Difference between revisions of "Trout Management Flows"

Treatment 1: Redd stranding flows (with mechanical removal of redds below the minimum flow elevation)

This treatment uses flow manipulation at Glen Canyon Dam to periodically dewater redds (nests trout build to lay their eggs in) during the rainbow trout spawning period thereby reducing the number of viable eggs that could hatch and recruit to the age-0 trout population. The objective of this treatment would be to dewater and/or mechanically remove between 50% and 90% of the redds produced over the spawning season. This is one of the mechanisms that is thought to have limited age-0 trout recruitment under pre-ROD conditions.

Redd stranding flows could be implemented within current ROD guidelines and would consist of a period of high steady flows for an extended period of time to encourage fish to spawn on higher elevation gravel bars and benches during the peak spawning period (February-April). Flows would then be reduced to the lowest allowable minimum flow for a dewatering treatment lasting 10-12 hours and occurring every 2-4 weeks over the incubation period (mid-March to mid-May). This treatment should occur during the daytime to take advantage of heating the spawning gravels, which is more effective at reducing the survival of eggs and alevins (newly hatched trout) than just dewatering them. Redds below the minimum flow elevation could be mechanically treated using a hydraulic pressure washer in shallow water or a suction dredge in deeper water to increase the effectiveness of this treatment. Mechanical removal of redds would be less labor intensive than mechanical removal of age-0 fish.

This treatment would likely be most effective during periods of extended high flows (i.e. equalization flows) due to the tendency of trout to spawn higher on gravel bars under these flow conditions. The effectiveness of this treatment is limited by how low flows could be reduced without impacting other resources in the canyon, such as aquatic foodbase resources used by adult rainbow trout. The effectiveness of this treatment is also limited by compensatory mechanisms where increased survival of young trout may increase under low density conditions. An initial test of this treatment from 2003-2005 resulted in strong compensatory survival of fry produced from redds located below the minimum flow level and resulted in no observable reduction in the number of age-0 trout later in the year.

• Attempted in January-March 2003-2005
• Killed between 25-50% of eggs
• Deemed ineffective because the number of fry produced was similar to years with normal operations (compensatory survival) [2]

Treatment 2: Age-0 Trout Displacement Flows

This treatment relies on increased daily flow fluctuations to reduce the habitat availability of age-0 trout (fry and juveniles). This would make age-0 trout more reliant on sub-optimal habitats where they would be subject to poorer growing conditions. Daily flow fluctuations have been shown to negatively impact age-0 trout without affecting larger trout (Makinster et al. 2011). Under this flow regime age-0 trout are more likely to remain in deeper, colder water with higher velocities. This should result in decreased growth rates and lower survival. Habitat limiting flows could be enhanced by increasing the allowable daily fluctuation when age-0 trout are most sensitive to flow fluctuations (May-August). A nighttime minimum flow treatment would be more effective than a daytime treatment because age-0 trout typically come closer into shore at night. Increasing limits on daily fluctuations beyond ROD limits on at least a weekly basis would likely increase the effectiveness of this treatment. A critical component of this treatment would be to ensure that flows drop to the lowest allowable minimum flow for 12-14 hours on at least a weekly basis to dewater shallow gravel bars and benches in the Lees Ferry reach. Fluctuating flows like these are another mechanism that is thought to have limited age-0 trout recruitment under pre-ROD conditions.

This treatment would likely be most effective during periods of time when releases from Glen Canyon Dam are already fluctuating for power generation. This treatment may be more effective at having a population level response than redd stranding flows because it is targeting an older age class that is less likely exhibit a density-dependent response.

• Suppression flow window: May-August [3]
• Age-0 trout generally do not adjust position to stay in shallow water as flows come up (restricted movement) [4]

