But Brian Hatfield, a biologist with the U.S. Geological Survey who has watched the rookery grow from a few seals in 1990 to an estimated 16,000 this year, said it had become more of a problem as the population exploded. "This year seems to be particularly bad ... I'm not sure if it's overcrowding or if the barriers have just eroded." The Piedras Blancas birthing ground is one of an estimated 17 rookeries dotting the Pacific coast and offshore islands from the Gulf of Alaska to Baja, Mexico. Full Article at Philly.com