U.S. Fish and Wildlife Service’s Response to Westerns concerns over the Humpback chub 

5-year Review 

This document is in response to your email dated December 12, 2012 that contained a discussion 

paper titled “Western Concerns with the Humpback Chub 5-year Status Review.” The U.S. Fish 

and Wildlife Service (Service) recognizes the time and thought that Western Area Power 

Administration (Western) put into developing this document and appreciates the opportunity to 

respond to the concerns Western has identified in the 2011 5-year Review. These discussions are 

particularly relevant given the update on the Humpback Chub 5-year Review scheduled for the 

next Glen Canyon Dam Adaptive Management Technical Workgroup meeting scheduled for 

February 2, 2012. To address your concerns, we have reviewed our thought processes leading to 

the conclusions contained in the 5-year Review and expanded on our rationale as appropriate. A 

5-year Review is not a full compendium of information on a species, but is intended to serve as a 

report card to gage our progress to date in achieving recovery. It is, as with any Service 

document, subject to changes and updates provided by more current data in our attempt to 

provide information with the best and highest scientific integrity. 

Demographic Downlisting Criteria for Humpback chub 

Lower Basin Recovery Unit Criterion 1a/b: The Service indicated that both these criteria were 

“partially met”. However Western cites the 2008 Recovery Goals (which were never finalized) 

which suggest a recovery period beginning in 2003 due to 5 years of increasing populations. 

Western also notes inconsistencies with other Colorado River basin fish, particularly the 

Colorado pikeminnow. In regard to Criterion 1b, Western cites new information from the 

Nearshore Ecology study which has shown high, mainstem juvenile survival together with higher 

population growth in the Little Colorado River. 

In making this determination of “partially met” for Criterion 1a/b, the Service felt that while the 

Age-Structured Mark Recapture model (ASMR) shows a clear upward trend in the Grand 

Canyon population since approximately 2003, there are factors with respect to humpback chub 

demographics throughout the occupied habitat that were still unresolved. At this time, data from 

recent aggregation sampling in the mainstem has shown no definitive increase or decrease in 

those populations away from the LCR. This is of particular importance since critical habitat for 

humpback chub extends nearly 181 miles in the mainstem Colorado River in Arizona, yet 

upwards of 90% of the population is centered in the Little Colorado River and inflow area. This 

disparate distribution is cause for concern given the large watershed above the Little Colorado 

River and the potential for catastrophic loss. 

While we agree that the increases seen in the adult population is the real target, the ASMR has a 

4 year lag time before which population fluctuations in adult numbers are manifested in the 

model output. Therefore, 2-3 years of life history failure could go unnoticed until several years 

later. Criteria that use a more “real-time” measure such as age-3 fish potentially provide a more 

responsive, “real-time” view of how the population is doing in response to different management 

alternatives. The ASMR is a valuable tool but has its limitations, particularly due to ageing 

errors and the resulting assignment of length at age. Its value is increased if these data are 

viewed in conjunction with more real time estimates of the age-3 fish 
In the 2002 Recovery Goals with respect to the Lower Basin demographic criterion the Service 

wrote that “The Grand Canyon population is maintained as a core over a 5-year period, starting 

with the first point estimate acceptable to the Service, such that: a) the trend in adult (age 4+; 

>200 mm TL) point estimates does not decline significantly, and...”. That language directs the 

Service to consider all acceptable population estimates in this determination; not to limit the 

analysis to the most recent 5 years. Although it is not clear in the 2002 version of the HBC 

recovery goals what constitutes estimates acceptable to the Service, based on more recent 

discussions relative to the 2008 draft revisions, the Service intends to accept the ASMR 

estimates and has indicated so in the 5-year Review. Therefore the Service will consider the 

complete dataset (1989 – 2008) of population estimates in their determination of whether 

Criterion 1a has been met or not. Whether one looks at the slope of a trend line through those 

twenty consecutive population estimates or tracks Pradel’s lambda () the overall result would 

indicate a negative trajectory or trend. While the recent trend is very encouraging, the Service’s 

concern and determination is justifiable when the entire data record is considered. 

While recent data from the Nearshore Ecology Study on juvenile survival rates in the mainstem 

is certainly encouraging, we advise that the area subject to project sampling was only a few 

kilometers and caution should be exercised in extrapolating these data riverwide. In addition, 

these data were not available at the time of the 5-year Review and hence were not incorporated 

into the review. 