https://pubs.usgs.gov/fs/2011/3002/fs2011-3002.pdf

https://pubs.usgs.gov/fs/2011/3002/fs2011-3002.pdf

Treatment 3: Age-0 Trout Stranding Flows

This treatment relies on a period of high steady flows to draw age-0 trout (fry and juveniles) onto high elevation gravel bars and benches and then stranding those fish by rapidly decreasing releases from Glen Canyon Dam. Age-0 trout stranding flows could be provided within ROD guidelines with the treatment consisting of a period of high steady flows for an extended period of time to encourage age-0 trout to inhabit high elevation gravel bars and benches. Flows would then be rapidly reduced to the lowest allowable minimum flow for a dewatering treatment lasting 10-12 hours and occurring every 2-4 weeks. This treatment would take place from May to August when age-0 trout are most likely to be in these near-shore habitats. A nighttime minimum flow treatment may be more effective than a daytime treatment because age-0 trout typically come closer into shore at night. Increasing downramp rates and reducing flows below ROD guidelines may make this treatment more effective. The ROD currently limits downramp rates to 2,500 cfs/hr to reduce the probability of stranding young fish in nearshore habitats. Operationally, down ramping from 33,200 cfs (maximum power plant capacity at Glen Canyon Dam) to the daily minimum could occur nearly instantaneously.

This treatment would be most effective during periods of extended high flows (i.e. equalization flows) due to the likelihood of age-0 fish of utilizing high elevation gravel bars and benches when flows are held high and steady for an expanded period of time. As with Treatment 2, this treatment may be more effective at having a population level response than redd stranding flows because it is targeting an older age class that is less likely to exhibit a density-dependent response. This treatment, however, may also strand larger, more desirable trout occupying nearshore habitat during the night as well. Any larger fish caught in the nearshore during a stranding event would likely be more susceptible to mortality than smaller, age-0 fish because they would not be able to escape or endure the stranding as readily as a smaller fish.

LTEMP FEIS

Treatment 4: Increase or Maintain Turbidity

• Growth rates largely determine the abundance of trout in Marble Canyon
• Lower growth can be due to lower feeding efficiencies
• Feeding efficiency of trout in Marble Canyon is lower in years with high sediment inputs but no HFE (i.e. 2016)
• Not having an HFE following a large sediment input extends the duration of turbid conditions
• Marble Canyon trout population (i.e. trout at the LCR) will collapse faster with an extension of turbid conditions
• Reduce frequency of HFEs in years with high trout immigration into Marble Canyon and high sediment inputs

Differences in the efficiency of Trout Management Flows suggest that each of the three treatments discussed above may be more effective under some flow scenarios than others. For example, redd stranding flow and age-0 trout stranding flows would likely be more effective when releases can be held high and steady for an extended period of time (i.e. spring HFEs and equalization flows) whereas age-0 trout habitat limiting flows would likely be more effective at lower flows more typical of normal operations. Releases from Glen Canyon Dam could also be manipulated for short periods of time to where the three treatments outlined above could be used sequentially to target different vulnerabilities of age-0 trout as they age over the course of the year. Several scenarios are presented below for how Trout Management Flows could be incorporated into various release schedules for a range of operations.

Scenario 1: Normal Operations

This scenario describes a combination of possible Trout Management Flows that could be implemented during normal operations. First, conduct a pre-treatment redd counts in February and March to get an estimate of trout production. Once every 2-4 weeks beginning in mid-March, reduce releases early in the morning to the lowest allowable minimum flow and hold for 10-12 hours. Remove redds located below the minimum flow elevation with a hydraulic pressure washer or a suction dredge when the water levels are low (Treatment 1). Repeat every 2-4 weeks until May. Beginning in May, proceed with age-0 trout displacement flows (Treatment 2) by increasing daily flow fluctuations to as high of level as allowable. Continue with these high flow fluctuations until the end of August. During the first week of September, perform a population estimate on the age-0 trout population to determine the effectiveness of this actions.

• Large fluctuations in daily flows is thought to have limited egg survival and age-0 trout recruitment under pre-ROD conditions.

Scenario 2: Year of high trout recruitment and immigration into Marble Canyon followed by a sediment input from the Paria

Scenario 3. Equalization flows that require full power plant releases for an extended period of time

This scenario describes a combination of possible Trout Management Flows that could be implemented during equalization flows. Conduct a pre-treatment redd count in February and March to get an estimate of trout production. Once every 2-4 weeks beginning in mid-March, reduce releases early in the morning to the lowest allowable minimum release and hold for 10-12 hours to dewater redds. During the day of the treatment when the water levels are low, remove redds located below the minimum flow elevation with a hydraulic pressure washer or a suction dredge (Treatment 1). Repeat every 2-4 weeks until the end of April. Beginning in May, downramp flows one day every 2-4 weeks as fast as allowable to the lowest allowable minimum flow for a nighttime stranding treatment lasting 10-12 hours (Treatment 3). Repeat every 2-4 weeks until the end of the equalization flow (probably September 30). During the first week of October, perform a population estimate on the age-0 trout population to determine the effectiveness of these actions.

