9716

• UCREFRP Catalog Number: 9716
• Author: Stone, D., and P. Sponholtz.
• Title: Translocation of young-of-year humpback chub above Chute Falls in the Little Colorado River, AZ, 2003 Interim Report.
• USFW Year: 2003.
• USFW - Doc Type: U.S. Fish and Wildlife Service
• Copyright Material: NO

based on the upper LCR being narrower and more canyon-bound, thereby making it more
susceptible to scouring flows than the lower corridor.
In the December 6, 2002 Biological Opinion concerning the proposed experimental
releases from Glen Canyon Dam and removal of nonnative fish from the Colorado River
(CR) a conservation action was identified to relocate small humpback chub (50-100 mm TL,
YOY) from <3 RKMs above the LCR-CR confluence, upstream to above Chute Falls (>14
RKMs) to offset any potential detrimental impacts from the proposed project. This size
class and area of capture were suggested to offset the large-scale loss of YOY humpback
chub that currently occurs during high flow events. Once they grow larger than 100 mm, it
is thought that they are better able to avoid predation and withstand cold mainstem
temperatures. It was hoped that this translocation would increase the numbers of younger
humpback chub that recruit to adulthood by allowing them an opportunity to exploit the high
food resources, warm-water temperatures, and reduced competition/predation by fewer
large-bodied fishes that are associated with this area. Ultimately, if this experiment is
successful, it will supply a viable action to expand humpback chub distribution within the
LCR into currently unoccupied yet suitable rearing habitats and provide additional security
while other successful recovery actions are being implemented in the CR or one of its
tributaries.
Our experimental design was developed to meet four major objectives: 1) determine if
transplanted humpback chub can survive and remain above Chute Falls; 2) determine if
humpback chub grow above Chute Falls given the increased food availability compared to
downstream areas but potential detrimental impacts that higher CO2 may have on their
basal metabolisms; 3) determine if any transplanted YOY humpback chub will recruit to
adulthood above Chute Fall; and 4) determine if a humpback chub spawning population will
develop above Chute Falls. This interim report details the methodology and results
gathered during the reconnaissance trip, translocation trip, and first monitoring trip of this
two-year experiment. At this time, we can only address the first two objectives.
METHODS
Reconnaissance Trip
We conducted a reconnaissance trip above Chute Falls from July 7-11, 2003 to collect
baseline ichthyofauna and water quality data and locate potential helicopter landing sites
that were above the typical flood zone where humpback chub could be released (Figure 1).
It was critical to assure that this area was truly unoccupied by humpback chub before
proceeding with translocation.
We deployed 20 baited miniature hoopnets (50 X 100 cm, 10 cm throat, 6 mm nylon mesh),
above Chute Falls from 14.2 to 16.74 RKM for three separate --24 hour hauls. Each net
was baited near it's cod end by attaching a nylon mesh bag (30 x 30 cm, 6 mm mesh)
containing AquaMaXTm Grower 600 for Carnivorous Species (Purina Mills Inc., Brentwood,
MO). All captured fish were identified to species and measured for total length (TL) to the
nearest mm. We released all native fish back into the LCR, but nonnatives were removed
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