Juvenile Salmon Summer Monitoring: Electrofishing Surveys in Redwood Creek

Staff conducting an electrofishing survey, July 2021

NPS / Samantha Kuglen

July 29, 2021 - The San Francisco Bay Area Inventory & Monitoring Network salmon team is continuing their summer juvenile salmon surveys and performing electrofishing surveys throughout Redwood Creek in Golden Gate National Recreation Area and Muir Woods National Monument. The team first snorkels a section of the creek to visually count fish. The next day they use electrofishing to confirm the number of fish counted during the snorkel survey. As the name suggests, electrofishing utilizes electricity to collect fish in freshwater systems. It is a common technique in fisheries biology for sampling fish populations and determining species health, abundance, and density.

Before starting an electrofishing survey, staff measure water quality and conductivity to determine a safe voltage. Next, biologists distribute a controlled electrical current in the water using a battery-powered backpack unit. The current runs between two electrodes: an anode ring (positive) and cathode (negative). The fish are drawn to the current, swim towards the anode ring, and are briefly stunned. Once stunned, the team can net them out of the creek to be counted, weighed, and measured. The fish recover within a matter of minutes and then are returned to the creek after measurements are taken. Electrofishing will continue in Redwood Creek throughout the summer and begin in Olema Creek in Point Reyes National Seashore in early fall.

For more information

• San Francisco Bay Area Network Salmonid Monitoring webpage
• Pacific Coast Science & Learning Center Coho & Steelhead webpage
  • San Francisco Bay Area Coho and Steelhead Blog
• Contact Fisheries Biologist Michael Reichmuth

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