By Craig Welch, The Seattle Times

ANACORTES, Wash. — The bird-counters stood in the windy bow chattering into headsets and scanning the Strait of Juan de Fuca with binoculars.

“Scoters,” Sherman Anderson said. “Three of them. At 11 o’clock. Look like surfs.”

“Marbled murrelets,” he added seconds later. “I see two.”

Inside the boat’s cabin, another Washington Department of Fish and Wildlife worker listened through a headset of his own so he could record the tally on a computer.

Bird surveys like this and others done by plane are tracking a significant ecological shift in our region — a major decline in once-abundant marine birds. From white-winged scoters and surf scoters to long-tailed ducks, murres, loons, and some seagulls, the number of everyday marine birds here has plummeted dramatically in recent decades.

Scoters are down more than 75 percent from what they were in the late 1970s. Murres have dropped even more. Western grebes have mostly vanished, falling from several hundred thousand birds to about 20,000.

The reasons often vary — from climate change and shoreline development to marine pollution and the rebound of predators such as bald eagles.

But several new studies now also link many dwindling marine bird populations to what they eat — especially herring, anchovies, sand lance, and surf smelt, the tiny swimmers often dubbed forage fish.

The relationship between marine birds and slick, fatty forage fish is complex. Some birds are here year-round while others pass through for just a few months. Some birds key in solely on silvery herring while others can just as easily eat flounder.

Some forage-fish species, such as herring, are a fraction of what they once were. But little information exists about the health of other species. But an exhaustive new analysis of bird diets and population trends found that marine birds relying exclusively on fish like herring were up to 16 times more likely to be in trouble than birds that ate nonschooling bottom-dwellers like sculpin.

“The result was remarkably strong,” said study author Ignacio Vilchis, formerly with the SeaDoc Society at the University of California, Davis. “It showed that it’s the diving birds that go after forage fish which are much more likely to have a declining trend.”

There’s certainly no shortage of crashes to evaluate. Five years ago one study showed the overall bird numbers in Puget Sound and British Columbia’s Georgia Strait were down 30 percent from the late 1970s. In Puget Sound alone, marine bird numbers have been cut in half.

Biologists for years have tried to understand why the change hit so many species at once. But only recently have they really started to examine some of the systemic shifts that may cause or exacerbate declines.

“It’s one thing to have a rare species decline,” said Joe Gaydos, with the SeaDoc Society. “But we’re not talking about a few plovers. We’re talking about big, common species, and a lot of them.”

There is no easier way to view this decline than through the once-ubiquitous Western grebe.

These black and white ducklike birds with their long necks and thin beaks settle in winter in colonies on lakes from southwest Canada to California but gather their food from marine waters.

While the bulk of that population once centered on Washington and lower British Columbia, sightings of larger flocks of grebes are unusual enough that when it happens “birders will talk about it on the Internet for days,” Gaydos said.

At first it wasn’t clear whether this was a local or continental-scale problem, said Scott Wilson, a biologist with Environment Canada. It’s both: Up and down the West Coast, the winter breeding population is half what it was in 1975.

But something else was going on, too.

While Puget Sound and lower B.C. declines top 95 percent, grebe populations in parts of California have tripled. The center of the bird’s range shifted 550 miles south.

“Food is one of the key resources species need to survive,” Wilson said. And grebes rely on forage fish.

In Puget Sound, the biggest stock of herring used to reside at Cherry Point, south of Bellingham. But since 1970 that herring stock has crashed, with more than 90 percent of the population all but gone.

The loss of herring probably drove grebes away, Wilson hypothesized, but it also did so just as sardine stocks were recovering to the south. Down to a few thousand metric tons in 1985, sardine populations in California have since exploded to more than 2 million metric tons, providing an alternative food for hungry grebes.

“The grebes were tracking this very large-scale change — the combined change to herring in the north and sardines in the south,” Wilson said. “And Western grebes are quite mobile.”

Changes in other bird populations, too, could to some degree be related to changes in forage fish.

Surf scoters, which primarily eat mussels and small crabs, also sometimes turn to herring eggs during spring migration. In 1978, bird surveyors counted 40,000 scoters near where herring were spawning. But in 2004 and 2005, surveyors counted fewer than 1,000 birds in the same location.

Some researchers suspect that since the herring spawn moves from year to year, bird counters probably missed quite a few scoters. But experts believe the general trend of decline is real.

“I think the herring absolutely did play a role in the scoter decline, but exactly what that role is, we just don’t know,” said Joe Evenson, of the Washington Department of Fish and Wildlife.”

At that time of year, scoters are eating roe because they’re storing up a lot of fat and that can help determine whether they are successful at breeding. But I think there’s not just one thing that contributed to the scoter collapse.”

Meanwhile, the chief threat to marbled murrelets is still believed to be logging in their breeding grounds high in ancient Douglas fir forests. But some researchers have suggested that along the coast, murrelets are being forced to abandon their fatty fish diets and are eating less-nutritious fish lower in the food chain — especially just before the important period when they mate.

At the same time, some scientists believe the herring problem itself may be far worse than others acknowledge.

Forage fish, particularly herring, are supposed to be so abundant they are eaten by almost everything, including hake, dogfish, and sea lions and whales.

“They are the central node of the marine ecosystem,” said Iain McKechnie, a coastal archaeologist with the University of British Columbia. “They aren’t the base, they aren’t the top, but they are the thing through which everything else flows.”

Photo: Seattle Times/MCT/Steve Ringman

Interested in national news? Sign up for our daily email newsletter!