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

would range from 0.8% of the fish community biomass in year 5 to 3.6% in year 8 to 2.3%
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 7 or 8, respectively, and
biomass estimates reaching 2 % in those years. Under 6-inch size or lO-inch size stocking
scenarios in both seasons, maximum exceedance of the target adult fish/mile is 179 % in year
8 for both with the biomass estimate reaching 1.8%.

The message from these stocking scenarios for each species is that the potential to
exceed the target stocking objectives (overstock) is certainly possible with implementation of
any two or more combinations of fish size and season, if survival rates are similar for each
combination. It is also clear that monitoring survival and numbers of fish/mile is vital to
adjusting numbers of fish to be stocked and modifying the stocking design to the most
effective size and season combination. The estimates of the number of juvenile and adult
fish per mile during and subsequent to stocking are also useful monitoring indices to evaluate
survival and stocking needs.

Recommendations

1) Razorback sucker, bonytail and Colorado pikeminnow should be stocked into the
designated river reaches at the sizes, seasons, and numbers prescribed in Tables 1-3
to meet the objective of a multi-age group adult population at the designated
population abundance level.

2) Monitoring of stocked fish should be initiated immediately after release, and
conducted at a frequency thereafter adequate to determine survival, distribution,
density, and causes for mortality (e.g. predation, starvation).

3) PIT tagging prior to stocking should be applied to Colorado pikeminnow, and batch
marking prior to stocking should be used for razorback sucker and bonytail.

4) Production of hatchery-raised fish and stocking numbers should be modified to
emphasize the most effective size/season combination and to achieve best survival and
post-stocking objectives based on monitoring results, and to minimize potential over-
stocking.

5) Stocking of a given size of fish in a given season in a given reach should be
discontinued if monitoring shows significant abandonment of the target reach via
downstream movement. Monitoring of this displaced cohort of stocked fish should be
continued to document distribution and survival.

19