Difference between revisions of "Trout Management Flows"

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.

• The Lees Ferry Rainbow Trout Fishery Page
• Brown Trout Page

Lees Ferry Anglers Trout Fishery Recommendations

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.

2017

• Is Rainbow Trout Control Necessary, and if so, What is the Most cost-effective approach?

2012

• A Research and Monitoring Plan for Evaluating Trout Management Flows below Glen Canyon Dam
• 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

2011

• The Effects of Glen Canyon Dam Operations on Early Life Stages of Rainbow Trout in the Colorado River
• 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.

2010

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

2009

• 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. Transactions of the American Fisheries Society, Volume 138, 2009 - Issue 1.

Trout Management Flows may be more effective if targeted towards juvenile trout and not eggs or hatchlings.
Juvenile trout are susceptible to fluctuating flows (adults are less so).
Reducing the number or density of juvenile trout at Lees Ferry may:

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