Coho salmon appear to have made the season’s last run in creeks brimming with rainwater from recent storms. Marin Municipal Water District ecologists surveyed areas in Lagunitas and San Geronimo Creeks after flows subsided, counting roughly 200 more between the end of January and early February.
The additional fish bring the preliminary season totals to 371 coho that survived the drought and recent water surges to navigate upstream and spawn before the end of their life cycles. Those coho dug 174 redds. “That’s an increase from three years ago, but below average and far below what we were hoping for,” said Eric Ettlinger, an M.M.W.D. aquatic ecologist.
The numbers suggest about only one in 20 of the cohort survived to return and spawn, or about half of what was expected. The reasons for the lower number are unclear, said Preston Brown, a watershed biologist for the Salmon Protection and Watershed Network, a nonprofit advocacy group. Problems may have begun three years ago, if not enough fish initially survived, or they could have originated more recently, possibly in association with the drought.
In a year with average rainfall, coho come with the first rains in early November or even late October, but this year they were not observed in large numbers until mid-December. Steelhead, on the other hand, are running strong and have been “far more abundant,” Mr. Ettlinger said, with 92 counted, plus 73 redds. “We saw more steelhead in the last week than we typically see in the entire month of February,” he said.
While the coho spawning is likely finished, the steelhead will continue with more rains. The heavy rainfall—over 21 inches recorded at the top of Mount Tamalpais—allowed fish to finally swim up to the upper San Geronimo Valley headwaters. Because of the drought conditions, waterfalls have been flowing at a trickle, but the rains provided a flow large enough for fish to jump up. What waits to be seen is how the young fish fare.
SPAWN and M.M.W.D. have completed much restoration work and have encouraged residents to reduce the impact of fertilizers, pesticides and trash in the creeks.
Juvenile counts will begin in spring. “It will give us data on how healthy our watershed is, how productive it is,” Mr. Brown said.