9489

• UCREFRP Catalog Number: 9489
• Author: Mueller, G.
• Title: The Role of Stocking in the Reestablishment and Augmentation of Native Fish in the Lower Colorado river Mainstream ‎(1998-2002)‎.
• USFW Year: 1998-2
• USFW - Doc Type: 03-288,
• Copyright Material: NO

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3. Stocking Risk Assessment

Managers have been stocking native fish in the 10werColorado River for over two decades. The reasons
have varied. The flannelmouth sucker was one of the first stocked (1976). Wild flannelmouth suckers were
captured and translocated for black fly abatement. Some years later razorbacks were stocked for the same
reason. Bonytail were stocked into Lake Mohave to augment an existing population and stocked downstream to
reestablish the species in Lake Havasu. Stocking protocols for the razorback sucker have been similar, to
augment and reestablish populations, but they have also been stocked for mitigation purposes.
The choice of stocking sites has been generally driven by logistics, politics, and convenience. The goal of
stocking Lake Mohave was population specific but sites varied all over the reservoir. The ultimate goal was to
augment existing communities. Fish were stocked adjacent to rearing areas and at common access points. The
same was true for bonytail.
Stocking downstream of Davis Dam has generally depended on formal or infonnal agreements among state
and federal agencies. Federal listing of the razorback sucker, bonytail, and Colorado pikeminnow has caused
its own unique challenges concerning the protection afforded the species under the Endangered Species Act.
Precedents have been set for razorback sucker and bonytml, since both now exist in the river. However,
differences in philosophy and issues pertaining to legal status have prevented the Colorado pikeminnow from
being reintroduced. How these differences will play out only time will tell.
To our knowledge, no attempt has been made to analyze stocking locations for any of the endangered fishes
in the lower basin. The question of what is the most secure reach of river for these fish to my knowledge has
not evaluated. More often than not, fish are stocked at the shortest route between the rearing pond or hatchery
to the closest boat ramp. Documentation of sucker passage through Davis Dam indicates this approach may
not be prudent.
The advent of Global Infonnation System (GIS) programs and data bases provides a robust method of
assessing habitat types. A . simple stocking assessment model was developed as an example of how this
technology could be used to best determine where fish should be stocked to optimize their chances for survival.
Susan Broderick and Debra Callahan (oral presentation 2000) developed a stocking risk assessment for the
lower Colorado River using ArcView GIS, ArcView Spatial Analyst, and ArcView Model builder. The
programs created a visual map that prioritized river reaches based on known survival risks such as: location of
diversions, type of dam withdrawal (surface or hypolimnetic), presence and surface area oflarge backwaters,
length of unobstructed river reach, and recent occurrence of razorback sucker.
They categorized or ranked specific reaches of river using a 1-6 rating system; 1 being poor and 6 being the
best chance for survival. Lake Mead and upper Lake Mohave received the highest ranking, a 6. The reach
below Davis Dam including upper Lake Havasu, received a ranking from 5-6. Lower Lake Havasu
downstream to Parker Dam received a poor rating of 2. The model can be easily modified or updated. Figure
2.1 (fold-out) shows the color coded representation for the reach between Davis and Parker Dams. If you have
any questions, please contact either Susan (303-445-2235) or Debra (303-445-2235).

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