Napa River Fish Report

May 7, 2020 at 12:10pm

Napa RCD, by Jonathan Koehler, Napa RCD Senior Biologist

The March through May steelhead and salmon monitoring season is quickly coming to an end. This winter was exceptionally dry, and low flow conditions made it difficult (often impossible) to catch fish using our rotary screw trap, as we have for the past 12 years.

The trap requires a steady downstream current to run efficiently and capture fish. This spring, there were only 11 days with enough flow to fish. The trap sat heart breakingly idle the remainder of the time.

 There were several highlights in this otherwise forgettable monitoring year. First, we managed to catch 43 steelhead and 33 Chinook salmon smolts during a brief 7-day sampling stint following a small storm in April. This was a surprisingly high number of fish in a short amount of time. It is reassuring that, although our ability to monitor was greatly limited this year, steelhead and salmon were still successfully spawning and migrating to and from the ocean, more or less as usual. 


 Another exciting result came in February and again in March when two tagged steelhead adults returned to the Napa River and were detected by our PIT tag antenna. These fish were both tagged as smolts in spring 2018 and have been at sea for approximately two years before returning to spawn. Since 2013, we have tagged over 500 steelhead smolts, and these fish represented just the fourth and fifth times we have confirmed their return. 


 Finally, 2020 had an unusually high abundance of Pacific lamprey, with approximately 964 juveniles caught and released in only 11 total days of sampling. This was a good year to have a lot of lampreys because we are collaborating with UC Davis and DWR to collect genetic samples to learn about this poorly understood native species throughout the state. Lampreys are an important part of the river ecosystem, so we are happy to contribute in whatever way we can.


 For more details, including graphs and tables, look for the full report later this year. You can also watch a Facebook Live video we did at the trap this year.