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

BIG THOMPSON RIVER DRAINAGE - HYDROUNfT 10190006
The Big Thompson River drainage originates in'Rocky Mountain National Park and ends
where the Big Thompson River flows into the South Platte River near LaSa1\e, Colorado. The
entire drainage covers 830 square miles. This sampling included transition zone and plains
portions of this drainage (approx. 25% of the total draijlage). .
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Most of the land-use in the sampling area consi$ts of irrigated cropland and pasture, but
the heavily populated Front Range urban corridor including the city of Loveland influences the
water flow and quality at the mid-reaches of the sampli,rig area. The upstream area drains rocky
clay soils, which blend into fertile silt-loams in the lower reaches.

The results from this sampling are stratified into information from the mainstem Big
Thompson River from near the mouth of the Big Thompson Canyon to its confluence with the
South Platte, and all tributaries from the foothi1\s eastward. This was done because there are
typically large differences in fish species and relative a~undance between mainstem populations
and tributary populations, and because the collection sizes on the mainstem sites would dominate
lumped data and mask any differences. .

Twelve sites were sampled on the mainstem Big Thompson River during 1994 (Table 21).
CDOW crews conducted complete sampling at eight sites, and used fish capture data from four
additional Colorado State University (CSU) biomonit6ring survey sites. Sampling conditions
were only fair due to higher flows than are considered! optimum; however, the relatively clear
water suggested sampling was reasonably effective, a~ few fish were known to have escaped past
the electrical fields. .

When compared to either the Cache la Poudre River to the north, or the St. Vrain River to
the south, the Big Thompson River is lacking in species diversity and numbers offish. An average
of 131 fish per sample site were captured, whereas th", St. Vrain River yielded 336 fish per site
and the Poudre River produced 999 fish from an aver~ge sample.

The three most common species (central ston~ro1\er, creek chub and longnose dace) made
up 76 percent of the total catch (Table 22). White sucker added 7.5 percent, and brown trout
(from the uppermost stations) added another 4.5 percent. These five species accounted for 87
percent of the entire catch. Johnny darter, sand shiner, longnose sucker, fathead minnow and
yellow perch ranged from 1 to 2 percent in abundance, with mosquitofish, black crappie, green
sunfish, and gizzard shad each providing 13 to 16 fisj1 or approximately 0.7 percent each.
Largemouth bass, Iowa darter, bigmouth shiner, common carp, plains topminnow, smallmouth
bass, and spottail shiner had fewer than 10 fish each (Table 22).

Uncommon or environmentally-sensitive species (in this case, stonero1\er, johnny darter,
Iowa darter, and plains topminnow) made up 29 percent of total collections which compare
favorably with other hydrounit co1\ections. Introduced species accounted for 7.3 percent of the
total, but brown trout from the uppermost stations on the river were responsible for 4.3 percent
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alone.

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