Alternative 2: Moderate Intensity Fisheries Management
Alternative 2 includes implementation of conservation measures for endangered fish species, but also addresses issues raised by Traditionally Associated American Indian Tribes and some anglers related to euthanizing non-native fish species, and involves moderate intensity management actions and less mechanical control of non-native fish than Alternative 3.
All actions described in Alternative 1 would be included in Alternative 2, in addition to action items described below:
Translocations
Humpback chub translocations were included among conservation measures in the most recent Biological Opinion for GCD operation (USFWS 2011). This Alternative element includes collection of larval or juvenile HBC from the Little Colorado River, rearing in a hatchery facility until large enough to mark with individually identifiable tags, and release to tributaries or downstream areas of the Colorado River in GCNP.
If abundance of other native fish, such as bluehead or flannelmouth sucker, declines, suckers may be translocated, or collected as larvae from tributaries and reared in a hatchery prior to release following development of a translocation and augmentation plan. The release plan would incorporate methods described for humpback chub relocations and NPS 2006 Management Policies direction for genetics management (Section 4.4.1.2, NPS 2006a). Additional interagency and tribal consultation and planning and compliance may be necessary prior to these activities.
Collection and Rearing of Fish
Humpback chub would be collected from the Little Colorado River during summer prior to monsoon onset (early to mid-July) or, if summer collecting trips are cancelled or ineffective due to flooding, a secondary collecting period would occur in fall (October or November). Trips would last approximately five days, and consist of six to eight biologists and volunteers. Equipment and staff would be flown into and out of previously established camps and landing areas via helicopter14 (up to four flights to/from camps from Salt Helipad near the head of Salt Canyon). Collections would target young-of-the-year fish using netting methods.
Young-of-the-year humpback chub collected from the Little Colorado River would be flown from collection areas and transferred to a hatchery truck for delivery to a USFWS-approved hatchery facility. Fish would be quarantined and treated for parasites and diseases, following standard hatchery procedures, and held until approximately four inches (in five to ten months), then tagged and released the following spring or summer. The number of individuals collected per year would depend on population viability modeling (Pine et al. in press), genetic augmentation needs, and hatchery rearing capacity. Initially (the first five years, due to initial hatchery capacity), approximately 500 individuals would be collected for translocations per year.
Translocation/Release of Fish
In late spring or early summer (the year after collection), tagged humpback chub would be flown from the NPS South Rim helibase in aerated coolers to release sites. Initially (the first five years), Havasu, Bright Angel, and Shinumo Creeks would be targeted for translocations; however, other tributaries, or areas of the mainstem Colorado River where sufficient habitat is determined to exist, may be considered for future translocations. Mainstem HBC aggregations (Valdez and Ryel 1995) would be targeted for translocations. Translocations in Shinumo Creek would be expanded to include another 0.6 mile (one km) of stream below White Creek to increase existing population size. Humpback chub translocation to Bright Angel Creek would only occur if brown trout were reduced from 2010 baseline estimates by greater than 80%. Brown trout would be monitored and maintained at or below 20% of the baseline population size by additional removals as needed. Following USFWS guidance (USFWS/ DNFHTC 2010), initial translocations of at least 200 fish would occur to each release area for a minimum of five years, and up to ten years (one generation, minimum 1,000 fish), depending on fish availability for translocation.
Adaptive Strategies for Management, Outcomes, and Triggers Translocation
Various Outcomes from humpback chub translocation into tributaries or mainstem areas would be anticipated. For humpback chub, three potential HBC Outcomes would be expected.
- HBC 1: Establishment of a second spawning and recruiting population in the mainstem or tributary
- HBC 2: Sufficient survival and growth to provide a rearing (“grow-out”) opportunity to augment the local mainstem aggregation
- HBC 3: Failure of at least 20% of HBC to survive in the creek or adjacent mainstem aggregation for at least one year
The NPS and its cooperators would strive to meet HBC Outcome 1, which would contribute the most toward humpback chub recovery goals; however, HBC Outcome 2 would result in benefits to humpback chub. HBC outcomes 2 and 3 would be evaluated five years following initial translocations. However, it may require ten years or more (Pine et al. in press) to determine whether HBC Outcome 1 has been observed.