As part of the ongoing process to revise the 2002 Recovery Goals, all new, available information 

will be incorporated, and the draft recovery goals will be subject to peer and public review prior 

to finalization. This will include information on the distribution of humpback chub given recent 

translocations, and survival rates being generated from the inflow area (Nearshore Ecology 

Study) and the Little Colorado River above Chute Falls. In addition, we wish to refine the 

current minimum viable population (MVP) estimate and have received funding from the Bureau 

of Reclamation to derive this value using captive humpback chub at Dexter National Fish 

Hatchery and Technology Center. Further, we intend to review and if appropriate, revise the 

demographic criteria so that the distribution of the fish in the mainstem and Little Colorado 

River can be more accurately captured. 

The Service cautions Western in applying upper Basin criteria for different fish species to criteria 

used in Grand Canyon for humpback chub. The reason for having definitive criteria specific to 

each basin is because these areas are much different with respect to management, recovery 

potential, and how threats are addressed. Colorado pikeminnow have some redundancy in the 

Upper Basin, providing more flexibility in the demographic criteria. Also as the recovery goals 

for pikeminnow are revised, our intention will be to include all acceptable population estimates 

in any future trend analysis. Grand Canyon is the largest given the high proportion of the total 

population found in the limited area of the Little Colorado River. 

 
Recovery Factor Downlisting Criteria for Humpback Chub to Minimize or Remove Threats to 

the Species

Factor A, Criterion 2: The Service indicated that this criterion had been “partially met”. 

Western felt that the Service’s justification for this determination was unclear given the ongoing 

and planned conservation projects under the 2008 Biological Opinion. Further, Western 

identifies a citation error in this section relevant to the incidental take statement that was 

remanded in September 2010. 

While significant progress has been made on the conservation measures included in the 2008 

Biological Opinion, uncertainty still remains about flow regimes and temperature that create 

“adequate spawning, nursery, and juvenile and adult habitat” per Criterion 2. While the 

conservation measures were designed to help answer these important questions, information to 

definitively resolve habitat and flow relationships for humpback chub is still largely unknown. 

To meet this criterion, we need to have a much better understanding of how flows and 

temperature regulate important habitat aspects for humpback chub. Implementation of the new 

2011 Biological Opinion and the conservation measures contain therein, should further progress 

in this regard. 

The error made regarding the incorrect citation is regrettable but does not change the outcome of 

this criterion determination. The correction will be made in the revision to the Recovery Goals. 

Factor C, Criterion 7: Western requests that the Service clarify what is needed to meet this 

criterion. 

In general, there is a poor understanding of warm water fish dynamics in the Little Colorado and 

mainstem Colorado Rivers. Monitoring programs used by the Grand Canyon Monitoring and 

Research Center (GCMRC) and others are not specifically designed to generate a comprehensive 

picture of warm water species but instead can only provide general trend information. Given the 

logistics associated with sampling difficult areas such as the mainstem Colorado River and the 

sampling frequency of general fisheries surveys, a sudden increase in a warm water species 

would largely go undetected before management efforts could be mobilized to address the issue. 

Further, there is no warm water sampling program in place in the Little Colorado River. Warm 

water species are by-catch during hoopnet monitoring aimed at sampling areas for humpback 

chub and other native fishes. Many warm water species such as channel catfish and carp are not 

susceptible to this method of capture so population levels of these species are unknown in the 

Little Colorado River or the Colorado River. 

To meet this criterion, sampling programs should be in place to better detect rare or hard to find 

warm water species and implementation plans generated on how to address this should these 

species be found. Also a targeted sampling program in the Little Colorado River that focuses on 

sources of warm water nonnatives and their population levels in primary humpback chub 

spawning and rearing areas should be in place and providing information to answer that question 

before this criterion can be met. 

 
Factor C, Criterion 8: Western requests what is needed to meet this criterion. 

GCMRC has repeatedly indicated that reduction via mechanical removal in both brown and 

rainbow trout from 2003-2008 cannot be definitively linked to increases in humpback chub and 

other nonnative fishes. Due to a concurrent increase in river temperatures due to low reservoir 

levels at Lake Powell, the effects of these two factors cannot be separated. Further, there was a 

system-wide decrease in trout populations independent of mechanical removal efforts. 

Mechanical removal of these species in cold water and without a system-wide decrease may not 

be feasible with projected immigration rates that may be encountered under current conditions. 

Therefore, this criterion is only partially met due to the uncertainty that surrounds mechanical 

removal and its apparent effect on humpback chub, particularly under current river conditions 

(high trout populations).