Tracking Natal Origins of Brown Trout In Grand Canyon 

 1

Through Otolith Microchemistry 

Michael Akland 

Karin Limburg 

Brian Healy 

William Pine III 
2

Many collaborators! 
 

 

Brown Trout In 

Grand Canyon 

• High rate of piscivory could have 

potential impact on native fish 

• Prior to 2013 - found in mainstem, 

but primary source was thought to 

be Bright Angel Creek 

• Conservation efforts have aimed to 

suppress them to benefit natives 

• Bright Angel Creek1 source 

suppression (2012-Present) 

Things changed... • Range expansion2 2013

-17 

• Pop. In Glen C. increasing since 

20143 

• Today – 20-year lows, very rare 

canyon-wide – wider recruitment 

1 - Schelly et al., 2017; 2- Healy et al., 2022; Runge et al., 2018 

BioWest, Valdez and Ryel (1995) 

Runge et al. 2018 
 

 

 

 

 

 

 

 

Background 

All that change... 

Goals of Research – Retrace the Past 

• Address previous hypotheses regarding expansion/invasion: 

• Observed fish in Glen Canyon either evaded detection while being reared or 

moved into Glen Canyon from elsewhere (1996-2012) – Runge et al. 2018 

• Inhibiting access to primary spawning areas (weir) + fall HFE’s contributed to 

upstream straying to Glen Canyon – Healy et al. 2022 

• Elucidate if invasion of Glen Canyon came from Bright Angel Creek 

• Compare natal origins of fish captured during years of invasion (2013-

2017) to post-invasion (2018-2022) 

• Inform/improve suppression effectiveness 

4 
 

 

- -

Theory 

Understanding Natal Origins With Otoliths 

Laser Transect 

• Calcium carbonate “ear-stones” 

• Grow throughout life 

• Incorporate elements into structure 

• Physiological (growth rate, ontogeny, etc.) 

• Environmental (ambient concs/movement) 

• Brown trout remain in natal stream during 

1st year of life1 

• Otolith core = natal period = origin2 

• We can use YOY otolith core chemistry to 

predict/categorize where adults were born 

• 55Mn, 63Cu, 88Sr, and 138Ba 

5 

1 Jonsson & Jonsson 2002;2 Mikheev et al, 2020 
 

 

 

 

Specimen Collection – Multiagency effort

(thanks to NPS, USGS, AZGFD) 

Otoliths – from 217 fish 

• Young-of-year – known origins: recruitment loci (N = 49) 

• Adults—unknown origins (N=168) 

• Glen Canyon to Pearce Ferry, and tributaries 

GLC 

TP 

BAC 

Young-of--year 

capture locations 

6 
 

 

Create Baselines from YOY otoliths Input adult otolith core chemistry Predicted Origin 

Mainstem Colorado % 

Bright Angel Creek % 

Tapeats Creek % 

 

 

 

 

 

 

 

 

 

Methods: Determining Natal Origins 

Create natal origin chemistry 

categories from YOY – assumed 

to be captured at their origin 

(Linear Discriminant Analysis) 

ID adult core chemistry: 

Determine likelihood that 

each adult originated in 

each natal origin 

(LDA probability) 

1. Sort/Predict Natal Origins 

Reject any below 70% 

probability 

2. Break up by capture location 

and era 

(during or after invasion) 
Results: Natal Origins with otoliths 

• Each rearing loci was distinct 

• 152 origins successfully predicted –to 

one of the three YOY sources 

• 16 “unsuccessful” – ambiguous chem 

• No relation to mainstem origins 

• Originated in unknown tributary 

• Mainstem vs Glen Canyon = 

Natal origin vs capture location 

8 

 
Results: 

Natal Origins 

• Invasion (2013-2017) 

• Glen Canyon: 

• 90% mainstem origin 

• 10% from Bright Angel 

• Marble Canyon: mixing 

• 47% mainstem origin 

• 30% Bright Angel 

• LCR Confluence area: no mainstem 

• Bright Angel: 

• Mostly Bright Angel origins 

• One mainstem fish 

• Western GC – low catch, mixed 

Predicted Natal Origin 

 

 

 

 

 

2018-2022

9 
Results: 

Natal Origins 

• Post-Invasion (2018-2022) 

• Glen Canyon: 100% mainstem origins 

• Marble Canyon: low numbers - mix 

• LCR Confluence area: no data 

• Bright Angel: 

• 77% Bright Angel origins 

• Lower reaches – lots of mixing 

• Western Grand Canyon: mixing 

• Every natal origin is found here! 

