This winter’s storms prevented clear salmon surveys, but biologists say the rains opened waterways, diversified sediment and added complexity to fish habitat that will benefit future generations.
Across the Lagunitas Creek watershed, geomorphic change occurred through the recycling of gravel and sediment and the creation of new riffles. Newly restored areas matured: at a floodplain near the headquarters of the Salmon Protection and Watershed Network, the creek opened significantly, forcing flows into side channels and strengthening rearing conditions. At the restored Roy’s Riffles, pools deepened and pockets opened up. “The whole area is a lot more complex after the storms,” said Preston Brown, a watershed biologist at SPAWN. “The habitat is showing evidence of good rearing and spawning conditions.”
The improvement of habitat provides juveniles with more food, greater space and a higher likelihood of surviving the winter. Yet the storms also made surveys difficult as turbid waters blocked access to creeks for nearly a month. “High flows just complicate everything,” Mr. Brown said.
Flows that reached a peak height of 18 feet in Lagunitas Creek made waters too opaque for proper viewing at the start of the year. Rough flows sometimes scour nests, but they can also simply cover nests with sand or gravel, obscuring the depressions but not damaging them.
When the water cleared, biologists were able to survey for spawning salmon and found stable numbers at San Geronimo Creek at the former golf course. Coho spawning season wrapped up in January.
Marin Water monitors Lagunitas Creek and its two principal tributaries, San Geronimo and Devil’s Gulch Creeks, all of which contain the highest salmon counts. Eric Ettlinger, an aquatic ecologist with the district, said not being able to monitor salmon for nearly half the season resulted in numbers well below average, though the cohort was already expected to be small. Prior to the storms, surveyors counted 28 nests, known as redds, in Lagunitas Creek, 48 in San Geronimo Creek and seven in Devil’s Gulch Creek.
Michael Reichmuth, a fisheries biologist for the Point Reyes National Seashore who surveys Olema, Pine Gulch and Redwood Creeks, spotted only one coho carcass in Olema Creek. Even after heavy storms, observers can usually see floating bits of carcasses or fish at the end of their life, he said, but Redwood Creek, where a recent collaborative project brought hatchery coho for three consecutive years, showed no trace of spawners or redds.
The lack of coho presence could be attributable to poor rearing conditions in the Pacific, where the fish spend half their lives. Biologists say that much of the information gathered since the storms is speculative. When Mr. Reichmuth’s team surveys the creeks in the summertime, and Marin Water and SPAWN carry out their respective counts, they will have hard data on juvenile populations.
Chinook salmon, meanwhile, offered some surprises. Mr. Ettlinger said they had one the highest counts the district has ever seen, with 153 chinook and 42 redds. And they seem to have returned to Redwood Creek, where they do not have a historical presence, for a second consecutive year.
Last week, Mr. Reichmuth spotted a large female chinook hovering above her nesting site. He said he was puzzled by the female’s presence in late January, as most fall-run chinook peak in September and end by December, while winter-run chinook don’t start spawning until mid-April. Mr. Reichmuth reached out to other salmon monitoring organizations to understand where the chinook could have come from, and days later, when his team found the female dead, they gathered tissue samples to send to a lab to learn what stock it had come from.
Unlike chinook and coho, which die shortly after spawning and thus make counting easier, steelhead trout leave for the ocean after laying their eggs. Their spawning season continues through April. Scant traces of steelhead trout redds have been observed across SPAWN-monitored tributaries.