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More than 40 miles out from the Golden Gate Bridge and over an undersea slope plunging from the edge of the continental shelf, a team of scientists lowered a specialized net into the cold, green Pacific Ocean.

Soon, the research vessel Fulmar, a 67-foot aluminum-hulled catamaran, began towing the net above the slope, known as the "shelf break," for a tiny but titanically important creature called krill.

Jaime Jahncke, director of marine ecology at Petaluma-based PRBO Conservation Science, already knew the catch would be slim.

"Honestly, right now there's not much of it here," Jahncke said last week aboard the Fulmar.

Echo soundings displayed on a screen inside the Fulmar's cabin showed a relatively small mass of krill, a transparent, shrimp-like crustacean, in the depths below.

Why the krill had cleared out wasn't clear, Jahncke said. And the meaning of the results on this particular day are neither good nor bad. But the consistent monitoring of the area enables scientists to assess patterns in the marine ecosystem, including possible impacts of climate change.

Last year, abundant krill drew record numbers of humpback and blue whales to the Farallones, and Cassin's Auklets, birds that dive 100 feet or more to catch krill, had unparalleled breeding success on the rocky islands.

Krill, found in all oceans of the world, are a cornerstone of the marine food chain. The half-inch long animals live in massive swarms, eating microscopic phytoplankton, and are, in turn, devoured by fish, seals, squid, penguins and even 40-ton whales.

Last week the scientists stationed on the Fulmar's top deck saw few birds or marine mammals in waters known as one of nature's most abundant pantries.

"There doesn't seem to be a lot of food," said Kirsten Lindquist, a field biologist with the Farallones Marine Sanctuary Association.

On a similar research cruise in July, the scientists came upon a "feeding frenzy," with about a dozen humpback whales, 4,700 birds, dolphins and sea lions roiling the ocean surface as they feasted on small Pacific mackerel.

The Farallones, a string of small, rocky islands barely visible from land on a clear day, play host to the largest seabird colony in the continental United States and are a key breeding ground for seals and sea lions.

Birds fly in from around the world — shearwaters from Chile and New Zealand; albatross from Hawaii — to feast in the surrounding waters from south of San Francisco up to Bodega Bay. About 50 bird species frequent the area, eating krill, scavenging on the ocean surface and diving for bait fish.

"It's a hot spot," Lindquist said. "One of the richest in the Pacific."

On last week's cruise, the scientists' best guess was that the whales and birds had moved on, possibly to the north, in search of more krill.

Nonetheless, they went about their chores on a daylong research cruise that departed from the Sausalito Marina shortly after 7 a.m. and motored west non-stop, bounding over the incoming swells for two and a half hours.

When there are no observers aboard, the scientists typically nap en route. They prefer working as the Fulmar returns eastbound, moving with the swells for a far smoother ride.

<NO1><NO><NO1><NO>The vessel cut to an idle over the shelf break at the west end of Line 6, a 26-mile east-west line running between the North and South Farallon Islands, within the Gulf of the Farallones National Marine Sanctuary.

A partnership called ACCESS, formed by PRBO and the Farallones and Cordell Bank marine sanctuaries, monitors the oceanic ecosystems in 8,000 square miles of federally protected waters from Bodega Bay to Cambria in San Luis Obispo County.

ACCESS scientists conduct four to five survey cruises a year along designated east-west lines through the marine sanctuaries, measuring water conditions and counting birds and mammals.

Data compiled by the monitoring is available to sanctuary managers and policymakers to guide conservation efforts, gauge the impact of climate change and natural conditions, such as freshwater outflow from the bay and rivers, and to evaluate possible ocean uses, such as aquaculture.

For last week's first chore, Dan Howard, the Cordell Bank sanctuary superintendent, lowered a CTD device 650 feet down on a boom-mounted cable off the Fulmar's rear deck.

The device measures ocean temperature, salinity, clarity, oxygen content and phytoplankton content (via a chlorophyll sensor) throughout the water column.

Just below the surface, a water sample was taken to assess the red tide that appeared off the Sonoma coast in late August and likely caused a massive abalone die-off and early closure of the abalone sport diving season.

"We were in the thick of it yesterday," Howard said last Monday.

Scientists prefer to call the phenomenon an algal bloom because the concentration of marine microorganisms is not always red — varying from purple to almost pink and normally red or green — nor is it typically associated with tides.

Four-ounce plastic bottles of phytoplankton-bearing water were prepared aboard the Fulmar and later delivered to the California Department of Public Health lab in Richmond for analysis.

When the sampling was done, hoop nets to catch zooplankton in the upper 160 feet of the water column went overboard, followed by a larger net, called a Tucker trawl, that goes down 650 feet for krill.

The trick to low-speed towing of a Tucker trawl is to play out about 1,200 feet of cable at an approximately 45-degree angle, hoping to get the Tucker as close to the bottom as possible, without wrecking it on the rocks or filling it with mud.

Manning the cable winch and boat controls from the back of the Fulmar's upper deck, boat operator Erik Larson and Hans Bruning, the mate, positioned the Tucker with care and seasoned guesswork, like anglers. Only when the trawl was retrieved would they know how deep it went and what it caught.

They landed some krill, but one hoop net came up jammed by an egg yolk jellyfish that kept everything else out. Howard and Jahncke hosed it clean and dropped the unwelcome jelly back into the ocean.

Whales, seals and birds were largely no-shows, but the scientists — again like persistent anglers — were back on the water the next day.