Predicted Natal Origin 

10 

2018-2022
 

 

 

 

 

 

 

Background 

What does this tell us about the invasion? 

• Recruitment within mainstem isn’t new 

• Large 10+ y/o fish captured in BAC and GLC with 

mainstem origins born 2003-2008 

• Specific area within mainstem? Can’t say. 

• Invasion of Glen C. + Marble C. was from multiple 

sources – mostly fish from within the mainstem 

• Fish found near LCR 2013-2016 mostly from 

Bright Angel Creek 

Likely brown 

trout sources 

circa 2009 

11 
 

 

 

- - –

What is means 

What does this tell us about the present? 

• Mainstem-origin fish are prevalent (relatively) 

• Found in most river reaches 

• Stray to BAC and Tapeats to spawn 

• Fish found in WGC are from all loci – mixing area 

• No eveidence of straying from BAC and Tapeats 

to Glen Canyon 

• One tributary fish found in Marble C. in April 2022 

12 1 Jonsson et al., 2001; 2 Limburg et al., 2003; 3 Yard et al. 2011 
What is means 

Some conclusions... 

• Observed fish (pre-invasion) in Glen Canyon evaded detection 

while being reared AND additional fish moved into Glen 

Canyon from elsewhere 

• Initial increases in GLC were potentially due to exceeding an Allee 

affect threshold through immigration (supporting Healy et al. 2022) 

• Inhibiting access to primary spawning areas + fall HFE’s 

contributed to upstream straying – Healy et al. 2022 

13 
What is means 

Some conclusions... 

• Expansion within mainstem was likely already

underway by 2013 

• Mainstem origin fish were not a minority in Marble and

Glen canyons 

• As far back as this analysis goes, BNT have

exhibited mixed natal origins 

• Contributions of each loci to overall population are

unclear 

• Brown trout are highly adaptive, and mixed natal

origins makes them likely to persist in GC 

14 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Many thanks 

Dr. Karin Limburg – SUNY ESF 

Dr. Brian Healy - USGS 

Dr. Bill Pine – UFL 

Deb Driscoll – SUNY ESF 

Dr. Bob Schelly – NPS 

Emily Omana-Smith - NPS 

Rebecca Koller – NPS 

Kerri Peterson - BOR 

State University of New York: ESF 

National Park Service – Grand 

Canyon 

Bureau of Reclamation 

US Geological Survey: Grand 

Canyon Monitoring and Research 

Center - Morgan and Mariah 

Arizona Game & Fish Department

– David Rogowski 

American Southwest 

Ichthyological Researchers 

Ray, Karen, JD, Nathan, Monika, 

Taryn, Ryan, Skye, Chris, Ed, Sue, 

Jeff, and many other fish folks 

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Questions? 

16 
 

 

 

 

 

 

Mainstem origin, 

captured in GLC 

BAC emigrant 

captured in 

mainstem 

Early trib 

emigrant – left at 

age-0 

Tributary 

emigrant + stayed 

in Tapeats after 

spawning season 

(captured in 

March) 

17 
Including Nankoweep Creek Rainbow Trout 

18 
 

 

Nankoweep Creek Rainbow Trout + 

Havasu Bluehead Suckers 

19 
 

 

Early Emigrant Fish 

Born in unknown tributary 

20 
Nankoweep Creek Rainbow Trout + 

Havasu Bluehead Suckers 

21 
 

 

Methods: Timing Emigration from Tributaries (otoliths) 

Methods 

• Strontium proven proxy in GC1 

• Manganese increases seasonally 

• Overlay on photos, confirm age of emigration 

22 

1 - Hayden et al. 2013; Limburg et al. 2013 

Sr of Brigh t Angel Winter Summer Sr of Colorado 
 

Laser Transect

Results: 

When do fish emigrate from natal streams? 

• 23% at age-0 

• 77% of fish emigrate at age-1 

• No evidence of emigration 

past age-1 

• 64% emigrated in spring 

• 27% emigrated in fall 

• Small portion in summer and 

winter 

35/66 : 31/66 

23 
 

By Length: 

Outer laminae concentrations of mercury 

Results 

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