Winter 2018-2019 Coho and Steelhead Spawner Survey Summary

A big thanks to all of our volunteers who participated in the 2018-2019 Coho and Steelhead Spawner Surveys! Through your dedication and flexibility, we were able to successfully complete all of our spawner surveys with the exception of missed survey opportunities due to the prolonged government shutdown.

2018-2019 Spawner Season Overview

Going on now!

Although our spawner season has come to a close, monitoring of coho and steelhead in West Marin marches on. Smolt trapping is underway and will continue through the month of May. The goal of the smolt trap is to estimate the number and health of coho salmon going out to sea. After leaving the creek these salmon will continue rearing in the ocean as they mature to adults. Smolt trapping is an excellent opportunity to monitor and handle a wide variety of aquatic species including coho salmon, steelhead, stickleback, sculpin, salamanders…and a whole lot more!

Coho salmon are three years old when they return to their natal stream to spawn. These spawners are the offspring of coho 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 salmon spawners in each creek, each with its own trends that may only be tracked every third year. The 2018-2019 spawner cohort is primarily descended from coho that spawned in the winter of 2015-2016.

During the third week of November, the Olema Valley rain gauge recorded over three inches of rainfall. Coho adults were observed moving upstream in both Olema and Redwood Creeks in late November as spawning habitat became accessible. With ideal weather and stream conditions forecasted in the middle of December, the California Department of Fish and Wildlife (CDFW) took the opportunity to perform the final adult coho release at Redwood Creek. Surveys performed during the third week of December revealed a large number of coho spawners and significant redd production in Olema Creek. The majority of coho in Redwood Creek were either holding in pools or still migrating toward preferred spawning habitat.

Two male coho fight for spawning rights to an awaiting female upstream in Olema Creek. A spawning female will often have several males vying for the opportunity to spawn with her. Sometimes while two larger males battle it out, a smaller male may sneak undetected for a chance to spawn.

NPS / Michael Reichmuth

Along with a healthy coho return, steelhead were seen in all four streams that were surveyed. Redwood Creek had the most steelhead redds with a count of 47, followed by Pine Gulch with 33 redds, Olema with 29 redds, and Cheda creek with one redd. For both Redwood Creek and Pine Gulch, this is the highest steelhead redd count since annual monitoring began in 1997-1998.

Preliminary Spawner Season Details

Although this season’s coho spawner surveys are complete, May rains could attract a handful of adult steelhead spawners, so our crew may perform one more survey before closing out the season. The totals reported below are preliminary, pending review. It should also be noted that live adult coho and steelhead totals may include repeat sightings.

Redwood Creek

On December 12, 165 coho (87 females, 76 males, and two immature fish of unknown sex) were released back into Redwood Creek to spawn as part of the Redwood Creek Coho Salmon Rescue and Captive Rearing Project. These fish were captured in the creek as juveniles and reared to adulthood at the Don Clausen Fish Hatchery in Sonoma County.

CDFW biologists, with the help of our non-federal crew members, completed two surveys on Redwood Creek during the government shutdown to allow for a more complete spawner dataset. A majority of this season’s spawning activity was observed during the first week of January. In total, we counted 93 live coho, three coho carcasses, and 55 coho redds. Of the 93 live coho , at least 88 were hatchery-reared, identified by colored tags attached near their dorsal fins. Sixty-two adult steelhead, one steelhead carcass, and 30 confirmed steelhead redds were also observed. An additional 23 redds could not be identified to species due to lack of fish on redd or stream conditions (i.e. high turbidity). Based on preliminary analysis, 6 of those redds have been reclassified as coho and 17 as steelhead. This brings the Redwood Creek total to 61 coho redds and 47 steelhead redds.

The number of coho redds increased significantly compared to the last return of this cohort, likely due to the release of adult coho into the system. One live coho and one coho carcass were documented in the watershed prior to the release and we suspect additional wild coho did return to spawn. Genetic analysis of tissue samples to be collected from juveniles this summer will help us determine the spawning success of wild versus hatchery-reared coho.

Olema Creek

We encountered the first live coho in Olema Creek on November 26, and the last coho carcass on January 25. The majority of coho redd observations also occurred during that period, and especially during the third week of December when 51 coho redds were recorded on a single survey day. In total, we counted 111 live adult coho, seven coho carcasses, and 57 coho redds. In addition to coho observations, we recorded 19 live adult steelhead, two steelhead carcasses, and ten steelhead redds. Twenty-five redds were documented for which species could not be determined. Based on preliminary analysis, six of those redds were reclassified as coho and 19 as steelhead. This brings the Olema Creek total to 63 coho redds and 29 steelhead redds. This would indicate that Olema Creek coho redd production held steady when compared to the last time this cohort was observed during the 2015-2016 season. However, due to the government shutdown we do not know if additional spawning activity took place in January. It is likely that the true coho redd count for this season is much higher.

Pine Gulch and Cheda Creeks

A total of five live coho, one coho carcass, and two coho redds were observed on Cheda Creek. In addition to these observations, crews counted one live steelhead, one steelhead redd, and seven redds that could not be identified to species. Based on preliminary analysis, six of the unknown redds were reclassified as coho bringing the coho redd count to eight for Cheda Creek. Although no coho were seen in Pine Gulch Creek, a total of three live steelhead, five steelhead carcasses, and 33 redds were counted. We will perform juvenile surveys in the summer of 2019 to validate spawner counts in Olema, Pine Gulch, and Redwood Creeks.

Trends in Coho Salmon Spawning

The 2018-2019 cohort on Olema has been the strongest cohort since monitoring began, and redd production this season is similar to what was documented three years ago. In comparison, redd abundance on Redwood Creek increased dramatically in 2018-2019 with the successful release of the hatchery-raised adults. Given the high number of hatchery-origin adult coho observed spawning, a much larger juvenile population is anticipated this summer than would have been expected from natural production. Although we have documented successful spawning of released adult coho, the true test will come in future generations of this cohort and its ability to persist in the watershed. For annual coho redd counts observed on Olema and Redwood Creeks over the last 20 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 2018-2019. Cohorts are designated by color (cohort 1 shown in yellow, cohort 2 shown in blue, cohort 3 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 2017-2018. Cohorts are designated by color (cohort 1 shown in yellow, cohort 2 shown in blue, cohort 3 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.