Indicators for evaluation of potential humpback chub outcomes are:
- A: Retention of translocated humpback chub over the first year
- B: Similar or increased juvenile survival relative to the Little Colorado River and mainstem Colorado River near the Little Colorado River inflow
- C: Similar or increased growth rates relative to the Little Colorado River and mainstem Colorado River near the Little Colorado River inflow
- D: Contribution to and retention of translocated fish to an adjacent mainstem aggregation
- E: Evidence of successful reproduction (presence of larval or young-of-year fish)
- F: Evidence of recruitment to mature size
HBC Outcome 1 would be achieved if monitoring detected conditions described in HBC Indicators E or F. HBC Outcome 1 would trigger additional humpback chub translocations to maintain genetic integrity, consistent with genetics management principles found in DNFHTC (USFWS 2010) and Mills and Allendorf (1996). In summary, a minimum adult population of 200 fish would be maintained, with at least ten migrants per generation or it would be necessary to introduce ten additional adult fish into the population to maintain genetic integrity (Mills and Allendorf 1996). Based on observations made during translocations at Shinumo and Havasu Creeks (unpublished NPS data 2009-2012; Spurgeon 2012), and the number of fish remaining and surviving to adult size, between approximately 45 and 1,000 total fish may need to be released in translocation sites over a generation (a humpback chub generation is approximately ten years) (R. Valdez, SWCA consultations, personal communication to B. Healy/NPS, August 3, 2012).
HBC Outcome 2 would be achieved if monitoring detected conditions described in HBC Indicators A, B, C, or D for translocated populations. HBC Outcome 2 may be considered intermediate and expected to lead to HBC Outcome 1, which would be determined through continued monitoring. Alternatively, the particular translocation project for which HBC Outcome 2 would be observed for ten years may be considered a humpback chub rearing opportunity, in which case a minimum 200 adult fish would be maintained.
HBC Outcome 3 would signify translocation failure in partially or fully meeting FMZ objectives, and translocations to a particularly tributary or other mainstem area would cease. If at least HBC Indicator A had not been achieved consistently after five years of translocations, and no other HBC Indicators had been observed, then translocations to a particular area would be considered a failure (HBC Outcome 3), the translocation project would be re-evaluated and discontinued, if appropriate, following additional interagency and tribal consultation.
Monitoring
A key component of this project element and adaptive management is monitoring translocated humpback populations’ survival, individual fish growth, and reproduction and recruitment. Further, monitoring and augmentation of translocated populations may be necessary to maintain genetic integrity (USFWS/DNFHTC 2010).
Access to monitoring sites, ideally up to three times per year, would follow GCNP’s Minimum Requirement Analysis process to minimize impacts to Proposed Wilderness. For tributary translocations, netting and/or electro-fishing may be necessary in both tributary and adjacent mainstem areas to determine humpback chub survival. Monitoring and continued control of non-native rainbow trout would also be employed during monitoring efforts at Shinumo Creek at least twice per year including a winter, one-week, raft-supported electro-fishing trip (February). No multiple-pass electro-fishing would occur in tributaries containing resident or transient populations of bluehead or flannelmouth sucker or humpback chub during April, May, or June to coincide with spawning periods. A temporary, previously installed fish detection system would be maintained for three more years to test release methods on humpback chub retention, and monitor movements of translocated fish at Shinumo Creek.
Lower Colorado River FMZ Razorback Sucker Augmentation and Adaptive Management
Uncertainty exists as to whether GCNP habitat is suitable to maintain a self-sustaining razorback sucker population. Recent GCNP detections of razorback sucker tagged and released in Lake Mead, and their return to the lake suggests razorback sucker may use project area habitat at least occasionally. Further, as razorback sucker spawn and recruit in Lake Mead’s Colorado River Inflow area, it is also possible populations will expand on their own into Lower Colorado River FMZ (RM 179.2 Lava Falls downstream to Lake Mead).
A three-year study, begun in 2010, in Lake Mead’s Colorado River Inflow confirmed wild razorback suckers were spawning and recruiting into the Lake Mead fish population (Kegerries and Albrecht 2011). Recent data confirms razorback sucker sonic-tagged in Lake Mead have moved into the Colorado River FMZ at Quartermaster Canyon (R. Keggeries et al., Bio-West Inc, unpublished data). In addition, an untagged, ripe male was captured in the Colorado River FMZ in October 2012 (A. Bunch, AZGFD, personal communication). In consultation with the Lake Mead Razorback Sucker Workgroup, a razorback sucker management strategy was developed (Valdez et al. 2012a). The release of sonic-telemetry-tagged razorback sucker is proposed, along with additional inventories to determine whether Colorado River FMZ habitat is suitable for razorback sucker.
