With endangered whales congregating in the food-rich waters around the Farallon Islands, the U.S. Coast Guard is asking large ships to slow down in hopes of avoiding fatal collisions with the huge cetaceans.
The Coast Guard's message, broadcast over marine band radio, asks heavy vessels — including tankers, container and cruise ships — to approach and exit San Francisco Bay at no more than 10 knots, about half their normal speed.
The slowdown is intended to reduce ship strikes on endangered blue and humpback whales, said Dan Howard, superintendent of the Cordell Bank National Marine Sanctuary, which covers 529 square miles off the Sonoma and Marin county coast.
Shipping lanes carry about 20 heavy vessels a day in and out of the bay cross the Cordell Bank and adjacent Farallon Islands marine sanctuaries, managed by the National Oceanic and Atmospheric Administration.
NOAA requested the slowdown message after biologists stationed on Southeast Farallon Island 30 miles outside the Golden Gate counted a remarkable concentration of whales in late June.
"There is food everywhere," Howard said, referring to an abundance of krill, a tiny shrimp-like crustacean that forms the cornerstone of the marine food chain.
Blue whales, the largest animals on the planet, feed almost entirely on half-inch-long krill that live in massive swarms.
The leviathans are of concern to scientists because their northeast Pacific population of about 2,000 has not rebounded in the 43 years since commercial whaling was ended in the United States.
During a one-hour break in the fog on June 27, the Farallon Island biologists counted 33 humpback whales, six blues and one fin whale, Howard said.
The following day, they spotted 25 humpbacks, seven blue whales, one fin and one gray whale.
"That's why this (radio) alert went out," Howard said.
The message, scheduled to continue until Friday, advises mariners from Point Reyes in Marin County to Point Ano Nuevo in San Mateo County to "keep a sharp lookout for large whales" and reduce speed around the two sanctuaries.
In mid-June, officials from the Marine Mammal Center in Sausalito helped confirm that a juvenile female humpback whale that washed ashore at Point Reyes National Seashore was killed by a ship strike.
Fractured vertebrae and bruising indicated the cause of death, said Jim Oswald, a spokesman for the center.
A handful of whale-ship collisions are reported every year — five likely or confirmed strikes in 2010, for example — but scientists say the mortality rate may be higher because most dead whales sink and their deaths are never recorded.
Rick Powers, a veteran Bodega Bay charter boat captain, said he has seen large blue whales "gorging themselves" on krill, abundant due to a strong upwelling of nutrient-rich waters this year along the North Coast.
"The ocean is the healthiest I've seen it in 10 years," Powers said.
Salmon are also feasting on krill, and Powers said he uses blue whale sightings to home in on the prized gamefish.
Last week a boatload of anglers hooked 76 salmon weighing up to 39 pounds and totaling nearly a ton of fish, Powers said.
Juvenile rockfish are also plentiful this year, adding to the food supply for salmon and humpback whales, Howard said.
(You can reach Staff Writer Guy Kovner at 521-5457 or firstname.lastname@example.org.)