U.S. Department of the Interior

U.S. Geological Survey

EXPLANATION

Study area

Colorado

Eagle River

Ski area Mill Creek

Gore

Creek

Red

Sandstone Cr.

Booth

Cr.

Bighorn Cree k

Gore

Range

Vail Pass

Black Gore Cr.

1

1

2

4

3

Urban: residential, commercial, 

or transportation

Urban: recreation 

Rangeland

Forest

Barren, tundra, or perennial snow

Sampling site and number

Lakes

Town of Vail corporate limit

Fish-Community Assessment in Gore Creek, Colorado, 1998

Introduction

Gore Creek drains an area of about 102 square miles, flows

about 19 miles from an area along the Gore Range through the

Town of Vail, and joins the Eagle River near Vail in Eagle County,

Colorado (fig. 1). To properly manage water resources in the

watershed, local managers are interested in a better understanding

of water quality and stream biology and their relation to land uses

and natural factors in the Gore Creek watershed. In response to

these concerns, the Town of Vail, the Eagle River Water and

Sanitation District, Vail Associates, and the Upper Eagle Regional

Water Authority created the Gore Creek Watershed Management

Program in 1996. The goal of this program is to provide information for the management and protection of water quality and

aquatic life in the watershed.

The lower 4-mile reach of Gore Creek,

including sites 3 and 4 in figure 1, has been

designated a Gold Medal trout fishery by the

Colorado Division of Wildlife. The Gold

Medal designation was made in recognition of

the exceptional recreational value of the

brown trout community in that stream reach

(Weaver and Jones, 1995). The U.S. Geological Survey (USGS), in cooperation with the

Town of Vail, the Eagle River Water and Sanitation District, and the Upper Eagle Regional

Water Authority, collected fish-community

data in four representative stream reaches

along the main stem of Gore Creek in August

1998. This report describes the condition and

structure of the Gore Creek fish community at

four sites and relates those results to predominant water-quality indicators including

instream habitat, water chemistry, and benthic

algae and macroinvertebrate (aquatic organism) community characteristics.

The Gore Creek watershed has undergone

significant land-use changes since the 1960s

as the Vail area shifted from traditional

mountain ranchlands to a four-season resort

Fish-community sampling in Gore Creek. (Photograph courtesy of

David Manzella.)

—Kirby H. Wynn

USGS Fact Sheet 186–99

December 1999

Figure 1. Fish-community sampling sites in the Gore Creek watershed.

In cooperation with the Upper Eagle Regional Water Authority,

Eagle River Water and Sanitation District, and the Town of Vail
community. Land use/land cover in the Gore Creek watershed is 8

percent urban, 63 percent forested land, 14 percent rangeland,

14 percent barren, tundra, or perennial snow, and 1 percent other

land-use/land-cover classifications (fig. 1). Although only 8 percent of the watershed is covered by urban land uses, nearly all of

the development has occurred in close proximity to Gore Creek

and its tributaries, causing concern that runoff from developed

areas may affect water quality or stream biology.

Data Collection

Fish-community samples were collected at four sites during

August 19–20, 1998. The sites were selected to identify any

effects that urban and recreational land use may have on the fish

community. Sites 1 through 4, in downstream order, represent

stream segments that integrate the effects of increasing amounts

of urban and recreational land uses. The fish-collection protocol

followed for this study is described in Meador and others (1993).

The sites were sampled using a towed barge direct-current electrofishing unit operated by personnel from the U.S. Fish and

Wildlife Service. The length of each sampling reach was about

500 feet, and each included three types of geomorphic units

(pool, riffle, and run). In order to ensure a reasonable approximation of the fish population using a similar amount of sampling

effort among sites, fish were collected from each sampling reach

using two complete passes with the electrofishing unit. Fish

have not been stocked in Gore Creek (Tom Kingsley, Colorado

Division of Wildlife, written commun., 1999); therefore, the fishcommunity data should accurately represent the community

structure of Gore Creek. However, the fish community at site 4,

which is located about 300 feet upstream from the confluence of

the Eagle River, may be influenced by fish migrating upstream

from the Eagle River, which has been stocked with rainbow and

cutthroat trout several times in the 1990s. To minimize the influence of habitat as a primary factor in observed fish-community

differences, the selected sampling sites all contained similar,

favorable instream and riparian habitat. Although site 4 was

somewhat channelized and contained less riparian vegetation than

the other sites, instream habitat conditions were comparable

among sites. The habitat for each site was qualitatively evaluated

onsite for available fish cover, streamflow and channel characteristics, bank stability, and riparian vegetation. Water temperature

was measured by using a digital temperature meter. Discharge

was estimated for each site from USGS streamflow-gagingstation records.

