The plan announced by the National Oceanic and Atmospheric Administration would expand the boundaries of the Gulf of the Farallones National Marine Sanctuary and Cordell Bank National Marine Sanctuary by 2,771 square miles, from west of Bodega Bay in Sonoma County to a point just north of Point Arena in Mendocino County.
The ocean refuges, designated as marine sanctuaries in 1981 and 1989, currently cover 2,049 square miles.
Two Democrats, U.S. Sen. Barbara Boxer and former Rep. Lynn Woolsey, had lobbied to have them enlarged starting a decade ago.
NOAA officials said the expansion is needed to protect whales, sharks, salmon and seabirds that feed and breed within the two regions, including a site off Point Arena that officials described as the most powerful in North America for generating the nutrients on which sea animals thrive.
Mary Jane Schramm, spokeswoman for Gulf of the Farallones National Marine Sanctuary, said the proposal would not limit commercial or recreational fishing within the sanctuary zones because NOAA does not regulate fishing.
The plan would, however, curtail the activities of other ocean users, including surfers who use personal watercraft to reach prime offshore swells, tour companies that use low-flying helicopters or small planes to spot migrating whales, and explorers searching for shipwrecks.
NOAA is soliciting public comment on the plan until June 30.