9528 ‎(2)‎

• UCREFRP Catalog Number: 9528
• Author: Martinez, P. and N. P. Nibbelink.
• Title: Colorado Nonnative Fish Stocking Regulation Evaluation.
• USFW Year: 2004.
• USFW - Doc Type: Grand Junction, Laramie.
• Copyright Material: NO

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EXECUTIVE SUMMARY
In accordance with Procedures for Stocking_Nonnative Fish Species in the Upyer
Colorado River Basin, the Colorado Division of Wildlife adopted regulations in 1999 to control
the stocking of nonnative fish species below 6,500 feet in elevation in the Colorado River Basin,
excluding the San Juan River Basin. The Colorado Wildlife Commission conditioned its
approval of these new regulations by requiring that an evaluation be conducted to assess whether
this strategy contributed to the control of target nonnative fish species within critical habitat for
endangered fishes.
The methodology chosen to address this question included use of a Geographic
' Information System (GIS) to provide a comprehensive framework for examining diverse
information. This information included pond locations, fish sampling data, and reclamation
treatments within the Colorado and Gunnison River corridors surrounding critical habitat,
' stocking activity for nonnative, nonsalmonid fishes, and sampling data from backwaters within
the Grand Valley reach of the Colorado River.

The original premise in the Stocking Procedures that 6,500-feet in elevation would serve
as an ecological demarcation above which few private waters would be stocked with nonnative,
warmwater sport fish appeared to be generally true, based on available data. Triploid grass carp
and fathead minnow were the most widely stocked nonnative, nonsalmonid species with stocking
sites ranging from ponds within or near the floodplain in critical habitat for endangered fishes to
waters near the Continental Divide. Based on available data for floodplain ponds sampled and
those ponds that received treatments to control abundance or escapement of nonnative fish
species within the Grand Valley reach of the Colorado River, green sunfish and largemouth bass
pose the highest risk of reaching critical riverine habitat for endangered fishes.
The poor response to the request for voluntary submission of private sector stocking data
for 1998-2000 precluded performing a meaningful risk assessment of the potential for stocking
nonnative fish in the general study area to serve as a source of these species entering critical
habitat for endangered fishes. Inadequacies in the reporting of stocking location descriptions
limited the spatial utility of a considerable number of stocking sites, compromising the capacity
to fully document or evaluate the relationship of locations and species stocked with other
available data.
The abundance of stocked fish species (e.g. fathead minnow and largemouth bass)
generally remained the same before and after treatments to control nonnative fish abundance in
or escapement from floodplain ponds or to control nonnative fish density in backwaters. While
there was no evident change in the backwater densities of the species examined during this study,
it appeared that the highest densities of some species shifted locations from year to year, which
could be a result of removal efforts dampening populations in particular locations. There was no
spatial pattern demonstrating a definitive relationship between nonnative species location and
density in critical habitat or potential sources of nonnative fishes such as nonnative fish stocking
events or fish populations in floodplain ponds.
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