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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5. The Role of Stocking in Management and Recovery

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The primary purpose of stocking endangered fish is to reestablish populations. Whether stocking simply
maintains a presence for the species or establishes self sustaining communities is dependent on the species'
ability to adapt and reproduce under existing environmental conditions. The reintroduction of native fishes
back into their historical ranges seems fairly straight forward, however, we seldom recognize all the factors that
caused their original demise. 'Three decades of stocking endangered fishes has shown that unless these
bottlenecks are identified and adequately addressed, recruitment failure will continue to occur.
Millions of small razorbacks have been stocked in the mainstream and larger tributaries with little or no
success. Predation is undoubtedly a major factor attributing to loses. Studies conducted in the upper basin
have found a similar correlation of size with survival (Burdick 2003). Burdick recommended that only suckers
>20 cm be stocked and that the role of site acclimation and survival be further investigated. Marsh and Brooks
(1989) recommended similar actions in the lower basin nearly 15 years earlier.
During the past decade, more than 85,000 larger (>25 cm) suckers have been stocked in an attempt to
counter predation losses, but unfortunately, survival rates continue to remain low and may be less than 10%.
Survivors have either joined or created new spawning communities. These fish are starting to spawn and while
larvae have been detected, natural recruitment has not. Young natives continue to fall victim to predators.
One of the primary challenges in measuring stocking survival is to recapture adequate numbers of fish.
Unfortunately, this has been difficult due primarily to poor survival. Initial information suggests current
augmentation efforts for the razorback sucker are falling substantially short (> 15%) of expected survival and
repopulation goals. Even less information is available for the bonytail. We simply are unsure whether our
sampling programs are ineffective or the fish simply have not survived.
Poor survival combined by the outcome of the telemetry experiments raises doubt regarding the
performance of hatchery-reared fish and our percei ved notion these communities can co-exist with sport fishes.
After nearly two decades, it appears a reassessment of goals and objectives, as well as the stocking location
and methods being used to rear and reintroduce fish are warranted. This chapter provides some alternative
methods that may increase the likelihood of recruitment and discusses other associated issues.

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Bony tail, Flannelmouth, and Razorback Suckers: Contrasting Survival Stories

The tlannelmouth sucker represents the first successful reintroduction of a native fish in the main stem
Colorado River. Historically they were rare in the mainstem with only five collections documented prior to
1975 (Minckley, 1973). A single stocking of611 tlannelmouths and the thousands of razorback suckers that
were stocked presents an interesting and revealing paradox.
The rapid success of the flannel mouth in view of the stocking failure of razorbacks has prompted biologists
to ask why flannelmouths could survive and produce young when razorback ,suckers have not. Both the
tlannelmouth and razorback are similar in size, color, and shape and evolved in the Colorado River. So why
has the flannelmouth, which was historically rare, out performed the razorback which was once abundant in the
main stem?
The answer may lay in the dramatic physical and biological changes that have taken place in the main stem
river. It also raises some impelling questions regarding stocking philosophies, targeted species, predator/prey
relationships, and the role of physical habitat.

Stocking Comparisons

The first obvious difference in the stocking approaches is the source of the fish. Wild fish taken from the
Paria River were used to stock flannelmouth while bonytail and razorback suckers that were stocked were
produced in hatcheries. The wild suckers undoubtedly possessed survival skills that the hatchery-reared fish
did not. They were accustomed to flow, finding natural foods, and recognizing and avoiding predators. Their

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