WSP04463

• File Number: 8460.500
• Description: Platte River Recovery Plan
• Basin: South Platte
• Date: 6/1/1997
• Author: Colo Div of Wildlife
• Title: Inventory and Status of South Platte River Native Fishes in Colorado
• Water Supply Pro - Doc Type: Publication

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hydrounit. Only 15 hydrounits are included here because one unit includes only the mountainous
area of South Park, and two others barely reach into Colorado from Wyoming and Nebraska.
The uppermost reaches of these latter drainages were cdmpletely dry during this inventory. A
total of839 sample sites were visited by sampling crews. Eighteen of the sites on the mainstem
South Platte River (Hydrounits 12 and 18) were sampled twice (spring and fall) resulting in a total
of857 samples. Forty percent (337 sites) of the locations were dry at the time of visit. Another
11 percent (95 sites) were wet but devoid offish. Numerous other sites in eastern Colorado were
bypassed when visited because they were dry, but wereinot documented due to sampling time
constraints. Many sites were monitored over time to 06serve water conditions which were
conducive to effective sampling. .

Slightly more than 62,000 fish were sampled in this inventory (Table 2). Twenty-five
native fish species and 16 nonnative (or introduced) fish species were identified. Native fishes
comprised 95.2 percent of the total fish sample. The native species were categorized according to
overall relative abundance and frequency of occurrence indices for the study area and placed in:
(1) an "abundant" group if their relative abundance exc~eded 7 percent and their frequency of
occurrence was 2:20 percent; (2) a "common" group ifitheir relative abundance was 1-6.9 percent
and their frequency of occurrence was 10-19 percent; or (3) an "uncommon" group if their
relative abundance was <1 percent and their frequencyi of occurrence was <10 percent. The
introduced fish species were grouped separately. Given these criteria, six native fish species were
considered to be abundant, nine were common, and ten were uncommon (Table 2). Multiple size
classes were noted for all but four of these species during collection, suggesting some degree of
successful reproduction. The specific status of these native species are discussed in greater detail
later. For the introduced fishes, only one species, the pommon carp, barely met the criteria for a
common species. All other introduced species c1early!fell into the uncommon grouping. Only
nine of the introduced species exhibited multiple size dlasses, which may be the result of instream
stocking (rainbow trout), escapement of juveniles from adjacent pond or lake habitat (bluegill,
bass, yellow perch, mosquitofish, carp), successful reproduction in cooler upstream reaches
(brown and brook trout), or successful reproduction within riverine or instream warmwater
habitat (carp, mosquitofish). None of the crappie or walleye collections suggested successful
reproduction.

The distribution of each fish species collected (in the 1993-1994 inventory was mapped
according to presence/absence at each sample site wi~hin the South Platte study area. These maps
are grouped by the abundance categories shown in Table 2, and are provided in Appendix B.

Biological assessments were made for each hydrounit. For consistency, the following
outline was used:

1. Species composition (include categorization by native and introduced).
II. Relative abundance
A. Percent relative abundance in sample, in l).ydrounit (all samples combined for unit).
B. Frequency of occurrence (all samples containing fish per hydrounit).