Children took turns with nets Tuesday scooping fish from little pools amid the recently dried gravel in the bed of Larsen Creek.
Their mission was to save endangered coho salmon and steelhead trout from the ravages of the unprecedented Bay Area heat wave that has been scorching Marin County’s lush San Geronimo Valley for more than a week.
Larsen Creek, which was flowing gently a week ago, has dried up, leaving hundreds of baby coho and trout stranded in quickly warming pools. The creek water is evaporating so fast that the Salmon Protection and Watershed Network organized an emergency fish-rescue operation Tuesday for the increasingly rare fish.
“This is a bad situation,” said Paola Bouley, the watershed biologist for SPAWN, the Salmon Protection and Watershed Network, which was created in 1997 to protect spawning coho in the San Geronimo Valley watershed. “We haven’t had heat like this that anyone can remember, not even the old-timers.”
There are more salmon in the waterways of this picturesque valley than anywhere else in California, but the threats keep mounting. Some 200 homes were built next to the two main creeks — San Geronimo and Lagunitas — and tributaries like Larsen Creek, on the northwest side of Mount Tamalpais. Fifty percent of the spawning grounds in the valley are in developed areas, so leaking septic tanks, collapsing roadways and sediment from runoff are already posing problems for the fish. The number of coho eggs, known as “redds,” found in the creeks and their tributaries during spawning season this winter was the third-fewest since SPAWNstarted tracking them in 1995. A total of 184 coho redds were found in the Lagunitas watershed this year compared with a record 492 the year before. SPAWNhas been organizing fish rescues every summer for a decade. More than 15,000 juvenile salmon and steelhead have been saved from drying pools over the years. Still, the unprecedented heat is adding to the concerns of experts. Creeks are not only drying up, Bouley said, but the water that remains is also heating up, causing algae blooms which, in turn, suck oxygen out of the water. “Fish need cold, clear water with lots of oxygen,” said Bouley, who has measured water temperatures between 10 and 30 degrees above normal, which could be lethal for growing fish. And there has been a noticeable lack of fog, which dampens the lush vegetation around the creeks. “When there is fog, you can actually observe the creek flow increasing,” said Bouley, who spent Tuesday helping area children capture fish with nets and put them in buckets for transport to nearby San Geronimo Creek. “This weather is something that is beyond our control. It is just brutal.”
The mounting issues facing salmon reproduction in the valley are troubling because the region has become a statewide model for fisheries restoration. That’s especially true since coho salmon were moved from threatened status to endangered last year under the Endangered Species Act.
Experts say Lagunitas and San Geronimo creeks and their tributaries support 10 percent of the state’s coho population. During winter rains, schools of the endangered coho wriggle up the creeks, drawing tourists, schoolchildren and naturalists who jostle for the opportunity to see the fish leap from the foaming rapids.
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 then die. Biologists believe the females wait to lay eggs until they’ve found the same location where they were born three years before. The fish that Bouley and the other volunteers were rescuing Tuesday were the babies that hatched three or four months ago. They will stay in the creeks and tributaries for a year, until they are large enough to survive the long swim to the ocean.