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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Conservation Board (CWCB 1995c, d, Vols. 3 & 4). These floodplain data layers for the Yampa
and the White Rivers were also completed from CWCB (1995a, b, Vols. 1 & 2) maps, and are
included on the project data CD, but were not used in any analyses in this report.
Pond Sampling and Reclamation Data
The goal of this section was to describe fish species composition of known ponds in the
ISA. These data were available from the pond reclamation project targeting reduction in
nonnative fish abundance and sources in Colorado and Gunnison River floodplain and adjacent
ponds, 1996-2002 (Martinez 2004). Anita Martinez provided a database containing a list of
known ponds in the ISA, and fish sampling records, if available. This database included
information on fish populations (for a subset that were sampled), and information on ponds
receiving reconnaissance and/or treatments to remove, eliminate and/or control escapement of
nonnative fishes. This database was linked to known ponds with "Mitchell codes" as described
above (ISAPonds). This GIS layer allowed us to look at the fish species composition of ponds
stratified by floodplain position, and also to identify ponds for which we have no information on
fish species.
We developed an index that would roughly identify a relative threat presented by each
fish species present in these ponds. Several key points are explained below to clarify the utility
of this index given the available data. The selection of ponds for sampling or reclamation of
their fish populations, while distributed throughout the primary study area, were selected on the
basis of practical factors such as accessibility, both physical and legal (most were private) rather
than in a random or stratified fashion. For our purposes here, we assumed that the ponds
sampled for fish species composition and the occurrence offish in this subset of ponds sampled
by Martinez (2004) were representative of this resource. However, we knew that this data was
not necessarily the result of exhaustive sampling of the fish in these ponds. The manner in which
Martinez (2004) sampled ponds was influenced by several constraints. These constraints
included 1) extremely high conductivity (> 3,000 µmhos) which precluded electrofishing, 2)
concern about inadvertent sampling mortality of endangered fishes that might inhabit some
ponds limiting the use of certain gear types, and 3) at least for the period of our evaluation,
treatments to control nonnative fish were assumed to actually have an affect in greatly reducing
or eliminating fish escapement from treated ponds into the river. We now know from Martinez
(2004) that certain measures to control nonnative fish abundance or escapement were temporary,
but for the period of this evaluation it was assumed the fishes sampled in ponds were
representative and that nonnative fish control treatments were effective. Last, it was assumed
that nonnative fish in untreated ponds could in fact escape, thus contributing additional,
problematic nonnative fishes to critical habitat.
Our Index of Threat indicates the relative threat posed by any one nonnative fish species,
accounting for both its overall occurrence in the study area, and the control measures that have
been taken on ponds containing that species. Theoretically, the value will scale from 0 (no
threat) to 1 (maximum threat). The calculation is as follows: