Every summer, the lower stretch of Olema Creek in Point Reyes National Seashore breaks into large, isolated pools that last through the dry season and shelter aquatic life. That's normal. What the San Francisco Bay Area Network's Coho and Steelhead Monitoring Crew found in September 2021 wasn't: fewer pools, shrinking fast — and some packed with the park's smallest aquatic species of concern, the California freshwater shrimp.
One of three shrinking pools in Olema Creek found holding many California freshwater shrimp, September 2021. Credit: National Park Service / Michael Reichmuth.
Meet the shrimp
| Range | Only a handful of creeks in Sonoma, Napa and Marin counties |
| Size | At most 2.5 inches |
| Diet | Decaying material in the water |
| Color | From nearly clear to dark brown or purple; females can change color quickly to blend in |
| Distinguishing feature | A wrist-like joint on the second pair of pincers |
| Toughness | Tolerates poor water quality and a range of temperatures, thriving in stagnant pools where coho and steelhead would struggle |
A juvenile California freshwater shrimp. Credit: National Park Service / Darren Fong.
The rescue
Even hardy shrimp can't survive a pool that disappears. Watching the pools shrink, the crew checked the weather forecast and the rate of drying and concluded the shrimp needed rescuing.
With butterfly nets and a pool skimmer, the crew moved more than 250 shrimp from three isolated pools to a large pool upstream over two days, testing water quality at every pool to make sure conditions stayed within what the species tolerates. They also found three coho salmon, thin and in poor condition, and moved them too, in hopes they would survive the rest of the dry season.
Rescued shrimp are counted before release into a new pool. Credit: National Park Service / Michael Reichmuth.
A surprise upstream
The drought may have helped the shrimp in one way. During summer monitoring for juvenile coho and steelhead, the crew found shrimp half a mile upstream of their previously known range in Olema Creek. Low flows the previous winter and spring may have let them move up and find new habitat. Whether that expansion continues will be worth watching.
More is on the Pacific Coast Science and Learning Center's California freshwater shrimp page and the San Francisco Bay Area Network's salmon monitoring page.
Sources
Based on "Looking Out for the Little Guy: Coho and Steelhead Monitoring Crew Helps a Tiny Crustacean Threatened by Drought," by Michael Reichmuth, fishery biologist (October 2021), National Park Service; a work of the United States government in the public domain.
In these publicationsPoint Reyes National Seashore
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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