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Project: Trout Recruitment and Growth Dynamics Modeling

Purpose The purpose of this project is to provide statistical modeling support to address high priority science questions related to the effects of Glen Canyon Dam operations on the rainbow trout fishery downstream of Glen Canyon Dam. This project is in support of the Glen Canyon Dam Adaptive Management Program’s three-year workplan (Triannual Workplan; TWP) between fiscal year (FY) 2025 and 2027 (https://www.usbr.gov/uc/progact/amp/amwg.html).

Background The Department of the Interior’s Long Term Experimental and Management Plan (LTEMP) identified potential Glen Canyon Dam high flow experiments (HFE) to improve conditions for fishes, benefit the food base, and improve sediment conditions and rebuild sandbars (U.S.

Department of the Interior, 2016). The LTEMP also establishes goals for the rainbow trout fishery downstream of Glen Canyon Dam, which includes maintaining a healthy, high quality recreational fishery while limiting downstream emigration into Grand Canyon National Park.

Some experiments originally proposed to limit rainbow trout recruitment in Glen Canyon (trout management flows; TMFs) may not occur during FY2025-27; however, new flow actions are being proposed and analyzed to suppress warm-water nonnative species reproduction that may also influence population dynamics of trout and other species (Bureau of Reclamation, 2024). It is likely that extrinsic factors such as dissolved oxygen (DO) and temperature variation are influencing trout growth rates and that more monitoring across years with and without HFEs is needed to determine if there is a measurable effect related to this type of flow and others.

With impending changes in basin-wide water availability and water management decisions, understanding how temperature and flow variability interacts with other extrinsic or intrinsic factors to influence trout population dynamics can help inform management strategies to meet LTEMP goals. Therefore, it is essential that the influence of different types of flows be evaluated on behalf of both rainbow trout and brown trout in the FY 2025-27 TWP. The project elements proposed herein are driven by six overarching research questions that apply to both rainbow and brown trout.

A multi-reach mark-recapture sampling design was established between the Glen Canyon Dam and Lees Ferry, with two sub-reaches, each with an assigned 3-km length (sum 24% areal coverage). These reaches are sampled with 2-passes 4 times per year (January, April, June, November). Trout (and potentially other species) will continue to be marked with a passive-integrated transponder (PIT) tag, and recapture data will be analyzed to estimate demographic parameters using appropriate mark-recapture models. We will also continue to monitor DO

140G0325Q0167Amd01 Page 3 of 5 levels in the Lees Ferry reach to understand how temporal and spatial variation relates to trout growth, body condition, and demographic rates.

Scope of Work

Salmonid Modeling Hypotheses and Science Questions

Using mark-recapture modeling methods, the project will address science questions identified below, through analysis of data collected as described above. This list of science questions places emphasis on changing environmental conditions and introductions of brown trout, because of the relatively unclear risk posed by this species to rainbow trout, new expansion of warm-water nonnative species, and recent declines in both trout populations in Glen Canyon.

1) What are the effects of changing conditions downstream of Glen Canyon Dam (i.e., DO, water temperature) on trout recruitment, growth, and survival?

2) What are the effects of flow experiments and other management actions (removals or flow management to suppress warm-water nonnative species) on trout population dynamics?

3) What controls rainbow and brown trout dispersal from Glen Canyon downstream into Marble and Grand canyons?

4) What factors control the quality of the rainbow trout fishery, and how does electrofishing capture efficiency influence interpretation of rainbow trout fishery metrics?

5) How do expansions of warm-water nonnative fish species influence trout population dynamics?

6) What factors regulate brown trout population dynamics in Glen Canyon, and what is the management efficacy of control actions?

7) How is climate change likely to impact the rainbow trout fishery below Glen Canyon Dam in short- and longer-term periods?

8) Are certain operations of Glen Canyon Dam more conducive than others to allow long-term coexistence of a high-quality rainbow trout fishery with downstream native fish species?

Methods Modeling approaches will vary by question and will be determined as investigators proceed through the analyses of mark-recapture data. The contractor will possess the knowledge and

140G0325Q0167Amd01 Page 4 of 5 expertise to contribute towards analysis of data, to address the science questions above, while also conducting quarterly analysis of mark-recapture data to provide estimates of rainbow trout life-stage specific abundance, survival, growth, and body condition.

Technical Requirements Analysis of mark-recapture data quarterly (following January, April, June, and November sampling trips) and production of estimates of rainbow trout life-stage specific abundance, survival, growth, and body condition. Data collected in the field by GCMRC staff will be provided to the contractor after each monitoring event. These estimates must be produced by the contractor within 60 days of each monitoring event and provided to the project officer.

Outcomes and Products Quarterly analysis of mark-recapture data would be needed between fall 2025 through September 2027 to provide estimates of rainbow trout life-stage specific abundance, survival, growth, and body condition (i.e., withing 60 days following January, April, June, November sampling trips).

We anticipate completing analyses of data and development of models for salmonid populations to estimate the efficacy of ongoing management actions and improve capacity to predict impacts to fish populations from future management actions and changing environmental conditions, including the introduction and expansion of warm-water nonnative fish populations.

In collaboration with GCMRC staff, the contractor would be required to support completion of multiple peer reviewed journal article(s), and a presentation of results at the GCDAMP annual reporting meetings and at other scientific meetings related to brown trout population abundance, efficacy of the NPS incentivized brown trout harvest program, rainbow trout population dynamics as related to experimental flows and other drivers, and integrated models to predict rainbow and brown trout recruitment and outmigration (e.g., Korman and others, 2021).

Personnel and Collaborations The overall project lead for this project is the project officerat GCMRC who specializes in population dynamics, quantitative ecology, and decision science. Other collaborators include staff from the Arizona Game and Fish Department, and others affiliated with GCMRC.

References Cited

Bureau of Reclamation, 2024, Glen Canyon Dam Long-Term Experimental and Management

Plan—Draft Supplemental Environmental Impact Statement: U.S. Department of the Interior, Bureau of Reclamation, Upper Colorado Basins, Interior Region 7, https://www.usbr.gov/uc/DocLibrary/EnvironmentalImpactStatements/GlenCanyonDamLon g-TermExperimentalManagementPlan/20240207-Draft-GCDLTEMP-SEIS_508.pdf.

https://www.usbr.gov/uc/DocLibrary/EnvironmentalImpactStatements/GlenCanyonDamLong-TermExperimentalManagementPlan/20240207-Draft-GCDLTEMP-SEIS_508.pdf https://www.usbr.gov/uc/DocLibrary/EnvironmentalImpactStatements/GlenCanyonDamLong-TermExperimentalManagementPlan/20240207-Draft-GCDLTEMP-SEIS_508.pdf

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Korman, J., Yard, M.D., Dzul, M.C., Yackulic, C.B., Dodrill, M.J., Deemer, B.R., and Kennedy, T.A., 2021, Changes in prey, turbidity, and competition reduce somatic growth and cause the collapse of a fish population: Ecological Monographs, v. 91, no. 1, e01427, p. 1-20, https://doi.org/10.1002/ecm.1427.

U.S. Department of Interior, 2016, Glen Canyon Dam Long-Term Experimental and Management Plan final Environmental Impact Statement (LTEMP EIS): U.S. Department of the Interior, Bureau of Reclamation, Upper Colorado Region, National Park Service, Intermountain Region, online, http://ltempeis.anl.gov/documents/final-eis/.

https://doi.org/10.1002/ecm.1427 http://ltempeis.anl.gov/documents/final-eis/

References Cited