Shared Fishery Goals for the lower 

Colorado River – NPS/AGFD ▪ Maintaining a quality recreational Rainbow Trout fishery in Lees Ferry ▪ Maintaining healthy populations of all native fish (including Humpback C

Razorback Sucker) populations in the lower Colorado River 
–

Background ▪ AGFD stocked Lees Ferry Since 1964 ▪ Last Stocked in 1998 ▪ In 2006, Game and Fish received a NOI to due from 

CBD to halt proposed stockings 

▪ Based on jeopardy for humpback and razorback sucker ▪ Population status was 3000-5000 ▪ No compliance in place 

▪ Today Game and Fish needs to stock 

▪ Poor catch rates and low abundance angler days down 

and business’ closing and guides suffering 

▪ Better data than in 2013 (out migration) ▪ Humpback Chub population status exceeding 11,000 
Comprehensive Fisheries Management Pl

2013 

▪ Resulted in BO – adverse affect – no incidental take established ▪ Would not result in Jeopardy for Humpback Chub or Razorback Sucker 
Parameters Objective Guideline Strategies if Objectives 

OBJECTIVE - Maintain a healthy population of Rainbow Trout at Lees Frecreational fishing. 

Recruitment Rainbow Trout ≤ 6 inches compose 

20% - 50% of the Lees Ferry population as determined by fall electrofishing 

 Stocking  Trout Management  HFEs 

Abundance Rainbow Trout electrofishing 

CPUE exceeds 1 fish per minute (all sizes of trout) 

 Stocking  HFEs  Change in regulatio

OBJECTIVE – Provide a quality trout fishing experience with catch frequency with the Blue Ribbon status of the fishery. 

Angler Catch Rate 

Angler catch rate ≥ 1 Rainbow Trout per hour 

 Stocking  HFEs  Change in regulatio
OBJECTIVE – Grow quality sized trout that are available to the angler, consiste

Ribbon status of the fishery. 

Angler Catch Quality 

10 Rainbow Trout 

≥ 14 inches 

caught by the angler in a 10-hour day, at least one 

≥ 20 inches 

Maintain trout condition factor 

≥ 1 

during the summer months. 

 Food base enhancem Trout Management F Change in regulation

OBJECTIVE – Avoid catastrophic failure of the trout population, and establish pemergency recovery from population loss. 

Water Quality Dissolved Oxygen 

≥ 5 mg/l as 

measured at outflow from GCD. 

 Flow manipulation  Temperature Contro Use of river outlet tu

Catastrophic If failure of multiple age classes is 

 Stocking 

Failure of documented by electrofishing and 

 Translocation of wild 

Population <0.25 trout per hour is documented 

in creel surveys, mitigation will be necessary. 

Colorado River downFerry 




Proposed Action 

▪ AGFD plans to stock 13,000 triploid Rainbow Trout annually between Ap

and October 15th 2021 
Joint Probability

P(A and B and C)=P(A)*P(B)*P(C)

A is defined as outmigration rate

B is defined as evacuation rateC is defined fish prey evacuated is an Humpback Chub

Upstream probability of Humpback Chub

Predation

Downstream probability of 

Chub Predation

P=0.00015943 P=0.000049896

The probability that a stocked triploid Rainbow Trout will not ingest a Hum

is 99.99984 and 99.99995 for the upstream and downstream reaches 

respectively.
Quantifying an estimate of ingested

Humpback Chub from trout stocking

Nt= IP*Np*f. (Yard et. al. 2011)

Year Upstream (Nt) Downstream (Nt) Combined (Nt)

2017 0.016 0.013 .029

2018 0.055 0.043 .0982019 0.056 0.044 .102020 0.057 0.045 .122021 0.058 0.046 .14
Coordination timeline to date 

▪ Discussed for over 2 years with NPS ▪ Notified via conference call on April 

4th 

▪ Letter sent notifying NPS, USFWS – 

April 21st 

▪ Planned stocking on May 18th ▪ NPS responded on May 15th with 

concerns 

▪ Call with ADWR on May 15th ▪ AGFD held stocking on May 16th for a 

minimum of 30 days 

▪ Call with Basin states June ▪ Coordination meeting Jun

NPS, Reclamation, USFWS 

▪ Multiple Coordination Call

14th to July 18th 

▪ Impact Analysis sent to Ba

for comments on July 9th a

▪ Webinar conducted with B

on July 25th. 

▪ Comments accepted and 

to date. 
Conservation Measures: 

1. Due to the hypothesis that out-migration may be a factor driven by den

stockings will not exceed more than 4,000 triploid Rainbow Trout stomonth. 

2. Although, the stockings are not expected to result in take and much le

population level declines, other variables (e.g. invasive species, flow opimpaired food base, and temperatures) may result in declines to the pHumpback Chub. If the population declines to below an estimated 750individuals, then the stocking actions will cease until the population of Chub increases back above 7500 adults. This “off-ramp” is consistent previously agreed to Rainbow Trout mechanical removal triggers.