The lack of rain this winter has contributed to what fisheries biologists say is, so far, the worst return of coho salmon in the recorded history of Marin County's Lagunitas Creek watershed, one of California's most critical ecosystems for the endangered fish.

Only a smattering of coho were spotted and only 20 egg nests, or redds, were seen in the two main tributaries - Lagunitas and San Geronimo creeks - during the annual winter survey of fish, watershed biologists said this week.

The paltry showing of redds represents an 89 percent drop in the number of returning offspring of parents that gave birth in the lush western Marin watershed three years ago. Last year at this time, 148 redds had been counted, then the lowest number in the 14 years that records have been kept, said Paola Bouley, the conservation program director for the Salmon Protection and Watershed Network, or SPAWN.

"It's just frightening, actually," Bouley said. "We were expecting 70 redds, which is still a 63 percent decline. It's definitely a crisis situation."

The waterway, which winds its way through the picturesque San Geronimo Valley on the northwest side of Mount Tamalpais, typically supports the largest wild run of salmon left in the state, historically about 10 percent of California's coho population.

During the first winter rains, the spawning fish swim 33 miles from the open ocean into Tomales Bay and up the creek through the redwood-studded valley to lay their eggs and die. The females lay their eggs only after they've found the place where they were born three years before. The decline this year is alarming given that 190 redds were counted in 2005 when the parents of these coho laid their eggs.

The plummeting coho numbers exacerbate a near catastrophic decline in the overall population of salmon along the West Coast. So few chinook salmon returned to spawn in the Sacramento-San Joaquin river system last year that ocean fishing had to be banned in California and Oregon.

The number of coho eggs throughout the state declined about 70 percent last year. The low number of coho in the Lagunitas watershed in 2007 was shocking given that a record 496 redds were counted in 2004, the year they were born.

"We had our best year class in 2004," Bouley said. "What happened is our best year class turned into our worst year class."

This year is looking even worse.

Fisheries biologists believe the primary cause is the unusually dry weather in Northern California, which has prevented salmon from swimming up the creeks. The rains in December were barely enough to breach sandbars on most beaches, forcing salmon up and down the coast to circle in the open ocean where they are vulnerable to sea lions and other predators.

"It's not looking good," said Sean Hayes, a National Marine Fisheries Service biologist who monitors salmon in Scott Creek, the southernmost coho run in California, north of Davenport (Santa Cruz County). "The fish have been hammered a couple of years in a row now. If it doesn't rain, there could be a spawning failure this year, which would be catastrophic."
Threat of extinction

Bouley said a big rainstorm could turn things around, but hardly any rain is expected in the next two weeks. If things don't improve, she said, this year's cycle of fish may go extinct.

The lack of salmon in Lagunitas Creek is a major concern, she said, because the watershed is a statewide model for fisheries restoration. The first winter rains normally bring schools of coho wriggling up the creeks, drawing tourists, schoolchildren and naturalists to watch the fish leap from the foaming rapids.

"The Lagunitas population is critical to the viability of the entire central California coho population. It is the keystone watershed along the coast," Bouley said. "Fisheries agencies look to Lagunitas as the key to the recovery for neighboring watersheds. We won't have any streams left to seed them if this one is gone."

The watershed is unique in that the primary spawning grounds are in the middle of developed communities. Since coho were listed as endangered in 2005 under the Endangered Species Act, many residents have taken a proprietary interest in the fish. Schools have become involved, organizing work parties and teaching children about the historic coho migration.

More than a century ago, about 6,000 coho spawned in the system of streams every year. At that time, the salmon swam from Tomales Bay virtually to the top of Mount Tamalpais, spawning in tributaries all along the way. But industry started taking a toll almost from the day Joseph Warren Revere spotted the valley in 1846 and saw "a copious stream, fed by mountain brooks."

The redwood forests surrounding the creek were logged between 1860 and 1900. Subsequent homes and roads built along the waterway removed about 60 percent of the original riparian habitat.

The first major dam, which created Lake Lagunitas, was built in 1873. Six more dams were constructed over the next century, the largest being Peter's Dam at Kent Lake, finished in 1953 and then raised 42 feet in 1982. The dams blocked 50 percent of the historic salmon habitat, reduced the amount of gravel and increased sedimentation in the creeks.

But the decline was slow. Old-timers told how they used to spear fish from decks or garage hatches overlooking the creek. In 1959, when the habitat was already in serious decline, the largest recorded coho in state history, a 22-pounder, was fished out of Lagunitas Creek.
Lobbying the county

The restoration effort began in the early 1980s when a group called Trout Unlimited began lobbying the county to stop the decline of the fishery.

SPAWN, which was created in 1996, sponsors salmon-watching creek walks during spawning season and has saved more than 15,000 juvenile salmon and steelhead from drying pools during the summer. The Marin Municipal Water District, which is required by the state to help the coho as mitigation for raising Peter's Dam, started counting coho redds in the early 1990s and now works with SPAWN to monitor releases from the dam, install woody debris in the creeks and replant vegetation.

"This is the beacon of hope for the California watershed," Bouley said, but "the fish are missing. They are gone."

E-mail Peter Fimrite at pfimrite@sfchronicle.com..

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This article appeared on page B - 1 of the San Francisco Chronicle