Coldwater Canyon Creek, Riverside County
Species / Location
Although steelhead trout (Oncorhynchus mykiss) continue to persist in southern California streams, populations are no longer present throughout much of the species’ historic range, and the species is listed as endangered under the federal Endangered Species Act (ESA). Steelhead trout have two life history forms: “anadromous” in which individuals migrate into the streams for spawning and rearing then to the ocean for growth; and “resident” (also referred to as “rainbow trout”) in which individuals stay in the stream for the entire life cycle. This species is well-known for its flexible life history strategies: anadromous individuals can switch to become resident and those that are resident can become anadromous.
Surveys for anadromous steelhead trout in the counties of San Diego, Orange and Riverside have resulted in very low number of detections since 2001. Recent research by Jacobson et al. (2014) into the genetics of steelhead and rainbow trout populations throughout southern California revealed a small resident population in Coldwater Canyon Creek to be the direct descendants (and not hatchery transplants from other areas) of Southern California steelhead (Figures 1 and 2). This is important because it shows that this population has potential to become genetic source for the ESA-listed anadromous population and that there is adaptation and evolution in the local area maximizing fitness. The Jacobson et al. (2014) study found only one other population of resident rainbow trout of coastal steelhead lineage in the three counties studied (San Diego, Orange, and Riverside counties). Due to these reasons, California Department of Fish and Wildlife (CDFW) believes that there is urgent need to protect, manage, and plan for the future of this fish population.
Coldwater Canyon Creek originates within the Cleveland National Forest, and outlets within private property, part of which is owned and maintained by the Riverside-Corona Resource Conservation District (District). District staff has been aware of the resident rainbow trout population for many years and have been monitoring Coldwater Canyon Creek on a regular basis.
Need for Drought Stressor Monitoring
Coldwater Creek has been greatly affected by California’s current drought. While Coldwater Canyon Creek is generally characterized as a perennial stream with consistent, year-round flows, portions of the creek dried rapidly in the summer and fall of 2014 and 2015. District staff described the summer of 2014 as the first season that sections of the creek have been observed to go dry (Figure 3).
Figure 3. Coldwater Canyon Creek contained intermittent surface flows during the summer and autumn of 2014. Depicted is an upper reach with subsurface flows. Photo: CDFW.
Figure 4. CDFW and District staff conducting habitat assessment. Photo: CDFW.
Stressor Monitoring Efforts
Drought monitoring was initiated in June 2014 by CDFW and District staff and continues on a bi-weekly to monthly basis. Monitoring efforts focused on collecting information on water temperature, dissolved oxygen, and pH of selected pools, and visually observing the water level throughout the habitable reach. During June through August of 2014, CDFW and District staff characterized available creek habitat utilizing the protocol described in the California Salmonid Stream Habitat Restoration Manual, Fourth Edition (Flosi et al. 2010).
Available habitat was assessed during the most severe drought conditions of 2014 to determine if the remaining habitat provided sufficient refuge for this population (Figure 4). During August 2015, an assessment was conducted using visual observation and snorkel survey methods to determine a population estimate within the 3 km of remaining habitat. To improve conditions for remaining habitat, restoration actions, including removal of fish migration barriers and vegetation management, were conducted during the winter, spring, and summer of 2015.
On December 10, 2014, CDFW staff installed two temperature loggers within the lower and upper portions of available rainbow trout habitat to measure long-term fluctuations in water temperature. On May 5, 2015, CDFW staff installed a dissolved oxygen logger in the same pool as the lower temperature logger.
From June 18 to August 14, 2014, CDFW and District staff characterized available habitat, and determined that pools and runs were the dominant habitat types (Table 1). While portions of the creek ran intermittently dry, deep pools remained wetted, ranging in depth from 0.5-1.4 meters. CDFW documented multiple size classes of rainbow trout throughout the creek, including in the uppermost pool.
Throughout the summer and fall of 2014, District staff took water quality measurements at approximately two-week intervals (Figure 5). While water temperatures reached up to 21.1°C in the large refuge pools, dissolved oxygen and pH remained within normal levels (Table 2).