• The 2012 equalization flow increased survival of YOY trout ultimately leading to an over population of trout in the ferry and a subsequent population crash during the winter of 2014-15.[5]

Scenario 4. Spring HFE

This scenario describes a combination of possible Trout Management Flows that could be implemented during a spring HFE. Conduct a pre-treatment redd count in February and March to get an estimate of trout production. Once every 2-4 weeks beginning in mid-March, reduce releases early in the morning to the lowest allowable minimum release and hold for 10-12 hours to dewater redds. During the day of the treatment when the water levels are low, remove redds located below the minimum flow elevation with a hydraulic pressure washer or a suction dredge (Treatment 1). Repeat every 2-4 weeks until the end of April. Implement the spring HFE at the end of April. At the conclusion of the spring HFE, downramp flows as fast as allowable to the lowest allowable minimum flow for a nighttime stranding treatment lasting 10-12 hours (Treatment 3). Then proceed with age-0 trout displacement flow treatments by increasing daily flow fluctuations to as high of level as allowable (Treatment 2). Continue with these high flow fluctuations until the end of August. During the first week of September, perform a population estimate on the age-0 trout population to determine the effectiveness of this actions.

• Run Spring HFE as late in the window as possible (lower survival before the HFE than after [6])
• Survival rates of YOY trout increased 4x following the March 2008 HFE [7]

https://pubs.usgs.gov/fs/2011/3002/fs2011-3002.pdf

• Rainbow Trout Page
• Brown Trout Page
• LTEMP EIS

Treatment 1: Redd stranding flows

Treatment 2: Age-0 Trout Displacement Flows

• Optimal fluctuation range
• Optimal ramp rates
• Timing and duration

Treatment 3: Age-0 Trout Stranding Flows

• Duration of high flows needed to lure YOY rainbow trout into near-shore habitats
• Magnitude of the high flow that would be more effective in luring YOY trout to near-shore habitats
• Whether or not moving to high flows first is needed to reduce YOY trout numbers (as opposed to simply dropping rapidly from normal flows to minimum flows)
• Timing of TMF cycles during the May–August period of trout emergence
• Number of cycles necessary to effectively limit trout recruitment
• Can an action like this overcome density-dependent mortality? [8]

Treatment 4: Increase or Maintain Turbidity

• Hydropower: value, capacity
• Foodbase: production, drift, availability
• Native fish: stranding
• Tribal sensitivities: sanctity of life
• Lees Ferry fishery: access, economics
• Boater safety: Glen Canyon, downstream
• Sediment transport: beaches

2017

• Korman et al. 2017. Trends in rainbow trout recruitment, abundance, survival, and growth during a boom-and-bust cycle in a tailwater fishery. TAFS
• Is rainbow trout control necessary, and if so, what is the most cost-effective approach? ppt

2016

• Boom-and-Bust Cycles in the Population of Rainbow Trout in Glen Canyon and Effects of Fall High Flow Experiments ppt

2015

• Avery et al. 2015. Effects of Increased Discharge on Spawning and Age-0 Recruitment of Rainbow Trout in the Colorado River at Lees Ferry, Arizona. NAJFM

2013

• Effects of Recent Flow Events on the Juvenile Rainbow Trout Population in Lees Ferry (poster)

2012

• Korman et al. 2012. Estimating recruitment dynamics and movement of rainbow trout (Oncorhynchus mykiss) in the Colorado River in Grand Canyon using an integrated assessment model. Can. J. Fish. Aquat. Sci
• A Research and Monitoring Plan for Evaluating Trout Management Flows below Glen Canyon Dam ppt
• Proposed Monitoring and Research Plan for Evaluating Trout Management Flows below Glen Canyon Dam PPT
• A Research and Monitoring Plan for Evaluating Trout Management Flows Below Glen Canyon Dam and PPT
• Trout Management Flows and Age-0 Habitat Use ppt

