9498

• UCREFRP Catalog Number: 9498
• Author: Nesler, T. P.
• Title: Stocking Plan for Endangered Coloraod River Fish Species.
• USFW Year: 2001.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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Another consideration in maintaining population numbers and biomass of Colorado
pikeminnow is the biomass of available prey fish species. From Anderson (1997), a prey fish
biomass for the Palisade to Rifle reach of the Colorado River was estimated for the main channel
based on electrofishing results for fish < 300 mm in length, and for the backwater habitat based
on July 1994 seine results. The average main channel biomass for prey fish species was estimated
at 119 kg/mi. Main channel prey species were dominated by flannelmouth sucker, bluehead
sucker, roundtail chub, and white sucker. For backwater habitat in this reach, a prey fish
population estimate was extrapolated from the number of fish sampled, the backwater area
sampled, and the estimated total backwater area based on 53 backwaters recorded and measured
in the 52.6 mile reach.

The biomass of this population was estimated by partitioning based on the relative
abundance of each species, the fish size components for each species < or > 150 mm in length,
and calculating the weight of each size component using length-weight relationships calculated in
Anderson (1997) for each species. An average weight of 3 gm for a 64 pun fish (based on data
in Car lander 1969) was used for the biomass calculation for fathead minnow. This resulted in an
estimate of 539 kg/ha for 3.9 ha total of backwater habitat, or 40 kg/mi. Backwater prey species
were dominated by flannelmouth sucker, bluehead sucker, roundtail chub, white sucker, and
fathead minnow. A further extrapolation was made to estimate a mainchannel shoreline biomass
for prey species based on an assumptions that this component would be composed of small-bodied
minnow species, would not be effectively sampled by the mainchannel electrofishing technique
used by Anderson (1997), and would equal only 10% of the biomass estimate for backwaters.
This resulted in an additional prey fish biomass of 74 kg/mi. Combining the biomass estimates
for these three components of the prey fish community available to adult Colorado pikeminnow
resulted in a total prey fish biomass of 233 kg/mi in the Palisade to Ri..fJ.e reach. The biomass of
500 adult Colorado pikeminnow in this reach would equal about 11 percent of the available fish
prey base biomass in this reach.

For the Gunnison River, Burdick (1995) showed a similar number of fish collected in
backwaters-22,988 in 1992 and 23,918 in 1993 versus 22,659 in Anderson (1997). Backwater
area sampled by the two studies showed Burdick (1995) sampled 3,391-4,446 m2 in the Gunnison
River compared to 6,261 m2 by Anderson (1997) in the Colorado River. Because of these
similarities, it is assumed the pikeminnow/prey biomass ration would aIso be similar for the
Gunnison River.

For each river reach, achievement of the stocking objectives would result in a stocked
adult population of 575 adult fish aged 7-9, and approximately 1,700 fish distributed over 150
river miles of three reaches in the Upper Colorado River subbasin. This includes the population
of 650 fish estimated for the currently occupied reaches of the Upper Colorado River in Colorado
and Utah. The population of adult fish distributed over three river reaches would represent one
presumptive genetic population in the Colorado and Gunnison rivers.

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