Coho Salmon & Steelhead Trout Monitoring in the San Francisco Bay Area

Media Included

  1. Monitoring Our Endangered Coho Salmon - While spawning coho in Central California once numbered in the tens of thousands, estimates now put their numbers at fewer than 500. Learning about the coho population through monitoring helps researchers target efforts aimed at helping the coho recover. Fishery Biologist Mike Reichmuth and Intern Ben Atencio discuss our endangered coho salmon and how they are monitored in the Bay Area National Parks.

Why Are Coho & Steelhead Important?

Map of streams in Golden Gate and Point Reyes supporting coho salmon and steelhead trout

Federally endangered coho salmon and threatened steelhead trout are large, charismatic fish that play crucial roles in both stream and ocean ecosystems. They transport nutrients, help keep insect populations under control, and serve as food for larger fish and mammals. They also have many known habitat requirements (e.g. cool streams with unobstructed flow, good water quality, gravel beds and plenty of large debris) that impact their survival and make them strong indicators of stream health and environmental change. The National Park Service Inventory and Monitoring Program and its partners began monitoring coho and steelhead in Golden Gate National Recreation Area and Point Reyes National Seashore in 1998.

Female coho salmon in Redwood Creek
An adult female coho spawning in Redwood Creek. Unlike steelhead which can make repeated spawning trips, coho perish in the creeks after their first spawning run. Coho and steelhead carcasses are one of the few sources of marine derived nutrients in coastal stream and terrestrial ecosystems.

Jessica Weinberg McClosky / NPS

Why Do We Monitor Coho & Steelhead?

  • To detect trends in the distribution and abundance of coho and steelhead at key life stages in creeks known to have coho, the species of primary concern
  • To determine trends in fish fitness (e.g. length, weight) at key life stages
  • To identify changes in coho and steelhead habitat

How Do We Use the Monitoring Data?

  • To identify impaired park habitats that hinder coho and steelhead recovery
  • To guide and evaluate stream habitat restoration and protection efforts
  • To predict and prepare for the effects of climate change, such as changing rainfall patterns, on stream habitats and associated fish populations
National Park Service biologist and volunteer measuring a coho smolt
National Park Service staff and volunteers collect data on a coho smolt--a year-old fish undergoing the physical changes that will enable it to survive as it migrates out to the ocean to grow and mature.

Jessica Weinberg McClosky / NPS

What Have We Learned?

Both coho and steelhead populations have declined dramatically as a result of habitat loss, overfishing and changing ocean conditions. Spawning Central California Coast coho populations are down to only about 1% of historic levels. Because the coho have a unique life cycle where adults are normally three years old when they spawn, adults in the creek one year aren’t descendants of adults that were in the creek the previous year, or the year before that. They are offspring of adults from three years prior. This means that there are three distinct coho “cohorts” monitored at each creek. Specific trends vary by cohort and by creek, but in general coho on the West Coast are still in need of recovery actions.

For More Information

Point Reyes Fisheries Biologist
Michael Reichmuth

Pacific Coast Science and Learning Center

San Francisco Bay Area Network


Summary by Jessica Weinberg McClosky, July 2013.

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Last updated: November 16, 2017