Potential outcomes related to razorback sucker suitability studies in Colorado River FMZ over the life of the plan are:
- RBS 1: Razorback sucker are present and reproducing in Colorado River FMZ
- RBS 2: Razorback sucker are present in substantial numbers in Colorado River FMZ, but are not reproducing or recruiting in the Colorado River
- RBS 3: Suitable razorback sucker habitat is available, but few individuals are present and no reproduction occurs
Depending on RBS outcomes, elements of the phased adaptive management strategy would be implemented:
- Phase I: Year 1-3: Conduct fish community survey of Colorado River FMZ including larval fish, large-bodied fish, and sonic-tagged razorback sucker to describe/quantify fish community and identify potential spawning sites
- Phase II: End of Year 3:Evaluate data collected years 1-3 to identify
- whether sonic-tagged fish remained in the area
- razorback sucker presence/absence
- whether the Lake Mead population is expanding into Grand Canyon
- Phase III: Year 4:If Phase II results show substantial numbers (25%) of sonic-tagged razorback sucker remain, or razorback sucker presence (larvae or other unmarked adults), or evidence of Lake Mead’s population expanding into Grand Canyon, then establish a long-term monitoring program for razorback sucker in Colorado River FMZ, and
- Suspend plans to augment razorback sucker in Colorado River FMZ if evidence of increasing abundance of razorback sucker or expansion of Lake Mead population into Colorado River FMZ (RBS Outcome 1) or
- Convene established workgroups (see Valdez et al. 2012a) to recommend continuing augmentation plan and implementation when there is a continued presence of Lake Mead razorback sucker but no evidence of expansion into Grand Canyon (RBS Outcome 2)
Non-native Fish and AIS Introduction Prevention, Detection, and Control
Outreach via development and placement of signs at likely public access points, website development, interpretive talks, and other materials or practices would be expanded to prevent accidental or purposeful introduction of new non-native aquatic species in the project area. Outreach efforts would also encourage harvest of all non-native fish species by anglers when appropriate.
Current fish and invertebrate monitoring conducted by cooperating agencies would continue at likely introduction areas in the Glen Canyon Reach, the Little Colorado River, and in the mainstem Colorado River upstream of Lake Mead. However, detection programs would be added or expanded to include other geographical areas considered high-risk pathways for non-native species introductions. Monitoring programs in tributary watersheds that include lands beyond the NPS boundary, and thus may be sources for new introductions including Havasu Creek and Kanab Creek would be added, with monitoring taking place on NPS-managed lands. Havasu Creek would be monitored using multiple fish-sampling gear types up to twice per year in conjunction with humpback chub monitoring (no additional trips), and Kanab Creek’s lower sections would be monitored early summer and fall to detect non-native species in conjunction with river trips supporting monitoring efforts at Shinumo Creek or other tributaries. Fish monitoring efforts would be expanded in Colorado River FMZ to detect invading or expanding populations of non-native fish from Lake Mead in conjunction with efforts to monitor for razorback sucker (see Table 2.4).
When new introductions of non-native fish species are encountered, depending on level of threat and magnitude of response needed, control measures may take place through Emergency Response procedures (see Chapter 2, Emergency Rapid Response, Non-native Fish and AIS, Alternative 2).
To the extent possible, NPS would coordinate with other management agencies, tribes, and/or land owners in watersheds that extend beyond GCNP or GCNRA to evaluate risk of new introductions from those areas and develop cooperative efforts to deter future invasions.
- Removal of Incidental Captures:
Under all Action Alternatives, unless specific research objectives warrant tagging and release, all high-risk non-native predatory fish species captured during monitoring efforts project-wide would be euthanized and put to beneficial use, when possible, according to consultation with Traditionally Associated American Indian Tribes. These species include brown trout (Salmo trutta), catfish species (including bullheads), bass and sunfish (Centrarchidae), striped bass (Moronidae), cichlids (Cichlidae), perch and walleye (Percidae), and other rare non-native species not previously detected in GCNP or the Glen Canyon Reach (e.g., burbot, Lota lota).