2011

• Melis, T. S., ed., 2011, Effects of three high-flow experiments on the Colorado River ecosystem downstream from Glen Canyon Dam, Arizona: U.S. Geological Survey Circular 1366
• The Effects of Glen Canyon Dam Operations on Early Life Stages of Rainbow Trout in the Colorado River. USGS Fact Sheet
• Korman et al. 2011. Effects of flow fluctuations on habitat use and survival of age-0 rainbow trout (Oncorhynchus mykiss) in a large, regulated river. CJFAS.
• Korman et al. 2011. Effects of Fluctuating Flows and a Controlled Flood on Incubation Success and Early Survival Rates and Growth of Age-0 Rainbow Trout in a Large Regulated River. TAFS

2010

• Hourly and Seasonal Variation in Nearshore Habitat Use by Age-0 Rainbow Trout In Lees Ferry: Implications for Nonnative Fish Suppression Flow Experiments ppt

2009

• Korman and Campana. 2009. Effects of Hydropeaking on Nearshore Habitat Use and Growth of Age 0 Rainbow Trout in a Large Regulated River. TAFS
• Korman et al. 2009. Effects of Fish Size, Habitat, Flow, and Density on Capture Probabilities of Age-0 Rainbow Trout Estimated from Electrofishing at Discrete Sites in a Large River. TAFS

Minimum release:

• 8,000 cfs between 7 a.m. and 7 p.m.??
• 5,000 cfs between 7 p.m. and 7 a.m.??
• Lower releases limited by boating safety concerns

Maximum release:

• 20,000 cfs (LTEMP example)
• 32,000 cfs (powerplant)
• 47,000 cfs (powerplant + bypass)
• Limited by powerplant maintenance and monthly volume

Daily range:

• No limit

Ramp rates:

• 4,000 cfs/hr up (LTEMP example)
• 15,000 cfs/hr down (LTEMP example)
• No limit up or down??

Recommendation #5.

Under certain conditions, rainbow trout at Lees Ferry have reproduced prolifically. Historically, when there is an over-abundance of young-of-year rainbow trout, the quality and condition of rainbow trout decline. This is likely due to the low quality and low abundance of food sources in Lees Ferry. Trout Management Flows (TMFs) are flow treatments that are hypothesized to reduce the abundance of young-of-year trout by stranding trout shortly after they emerge from their redds (Korman, Ecometric Research, Inc., personal communications, 2015).

We believe the best long term and ecologically appropriate solution to controlling trout densities is to increase invertebrate diversity and manage Grand Canyon Dam flows to avoid excessive trout spawning and recruitment (see recommendations related to the aquatic food base and equalization flows). We are concerned about the collateral damage that TMFs could have on other resources especially the aquatic food base and native fish. TMFs may be especially useful when spring HFE's are implemented or in years when high equalization flows are required.

TMF's should only be implemented in a carefully designed experimental framework that includes quantified criteria for success (for managing trout recruitment and improving the humpback chub population) and the impacts to other resources, especially the aquatic food base, are fully assessed. TMF's should only be used when the rainbow trout population is stable and includes a healthy abundance of all size classes of rainbow trout. Mitigation measures such as emergency stocking of trout need to be in place prior to the implementation of TMFs in case of catastrophic loss to the fishery (see recommendations on Trout Stocking). In conclusion, the experimental evaluation of TMFs needs to recognize the trout fishery as a highly valued asset. The AZGFD should have a seat at the table along with Federal agencies on any discussion and decisions related to implementation of TMFs.

LTEMP FEIS Chapter 2, pages 39-40

TMFs are a special type of fluctuating flow designed to reduce the recruitment of trout by disadvantaging YOY trout (Figure 2-15). TMFs have been proposed and developed on the basis of research described in Korman et al. (2005). The underlying premise of TMFs is based on observations that YOY trout tend to occupy near-shore shallow-water habitats to avoid predation by larger fish. TMFs feature repeated fluctuation cycles that consist of relatively high flows (e.g., 20,000 cfs) sustained for a period of time (potentially ranging from 2 days to 1 week) followed by a rapid drop to a very low flow (e.g., 5,000 cfs to 8,000 cfs). This low flow would be maintained for a period of less than a day (e.g., 12 hr) to prevent adverse effects on the food base. Low flows would be timed to start in the morning, after sunrise, to expose stranded fish to direct sunlight and heat. Up-ramp rates to the TMF would be the same as the limit for this alternative overall (i.e., 4,000 cfs/hr). The down-ramp from peak to base would be over a single hour (e.g., 15,000 cfs/hr for a drop from 20,000 cfs to 5,000 cfs). In a TMF flow cycle, YOY trout are expected to occupy near-shore habitat when flows are highest, and would be stranded by the sudden drop to low flow. Because older age classes of trout tend to occupy deeper habitats toward the middle of the river channel, they are less susceptible to stranding and are less likely to be directly affected by TMFs. TMFs would be used to control trout recruitment in the Glen Canyon reach to manage the rainbow trout fishery, and to limit emigration of juvenile trout to downstream reaches, particularly to habitat occupied by humpback chub near the confluence with the Little Colorado River. Triggers for implementation of TMFs would be determined in consultation with the AZGFD.

