U.S. Department of the Interior

U.S. Geological Survey

Humpback chub that spawn in 

the LCR: status and drivers

Annual Reporting for FY16

January 24, 2017

Charles B. Yackulic (U.S.G.S. – GCMRC),

email: cyackulic@usgs.gov
2

• Majority of chubs recruitment in the 

LCR.

• Some proportion of juvenile chub 

leave Little Colorado, and most of this 

outmigration occurs during july – sept. 

of their first year.

• Juvenile chub 

growth is slow in 

the Colorado River 

(little to no growth 

below 12 C). 

Juvenile chub 

survival thought to 

be affected by 

trout.

• Most adults live in Colorado River and migrate back to Little Colorado to spawn, 

small proportion of adults appear to live year-round in Little Colorado.

Basics of Chub Life History around the LCR
Outline

 Juvenile recruitment

 Juvenile rearing in the Colorado River

 Setting a target

 Adult body condition and skip-spawning

 Future steps

LCR recruitment is a large contributor to 

uncertainty in predictions.

Preliminary data. Do not cite.
Abundance (1000s)

2013 2014 2015 2016

| | | | |

0

10

20

30

40

16307 9065 25481 3059

Preliminary data. Do not cite.

Average LCR early july juvenile 

abundance (recruitment) ~ 14K.
Outline

 Juvenile recruitment

 Juvenile rearing in the Colorado River

 Setting a target

 Adult body condition and skip-spawning

 Future steps
How do temperature, 

turbidity, rainbow trout, and 

density dependence affect 

juvenile survival, growth 

and capture?
Model improvements

 Now deal with uncertainty in rainbow trout 

abundance (joint population model).

 Test alternative hypotheses about density 

dependence.

 Two forms of model selection:

 Out of sample prediction.
Preliminary data. Do not cite.
Juvenile humpback chub survival is negatively related to increased rainbow 

trout abundances. This is the most consistent relationship across years.

Preliminary data. Do not cite.
Growth of juvenile chub is higher under warm and turbid conditions.

Growth declines when abundances are greater (density dependence).

Preliminary data. Do not cite.
Temperature is the primary driver of juvenile chub 

detection probability, but rainbow trout also affect chub 

detection.

Preliminary data. Do not cite.
Outline

 Juvenile recruitment

 Juvenile rearing in the Colorado River

 Setting a target

 Adult body condition and skip-spawning

 Future steps
Given our understanding of HBC life-history (and associated uncertainty), what is 

the average annual juvenile survival required to maintain a population of 

7000...and how does this also depend on juvenile recruitment estimates.

Preliminary data. Do not cite.
Outline

 Juvenile recruitment

 Juvenile rearing in the Colorado River

 Setting a target

 Adult body condition and skip-spawning

 Future steps
Preliminary data. Do not cite.
2010-2014

2010-2014

2015-2016

2015-2016

Both smaller and larger adults are spawning less frequently

Preliminary data. Do not cite.
Adult HBC numbers appear stable. 

Preliminary data. Do not cite.
Take home messages

 Adult populations appear stable, however adults 

remain skinny and rates of spawning are low.

 Rainbow trout negatively effect juvenile chub 

survival, however, the effect is modest. They also 

affect chub detection.

 Temperature, turbidity, and density drive growth.

 Juvenile recruitment may determine whether rainbow 

trout management is necessary.
Outline

 Juvenile recruitment

 Juvenile rearing in the Colorado River

 Setting a target

 Adult body condition and skip-spawning

 Future steps
Future steps

 Continue HBC field sampling in LCR and CR, 

including juvenile recruitment estimation.

 Increase use of remote sensing array in both 

CR and LCR and integrate data into our 

population models.

 Explore feasibility of JCM-like sampling at a 

western Grand Canyon site. 
Acknowledgements

 Mike Yard , Josh Korman, Ted 

Kennedy, Mike Dodrill, David Ward, 

Luke Avery, Scott Vanderkooi

 US Fish and Wildlife Service 

 Near Shore Ecology Group

 David Ward, Luke Avery, Michael 

Dodrill and others involved with July 

LCR

 Glen Canyon Adaptive Management 

Group

 Bureau of Reclamation

 Navajo Nation Department of Fish 

and Wildlife