Coho Have a Surprisingly Strong 2023-2024 Spawning Season

By Science Communication Specialist Jessica Weinberg McClosky, San Francisco Bay Area Inventory & Monitoring Network

January 2024 - Some years, the San Francisco Bay Area Network coho and steelhead monitoring team is alarmed by the low number of coho salmon returning to spawn in Marin County creeks. Last year, they didn’t spot a single live adult coho salmon. This has not been one of those years!

Several adult coho swim up the John West Fork of Olema Creek on January 2nd. This season is on track to be the best spawning season on Olema Creek in more than 15 years.

NPS

With the coho spawning season just about over, the monitoring team has counted over 200 adult coho and over 50 coho redds (nests) in Point Reyes National Seashore’s Olema Creek. Fishery Biologist Mike Reichmuth recalled one memorable day in late December, “We had an epic day on Olema, with a single-day count of 150 adult coho salmon. This is the highest single-day count that we have [ever] recorded.” Overall, this season is on track to be the best spawning season on Olema Creek in more than 15 years!

Adult male coho seen swimming up Cheda Creek in December to mate with a female in search of a suitable spot to lay her eggs.

NPS / Michael Reichmuth

The monitoring team has also found coho in two other Point Reyes creeks—Pine Gulch Creek and Cheda Creek. Last year, they didn’t find any evidence of spawning in either one. But coho returning to Pine Gulch this year could represent another generation of the cohort to first re-colonize the creek in 2020-2021 after a decade-long absence.

It has also been an exciting year in Muir Woods’ Redwood Creek. The final phase of the Salmon Habitat Enhancement project was completed there this fall. Then, in early December, National Park Service staff and partners helped release about 4,000 hatchery-reared juvenile coho into the creek. These little fish from the California Department of Fish and Wildlife and US Army Corps of Engineers will help sustain the cohort of coho that failed to spawn in Redwood Creek last winter.

National Park Service staff and partners teamed up to release 48 adult coho (left) and around 4,000 juvenile coho (right) into Redwood Creek in December.

Left: NPS; Right: NPS / PRNSA / Avani Fachon

The following week, staff and partners gathered again to release 48 adult coho into Redwood Creek. In the weeks since, the monitoring crew has recorded both the released coho—which carry hatchery marks—and naturally returning coho spawners. They have so far counted at least 22 live adults and over a dozen redds. That’s a big improvement for this cohort in Redwood Creek!

The coho and steelhead monitoring team is hopeful that this strong spawning season will translate into lots of juvenile coho in park creeks this summer. Until then, they will be busy keeping a close eye on steelhead spawning activity and monitoring salmonid smolts journeying out of Redwood and Olema Creeks in the spring.

UPDATE, February 8, 2024:

Although this has been a very wet season, the coho and steelhead monitoring team was able to sneak in a few spawner surveys between storms in recent weeks. Surveys in the last days of January and first days of February revealed that coho spawning has concluded in Olema Creek. In Redwood Creek, the team saw a few coho still spawning, including one female that was among the adult coho released into the creek in December.

Though the team has yet to process and analyze their data, the season continues to look like a great success. The latest coho redd estimate stands at over 70 for Olema Creek, which is at least five times more than when this generation of fish last spawned three years ago. In Redwood Creek, the team has now counted around 20 redds—a huge improvement over the single redd found in winter 2020-2021.

The biggest lingering question of the season is how all the salmon’s little eggs have fared through the recent storms. None of the downpours were severe enough to flood our creeks, so Reichmuth isn’t concerned about a major loss of eggs. But he does expect that some redds may have been swept away, and the rainy season is not over yet. “February can be one of our wettest months, so hopefully we don't see any gully-washers this month,” he noted.

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 Fishery Biologist Michael Reichmuth

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