U.S. Department of the Interior

U.S. Geological Survey

Fish modelling to support management decisions

Charles B. Yackulic, Grand Canyon Monitoring & Research Center, Southwest 

Biological Science Center, US Geological Survey

H.4 Salmonid modelling

Using data collected by AZGF and TRGD as part of project H

Thanks to Josh Korman, Michael Yard, Mariah Giardina, Jan Boyer and Kim Dibble

Linking water management decisions with fish populations

Funded primarily by USGS, non-AMP

Thanks to Lindsey Bruckerhoff, Drew Eppehimer, Kevin Bestgen, Jian Wang, Kim 

Dibble, Bryce Mihalevich, and Jack Schmidt

Resource Goals: Invasive Species

Annual Reporting

January 10, 2022
Outline

 Brown trout model update.

 Coupled outflow and smallmouth bass model.
Basic modelling framework

• Fit to cpe data 

(2000 – present) 

and markrecapture data 

(2012-present)

• 1 mark-recapture 

site (2012-2016), 

3 sites (2017-

2020), 2 sites 

(2021).

• Gap in markrecapture data 

when culling 

required.
Modelling assumptions

 Seasonal time step.

 Size and seasonal variation in growth and 

survival (but not among years).

 Survival informed by a Lorenzen relationship.

 Capture probability allowed to vary by trip 

and size class (random effect).

 Immigration for large adults allowed to vary 

for each interval (random effect).

 Recruitment varies between years (random 

effect).
Recruitment this year similar to last year

(Preliminary, 

do not cite)
Brown trout adult abundances continue to increase

(Preliminary, do not cite)
Brown trout recruitment, and by extension population 

growth rate (not including immigration), negatively 

correlated to rainbow trout spawner abundance

(Preliminary, 

do not cite)
Recruitment variation drives most, but not all 

variation in brown trout lambdas.

(Preliminary, 

do not cite)
Outline

 Brown trout model update.

 Coupled outflow and smallmouth bass model.
Background

 Smallmouth bass (and other warmwater

nonnatives) are a huge issue in the upper

basin.

 Project focused on developing coupled

smallmouth bass and Colorado

pikeminnow population models.

 Provides some opportunity for learning

that is relevant to Grand Canyon.

(Dibble et al., 2021)
Questions driving development of tool 

for Grand Canyon

 What thermal regimes are suitable for

smallmouth bass to increase (assuming they

are present in sufficient numbers to

reproduce)?

 To what extent do changes in monthly

volumes and/or use of jet tubes alter

predicted thermal regime?
Model framework: Part 1

Inflows –

resample 

2000 to 2020

Evaporation, etc. 

using same 

equations as CRSS

Releases –

user specified

Storage / 

Elevation

Critical 

elevation 

when switch 

to jet tubes

Depth vs. 

water 

temperature 

2000 to 2020

Withdrawal 

depth

Daily 

temperature 

or releases

Delta
Model framework: Part 2

Daily 

temperature 

or releases

Hatch date “summer” water 

temperature

Winter starvation 

days

Lengths of 3 age-0 

cohorts Overwinter 

survival

Minimum 

length

Predicted 

lambda

Other vital 

rates
Baseline

3b

(Preliminary, 

do not cite)

Red traces are ones in which SMB 

are predicted to increase

Gray traces are ones in which they 

are not predicted to increase

The blue line is 2021 temperatures at 

the Lees Ferry gage.
(Preliminary, 

do not cite)

Baseline

Change 

critical 

elevation 

from 

3490 to 

3510
One important uncertainty

 Translating water temperature in depth 

profiles to outflow water temperature as lake 

elevation approaches penstocks.
Baseline

Delta = -15

3b

Delta = -15

(Preliminary, 

do not cite)
(Preliminary, 

do not cite)

Baseline

Delta=-15

Change 

critical 

elevation 

from 3490 to 

3510

Delta=-15
Future work

 Extend predictions downstream.

 Consider improvements to depth to release water 

temperature component.

 Could explore other scenarios.

 Canyon wide model.

 But near term plan is to shift focus back to upper basin.
Questions

cyackulic@usgs.gov