Table 1. Total stream features measured in the assessment of available habitat of Coldwater Canyon Creek (Flosi et al. 2010).
Figure 5. District and CDFW staff monitors water quality. Photo: Riverside-Corona Resource Conservation District.
The population assessment resulted in the visual identification of at least 167 individual rainbow trout within the 3 km of available habitat. The trout of the different year / size classes were found exclusively in refuge pools and distributed throughout the creek.
Table 2. Temperature and D.O. measurements taken by District staff from July 2013 to December 2015. Pool 1 describes the furthest downstream pool on the DISTRICT property, and one of the two pools from which fish were rescued in August of 2013. Pool 3 describes the pool where the temperature and D.O. loggers were deployed, approximately 1 km upstream from the start of the available habitat. Water quality measurements were taken directly under the inflow.
Figure 6. Temperature and dissolved oxygen (D.O.) measurements from CDFW loggers deployed within the largest pool of the lower reach (Pool 3), from May 2015 to December 2015. Loggers were installed on the periphery of the pool to avoid potential dislodging during high flow events..
Temperature and water levels remained within minimum acceptable ranges through July 2015. Temperatures were below 20°C and refuge pools continued to maintain water in the lower reach of the creek (Figure 6). While conducting the population assessment from August 12-20, CDFW and District staff observed a rapid decrease in water level in the downstream 0.5 miles of available habitat, affecting the refuge pools which had been relatively stable throughout the driest period of 2014. In addition to decrease in water level, dissolved oxygen concentrations in the refuge pools decreased rapidly (Figure 6). Due to these rapid changes in stream condition, a rescue was scheduled to rescue rainbow trout from the lower portion of Coldwater Creek.
On August 26, 2015, a total of 14 rainbow trout were rescued from two large pools within the lower half mile reach of Coldwater Creek through a collaborative effort by CDFW staff and District staff (Figure 7). The rainbow trout were captured, transferred to 5-gallon buckets with creek water and aerators, and slowly acclimated to the water temperature of the hatchery truck tanks (Figure 8). Backpack electrofishing gear and dip-nets were used for these efforts.
All fish were weighed, measured, and placed in the transportation tank. Because there was not enough suitable habitat within Coldwater Creek to which to relocate the rainbow trout, they were taken to Mojave River Hatchery for holding until stream conditions become suitable again for release.
At the hatchery, the 14 rescued rainbow trout were inspected for disease, treated, and observed overnight then placed in two large circular tanks containing habitat structure and covered by shade cloth to reduce stress. The fish are currently being fed a natural diet of insects collected on-site.
Figure 7. CDFW and District staff rescue native rainbow trout in the lower reach of Coldwater Canyon Creek. Photo: Riverside-Corona Resource Conservation District..
Figure 8. Rescued rainbow trout to be transported to the hatchery truck. Photo: CDFW
During post-rescue monitoring the following week, additional rainbow trout were found remaining in the rescue reach. On September 2nd, 2015, a total of six rainbow trout were captured and translocated to upstream pools using a combination of backpack electrofishing gear, dip-nets, and water pumps.
CDFW plans to continue monitoring the Coldwater Canyon Creek trout population at a minimum of once every three months and more frequently if stream flow decreases to a level that additional rescues may be required.
Long-term management plans to ensure the persistence of the Coldwater Canyon Creek trout population will be developed from the data collected. Provided that there is sufficient funding, monitoring is expected to continue to track the population status and health. CDFW is currently formulating plans to return the rescued trout to Coldwater Canyon Creek.
Flosi, G., S. Downie, J. Hopelain, M. Bird, R. Coey, and B. Collins. 2010. California Salmonid Stream Habitat Restoration Manual, Fourth Edition. California Department of Fish and Game Wildlife and Fisheries Division.
Jacobson, S., J. Marshall, D. Dalrymple, F. Kawasaki, D. Pearse, A. Abadia-Cardoso, and J. C. Garza. 2014. Genetic analysis of trout (Oncorhynchus mykiss) in southern California coastal rivers and streams. Final Report for California Department of Fish and Wildlife, Fisheries Restoration Grant Program; Project No. 0950015.