Tissues or bony parts of high-risk non-native fish removed incidental to monitoring efforts would be analyzed to determine source when possible and when funding is available. For example, the microchemistry of humpback chub otolith bones has been used to determine natal origin in Grand Canyon (Hayden et al. 2012). Additionally, the NPS would engage resource managers (AZGFD, USFWS, Tribes) or landowners in the watersheds immediately adjacent to GCNP and GCNRA to prevent future introductions of non-native species. Information sharing would assist managers in targeting areas if/when expanded or emergency control efforts are needed.
- Targeted Angling, Non-native Fish Removal Trips
Non-native fish removal excursions would be implemented through a non-commercial administrative permit, when necessary, to remove cold-water non-native fish, primarily rainbow trout using angling equipment, primarily in Marble Canyon and downstream (Paria Riffle to approximately RM 60). Other rare non-native species may be captured and removed as well.
- Emergency Rapid Response to Detected Expansion or New Non-native Species Introduction
As in Alternative 1, and consistent with NPS Director’s Order-12 (2001, Section 2.14, Emergency Actions), for emergencies including
- discovery of expansion in distribution or abundance of an existing high-risk non-native species, particularly in sensitive areas for native fish (e.g., Havasu Creek or Little Colorado River Inflow areas); or
- new detection of a rapidly spreading aquatic invasive species or non-native fish species
The Superintendent could approve a temporary, short-term, targeted removal effort to treat known occurrences of the new threat using mechanical methods including angling, electro-fishing, and passive (i.e., trap nets) or active (e.g., seining) netting. Simultaneously, additional planning and compliance may be considered if a long-term response, such as maintenance control using a variety of methods, would be necessary.
- Comprehensive Brown Trout Control
NPS fisheries biologists would expand past trout reduction activities (weir and tributary electro-fishing, NPS 2006c) in Bright Angel Creek to the Bright Angel Creek Inflow area of the Colorado River. Both brown and rainbow trout and other non-native fish encountered would be removed during these efforts to meet goals and objectives identified in Chapter 1. Experimental mechanical control methods would be implemented for five consecutive years and then re-evaluated to determine whether reduction targets and native species objectives had been achieved. Integrated project activities would include
- Multiple-pass electro-fishing using two motorized electro-fishing boats for up to 20 nights, sufficient to reduce trout by at least 80% between Zoroaster and Horn Creek rapids (approximately five miles of the Colorado River). A single trip is proposed during fall
- Weir (fish trap) installation downstream of Phantom Ranch during spawning seasons for rainbow (fall/winter/spring) and brown trout (fall) to capture mature adults entering Bright Angel Creek to spawn. The weir may be installed in late summer or early fall and extend into spring months (April) depending on ability of equipment to withstand higher spring snowmelt runoff flows
- Backpack electro-fishing by an eight-person crew in all fish-bearing waters in the Bright Angel Creek watershed (approximately 13 miles of stream) for between approximately 70 and 100 continuous days over fall and winter. One remote camp and helicopter transport16 of gear may be necessary near Bright Angel Canyon and in Bright Angel Creek headwaters
- Removing brown trout incidentally captured throughout the project area during monitoring (see Comprehensive Brown Trout Control), and encouraging harvest of brown trout by anglers. Through adaptive management, anglers may be encouraged to harvest brown trout via public outreach activities, changes in harvest regulations, or other means. Additional consultation may be necessary
- Mechanical removal (electro-fishing, angling, netting, etc.) of brown trout may be employed in other tributaries or mainstem areas if natal origin studies conducted during the first five years indicate other areas are sources of brown trout in Grand Canyon, and project-wide declines in brown trout are not observed initially. Efforts would be focused where individuals are aggregating and populations can be feasibly controlled and suppressed using mechanical removal methods (additional planning and compliance may be necessary)
Monitoring would occur annually to determine project success during and following the initial five-year effort. Monitoring metrics include abundance, size structure, and recruitment of native and non-native species, as well as apparent survival of bluehead sucker (may require additional sampling occasions).
Depletion monitoring using electro-fishing gear would be the initial focus for both the tributary and Colorado River; however, additional netting may be conducted in both areas in coordination and consultation with the AZGFD, USFWS, and GCMRC to improve native fish survival or abundance estimates.
