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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we recommend the use of artificial passageways to facilitate the movement of wild Colorado
pikeminnow into the target reaches receiving stocked fish.

The target stocked adult population objective of 1,150 fish at ages seven through nine are
based on the draft recovery goal delisting criteria for abundance of 1,000 fish for the Upper
Colorado River (USFWS 2001a), the survivorship curve estimates in Table 2, plus a 15 % buffer
based on a presumed annual natural mortality of 15 % for adult fish. The 2,680, age 3 +, 150 mm
fish to be stocked annually would be split equally between the upper Colorado and Gunnison
Rivers upstream of the instream barriers that historically defmed the upper boundary of occupied
habitat for Colorado pikeminnow. Assumptions made that influence stocking numbers and target
reaches include:

1) Populations of Colorado pikeminnow extended naturally upstream prior to placement of
the instream barriers within the Colorado and Gunnison rivers, and were comprised largely
of adults, similar to the size and age composition of Colorado pikeminnow populations in
other Colorado tributary streams. Burdick (1995) documented the existence of a remnant
population of adult Colorado pikeminnow in the Gunnison River upstream of Redlands
Diversion Dam. An anecdotal account exists of the capture, by angling, of a 15-inch
Colorado p~eminnow, above Glenwood Springs on the Colorado River (Pressey 1968).

2) The Upper Colorado River reach and the Gunnison River reach are similar with respect
to available habitat and carrying capacity based on similar geohydrology and
predominating native fish communities based on obseived native/nonnative species relative
abundance as described in Burdick (1995) and Anderson (1997). The target stocking
numbers are assumed to be within constraints of existing habitat and carrying capacity.

3) Depletion and extirpation of adult populations above the barriers occurred as the result of
some combination of downstream spawning movements by adults over the barriers, and
prevention of upstream dispersal movement and recruitment by late juvenile or adult fish,
or return migration by spawning adults.

4) As top predator, Colorado pikeminnow numbers and biomass as a percent of the system
should be, and would naturally be low ( < 1 %).

Further, the following species interactions and recovery actions are anticipated:

1) Biomass and production of system occupied by common carp, white sucker, and other
nonnative fish species may be reduced by control efforts, expanding production potential
within the native fish prey base for Colorado pikeminnow.

2) With successful establishment of this species, abundance of other native and nonnative fish
species may be reduced as a result of predation.

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