Coho salmon scarce in Marin County tally
The pouring rain this winter brought with it a buoyant optimism among fisheries experts about the celebrated run of coho salmon in western Marin County, but the expected swarm of leaping pink fish never showed up.
Fewer than 90 coho have made their way up meandering, forested Lagunitas Creek and laid eggs on the northwest side of Mount Tamalpais, one of California’s last great strongholds for embattled wild salmon that have never mingled with hatcherybred fish.
It is among the worst showings of the coldwaterloving coho in nearly a quarter century, and researchers are trying to figure out what went wrong.
“We’ve been collecting this data for 24 years, and this is likely to be the secondlowest count we’ve seen in that time,” said Eric Ettlinger, the aquatic ecologist for the Marin Municipal Water District, one of four agencies that conduct the annual spawning surveys. “It’s quite bad.”
The season isn’t quite over — Thursday’s rain will probably inspire a few more salmon to wriggle their way into the waterway before the spawning
window closes at the end of the month. So far, though, only 44 egg clusters, known as “redds,” have been counted in Lagunitas and its tributaries, including San Geronimo, Woodacre, Arroyo and Olema creeks.
The worst spawning year was 200809, when only 26 redds were counted in the watershed. The average annual count is 250 nests going back to 1995, when the water district, Watershed Stewards Program, National Park Service and the Salmon Protection and Watershed Network began annual surveys.
The paltry showing comes despite plenty of rain — about equal to the longterm average — which is usually a big help to anadromous fish. Heavy rains last year were credited with attracting more than 700 spawning coho, which deposited 369 egg nests in the watershed.
Because a male and female produce each egg cluster, the number of fish is calculated by doubling the number of redds — although sometimes the fish count is higher for a variety of reasons, particularly when more males than females are present.
“Normally, we’d see the fish holding in deeper pools between storms waiting to migrate upstream from Tomales Bay, but we’re not seeing that,” said Todd Steiner, executive director of the watershed network, known as Spawn. “So the $60 million question is: Why?”
The reasons aren’t clear. The halfdozen or so river otters that frequent the watershed clearly take a toll, but biologists think something else is killing them off.
One clue, Ettlinger said, is the fact that 7,800 coho entered the ocean 18 months ago when they were juveniles, or smolts — the halfway point in their lives. The returns this year at age 3 mean only about 1% of them survived. That’s compared with the longterm survival rate of about 4%, he said.
What that means is that an unusually high number of coho died in the ocean.
Bill Sydeman, a biological oceanographer and senior scientist with the Farallon Institute, said there probably wasn’t enough for the coho to eat in 2018 when they swam out to sea. Higherthannormal water temperatures disrupted the food web that year, killing off most of the tiny crustaceans known as krill.
“We had low food availability for the smolts,” Sydeman said. “As a result, they either starve or they are weak and are subject to more predation.”
Sea lions and other ocean predators, like orcas, eat salmon, but many of these fish eaters have also suffered as a result of the temperature fluctuations, which have been linked to toxic algae blooms, starfish and seaweed dieoffs and other problems in the ocean ecosystem.
“We’re dealing with animals that have this very complicated life cycle, where they live in rivers and streams and then they go out in the ocean, and it all has to align correctly,” Sydeman said. “With climate change ... we are going to see more swings in production. It’s something we should expect more of in the future.”
It’s an issue not only because of concern over the survival of the Marin salmon run but because the annual migration is a spectacle that attracts thousands of spectators to Samuel P. Taylor State Park and other viewing areas over the course of each winter.
The crimsontinted fish swim from the ocean into Tomales Bay and then travel 33 miles through the redwood and oakstudded San Geronimo Valley, where half their spawning grounds are in towns like Forest Knolls, Lagunitas, San Geronimo and Woodacre.
They lay eggs in view of some people’s backyards and then die. Their progeny then migrate to the ocean to become adults, returning to the watershed at age 3 to repeat the cycle.
Three years ago, when the parents of this year’s coho gave birth to them, surveyors counted 170 egg nests, below normal but not particularly worrisome. Clearly, conditions have gotten worse for their offspring, Steiner and Ettlinger said.
Despite the problems this year, the Lagunitas watershed is home to the largest run of wild coho between Humboldt and Monterey counties, where hatcheryraised coho dominate.
At least 10,000 coho once swam through the picturesque valley and bred in tributaries that snaked all the way up the side of Mount Tamalpais. They were once so plentiful that, legend has it, folks could spear them from decks overlooking the creek.
The fish continued to thrive despite rampant logging and construction of five major dams, starting in 1873. The spectacular runs finally came to a halt when Seeger Dam, which formed Nicasio Reservoir, was built in 1961, wiping out the salmon population in Nicasio Creek.
All together, the dams blocked 50% of the historic spawning habitat in the Lagunitas watershed.
It’s not an isolated problem. Coho, also known as silver salmon, now total only about 1% of their historic population along the coasts of California and Oregon. Central California coho were listed under the U.S. Endangered Species Act in 1996.
The federal Coho Recovery Plan, by the National Marine Fisheries Service, says a population of 2,600 spawning fish must be maintained for 10 years in the Lagunitas watershed before the species can be upgraded to threatened. The best winter since biologists began keeping annual records in 1994 was 200405, when 1,342 coho were counted.
The water district and watershed network have been working together for years trying to improve fish habitat in the creeks and were hoping last year’s surge was a sign that things were getting better. The two recently collaborated on a project that used state and federal grants to build floodplains for coho along the creek where the towns of Tocaloma and Jewell once stood.
People living in the area have participated in habitat restoration programs — including school work parties — and Marin County has limited creekside development to protect the fish.
“We are trying to repair the mistakes of the past and give these fish a fighting chance,” said Steiner, who, despite the paltry run, is adamant that the restoration work has helped. “Without these efforts, we might have no returning fish this year.”