To inform our conservation work on the Eel, CalTrout works with the California Department of Fish and Wildlife (CDFW) to try to answer the question: how many salmon and steelhead are there in the South Fork Eel River? In the 2022-2023 season, we estimated almost 5000 fish passing through the system. Although 5000 may sound like a lot, these populations are well below the level needed to recover these species.
We estimated this number using a Sound Metrics Dual Frequency Identification Sonar (DIDSON) camera system. The sonar camera is located at Meyers Flat, ten miles above the South Fork Eel River confluence with the Eel River, and it records video of fish as they migrate upstream to their spawning grounds. Providing a cross section view of the river, the camera records 24 hours a day, except during hazardous flows. These videos help us estimate the abundance of spawning Chinook salmon, coho salmon, and steelhead in the watershed.
Salmon and steelhead often spawn in muddy and turbid reaches which make it impossible to count fish using traditional spawner surveys. Sonar technology allows us to more accurately monitor salmon which under past survey techniques may have been un-detectable.
An estimated 4857 fish passed the counting station at Meyers Flat between October 31, 2022 and March 31, 2023. Based on typical run times for the South Fork Eel River and fish measurements, we can estimate the number of Chinook salmon versus coho salmon and steelhead. We estimated 3,878 fish over 40 cm passing the sonar in November and December to be Chinook salmon, and 980 fish over 40 cm passing the sonar from January through March to be a mixture of coho salmon and steelhead. View the team’s full 2022-2023 update here.
This population status information is invaluable to threatened species recovery planning and helps us to know what restoration practices have been most effective.
Counting fish using this system has many advantages. Our team counting DIDSON fish images can slow down, replay, and even stop the video if they are fatigued or lose their place, which cannot be done using traditional counting methods. Imaging sonars can produce high-resolution video images of fish, in part because it uses high-frequency sound waves that enable it to detect the entire surface of the fish. Using DIDSON, field scientists can better distinguish between fish that are swimming side-by-side or head-to-tail and determine which direction fish are swimming.
Mathew Metheny, CalTrout's North Coast Program Manager, organized and obtained funding for the South Fork Eel River monitoring effort. With support from project partners and CalTrout Field Technician Jason Shaffer, he operates the system each year to piece together a larger narrative around annual salmon numbers in the watershed. The monitoring effort is funded by California Department of Fish and Wildlife, a key project partner.
Cover Photo: Aerial view of South Fork Eel River near Meyers Flat by Matt Metheny
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Peter Moyle is the Distinguished Professor Emeritus in the Department of Wildlife, Fish and Conservation Biology and Associate Director of the Center for Watershed Sciences, at UC Davis. He is author or co-author of more than 240 publications, including the definitive Inland Fishes of California (2002). He is co-author of the 2017 book, Floodplains: Processes and Management for Ecosystem Services. His research interests include conservation of aquatic species, habitats, and ecosystems, including salmon; ecology of fishes of the San Francisco Estuary; ecology of California stream fishes; impact of introduced aquatic organisms; and use of floodplains by fish.
Robert Lusardi is the California Trout/UC Davis Wild and Coldwater Fish Researcher focused on establishing the basis for long-term science specific to California Trout’s wild and coldwater fish initiatives. His work bridges the widening gap between academic science and applied conservation policy, ensuring that rapidly developing science informs conservation projects throughout California. Dr. Lusardi resides at the UC Davis Center for Watershed Sciences and works closely with Dr. Peter Moyle on numerous projects to help inform California Trout conservation policy. His recent research interests include Coho salmon on the Shasta River, the ecology of volcanic spring-fed rivers, inland trout conservation and management, and policy implications of trap and haul programs for anadromous fishes in California.
Patrick Samuel is the Conservation Program Coordinator for California Trout, a position he has held for almost two years, where he coordinates special research projects for California Trout, including the State of the Salmonids report. Prior to joining CalTrout, he worked with the Fisheries Leadership & Sustainability Forum, a non-profit that supports the eight federal regional fishery management councils around the country. Patrick got his start in fisheries as an undergraduate intern with NOAA Fisheries Protected Resources Division in Sacramento, and in his first field job as a crew member of the California Department of Fish & Wildlife’s Wild and Heritage Trout Program.