Available information from previous studies describing water

quality (nutrients, specific conductance, and dissolved oxygen)

and spatial distribution of benthic algae and macroinvertebrates at

the same sampling sites was compiled from Wynn and others

(1999) and Wynn and Spahr (1998). The data-collection protocols

for those data are described in each respective report. The algae

and macroinvertebrate data were collected in September 1997 and

are thought to be representative of the low-flow stream conditions

that existed during the fish-community assessment.

Factors that Affect Fish

The species, abundance, and condition of fish present in a

stream are strongly influenced by environmental and waterquality factors including available habitat, land-surface elevation,

streamflow, water temperature, dissolved-oxygen content, and

specific conductance (a measure of the dissolved mineral content

of water). Fish communities typical of streams in the Southern

Rocky Mountains physiographic province require adequate

habitat, perennial streamflow, and favorable water-temperature,

dissolved-oxygen content, and specific-conductance conditions to

grow and reproduce successfully. All sites were found to have

adequate and similar instream habitat characteristics. This was an

important finding because large differences in habitat can be the

primary factor causing variation in fish-community structure

among sites and can obscure the effects of other important factors

such as water-quality conditions. Brown trout commonly found in Rocky Mountain streams.

Mottled sculpin, a fish native to the Upper Colorado River Basin.
1234

Gold Medal Fishery

Riparian vegetation was slightly degraded at sites 3 and 4

when compared to sites 1 and 2, and at all four sites a small

degree of sedimentation was evident. Each site, however, contained ample amounts of cover in the form of cobble substrate,

undercut banks, and overhanging vegetation suitable for fish

typically found in streams of the Southern Rocky Mountains

province. The land-surface elevation at sampling sites ranged

from about 7,700 to 8,300 feet above sea level. Streamflow

ranged from about 30 to 50 cubic feet per second among sites.

Water temperature ranged from 46 to 60 degrees Fahrenheit

among sites, increasing slightly as Gore Creek flowed through the

Town of Vail. This temperature range is well below the thermal

maximum of approximately 82 degrees Fahrenheit that can be

tolerated by trout (Lee and Rinne, 1980). Dissolved-oxygen

content was high and near saturation at all sites. Specific-conductance values generally were low in Gore Creek, with maximum

values occurring at site 4, near the mouth of the creek. During

the 1-year period from October 1996 through September 1997,

hourly specific-conductance measurements at site 4 yielded

average and maximum specific-conductance values of 284 and

460 microsiemens per centimeter, respectively, indicating the

dissolved mineral content of Gore Creek is not excessive.

Fish Community

A fish community is an assemblage of fish that share the

same area of a stream and interact with each other. The structure

of a fish community is determined by the species present, their

relative abundances, their life stages and size distributions, and

their distributions in space and time (Meador and others, 1993).

Natural variability in fish communities can be attributed to differences in land-surface elevation, water temperature, water chemistry, food resources, and physical habitat. The abundance,

condition, and species composition of fish communities can be

influenced by water quality and habitat that are modified by surrounding land uses (Deacon and Mize, 1997). Fish-community

data can have a high degree of variability, even when data are

collected for the same site several times in one season. Therefore,

the data presented in this report should be considered as more of a

“snapshot” of the fish-community characteristics at sites in Gore

Creek during August 1998 rather than a description of the longterm fish-community characteristics.

The fish-community structure differed among sites in Gore

Creek. All sites contained abundant mottled sculpin (fig. 2).

Large numbers of mottled sculpin, which are a native species in

Colorado, are indicative of cold-water conditions found in the

Southern Rocky Mountains province (Deacon and Mize, 1997).

Mottled sculpin abundance ranged from 46 fish at site 1 to 306

fish at site 4. Four trout species—cutthroat, brook, rainbow, and

brown—were present at each of the four sampling sites. Total

numbers of trout were similar among sites, ranging from 63 at

site 1 to 119 at site 4. The channel of Gore Creek generally

becomes larger (wider and deeper) in a downstream direction.

Therefore, part of the increased fish abundance at site 4 may be

attributable to a slightly larger sampled surface area of the stream.

Ten percent of the trout at upstream sites 1 and 2 were 12 inches

or more in length; however, 25 percent of the trout were larger

than 12 inches at downstream sites 3 and 4 in the Gold Medal

reach of Gore Creek.

Generally, rainbow and brown trout were more abundant

than cutthroat and brook trout. At site 1, all four trout species

were present in relatively equal proportions, whereas the trout

community was dominated by rainbow and brook trout at site 2

and rainbow and brown trout at sites 3 and 4. Brook trout are

commonly associated with the more pristine headwater (higher

elevation) parts of streams and were most abundant at sites 1 and

2, upstream from most of the urban land use in the Vail area.

