Brown Trout

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Brown trout in the Lees Ferry reach of the Colorado River—Evaluation of causal hypotheses and potential interventions

Brown Trout Brown trout are native to Europe and were introduced to tributaries in the Grand Canyon in the 1920s. They are capable of withstanding slightly higher temperature than rainbow trout. Unlike most other trout species, brown trout spawn in the late fall. Their spawning behavior, however, is similar to other trout species. Like rainbow trout, young brown trout feed on aquatic and terrestrial insects and invertebrates but brown trout are more apt to switch to eating other fish as they get bigger. The rainbow trout found in Grand Canyon are more likely to continue to eat mostly insects and invertebrates even as adults. [1] [2] Studies have shown that rainbow trout and native fish like humpback chub often have a difficult time persisting in the presence of a large population of brown trout. [3] [4] [5] Desired Future Condition for the Lees Ferry Trout Fishery A high quality trout fishery in GCNRA, as further described in the Recreation DFC that does not adversely affect the native aquatic community in GCNP. • Minimize emigration of non-native fish from the Lees Ferry reach in Glen Canyon National Recreation Area to downstream locations. • Minimize emigration of non-native warm water fish to the mainstem Colorado River.

Rainbow Trout	Brown Trout

Updates [1] Brown trout are much more likely to eat other fish (piscivory) but since there are many more rainbow trout in the Colorado River between Glen and Marble Canyons, rainbow trout probably eat more fish numerically than brown trout.https://pubs.er.usgs.gov/publication/70003950 Brown trout caught at the LCR during the 2013 summer Natal Origins trip An increasing brown trout population in Glen Canyon could pose a problem for both the Lees Ferry rainbow trout fishery and native fish in Grand Canyon because brown trout eat both rainbow trout and native fish alike. Above is a photo of a brown trout collected during 2016 trout monitoring below Flaming Gorge dam that had just eaten a 10" stocked rainbow trout.