It should be noted that several Tribes have expressed concerns about TMFs as a taking of life within the canyon without a beneficial use. The Pueblo of Zuni has expressed concern that the taking of life by trout stranding has an adverse effect on the Zuni value system. The jointlead agencies will continue to work with the Tribes regarding options for trout management.

TMFs may be tested under this alternative early in the LTEMP period, even if not triggered by high trout recruitment. The intent of these early tests would be to determine the effectiveness of TMFs in reducing trout recruitment and the emigration of young trout to Marble Canyon and the Little Colorado River reach. The condition of the trout fishery, as determined in consultation with AZGFD, and potential impacts on other important resources would be considered prior to implementing TMFs. If TMFs are determined to be effective for these goals while minimizing impacts on other resources, they may be deployed on a regular or triggered basis. TMFs would be tested two to three times in the early part of the LTEMP period while attempting to minimize confounding effects with other experimental treatments. Tests would start with a conservative application of two cycles in June and July (Figure 2-15), but could be increased based on experimental testing to as many as three cycles per month for 3 months (May, June, and July).

LTEMP FEIS Chapter 2, pages 63-66

TMFs (described in Section 2.2.3.2) are a potential tool that could be used to control annual trout production in the Glen Canyon reach for purposes of managing the trout fishery and for limiting emigration from the Glen Canyon reach to Marble Canyon and the Little Colorado River reach. If resource conditions are appropriate, TMFs may be tested under Alternative D early in the experimental period, preferably in the first 5 years. These first tests could be triggered by modeled trout recruitment levels or otherwise implemented to test the effectiveness of TMFs. The intent of these early tests would be to determine the effectiveness of TMFs and a best approach to trout management. If TMFs are determined to be effective for controlling trout numbers while minimizing impacts on other resources, they may be deployed as an adaptive experimental treatment triggered by estimated trout recruitment.

It should be noted that several Tribes have expressed concerns about TMFs as a taking of life within the canyon without a beneficial use. The Pueblo of Zuni has expressed concern that the taking of life by trout stranding has an adverse effect on the Zuni value system. The jointlead agencies will continue to work with the Tribes regarding options for trout management, and to determine the most appropriate means of mitigating impacts on Tribal values if TMFs are implemented.

As many as three TMF cycles/month (see Section 2.2.3.2) in a period of up to 4 months during May through August could be tested, depending on the results of early tests. Aspects of TMF design that would be investigated include:

• Duration of high flows needed to lure YOY rainbow trout into near-shore habitats,
• Magnitude of the high flow that would be more effective in luring YOY trout to near-shore habitats,
• Whether or not moving to high flows first is needed to reduce YOY trout numbers (as opposed to simply dropping rapidly from normal flows to minimum flows),
• Timing of TMF cycles during the May–August period of trout emergence, and
• Number of cycles necessary to effectively limit trout recruitment.

If TMFs prove to be effective in controlling trout production and emigration to the Little Colorado River reach, and they become an integral part of the LTEMP, regular implementation of TMFs may need to include variable timing to prevent adaptation of the population to specific timing (e.g., increase in recruitment by fall-spawning rainbow trout).

Certain aspects of TMF effectiveness can be addressed through observational studies (e.g., the number of YOY rainbow trout observed in the near-shore environment in daily increments after the high flow is initiated); others may be addressed through consideration of the physical environment in Glen Canyon (i.e., what areas are inundated or exposed at different flows). Ultimately, however, effectiveness would be judged based on comparison of fall trout recruitment estimates to expectations based on prior years. It may take several years to make this determination, depending on the strength of the response and the type of TMFs tested. Ultimately, however, effectiveness would be based on the ability of TMFs to reduce recruitment in and emigration from the Glen Canyon reach. The driving forces behind emigration are not fully understood, but are expected to be related to population size and food base in the Glen Canyon reach.