Site 4 was unique among sites in that the brown trout community

greatly outnumbered the rainbow trout community. As part of an

ongoing water-quality and aquatic-ecology study of the Upper

Colorado River Basin by the USGS, the fish community was

assessed at site 4 during August of 1996 and 1997; brown trout

dominated the trout community each year (Wynn and others,

1999). This dominance by brown trout at site 4 may be caused, in

part, by brown trout migrating into Gore Creek from the Eagle

Generally, trout were larger and more abundant at

sites 3 and 4 within the Gold Medal fishery reach of

Gore Creek than at sites farther upstream.

Figure 2. Fish-community structure, by site and species abundance.
River, where brown trout is the dominant trout species (Woodling

and Chase, 1998). Also, August is within the spawning season for

brown trout, thereby increasing the likelihood that some of the

brown trout collected at site 4 had recently migrated into Gore

Creek from the Eagle River. However, sampling of a 60-foot

reach at site 4 during April 1998 also yielded a trout community

dominated by brown trout (Kirby H. Wynn, unpub. data, 1998).

Inspection of fish for anomalies such as skeletal deformities or

eroded fins can give an indication of the condition of the fish

community at a site. The occurrence rate for anomalies increased

only slightly from about 2 percent at upstream sites 1 and 2 to

about 9 percent at downstream sites 3 and 4. This increase in

anomalies at downstream sites suggests there may be more environmental stress affecting the trout at sites 3 and 4. Environmental stress could be related to a combination of factors including

fishing pressure and urban development. However, the overall

anomaly rate was not elevated, and determination of the causes

for environmental stress on the fish community in Gore Creek

was beyond the scope of this study.

Relation of Fish Community to Land Use, Water Quality,

and Stream Biology

Analysis of the condition and structure of the fish community

in Gore Creek is enhanced by integrating the fish data with interpretive results of additional indicators of stream quality such as

nutrients, algae, and macroinvertebrates. Because these indicators

are interdependent, an integrated approach can use multiple lines

of evidence to develop hypotheses and support conclusions about

the effects of land use on the quality of aquatic resources such as

fish. Gore Creek drains larger areas of residential, commercial,

transportation, and recreational urban land uses as water flows

from site 1 through the Town of Vail to site 4 (fig. 1).

Benthic algae depend on adequate available resources (nutrients and sunlight) to reproduce and grow. Many types of macroinvertebrates depend on benthic algae as a microhabitat, a food

source, or both. The abundance of algae-dependent macroinvertebrates may increase or decrease, depending on the abundance of

their microhabitat and food resources. Because the fish in Gore

Creek are insectivores, their abundance and growth rates are tied

directly to the abundance and composition of the macroinvertebrate community and indirectly to the spatial distribution of nutrients and benthic algae.

The Gold Medal trout fishery appears to benefit from

increased nutrients, algal biomass, and food resources

associated with urban land use in the Town of Vail.

Figure 3. Macroinvertebrate abundance and algal biomass.

Two previous studies provided valuable insight into the relation between land use, water quality, and stream biology in Gore

Creek. Wynn and others (1999) reported on the relation between

land use, available nutrients (nitrogen), and the size and condition

of the algae, macroinvertebrate, and fish communities at sites in

Gore Creek. As part of a synoptic water-quality study in August

1996, Wynn and Spahr (1998) evaluated the change in nitrogen

and phosphorus concentrations at sites in the main stem of Gore

Creek. Both studies indicated that nitrogen and phosphorus concentrations are much lower at upstream sites 1 and 2 than at

downstream sites 3 and 4. The spatial distribution of nitrate nitrogen concentrations was consistent with the observed spatial distribution of algal biomass (chlorophyll-a, in milligrams per

square meter) and macroinvertebrate-community characteristics.

Algal biomass and macroinvertebrate abundance generally

increased as Gore Creek flowed through increasingly urban areas

between site 1 and site 4 (fig. 3). Although the increase in algal

biomass was moderate from site 1 to site 4, the macroinvertebrate

abundance increased by two orders of magnitude. Much of the

increased macroinvertebrate abundance consisted of pollutiontolerant midges and worms in response to moderate levels of

organic enrichment and increases in nutrients and algae.