Information and Links NPS Brown Trout Incentivized Harvest page Lees Ferry Rainbow Trout Fishery Page Trout Management Flows Page The HFE Page Humpback Chub Page The Temperature Page 2016 Fish Protocol Evaluation Panel (PEP) 2019 National Park Service Expanded Non-native Aquatic Species Management Plan 2013 National Park Service Comprehensive Fisheries Management Plan Projects Trout Reduction Efforts Presentations and Papers 2024 Fisheries Review: Annual Reporting FY2023 Angler response to the Brown Trout Incentivized Harvest Population effect of incentivized harvest on Brown Trout 2023 Effects of the 2023 Spring HFE and Balancing Flows on Rainbow and Brown Trout in Glen Canyon Tracking Natal Origins of Brown Trout In Grand Canyon Through Otolith Microchemistry Brown Trout - Incentivized Harvest Program What do we know after two years of the brown trout incentivized harvest program? Part I: Update on Rainbow and Brown Trout Growth, Abundance, and Recruitment in Glen Canyon (TRGD) Grand Canyon National Park Fisheries Program Updates, FY 2022 2022 Population Dynamics of Rainbow (Oncorhynchus mykiss) and Brown (Salmo trutta) Trout in Glen Canyon Fish modelling to support management decisions Preliminary insights into angler response to the brown trout incentivized harvest program 2022 Fisheries review: Annual Reporting FY2021 2021 GCDAMP Annual Reporting Meeting Update: Fishes Brown Trout - Incentivized Harvest Program Brown Trout Population Modeling 2020 Incentivized Harvest Program Implementation Update – contact Ken Hyde, NPS TRGD: Trout Recruitment, Growth and Population Dynamics 2018 Runge et al., 2018, Brown trout in the Lees Ferry reach of the Colorado River—Evaluation of causal hypotheses and potential interventions: USGS Open-File Report Brown Trout in Lees Ferry: Evaluation of Causal Hypotheses and Potential Interventions PPT Brown Trout Telemetry at Lees Ferry and Grand Canyon, Arizona PPT Brown Trout in Lees Ferry: Evaluation of Causal Hypotheses and Potential Interventions 2017 Lees Ferry Trout Fishery Status Brown Trout in Glen Canyon: Insights from Two Expert Elicitation Surveys Bright Angel Brown Trout Removal and Humpback Chub Translocations Brown Trout Management Considerations: An Update System Wide Monitoring 2016 Grand Canyon Monitoring and Research Center Science Updates (BO Compliance, Trout Updates, Green Sunfish, Fisheries PEP, Partners in Science) Brown Trout Update Lees Ferry Bright Angel Creek Non-Native Trout Reduction, Grand Canyon National Park 2015 Dibble et al. 2015. Flow management and fish density regulate salmonid recruitment and adult size in tailwaters across western North America 2014 Whiting et al. 2014. Macroinvertebrate prey availability and food web dynamics of nonnative trout in a Colorado River tributary, Grand Canyon. Freshwater Science. 2013 Science Update: Fisheries Diets and Food Availability of Nonnative Trout in Bright Angel Creek, Grand Canyon: Implications for Native Fish Conservation Nonnative fish control in GCNP tributaries 2011 Yard et al. 2011 Trout piscivory in the Colorado River, Grand Canyon: Effects of turbidity, temperature, and fish prey availability. Transactions of the American Fisheries Society The 2017 Brown Trout Workshop Runge et al., 2018, Brown trout in the Lees Ferry reach of the Colorado River—Evaluation of causal hypotheses and potential interventions: USGS Open-File Report Brown Trout Workshop Agenda Brown Trout Workshop Notes Brown Trout Below Glen Canyon Dam: A Preliminary Analysis of Risks and Options White Paper Brown Trout Workshop Overview Pueblo of Zuni Perspectives on Fish Research and Management Context and Objectives Scientific Background Preliminary Review of Bright Angel Creek Trout Control Operations Root Causes for the Increase in Brown Trout in Lees Ferry Reach Risks, Current and Potential Comparison of Management Options Summary of Day One Presentations Brown Trout Monitoring and Research Action requested. Proposed draft motion AMWG meeting 2/15/17: The AMWG believes that before moving forward with any new actions to manage brown trout in the Lees Ferry reach of the Colorado River, it would be beneficial to work to develop a plan based on the most up to date information and that has involvement from interested members of the AMWG. Accordingly, the AMWG requests that the Secretary of the Interior direct the National Park Service, and request the Arizona Game and Fish Department, to organize and facilitate a workshop among scientists, managers, tribes, and interested stakeholders to address: The root causes of the increases in brown trout, The risks associated with an expanding brown trout population to a quality rainbow trout fishery in Lees Ferry and the recovery/conservation of humpback chub and other native fish down river, The pros and cons of different management options to address those risks, and The research needs to support more informed decisions moving forward. The workshop should also review the efficacy of the current High Flow Experiment protocol in light of new scientific information and how it could be modified to allow for more frequent Spring HFEs to conserve sediment and enhance biological resources in the Colorado River below Glen Canyon dam. Results from the workshop, and any recommended actions based on them, should be reported to the TWG for consideration in development of the Triennial Work Plan and presented to the AMWG at the August 2017 meeting. Letter from Brent Rhees, Acting Secretary's Designee, to NPS requesting a 2017 brown trout workshop. Stakeholder Concerns AZDGF recommends to immediately offramp Fall HFEs and to hold a stakeholder workshop to determine the root causes of the increases in BT, the risks associated with an expanding BT population to a quality RBT fishery in Lees Ferry and the recovery/conservation of humpback chub and other native fish down river, the pros and cons of different management options to address those risks, and the research needs to support more informed decisions moving forward. [6] Zuni Governor Panteah's Letter to Acting Secretary's Designee Regarding Brown Trout removal in Lees Ferry Reach Letter from GCDAMP Angling Representatives on Brown Trout Removal Planning LTEMP BiOp Triggers for Trout Removals at the LCR (LTEMP BA Appendix D) Tier 1 Trigger – Early Intervention Through Conservation Actions: 1a. If the combined point estimate for adult HBC (adults defined ≥200 mm) in the Colorado River mainstem LCR aggregation; RM 57-65.9) and Little Colorado River (LCR) falls below 9,000 as estimated by the currently accepted HBC population model (e.g., ASMR, multi-state). -OR- 1b. If recruitment of sub-adult HBC (150-199mm) does not equal or exceed estimated adult mortality such that: Sub-adult abundance falls below a three-year running average of 1,250 fish in the spring LCR population estimates, or Sub-adult abundance falls below a three-year running average of 810 fish in the mainstem Juvenile Chub Monitoring reach (JCM annual fall population estimate; RM 63.45-65.2). Tier 1 Trigger Response: Tier 1 conservation actions listed below will be immediately implemented either in the LCR or in the adjacent mainstem. Conservation actions will focus on increasing growth, survival and distribution of HBC in the LCR & LCR mainstem aggregation area. Tier 2 Trigger - Reduce threat using mechanical removal if conservation actions in Tier 1 are insufficient to arrest a population decline: Mechanical removal of nonnative aquatic predator will ensue: If the point abundance estimate of adult HBC decline to <7,000, as estimated by the currently accepted HBC population model. Mechanical removal will terminate if: Predator index (described below) is depleted to less than 60 RBT/km for at least two years in the JCM reach and immigration rate is low (the long term feasibility of using immigration rates as a metric still needs to be assessed), -OR- Adult HBC population estimates exceed 7,500 and recruitment of sub-adult chub exceed adult mortality for at least two years. If immigration rate of predators into JCM reach is high, mechanical removal may need to continue. These triggers are intended to be adaptive based on ongoing and future research (e.g., Lees Ferry recruitment and emigration dynamics, effects of trout suppression flows, effects of Paria River turbidity inputs on predator survival and immigration rates, interactions between humpback chub and rainbow trout, other predation studies). Other Stuff A Review of the Effects of Flow on Brown Trout A telemetry study showing that fall floods trigger upstream spawning migrations in brown trout. Environmental unpredictability rules the autumn migration of brown trout (Salmo trutta L.) in the Belgian Ardennes Advances in Invertebrates and Fish Telemetry, Volume 130 of the series Developments in Hydrobiology pp 263-274 Hasegawa, K., N. Ishiyama, H. Kawai. 2014. Replacement of nonnative rainbow trout by nonnative brown trout in the Chitose River system, Hokkaido, northern Japan. Aquatic Invasions. Vol. 9 Issue 2, p221-226. 6p. Study showing that late summer floods may be advantageous for brown trout recruitment. S.D. George, B.P. Baldigo, A.J. Smith, and G.R. Robinson. 2016. Effects of extreme floods on trout populations and fish communities in a Catskill Mountain river. Freshwater Biology. "The divergent responses of brown trout and rainbow trout populations to the summer flood could be explained by competitive interactions. Brown trout are autumn spawners, whereas rainbow trout are spring spawners, and thus, YOY brown trout emerge earlier, are larger and may outcompete YOY rainbow trout (Gatz, Sale & Loar, 1987; Strange et al., 1992 ). Conversely , the autumn spawning of brown trout increases the risk of egg loss if autumn or winter floods occur. Several investigations showed that YOY brown trout or brook trout were generally more numerous than YOY rainbow trout except during years when floods scoured the eggs of the autumn spawners (Seegrist & Gard, 1972; Strange et al., 1992; Warren et al., 2009 ). " [7]