Current Levels of Threats from Non-Native Aquatic Species 

in Glen Canyon National Recreation Area and Grand Canyon 

National Park – An Update to Appendix F from the 

Expanded Non-Native Aquatic Species Management Plan 

Environmental Assessment

Brian Healy

Native Fish Ecology and Conservation Program

Grand Canyon National Park
Outline

• Why assess threat levels?

• Implications of threat level to management

• Process for updates

• 2021 changes and updates by species

• Future and ongoing research highlights
Why assess threat levels?

From NPS Comprehensive Fisheries 

Management Plan (2013):

• Consistent with NPS Director’s 

Order-12, for emergencies including:

• discovery of expansion in distribution or 

abundance of 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 would be considered if 

necessary. 

From the NPS Expanded Non-native 

Aquatic Species Management Plan 

(2019):

• The Proposed Action considers the risk or threat 

associated with potentially harmful non-native 

species as defined in Section 1.2 and as listed in 

Appendix F, Table F-1. 

• Example: Mechanical Disruption of Early 

Life Stage Habitats (Action M1; Tier 2). This 

Tier 2 action would use ongoing and new 

technologies to limit the success of spawning of 

high to very high risk species in known or 

suspected spawning beds. 
Process for Threat Level Updates

• 2021 Update:

• Literature review:

• Changes in distribution or abundance

• Additional published research related to negative effects at different 

scales:

• Individual level – piscivory, competition

• Population level – demographic rates, distribution/abundance, etc.

• Invasiveness – potential to become important threat (life history, etc.)

• Peer review:

• GCMRC, AZGFD, BOR, FWS, NPS

• Revised based on additional information (GCMRC, AZGFD)

• Distributed to stakeholders 
Updates – Smallmouth Bass

• Threat level: 

• No change

• “Very High”

• Update:

• Increased abundance in 

Lake Powell (Pennock & 

Gido 2021)
Updates – Walleye

• Threat level: 

• No change

• “Very High”

• Update:

• Increased abundance in 

Lake Powell (Pennock & 

Gido 2021)

• Closer to Colorado River 

inflow in Lake Powell
Updates – Flathead Catfish

• New addition

• Threat level: 

• “Very High”

• Background:

• Not present in directly 

connected waters

• High piscivory- turbid 

water (Ward & Vaage 2018)

• Reduce native fish 

distribution (Whitney et al. 2014)

• Limited by cool 

temperatures
Updates – Brown Trout

• Threat level: 

• Unchanged

• “Very High”

• Update:

• Additional literature 

(Healy et al. 2020)

• Threat to GLCA rainbow 

trout- predation, 

competition 
Updates – Rainbow Trout

• New addition (GRCA)

• Threat level: 

• “High”

• Background:

• Additional literature 

(Healy et al. 2020, 

Yackulic et al. 2018)

• Threat to native fish, 

humpback chub 

survival, growth
Updates – Green Sunfish

• Threat level: 

• Increase

• “High”

• Background:

• Additional literature 

(Ward & Vaage 2018)

• Condition-dependent, 

drought/climate change 

expansion (Rogosch and 

Olden 2020)
Future Updates - Further Research

• Didymo occurrence

• Crayfish distribution updated; impacts?

• Invasive mollusks

• Egg & larval native fish consumption by common 

carp (D. Ward, GCMRC)

• Plains killifish & humpback chub recruitment

• Brown trout & rainbow trout recruitment (C. 

Yackulic, others, GCMR)

• Rainbow trout & translocated humpback chub vital 

rates (Healy and others – in review)
References

• Healy, B. D., R. C. Schelly, C. B. Yackulic, E. C. O. Smith, and P. Budy. 2020. 

Remarkable response of native fishes to invasive trout suppression varies with 

trout density, temperature, and annual hydrology. Canadian Journal of Fisheries 

and Aquatic Sciences 77(9):1446–1462.

• Pennock, C. A., and K. B. Gido. 2021. Spatial and temporal dynamics of fish assemblages in a desert reservoir over 38 years. Hydrobiologia 0123456789. 

Springer International Publishing.

• Rogosch, J. S., J. D. Tonkin, D. A. Lytle, D. M. Merritt, L. V. Reynolds, and J. D. Olden. 2019. Increasing drought favors nonnative fishes in a dryland river: evidence from a multispecies demographic model. Ecosphere 10(4):1–19.

• Ward, D. L., and B. M. Vaage. 2018. What environmental conditions reduce 

predation vulnerability for juvenile Colorado River native fishes? Journal of Fish 

and Wildlife Management (December 2018).

• Whitney, J. E., K. B. Gido, and D. L. Propst. 2014. Factors associated with the success of native and nonnative species in an unfragmented arid-land 

riverscape. Canadian Journal of Fisheries and Aquatic Sciences 71(8):1134–1145.

• Yackulic, C. B., J. Korman, M. D. Yard, and M. Dzul. 2018. Inferring species interactions through joint mark–recapture analysis. Ecology 99(4):812–821.