Because macroinvertebrates are the primary food supply for

trout and macroinvertebrates were much more abundant at downstream sites 3 and 4, a site-to-site comparison of the relative

plumpness of the trout community was done to determine if the

fish communities had benefited in terms of enhanced plumpness

at those sites. Relative weight, a plumpness index (Wege and

Anderson, 1978; Anderson and Neumann, 1996, p. 446), was calculated for the comparisons of relative plumpness of trout among

sites. Because rainbow trout were abundant at all four sites, they

were the species chosen for relative plumpness comparisons

among sites. Brown trout were excluded from the relative plumpness comparisons because they were most likely experiencing
Above average

Below average

MEAN RELATIVE WEIGHT (PLUMPNESS)

SITE

1234

Gold Medal Fishery

temporary changes in body mass related to their annual spawning

season, which coincided with the study. These temporary weight

changes would have corrupted the test results.

The mean relative plumpness of rainbow trout is plotted for

each site in figure 4. Values for mean relative plumpness greater

than 100 are considered to come from a fish community of above

average plumpness. The mean relative plumpness values were

greater than 100 at downstream sites 3 and 4 and less than 100 at

upstream sites 1 and 2. The site-to-site difference in mean relative

plumpness was statistically tested using Tukey’s significant difference test (Helsel and Hirsch, 1992). The mean relative plumpness of rainbow trout at site 1 was not significantly different from

the other sites. However, mean relative plumpness of rainbow

trout at downstream sites 3 and 4 within the Gold Medal reach

was significantly (with 95-percent confidence) higher than at

site 2, indicating the trout were plumper at the downstream sites.

The greater plumpness of rainbow trout at the downstream sites

likely was caused by increased food resources related to a combination of moderate increases in nutrients and algae and large

increases in macroinvertebrate abundance.

Acknowledgments

The author appreciates the assistance of the following people

who made significant contributions to this fish-community

assessment: Rick Krueger, U.S. Fish and Wildlife Service, provided expertise and equipment for collecting the fish-community

data; Jeffrey R. Deacon, USGS, reviewed the manuscript and

assisted with collection of the algae, macroinvertebrate, and fishcommunity data; and Lawrence R. DeWeese, USGS, reviewed

the manuscript.

References

Anderson, R.O., and Neumann, R.M., 1996, Length, weight, and

associated structural indices, in Murphy, B.R., and Willis,

D.W., eds., Fisheries techniques, 2d edition: Bethesda,

Maryland, American Fisheries Society, 732 p.

Deacon, J.R., and Mize, S.V., 1997, Effects of water quality and

habitat on composition of fish communities in the Upper

Colorado River Basin: U.S. Geological Survey Fact Sheet

122–97, 6 p.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in

water resources: Amsterdam, The Netherlands, Elsevier,

529 p.

Lee, R.M., and Rinne, J.N., 1980, Critical thermal maxima of five

trout species in the southwestern United States: Transactions

of the American Fisheries Society, v. 109, p. 632–635.

Meador, M.R., Cuffney, T.F., and Gurtz, M.E., 1993, Methods for

sampling fish communities as part of the National WaterQuality Assessment Program: U.S. Geological Survey

Open-File Report 93–104, 40 p.

Weaver, R.M., and Jones, J.E., 1995, Gore Creek watershed

management program white paper: Wright Water Engineers,

Inc., and Hydrosphere Resource Consultants, 24 p.

Wege, G.J., and Anderson, R.O., 1978, Relative weight (Wr)—

New index of condition for approaches to the management

of small impoundment, in Novinger, G.D., and Dillard, J.G.,

eds., New approaches to the management of small impoundments: Bethesda, Maryland, American Fisheries Society,

North Central Division, Special Publication 5, p. 79–91.

Woodling, John, and Chase, Dan, 1998, Annual biological assessment of the Eagle Mine Site superfund site, Eagle County,

Colorado: Colorado Division of Wildlife, Denver, Colorado,

97 p.

Wynn, K.H., and Spahr, N.E., 1998, Low-flow water-quality

characterization of the Gore Creek watershed, Upper

Colorado River Basin, August 1996: U.S. Geological Survey

Fact Sheet 167–97, 4 p.

Wynn, K.H., Bauch, N.J., and Driver, N.E., 1999, Gore Creek

watershed, Colorado—Assessment of historical and current

water quantity, water quality, and aquatic ecology, 1968–98:

U.S. Geological Survey Water-Resources Investigations

Report 99–4270.

Design: John Evans

Editing: Mary Kidd

Manuscript and Layout: Alene Brogan

Figure 4. Mean relative weight (plumpness) of rainbow trout.

U.S. Geological Survey, Water Resources Division

Denver Federal Center, Bldg. 53, MS 415

Denver, CO 80225-0046

e-mail: khwynn@usgs.gov
Site 1 Site 2

Site 3 Site 4

Printed on recycled paper