Green Sunfish –

Status and Trends in the 

Western Grand Canyon

Brian Healy- Native Fish Ecology and Conservation Program, Grand Canyon National Park

David Ward- Grand Canyon Monitoring and Research Center, U.S. Geological Survey

Kirk Young- Arizona Fish and Wildlife Conservation Office, U.S. Fish and Wildlife Service
Acknowledgements

• Pilar Wolters, USFWS

• Mike Yard, GCMRC

• Emily Omana Smith, Melissa Trammell, Bob Schelly, NPS

• Brandon Albrecht, Ron Kegerries, Justin Handtke, BIO-WEST, Inc.

• Susan Wood, ASIR, Inc.

• Tim Walsworth, Phaedra Budy, and the USU Fish Ecology Lab
Outline

• Background

• Green sunfish distribution, ecology, life history 

• Ecological impacts

• Temporal and spatial trends in occurrence in Grand Canyon

• “Hotspots” and possible sources

• Potential for expansion – limiting factors

• Relative risk to native fishes

• Potential management and monitoring options
Background – Green Sunfish Range

• Mississippi River Basin, Hudson Bay, 

Great Lakes, Gulf of Mexico

• Reference: Pam Fuller, Matt Cannister, 

and Matt Neilson, 2020, Lepomis

cyanellus Rafinesque, 1819: U.S. 

Geological Survey, Nonindigenous 

Aquatic Species Database, Gainesville, 

FL.
Green Sunfish Ecology

• From Fishes of Arkansas (Robison and 

Buchanan 1984)- “....tolerance of a wide 

range of ecological conditions, 

particularly to extremes of turbidity, 

dissolved oxygen, temperature, and flow. 

It is also a pioneering species, readily 

populating new bodies of water and is 

among the first fishes to repopulate 

streams after droughts.” 

• Photo credit: www.fieldherpforum.com
Habitat and Ecology

• Tolerant to wide range of 

temperatures- Near freezing to 35 °C

• Spawning 

• 19 - 30°C

• Males build and guard nests

• Prolonged spawning period

• Morphology – suited for slow velocity 

habitats and altered flow regimes

• Photo – green sunfish on nest, © Alan 

Marshall 2007
Habitat and Ecology- continued

• Drought conditions – advantageous (Rogosch et al. 2019)

• Crowding into limited habitat

• Intensifies competition & predation

• High spring flow disadvantage? 

• Monsoon flooding - potential 

displacement or interrupted 

reproduction? 

• Flooding may facilitate dispersal

• Photograph of a green sunfish 

removal effort, from Bogan et al. 

2019
Green Sunfish in the Upper Basin

• Occur in off-channel ponds, 

backwaters, wetlands, canals and 

ditches with emergent vegetation –

also native fish habitat

• Uncommon in main-channel areas, 

where temperatures are suitable 

and warm 

• Sampling efficiency?

• Photo of Skippers Island near 

Grand Junction, from Google Earth
Green Sunfish as an Invasive Species

• Rapid colonizer

• Varied diet – prey on or compete with larval/juvenile fish (Ehlo et al. 2017)

• Responsible for extirpations or 

suppression of native species (examples):

• First-order streams of the Piedmont, N. 

Carolina (Lemly 1985)

• California roach (Moyle and Nichols 

1974)

• Gila chub predation in Arizona – eliminating recruitment (Dudley and Matter 2000)

• Potential adverse impacts on juvenile 

Colorado pikeminnow survival (Karp and Tyus 1990)
Lab studies of Colorado 

River predatory fishesRainbow Trout

From: Ward and Morton Starner. 2015. 

Effects of water temperature and fish size on 

predation vulnerability of juvenile Humpback 

chub to rainbow and brown trout. 

Transactions of the American Fisheries 

Society 144: 1184-1191.
Lab studies of 

Colorado River 

predatory fishesBrown Trout

From: Ward and Morton Starner. 2015. 

Effects of water temperature and fish size on 

predation vulnerability of juvenile Humpback 

chub to rainbow and brown trout. 

Transactions of the American Fisheries 

Society 144: 1184-1191.
Lab studies of Colorado 

River predatory fishesSmallmouth Bass

• This is the same type of data for 

smallmouth bass. In this case the size of 

the predator is varying, and 3 different 

sizes of prey are shown. But the results 

are similar and the curves are very flat.

• From: Laura Tennant, MS Thesis, 2018
Lab studies of Colorado 

River predatory fishesGreen sunfish

This is the same type of 24-hour predation 

trial in the laboratory at 20 C. The curve is 

very different. Why? All of the humpback 

chub are 100 % vulnerable to predation if 

green sunfish can fit them in their mouth –

but as soon as they are too big to fit in the 

mouth then predation vulnerability rapidly 

goes to zero. This is very different than all 

the other predators examined, and indicates 

that green sunfish are a very effective, very 

aggressive predator. Behaviorally small chub 

are not able to escape this predator if they fit 

into the mouth of a green sunfish.
Why worry about Green Sunfish?

