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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stocking as a potential source of nonnative, nonsalmonids entering critical habitat for endangered
fishes. As a consequence, the third objective for this project, assessing the relative significance
of nonnative fish stocking and its potential for introducing nonnative fish into critical habitat,
could not be achieved (Tom Nesler, CDOW Native Fishes Coordinator, personal
communication).
Appendix III provides a complete summary of the spatial utility of all of the stocking
records received from various sources from 1998 to 2001 (Appendix I17. Because many of these
records were not specific enough with respect to spatial location, many were not suitable for
mapping, therefore limiting our knowledge of the extent of nonnative stocking activity
throughout the study area. For example, Figure 12a is a plot of all the known stocking events
(336). If we assume a random distribution of the remaining unknown stocking events (243),
there is a substantial amount of missing information (Figure 12b). However, in looking at Figure
12a, we can assume that there is not a random distribution of unknown locations. In fact, these
locations are likely distributed much like the known locations, primarily below the 6,500-feet
contour, with many probably falling within at least the 100-year floodplain within the primary
study area.
Table 8 summarizes available private sector stocking records found in Appendix III,
including importation permits, private and commercial lake licenses, stocking permits and
voluntarily submitted vendor records, and their "spatial" utility in GIS. Importation records do
not provide spatial data as they are typically issued as "statewide," therefore, the ultimate
destination of the fish within the state is unknown. Private and commercial lake licenses
typically provide usable location data, however, the frequency of stocking and the numbers and
sizes of fishes stocked, if any, is unknown. In fact, it is unknown whether the fish species
permitted for stocking on lake licenses are even stocked at all.
For the purpose of this project, it was assumed that the fish listed on the permits were in
fact stocked, but this is simply a stocking occurrence, as the other details of the stocking activity
cannot be documented. Stocking permits and vendor's records are a-mixed bag in terms of
having sufficient detail to document the locations where fish were stocked. However, these
records tend to be more specific (believable) on the number, size range and frequency of
individual species being stocked than importation records or lake licenses. Stocking locations
with sufficient information to be pin-pointed within one square mile, and thus be considered
"spatial" data included 21 sites in 1998, 60 sites in 1999, 132 sites in 2000, and 106 sites in
2001. Many stocking events from vendor records could not be tracked to a spatial location
(Appendix IIn.
Figures 13a-f show the spatial distribution of stocking events for six species in western
Colorado: triploid grass carp, channel catfish, bluegill, black crappie, largemouth bass, and
fathead minnow. The events are ranked as being high, medium, and low-density events. The
density ranges used for these designations for each species are given in Table 9. By far the most
frequently stocked species was triploid grass carp at 891ocations west of the Continental Divide.
The species stocked at the highest densities was fathead minnow at up to 250,000 individuals per
stocking event. Triploid grass carp was the only species known to be stocked by the private
sector in designated floodplains (12 stocking events in 100-year and 11 stocking events in 50-
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