Piedras Blancas has grown from a few seals in 1990 to an estimated 16,000 in 2008.

"This year seems to be particularly bad," Hatfield said. "I'm not sure if it's overcrowding or if the barriers have just eroded."

Piedras Blancas birthing ground is the only rookery that is next to a major highway. It is one of the newest of an estimated 17 rookeries along the Pacific coast from the Gulf of Alaska to Baja, Mexico.