- Adaptive Management, Outcomes, and Triggers
Non-native fish control is proposed in Alternative 2 to benefit GCNP native fish species (see Chapter 1 GCNP Goal 2); however, the response of native fish to non-native control actions, and the level of control necessary to elicit a positive response in native populations is difficult to predict and variable (reviewed by M. Trammell, unpublished report 2005). While measures are taken to reduce likelihood of injury to individual native fish during electro-fishing, fish injuries or deaths can and do occur on occasion. The uncertainty relates to whether benefits to native fish populations of removal of non-native predators outweigh potential effects of injury to individual fish through electro-fishing and subsequent handling prior to release. Additionally, environmental factors (e.g., climate, flooding, drought, fire, etc.) not influenced by active management may have an overriding influence in driving native fish population dynamics in project area waters. Potential outcomes for non-native fish removal activities for both existing native and non-native fish in tributaries are:
- NNF 1: Native fish survival, abundance, and recruitment is maintained or increases as non-native fish species abundance is reduced in tributaries
- NNF 2: Native fish survival, abundance, and recruitment declines as non-native fish species abundance is reduced in tributaries
- NNF 3: Non-native fish abundance does not decline in tributaries with control method implementation
Non-native fish and native bluehead sucker and speckled dace population dynamics would be monitored in all tributaries where non-native fish control actions would be implemented. A monitoring program is currently in place (see Alternative 1) for these species in Havasu, Shinumo, and Bright Angel Creeks. Flannelmouth sucker are not generally found as residents in tributaries outside the Little Colorado River, and thus, monitoring efforts in tributaries may be focused on other native species (speckled dace and bluehead sucker). Flannelmouth sucker trends in GCNP and the Glen Canyon Reach are monitored during AZGFD’s and USGS-GCMRC’s mainstem electro-fishing trips on the Colorado River between Lees Ferry and Lake Mead, and during Glen Canyon electro-fishing monitoring efforts. Only abundance indicators (Table 2.6) are proposed for monitoring speckled dace due to lack of feasible methods to assess individual survival for the species. Outcomes for each non-native control project would be assessed after five years, using indicators described in Table 2.6.
- A: Measures of abundance or density (e.g., relative abundance: number of fish/unit area) or trend in catch rates (i.e., catch-per-unit-effort)
- B: Survival (estimated via mark-recapture)
- C: Recruitment (either number of new fish tagged or percent of population less than 100 or 150 mm)
- D: Size structure (i.e., numbers of fish at each size class)
Fisheries managers would strive for NNF Outcome 1 for each project, and if achieved, non-native control projects may proceed at an appropriate level of maintenance control effort, which could include continued or reduced effort.
If after five years, monitoring indicates that NNF Outcome 2 or 3 has occurred, non-native fish control projects would cease and be re-evaluated for at least one year. Data and trends from previous years and newly emerging science and technologies would be reviewed, and methods may be adapted for the future to achieve NNF Outcome 1. Translocations of other native species may be considered if it is determined species declines are severe, and augmentation is needed. Following review, and depending on the most appropriate course of action proposed, additional planning and compliance may be necessary.
During the evaluation phase of non-native fish control projects, NPS would share data, results, and future plans with collaborating agencies, Traditionally Associated American Indian Tribes, stakeholders, and interested public.
- Feasibility Study for Use of Chemical Fish Control Methods
Data to assess use of chemical fish control methods were not available during preparation of this CFMP EA. Aside from stream dewatering, chemical piscicides (fish poisons) may be the only means to ensure complete removal of non-native fish species from streams (Moore et al. 2008). During implementation of initial five-year mechanical non-native fish removal efforts for brown trout, additional data would be collected to determine chemical use feasibility, and possibly barrier installation for trout control in Bright Angel Creek and other tributary streams. Data collection for invertebrates, water quality, distribution of native and non-native fish species and non-target organisms, and physical habitat would be guided by published NPS guidance for the use of chemical piscicides (see Moore et al. 2008). Future potential use of chemical fish control methods would also be informed through interagency and tribal consultation. Additional NEPA documentation, planning, and accompanying compliance would be necessary if chemical means for controlling non-native fish in GCNP are considered in the future.
- Beneficial Use of Non-native Fish Removed
The NPS would employ a beneficial use policy for all non-native fish removed from the project area following consultation with Traditionally Associated American Indian Tribes. Beneficial use policies would be employed to reduce disease-transfer risk from one location to another, consistent with state and federal laws and statutes. Non-native fish euthanized during non-native control efforts would be put to a beneficial use, to the extent possible, and within limits of health and safety for human consumption, fed to captive wildlife at wildlife rehabilitation centers, or recycled into the ecosystem through returning fish into the water following euthanization.