For the EIS modeling, a trigger of 200,000 YOY trout was used to determine when TMFs would be implemented. A regression equation based on annual volume, the variability in flows from May through August, and the occurrence of a spring HFE was used to predict the number of YOY. The actual trigger used could be higher or lower depending on the results of experiments that will be conducted on the effectiveness of TMFs. In addition, the predictive regression equation could be modified based on new information. The trigger and predictive equation used would be modified as needed in an adaptive management context utilizing the process described in Section 2.2.4.3. Triggers for implementation of TMFs would also be developed in consultation with the AZGFD and other entities as appropriate.

Monitoring of other resources, particularly food base and the physiologic condition of adult rainbow trout, would also be considered. In addition, the number of YOY trout at the end of the summer would be estimated to determine if it equals or exceeds the estimated number of recruits needed to sustain the desired number of adult trout. If the estimated number of recruits is less than the recruitment target, TMFs would be re-evaluated for modification before implementation in subsequent years. It is anticipated that the trout population could rebound from a 1-year drop below this target level.

As discussed in relation to sediment experiments above, there is concern among scientists and stakeholders with regard to the risk associated with implementation of spring HFEs as related to trout response and subsequent effects on the humpback chub population. For this reason, TMFs would be implemented and tested for effectiveness as early in the LTEMP period as possible, preferably before the first spring HFEs are triggered, even if not triggered by high trout recruitment. TMFs could be implemented in years that feature a spring HFE and in the water year that follows an equalization flow because of the expected positive effects of equalization on rainbow trout recruitment. Any implementation of TMFs would consider the status of the trout fishery prior to implementation. Modeling indicates TMFs would be triggered by trout recruitment numbers in 32% of the years in the LTEMP period.

There is potential for confounding effects when coupling TMFs with HFEs. If trout recruitment is still high after implementation of TMFs that follow HFEs, this would suggest TMFs were not effective as designed for that trial. If recruitment is lower than expected after TMF implementation, however, uncertainty will remain about whether an HFE failed to stimulate trout recruitment or whether TMFs were effective in suppressing otherwise strong recruitment. It may not be necessary to determine the underlying effect on trout numbers unless TMFs have undesirable side effects on other resources or the trout population.

If TMFs are found to be highly effective in controlling trout recruitment and emigration of trout, and emigration only occurs or primarily occurs immediately following high recruitment years, it may be possible to limit TMF implementation and achieve multiple resource goals, particularly if unintended impacts of TMFs on other resources such as native fish become evident. Timing of TMFs may also be adjusted based on the best scientific information available related to trout emigration behavior. If adverse impacts of TMFs become evident, this may also suggest revisiting whether or not TMFs are necessary in response to spring HFEs. Lastly, if, there is an observed increase in trout recruitment due to fall HFEs, then application of TMFs in the spring following a fall HFE would be considered.

Implementation of TMFs would consider resource condition assessments and resource concerns using the processes described in Sections 2.2.4.3 and 2.2.4.4. TMFs may not be tested when there appears to be the potential for unacceptable impacts on the resources listed in Section 2.2.4.3.

LTEMP Biological Assessment, pages 30-41

Experimental Trout Management Flows (TMFs) could be used to control annual rainbow trout production in the Glen Canyon reach for the purposes of managing the rainbow trout fishery and for limiting emigration to Marble Canyon and the Little Colorado River reach. TMFs would be tested early in the experimental period, preferably in the first 5 years. Under the LTEMP EIS, TMFs could occur from May to August.

Trout Management Flows may be more effective if targeted towards juvenile trout and not eggs or hatchlings.
Fry are more susceptible to fluctuating flows (juveniles and adults are less so).

Reducing the number or density of juvenile trout at Lees Ferry may:

• reduce competition with adult trout and maintain/improve the Lees Ferry trout fishery (size, condition)
• reduce downstream migration (emigration) and conflicts with humpback chub

TMFs were modeled in LTEMP to reduce the rainbow trout recruitment rate to 0.1 and 0.5.