They were once abundant in the cold, clear water of North Bay creeks and streams. Now, the survival of coho salmon is being challenged like never before.
The coho has a three-year life cycle that takes it from stream to ocean and back to stream to spawn the next generation.
But the changing climate now threatens the species at every life stage, raising new questions about their recovery.
It’s not just a species at stake. At risk is the very resilience of the forest and watershed that evolved around them, fed by marine nutrients brought upstream and deposited inland by adult spawners that, after reproducing, die and decompose.
“Salmon are a keystone species, which means they perform a really important ecosystem service,” said Sarah Nossaman Pierce, a California Sea Grant fisheries biologist with the Russian River Monitoring Program. “Salmon and steelhead (trout) bring marine-based nutrients into the system and essentially feed the forest, plants, birds and wildlife.”
The challenge, she said, is “ecosystem resilience”
“People say, ‘Why do you care about the salmon?’ Unfortunately, if they can’t survive, human beings aren’t far behind,” she said.
Rains bring false hope
Recent rains in the Russian River watershed swelled streams as the peak migration of yearling coho salmon, called smolts, was getting under way in early May. But stream levels are beginning to decline again to levels of a few weeks earlier, when the young fish faced the lowest stream flows ever seen so early in the year.
Some creeks ran dry, requiring an annual smolt rescue and relocation program — fish and wildlife personnel pull stranded fish from isolated puddles and pools and transport them to survivable streams — to begin earlier than ever.
“It’s not happy news,” said Mariska Obedzinski, an expert with California Sea Grant and coordinator of the Russian River Salmon and Steelhead Monitoring Program.
The Russian River’s once celebrated salmon populations have long been imperiled by logging, development, gravel mining and other human activities that have eliminated flood plains, channelized river and stream flows, and limited the woody debris and shade that keeps the water cool enough for young fish to survive.
More intense and frequent droughts have further eroded conditions, not just for the coho, but for steelhead and chinook salmon, both listed as threatened under the federal Endangered Species Act.
Dry years once were viewed as a threat primarily to tiny fry summering in small, coastal streams.
But recently, streams have been low for so much of the year that adult fish sometimes struggle to swim upstream to spawn in the winter. The gravel nests, or redds, where they deposit their eggs may become stranded and dried out before the eggs hatch.
Summer heat has left young fish trapped in shrinking pools of warm and oxygen-poor water until they die from heat or suffocation as those pools evaporate. Those that survive may be challenged to find sufficient flows to get downstream when spring comes.
The threat to multiple life stages at once for an already vulnerable species is alarming, especially over successive years.
A helping hand
The region’s coho were on the brink of extinction 20 years ago when a few hundred wild juveniles were collected from West Sonoma County’s Green Valley Creek and other small streams. That effort led to the Coho Recovery Broodstock Program at Lake Sonoma, which hopes to rebuild a self-sustaining population.
The Russian River Monitoring Program, meanwhile, was established to gauge the recovery program’s effectiveness and identify bottlenecks to reproduction. Teams from California Sea Grant, Sonoma Water and other partners trap and measure smolts, count young fish, survey salmon in later stages of development and assess stream conditions. Individual fish also are tracked through transponders implanted inside them.