Glen Canyon Rainbow Trout Management
- Sterile Trout Experimental Stocking
NPS 2006 Management Policies (NPS 2006, Section 4.4.3) allow for exotic species stocking for recreational fishing in altered water bodies when allowed by law, such as in GCNRA’s enabling legislation, when the activities will not result in unacceptable impact to park natural resources or processes. Sterile trout would not reproduce, and could be stocked in an experimental context to maintain GCNRA fishing opportunities. Experimental stocking of sterile, triploid rainbow trout (stocking plan to be determined) could be initiated, specifically if one or more elements are met:
- Recruitment (wild young fish) is low for multiple years: rainbow trout recruits (fish less than six inches) comprise less than 20% of the fish community during AZGFD fall monitoring events for more than three consecutive years; or
- AZGFD electro-fishing estimates of relative abundance are less than one fish/minute for two consecutive years of fall sampling; or
- If angler catch rates in Glen Canyon Reach decline to less than or equal to 0.5 rainbow trout/hour, and average size less than 14 inches for two consecutive years; in other words, if trout density and angler catch rates are very low, but average fish size is very large, then goals for the fishery would have been met and no sterile triploid trout stocking would be necessary
Sterile rainbow trout stocking would be limited to the Glen Canyon Reach. Stocking would likely continue until electro-fishing relative abundance estimates and/or angler catch rate criteria in Table 2.7 are met. Relative abundance of all fish caught would be greater than one fish/minute or angler catch rates exceeded 0.5 fish/hour for two consecutive years. Depending on conditions that may lead to a potential decline in the fishery in the future, sterile trout may be stocked for a number of years until the fishery objectives are met (Chapter 1), at which time stocking would potentially cease until triggers are met, and stocking would be re-initiated. Stocking could be reinitiated as appropriate, following GCNRA’s rainbow trout adaptive management strategy described in the next paragraph.
A stocking and monitoring plan including number and size of sterile trout stocked would be developed before sterile trout stocking would be implemented. At a minimum, sterile fish released would be marked to assess their performance. Short- and long-term Outcomes, monitoring metrics, and an adaptive management framework would be defined and determined. Depending on the final stocking and monitoring plan, additional planning and compliance may be necessary. For example, experimental stocking of triploid rainbow trout would include extensive marking of hatchery fish to monitor multiple metrics including, but not limited to, return to anglers, movement, growth, and survival. If marked fish are not returned/captured by anglers as intended or are found moving out of the stocking-approved area (i.e., into Marble Canyon/Little Colorado River area), stocking would be reassessed. Reassessment could include altering location of stocking, size of fish stocked, timing of stocking, and number of fish stocked. If stocking was deemed sustainable at a given level (i.e., acceptable catch rates, minimal impacts outside the fishery), it would continue. Essentially, the experiment would be successful if, through triploid trout stocking, fisheries objectives could be maintained and an adequate control of the rainbow trout population could be achieved while minimizing impacts on resources outside the fishery. If, through monitoring of stocked fish, there is minimal return to anglers or unacceptable levels of impact on resources outside the fishery, stocking would cease.
Extirpated Species
- Extirpated Species Reintroduction Feasibility Studies
Feasibility studies for extirpated fish species reintroduction would be conducted over the life of the plan, and if potential exists, additional NEPA, ESA, NHPA and associated planning and compliance would be initiated prior to reintroduction plan development. Prior to summer 2012, razorback sucker had not been detected in the project area since the 1990s, and was considered extirpated. However, since 2012, five tagged razorback sucker were found upstream of Pearce Ferry Rapid (River Mile 280) including four detected in GCNP upstream of River Mile 277.4 (B. Albrecht, BIO-West, Inc., personal communication), and another individual captured in October 2012 near Spencer Canyon (RM 246) (A. Bunch, AZGFD, personal communication). Thus, razorback sucker is no longer considered extirpated (see Chapter 3).
At this time, only Colorado pikeminnow would be prioritized for reintroduction feasibility studies. Potential hybridization between roundtail chub, bonytail, and humpback chub preclude introduction of additional chub species (Gila sp.) in humpback chub habitat. Pikeminnow reintroduction feasibility studies would primarily rely on expert opinion, literature reviews of habitat requirements, and evaluation of existing biological and physical data (e.g., food base, fish community). However, a field survey may also be required to assess physical habitat or collect biological data.
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