Muir Woods coho salmon vanish, fanning fears of extinction

Laura Chariton, director of the Watershed Alliance of Marin, visits Redwood Creek, where the coho didn’t spawn this year. Laura Chariton, director of the Watershed Alliance of Marin, visits Redwood Creek, where the coho didn’t spawn this year. Photo: Leah Millis / The Chronicle Photo: Leah Millis / The Chronicle Image 1 of / 14 Caption Close Muir Woods coho salmon vanish, fanning fears of extinction 1 / 14 Back to Gallery

The cherished coho salmon that historically wriggled their way past beachgoers up Redwood Creek into Muir Woods vanished this year and are now on the verge of extinction, prompting a last-ditch attempt by fisheries biologists to save the genetically unique species.

No salmon eggs were spotted in the shade of the world-famous redwood grove this past winter, and not a single baby coho could be found in the summer. The situation was so bad in August that 105 juvenile salmon had to be removed from the creek and brought to a hatchery.

“It’s a crisis in terms of this kind of intervention has never happened before” in Redwood Creek, said Laura Chariton, the director of the Watershed Alliance of Marin. “Historically these fish evolved in this watershed, so it could be the beginning of local extinction or extirpation.”

State fisheries biologists believe the 2014 generation of the beleaguered species is extinct — although their demise has not yet been confirmed. The Redwood Creek coho were done in, officials said, by decades of environmental pollution and habitat degradation combined with drought.

“We believe the persistent drought and restricted access into the creek could have been the last straw,” said Manfred Kittel, the regional coho salmon recovery coordinator for the California Department of Fish and Wildlife. “When abundance is already so low, any little thing can wipe out the year class.”

Few fish spawning

The spawning run isn’t expected to be any better this winter. Fewer than 10 fish returned to spawn in five of the past seven years, not including 2014. In 2011 and 2013 only eight spawning coho were counted in Redwood Creek.

The 8.9-square-mile Redwood Creek watershed is the historic home of the southernmost continually returning natural population of coho salmon in the Western United States. Coho, which are also known as silver salmon, were once so plentiful that Miwok Indians used the area as a seasonal fishing village, competing with grizzly bears for the bounty. The fish thrived in a network of wetlands, dunes and a 13-acre open freshwater lagoon.

Over the past century, the creek was forced into a narrow channel as road construction, agriculture and recreation eliminated the natural floodplain. Although coho have been disappearing throughout their range, the decline in Redwood Creek has been precipitous.

No baby fish found

Things were looking so bleak last winter that fish and wildlife biologists got together with experts from the National Marine Fisheries Service, the U.S. Army Corps of Engineers, National Park Service and State Parks to discuss the situation. The group decided to rescue all the baby fish in the creek and raise them in a hatchery.

Problem was, there were no baby fish left in August when biologists went to collect them. Instead, they removed the 105 smolts, which, Kittel said, should have already migrated out to the ocean in preparation for their return in 18 months. He believes the juvenile coho got stuck inland because of low water.

The coho spawning runs last winter were dismal all up and down the coast. All the creeks were blocked by sandbars until late January and February because of the lack of rain. Only a small number of coho reached their native streams before the rains stopped and the sand bars were exposed again.

“The surprising thing was that we didn’t find any fish that were born this year — young fish about 6 or 7 months old — which indicates to us that there was no successful reproduction this past winter,” Kittel said. “So the very thing we were trying to prevent — the year class extinction — may have happened in the very year that we initiated this captive breeding program.”

The surviving fish were brought to the Warm Springs hatchery, in Sonoma County, where they will be raised to adulthood and returned to the creek during the winter of 2015-16, when they are 3 years old.

The calamity this year doesn’t mean that endangered coho are gone forever, but the overall situation is dire. Coho return from the ocean to the streams where they are born at age 3 to spawn and die. The three-year coho life cycle means that although the 2014 population may be gone, there are two more generations, one of which would normally begin swimming up Redwood Creek around now, after the first heavy rains.

“Two out of those three year classes were very close to becoming extinct” before this year, Kittel said. “There were only a handful of adults coming back from those year classes.”

In 2012, 50 coho spawned in the creek, the best return in the past three years, but nothing compared to the 180 spawners in 2004. Those 50 salmon are from the same year class as the 105 juvenile fish that had to be taken out of the creek in August, meaning that generation too could be in trouble, Chariton said.

Recent restoration work

The whole thing is all the more troubling to conservationists in light of the recent restoration of the historic marshlands and tidal lagoon at Muir Beach, which was supposed to be a bonanza for coho. The $15 million project by the National Park Service and the nonprofit Golden Gate National Parks Conservancy included the re-routing into the ocean of the creek, which flows from Mount Tamalpais, through Muir Woods, past the cozy Pelican Inn and out to Muir Beach.

Kittel said the idea now is to restore salmon populations, possibly by mixing fish from other watersheds with the 105 fish taken from Redwood Creek. Genetic diversity of the fish population is a major concern, he said.

“These year classes are very small, and they have gone through a genetic bottleneck, meaning there is a good likelihood that they are suffering from some inbreeding,” he said. “By mixing in other fish populations you would have the genetic effect of counteracting this inbreeding.”

Either way, he said, the fish in the hatchery represent an insurance policy against further extinctions and may be crucial in the quest to rebuild a lost generation of fish.

“I see it as a very interesting combination of having a huge problem, with the threat of imminent extirpation of this species, coupled with an opportunity to solve the problem,” Kittel said. “It’s a great restoration and recovery opportunity.”

Peter Fimrite is a San Francisco Chronicle staff writer. E-mail: pfimrite@sfchronicle.com Twitter: @pfimrite

Know the coho

Range: Coho salmon are found on both sides of the North Pacific Ocean from Hokkaido, Japan, and eastern Russia, around the Bering Sea to mainland Alaska, and south all the way to Monterey Bay.

Description: Adults typically weigh 8 to 12 pounds and are 18 to 30 inches long, though individual fish weighing 31 pounds have been caught.

Life cycle: Anadromous, meaning adults re-enter natal freshwater streams to spawn after spending half of their three-year life cycle in the salty Pacific Ocean. Adults die within two weeks of spawning. Fry grow to 4 to 5 inches long before heading to the Pacific.