Butte Creek, Butte County
Species / Location
In 2015, California experienced its fourth consecutive extremely dry year, providing the state with one of the worst droughts in recorded history. Historically, spring-run Chinook Salmon (spring-run, Oncorhynchus tshawytscha) populations were found in most of the eastern tributaries of the Sacramento and San Joaquin rivers, and large dams and water development eliminated access to all but the few remaining self-sustaining tributaries (CDFG, 1998). Butte Creek is one of only three Central Valley streams that continue to harbor a self-sustaining population of spring-run (Figures 1 and 2). The other two are nearby Deer and Mill creeks. Spring-run were listed as “threatened” under the California Endangered Species Act and federal Endangered Species Act in 1999. As anadromous fish, spring-run hatch in freshwater, migrate to the ocean to mature, and return to their birth stream to spawn as adults. Uniquely, spring-run adults enter freshwater in the late winter and spring, spending up to eight months in streams prior to spawning. This extended fresh water residency requires that adults have access to suitable habitat--deep, cool, highly oxygenated pools--to survive high summer temperatures in the Central Valley.
Need for Drought Stressor Monitoring
One of California’s high priority streams for monitoring is Butte Creek. With California experiencing an unprecedented drought, monitoring the health of spring-run during their summer holding period in Butte Creek was a top priority for the California Department of Fish and Wildlife (CDFW). Since 1994, CDFW has been studying the life history of spring-run within this creek. The recent expansion of the long-term monitoring efforts has allowed CDFW to better document the environmental conditions that anadromous salmonids have been susceptible to during these historical low stream flows. Continuing to document habitat conditions, as well as spring–run presence throughout the watershed and fish health is a vital tool to protect this population
Stressor Monitoring Efforts and Findings
CDFW collaborated with California State Water Resources Control Board, National Marine Fisheries Service, U.S. Fish and Wildlife Service and PG&E Operations Team to proactively manage water delivery and timing from the West Branch of the Feather River, a nearby tributary to the Sacramento River, into Butte Creek. The cooperation of these agencies played an important role in helping the spring-run cope with low flows and high water temperatures from the current drought conditions. Group decisions were made each week based on environmental factors on how to adaptively manage the available water to best benefit the holding spring-run. In addition to the interagency efforts, CDFW personnel also conducted weekly snorkel surveys of the entire holding habitat, a 17.7 km reach of stream (Figure 2). Survey crews documented the number of spring-run that died-off prior to spawning (pre-spawn mortalities), determined fish distribution within the creek, and documented any change in holding patterns over the summer period.
Water Temperature Monitoring
CDFW monitored water temperature at eight different sites. Drought funding enabled crews to deploy an additional five water temperature loggers in key stream reaches. Thermographs were used to track stream conditions and any changes in temperature based on the flow releases made from upstream PG&E project reservoirs. Generally, elevated creek temperatures during the hot summer holding period can result in an increase of spring-run mortalities; however, mortalities can be reduced when the Operations Team implements water release strategies to help mitigate “heat storms” thereby reducing water temperatures in Butte Creek. Water temperature plays an important role in fish distribution within the holding habitat. As water temperatures increase during the summer months, spring-run tend to migrate further upstream seeking cooler refugia.
Figure 3. Adult spring-run Chinook through Vaki Riverwatcher. Photo CDFW.
One key monitoring component is the operation of the Vaki Riverwatcher (VRW), which is used to monitor fish migration patterns. The VRW is installed in Durham Mutual fish ladder, just upstream from where California Highway 99 crosses Butte Creek. This technology provides an infrared scanning image and high resolution video of fish species that pass through the ladder (Figure 3). The VRW is operated year round and documents the arrival of spring-run into Butte Creek.
The VRW can also be used as tool to temporally and spatially delineate the different runs of Chinook salmon on Butte Creek. Video obtained during February through June show spring-run arrival into Butte Creek when flows are relatively high and water temperatures are low. As flow decreases and water temperatures increase, Chinook salmon immigration slows and ceases during the hotter summer months. Video obtained during October through December show a typical fall-run Chinook salmon timing pattern of immigrating when stream flows are increasing water is cooler (Figure 4).
Figure 4. Adult Chinook upstream migration through Vaki Riverwatch
Pre-spawn Mortality Survey
Another key component of the Butte Creek monitoring program are annual pre-spawn mortality surveys. These surveys are typically funded by PG&E as part of the DeSabla-Centerville Hydroelectric Project; however, drought funding allowed for surveys to begin earlier in the year and to cover broader reaches of the stream. Due to low stream flow, crews began surveying in early spring and recorded spring-run distribution patterns, reporting any potential delays in migration, and documenting any pre-spawn mortalities. Pre-spawn surveys continue until the start of spawning, usually by mid-September. During the 2014 pre-spawn survey period, June 3 through September 18, there were 115 carcasses encountered and an expanded pre-spawn mortality total of 232 (Figure 5). In 2015, despite pulse flow efforts to trigger late arriving spring-run to move upstream into holding habitat, only 68 carcasses were encountered during the survey with an expanded pre-spawn mortality total of 152 (Figure 6).
Figure 5. Temperature and number of SPRING-RUN that died per day before spawning in Butte Creek from June 1- September 17, 2014.
Figure 6. Temperature and number of SPRING-RUN that died per day before spawning in Butte Creek from June 1- September 17, 2015.
Following pre-spawn mortality surveys are carcass surveys. These surveys begin at the initiation of spawning, beginning in mid-September, to estimate the number of spring-run that survived over the summer to spawn.
Collaboration coupled with real time adaptive management strategies of water releases contribute to the annual success of spring-run surviving the long, hot summer drought conditions and making it into the spawning season.
The 2014 carcass survey indicated that 4,851 spring-run successfully spawned in Butte Creek whereas only 413 were successful in 2015. Prior to the 2015 carcass survey, crews reported 1,000 live salmon in the creek; therefore, the 2015 survey estimate may be low due to environmental factors and likely predation.
While ongoing real-time monitoring of Butte Creek’s spring-run continues each year to document abiotic factors, fish distribution, pre-spawn mortalities, and behavioral patterns, the funding provided as part of the state's comprehensive drought response increased and enhanced monitoring efforts. This helped inform targeted drought response actions. Continued coordination and collaboration will play a vital role in ensuring that the returning future populations of Butte Creek spring-run will have the best chance at surviving and contributing to the overall resources of California.
Brown, E.G. 2014. California Water Action Plan 2016 Update.
California Department of Fish and Game (CDFG). 1998. A Status Review of the Spring-run Chinook Salmon (Oncorhynchus tshawytscha) in the Sacramento River Drainage. Prepared by the California Deptartment of Fish and Game, June.