• Consume larger prey relative to 

their size

• Aggressive/group hunting behavior

• Small size allows them to access 

prey in shallow, near-shore 

environments

• Highly fecund

• Spread with flood events

• Typically overtake natural systems
What are the trends in Grand Canyon?

• Grand Canyon, Colorado River data 

only

• 2020 captures include BIO-WEST, Inc., 

GCMRC data through August (n=77; 

preliminary data – may not be allinclusive)

• Catch NOT standardized by effort –

but consistent in recent years
Where are they captured in Grand Canyon? 

(includes tributaries - adjacent RM)
Where are they captured in Grand Canyon? 

(includes tributaries - adjacent RM)
Map showing locations of larger Green sunfish 

captures within Grand and Glen canyons

• Green sunfish have been 

captured, from upstream to 

downstream, at:

• -12 mile slough in Glen Canyon

• Little Colorado River in Grand 

Canyon

• Around Fall Canyon (river mile 

212)

• River mile 243
Hotspot – Glen Canyon (-12 mile)

• Continued green sunfish 

production since at least 2015

• Removal efforts planned 
Hotspot – Little Colorado River

• Critical humpback chub population

• Concern - dispersal from upstream sources: Upper LCR watershed, -12 mile 

Slough, Lake Powell

• Slow-velocity, vegetated habitats

• Flooding and associated turbidity may limit green sunfish (continued drought)

• CO2 may limit dispersal from Upper LCR Watershed
Hotspot – Kanab Creek

• Monitored ~twice/year via seining -

reproduction in 2020

• Subject to extreme flood events

• Watershed extends in Southern Utah
Hotspot – River Mile 243

• Inundated at higher flows

• Humpback chub present

• In 2020 sampling event: ~50-60

green sunfish 

• ~27°C
Will the Colorado River support large 

numbers of green sunfish?

• -12 mile slough – rapid/explosive 

reproduction noted

• Green sunfish minimum spawning 

temperature ~19 ̊ C- temperatures 

in the slough rarely go below this
Will the Colorado River support large 

numbers of green sunfish?

Little Colorado River

• Little Colorado River –

reproduction?

• Green sunfish minimum 

spawning temperature ~19 ̊ C
Will the Colorado River support large 

numbers of green sunfish?

Kanab Creek

• Kanab Creek – reproduction 

noted, 2019-2020

• Green sunfish minimum 

spawning temperature ~19 ̊ C
Will the Colorado River support large 

numbers of green sunfish?

National Canyon and Spencer Creek

• Temperature suitable?

• Green sunfish minimum 

spawning temperature ~19 ̊° C
Potential to expand?

• Potential limitations:

• Colorado River temperatures

• Fluctuating flows

• Turbidity may limit predation

• Limited backwater/off channel 

habitat

• Uncertainties –

• Future river temperatures?

• Sources?

• Is monitoring adequate?

• Electrofishing may be less effective
Map of Current Monitoring Areas in Grand 

Canyon

• “GRTS” sampling locations as 

part of a razorback sucker study 

are numerous from river mile 89 

to river mile 280

• Juvenile chub monitoring west 

study focuses on the river 

around mile 212
Possible control actions – next steps?

• Potential tools

• Mechanical removal

• Chemical control in high density areas

• Best options

• Source identification and control

• Review and expand hot spot monitoring if necessary- Consider patchy 

distribution and gear efficiency

• Prioritize efforts relative to risk (e.g., rainbow and brown trout)
References

• Bogan, M. T., R. A. Leidy, L. Neuhaus, C. J. Hernandez, and S. M. Carlson. 2019. Biodiversity value of remnant pools in an 

intermittent stream during the great California drought. Aquatic Conservation: Marine and Freshwater Ecosystems 29:976–989.

• Dudley, R. K., and W. J. Matter. 2000. Effects of small green sunfish (Lepomis cyanellus) on recruitment of Gila chub ( Gila intermedia ) in Sabino Creek , Arizona. The Southwestern Naturalist 45:24–29.

• Ehlo, C. A., A. Llc, S. A. Avenue, M. J. Saltzgiver, T. E. Dowling, P. C. Marsh, and B. R. Kesner. 2017. Use of molecular techniques to confirm nonnative fish predation on razorback sucker larvae in Lake Mohave , Arizona and Nevada. North American Journal of 

Fisheries Management 146:201–205.

• Fuller, P., M. Cannister, and M. Neilson, 2020, Lepomis cyanellus Rafinesque, 1819: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=380, Revision Date: 

8/14/2019

• Karp, C. A., and H. M. Tyus. 1990. Behavioral interactions between young Colorado squawfish and six fish species. Copeia 1990:25.

• Lemly, A. D. 1985. Suppression of native fish populations by green sunfish in first-order streams of Piedmont of North Carolina. 

Transactions of the American Fisheries Society 705:705–712.

• Moyle, P. B., and R. D. Nichols. 1974. Decline of the native fish fauna of the Sierra Nevada foothills, Central California. American 

Midland Naturalist 92:72.

• 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 10:1–19.

• Ward and Morton Starner 2015. Effects of water temperature and fish size on predation vulnerability of juvenile Humpback chub to rainbow and brown trout. Transactions of the American Fisheries Society 144: 1184-1191.