Trout Management Flows

The purpose of implementing Trout Management Flows (TMFs) is to evaluate methods for using releases from Glen Canyon Dam to reduce the production of large numbers of age-0 rainbow trout in order to improve the quality of the Lees Ferry trout fishery and conserve the endangered humpback chub and other native fishes in Grand Canyon. We identified three objectives that need to be addressed to support management decision making: Sustain a healthy Lees Ferry trout population with a balanced age and size structure; Reduce annual production rates of rainbow trout in the Lees Ferry reach; Reduce emigration rates of rainbow trout from Lees Ferry to downstream reaches occupied by humpback chub. [1] LTEMP Experimental Action: Aquatic Resource-Related Experimental Treatments (BA, pages 30-41) [2] 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.

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Updates [3] Information 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. Presentations and Papers 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 2010 Hourly and Seasonal Variation in Nearshore Habitat Use by Age-0 Rainbow Trout In Lees Ferry: Implications for Nonnative Fish Suppression Flow Experiments Other Stuff 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)