Winter 2020-2021 Coho and Steelhead Spawner Survey Summary

A big thank you to all our staff who participated in the 2020-2021 coho and steelhead spawner surveys! Since we couldn’t have volunteers join us this season due to COVID-19 mitigation measures, we relied heavily on crew members to survey longer than normal reaches throughout the season. Through their dedication and flexibility, we were able to successfully complete all of our surveys throughout the season.

2019-2020 Spawner Season Overview

Looking ahead to next season!

We anticipate more promising numbers of adult coho for the 2021-2022 spawner season, especially on Olema Creek. During the spring of 2020, we were unable to operate our smolt traps due to the COVID-19 global pandemic. However, based on reports from other nearby organizations that did operate traps, the survival rate for this cohort was likely high. We estimated nearly 10,000 juvenile coho in Olema Creek during the summer of 2019. With average to high survival rate this would equal 6,000 to 7,000 smolts. Assuming average ocean conditions, we would anticipate 100 to 150 adults returning to Olema Creek this winter. Let’s keep our fingers crossed for a good rain year to help this cohort out!

Coho salmon are three years old when they return to their natal stream to spawn. These spawners are the offspring of salmon that spawned three years prior, and the parents of the generation that will spawn in another three years. As a result of this life history strategy, there are three distinct year classes, or cohorts, of coho spawners in each creek. Each has its own trends that may only be tracked every third year. The 2020-2021 spawner cohort is primarily descended from salmon that spawned in the winter of 2017-2018.

Due to drier than normal conditions, the 2020-2021 spawners needed a very wet start to the spawning season to access their creeks. That did not occur. The Olema Valley Rain Gauge only recorded 2.37 inches of rain in November. This was okay, but not enough to get the spawning season underway. To our dismay, storm after storm went by with only small amounts of rain each time. Finally, the creeks rose enough at the end of December to allow some coho to migrate upstream. We observed spawning during the first part of January in the lower sections of Olema and Redwood Creeks. Unfortunately, the rain did not keep coming and flows receded. It was not until the end of January that enough rainfall returned to our region to allow both adult coho and steelhead to migrate upstream again and spawn.

Surveying Redwood Creek for live adult salmonids, carcasses, and redds. Crews always hike upstream to reduce the chance of disturbing spawning adults. They rely on polarized sunglasses and a wading rod for visibility and stabilility, and are careful to avoid sensitive spawning areas.

NPS / Michael Reichmuth

Even with the dismal rainfall during the peak coho spawning period, the overall spawning run in Olema Creek was stronger than we anticipated. This was not the case in Redwood Creek in which we counted far fewer coho than expected.

Like the coho run, steelhead spawning favored Olema Creek compared to Pine Gulch and Redwood Creeks. In fact, steelhead spawning was above average in Olema Creek, indicating that the watershed continues to be important for this species’ recovery.

Preliminary Spawner Season Result Details

Note that live adult coho and steelhead totals may include repeat sightings.

Redwood Creek

The Redwood Creek lagoon did not breach until mid-December and was only connected for a brief period with little flow making it to the sea. It wasn’t until January 4^th that the sand bar was breached enough to allow spawning coho access to the lower portions of Redwood Creek. Monitoring crews observed one live coho on a redd (nest) shortly after, on January 5^th. Unfortunately, this was the only adult coho and redd sighting in Redwood Creek for the entire season. This is a significant decrease compared to the number of redds expected based on the estimated number of smolts that exited the creek during the spring of 2019. Coho weren’t the only ones that had trouble accessing Redwood Creek. Monitoring crews observed very little adult steelhead activity during the late winter and spring months. We counted a total of five live steelhead, one steelhead carcass, and four steelhead redds from mid-February through late-March.

Olema Creek

We encountered the first live coho in Olema Creek on January 13^th. Our last coho observation was that of a carcass that we found on February 18^th. Overall, we counted seven live coho, eight coho carcasses, and 14 coho redds. Staff observed spawning much lower in Olema Creek than normal during surveys in mid-January. This is in contrast to the end of January, when we found a female coho on a redd in the John West Fork tributary upstream of the Hwy 1 culvert.In addition to coho observations, we recorded seven live adult steelhead, four steelhead carcass, and 36 steelhead redds. The total number of steelhead redds counted in Olema Creek was above average. Unlike Redwood Creek, Olema Creek coho redds were comparable to the last time this cohort returned to spawn. Juvenile surveys in the summer of 2021 will help validate coho spawner counts in Olema and Redwood Creeks.

Cheda and Pine Gulch Creeks

Crews recorded no coho observations and one steelhead redd in Cheda Creek this season. And to our surprise, crews observed one potential coho carcass and redd in Pine Gulch for the first time in over a decade. This observation was later confirmed when we found juvenile coho in the same location while conducting juvenile monitoring in July of 2021. In addition, we counted one live steelhead, three steelhead carcasses and five steelhead redds on Pine Gulch.

Coho Salmon Spawning Over Time

The 2020-2021 cohort on Redwood Creek has suffered a significant decline since the last time this cohort was observed. However, the redd count during the 2017-2018 season was artificially higher than the anticipated natural production due to the release of hatchery reared adult coho into the creek to help augment the population. It appears that this release did not result in improving the abundance of this cohort for subsequent years. In contrast, the Olema Creek returns for this cohort were similar to what was observed the last time this cohort returned during the winter of 2017-2018. For annual coho redd counts observed on Olema and Redwood Creeks over the last 24 years, please see Figures 1 & 2 below.

Figure 1. Coho salmon redd results for the Olema Creek watershed by cohort for winter 1997-1998 through winter 2020-2021. Cohorts are designated by color (cohort one shown in yellow, cohort two shown in blue, cohort three shown in red) and creeks are designated by pattern (Olema Creek in horizontal lines, John West Fork in vertical, and other Olema tributaries in a solid color).

Figure 2. Coho salmon redd numbers in the Redwood Creek watershed by cohort winter 1997-1998 through winter 2020-2021. Cohorts are designated by color (cohort one shown in yellow, cohort two shown in blue, cohort three shown in red), and creeks are designated by pattern (Redwood Creek in horizontal lines, Fern Creek in vertical, and Kent Creek in a solid color).

For More Information

For more information about the San Francisco Bay Area Coho and Steelhead Monitoring Program, contact [e-mail] or call 415-464-5191.

The National Park Service shall not be held liable for improper or incorrect use of the data described and/or contained herein. These data and related graphics (if available) are not legal documents and are not intended to be used as such. The information contained in these data is dynamic and may change over time. The National Park Service gives no warranty, expressed or implied, as to the accuracy, reliability, or completeness of these data.