From the Field: Winter 2021 Low Rainfall Impacting Salmonid Populations

A stream channel links the lagoon and the ocean at Muir Beach, near Redwood Creek.

NPS

April 2021 - The Bay Area experienced an unusually dry winter, with monthly rainfall totals being some of the lowest on record. From October 2020 through February 2021, the Redwood Creek rain gauge recorded 11.57 inches of rainfall. This is over 40% lower than the average of 19.39 inches of rainfall during this same time of year for Water Years 1999-2020.

So what does this mean for the salmonids in Point Reyes National Seashore and Golden Gate National Recreation Area? These extremely dry winters are worrisome when considering the small salmonid populations and the potential for species extirpation in Marin County watersheds. Observed coho salmon and redd numbers remain at historically low levels, especially in Redwood Creek. With only one coho redd counted in Redwood Creek during the 2020-2021 spawner season, there was considerably less activity compared to the last time adults from this cohort were in the system. Adult salmonids cannot access Redwood Creek until flows are high enough to breach a sandbar at Muir Beach. This season, the sandbar was not breached until the first week of January after a relatively minor storm event. Some adult coho awaiting access to the stream may have been eaten by predators, while others hopefully strayed to neighboring watersheds.

Steelhead trout are more resilient than coho salmon due to the species’s life history strategy and ability to spawn multiple times before dying. Steelhead redd production has been consistent over the past few seasons in Olema and Redwood Creek. Adult steelhead were recently observed spawning in both creeks with the storm event in mid-March, when flows peaked at 40 cubic feet per second (cfs) in Redwood Creek and 95 cfs in Olema Creek. These modest increases in streamflow assisted steelhead moving upstream in search of ideal spawning habitat. We will continue monitoring the streams for adult steelhead through April after spring freshets.

Smolt trapping season is underway, and we have already observed Olema Creek coho smolts making their way out to sea. Only steelhead smolts have been captured on Redwood Creek, but we expect to see some coho in the coming weeks. Redwood Creek is still connected to the Pacific Ocean, but this will change quickly if sunny days continue with no spring rains.

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