8174

• UCREFRP Catalog Number: 8174
• Author: Martinez, P. J.
• Title: West Slope Warmwater Fisheries.
• USFW Year: 1997.
• USFW - Doc Type: \
• Copyright Material: NO

RESULTS AND DISCUSSION
My comments on Nonnative fishes in the upper Colorado River Basin and a strategic plan for their
control (Tyus and Saunders 1996) are given in Appendix J. Tyus and Saunders (1996) contended that bag
limits for riverine population of nonnative sport fish could be liberalized in Colorado's western rivers to
facilitate increased angler harvest of predatory species. Furthermore, the Colorado Water Conservation
Board passed a resolution in July, 1996 that included a recommendation to remove bag limits on nonnative
sport fishes within Critical Habitat. My comments on the removal of bag and possession limits for nonnative
sport fish within Critical Habitat in western Colorado are given in Appendix K. During discussions regarding
the bag and possession limit removal before the Wildlife Commission, my research project was committed to
provide an evaluation of the lifting of bag limits on nonnative warmwater sport fishes and resulting benefits
to endangered fishes (Malmsbury 1997). The finalized brochure on nonnative fish control strategies and
warmwater fisheries in western Colorado is given in Appendix L.
Job No. 5: Native/Nonnative Fish Trophic Economic in Riverine Habitats
Job Objective: To estimate trophic impacts of predation by selected nonnative fish fishes and size structures
on selected native fishes under varying programs of nonnative fish control and floodplain
habitat restoration.
Segment Objective 1: No evaluations scheduled under this Job during this segment.
INTRODUCTION
An approach that will be tested under this Job will be the use of stable isotope analysis (SIA) for
food web analysis in the Colorado and Yampa rivers. Stable isotopes represent different atomic weights
(neutrons) of elements. The elements C, N, S, H, and O all have more than one isotope. Isotopic
composition of natural material can be measured with great precision using an isotope ratio mass
spectrometer. The mass spectrometer measures the ratio of light and heavy isotopes in a sample and
compares this value to a standard (Peterson and Fry 1987, Lajtha and Michener 1996).
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Stable isotopes are useful in trophic studies of food webs because the isotopes move with little or
predictable alteration in food chains (Angradi 1994). Typically, the ratio of 13C/12C is used to identify plant
source (habitat-based food dependencies) consumed while the ratio of I INI"N is used to delineate trophic
position of an organism or differences in the lengths of food chains (France and Steedman 1996, Michener
and Schell 1996). Stable isotope ratios reflect the C and N assimilated by organisms rather than simply what
was consumed by an organism (Angradi 1994, Rosenfeld and Roff 1992). Because stable isotopes reflect
material assimilated over a period of weeks or months, they may help overcome several shortcomings of
traditional food habits investigations such as empty stomachs, regurgitated contents, unidentifiable remains
of food items, rapid digestion of key diet components or seasonal shifts in food preference or availability
(France and Steedman 1994).
The use of stable isotopes to track energy provenance in food webs relies on there being distinct
isotopic differences between the sources of material in the environment (France and Steedman 1994, Lajtha
and Michener 1996, Peterson and Fry 1987). Recent literature has debated the utility and accuracy of the
stable isotope techniques for application in lotic environments since the origins and pathways for assimilating
carbon and nitrogen through the foodweb may not be as distinct as in lentic environments (Doucett et al.
1996, France 1996). However, this techniques has been applied in the lower Colorado River Basin and was
found to distinguish between four bases of aquatic secondary production including upland vegetation, riparian
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