8114

• UCREFRP Catalog Number: 8114
• Author: Nesler, T. P.
• Title: Five-year Stocking Plan for Endangered Colorado River Fish Species in Colorado.
• USFW Year: 1998.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

contribute to dispersal behavior in Age 2-3 Colorado pikeminnow, the upstream dispersal of
late-juvenile/early adult Colorado pikeminnow observed by Osmundson et aI. (1997), or the
selection of home ranges are unknown. Experience with stocking Colorado pikeminnow
young-of-the-year in riverine habitat in the San Juan River (SJRB Biology Committee (1998
draft) demonstrated no large-scale downstream evacuation similar to that observed in Kenny
Reservoir by Trammell et al. (1993). With more rigorous monitoring in place, the
opportunity will be present to learn more about the movements, disposition, and ultimate
contribution of these displaced fish to the system. The presence of adult populations of
Colorado pikeminnow in these river reaches will provide the opportunity to assess factors
such as water supply diversions, instream barriers, availability of spawning habitat in
associated canyon reaches, larval driftldispersal mortality, and recruitment with respect to
needed recovery actions.

Effects of Survival Rate and Modifications to Stocking

The stocking approach used in this plan uses multiple fish sizes per species in two
seasons to permit an evaluation of the most effective combination in terms of survival of
stocked fish. If the survival rate used in Table 4 is similar to that experienced by the stocked
fish in the wild, and each stocking combination of fish size and season experienced the same
survival, implementation of the full stocking design would result in a significant exceedance
of the target fish/mile objective. Tables 5-7 demonstrate expected numbers of juvenile and
adult fish in the river for each species for each year from the first year of stocking for a ten-
year period based on various size-season scenarios.

For razorback sucker (Table 5), adult fish/mile in the river with full implementation
of all size/ season stocking combinations would range from 83 % of the target in year 5, to
362 % in year 7, to 205 % in year 10. Estimated adult razorback biomass would range from
4% of the fish community biomass in year 5 to 18% in year 8 to 10% in year 10. Under
fall only or spring only stocking scenarios using both fish sizes, the maximum exceedance of
the target adult fish/mile is 201 % in year 7 or 8, respectively, and biomass estimates
reaching 10% in those years. Under 8-inch size or 12-inch size stocking scenarios in both
seasons, maximum exceedance of the target adult fish/mile is 181 % in year 8 for both with
the biomass estimate reaching 9 %.

For bonytail (Table 6), adult fiSh/mile in the river with full implementation of all
size/season stocking combinations would range from 82 % of the target in year 4, to 360% in
year 7, to 164% in year 10. Under fall only or spring only stocking scenarios using both
fish sizes, the maximum exceedance of the target adult fish/mile is 200 % in year 6 or 7,
respectively. Under 4-inch size or 8-inch size stocking scenarios in both seasons, maximum
exceedance of the target adult fish/mile is 180 % in year 7 for both.

For Colorado pikeminnow (Table 7), adult fish/mile in the river with full
implementation of all size/season stocking combinations would range from 82 % of the target
in year 5, to 358% in year 8, to 232% in year 10. Estimated adult pikeminnow biomass

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