9473

• UCREFRP Catalog Number: 9473
• Author: Anderson, R. and G. Stewart.
• Title: Riverine Fish Flows Investigations.
• USFW Year: 2001.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

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netters caught as many fish as they could while the shocker was in operation. All fish were

measured to the nearest millimeter. Only fish over 150mm were marked and therefore used

for mark and recapture population estimates. Density estimates were made for the each study

site on the Yampa, Colorado and Dolores Rivers. The Darroch multiple mark method

(Everhart and Youngs 1981) was used to estimate abundance with ninety-five percent
confidence intervals.

The fish data was further summarized into sampling sub-units referred to as polygons

for future habitat suitability analysis. A polygon refers to a specific section of river and could

vary in size, but typically a polygon is 25m to 50m in length depending on habitat

homogeneity. Each polygon has a set offish attribute data, which allows for a qualitative

assessment of species composition and relative abundance within subsets of the study area.

Following completion of hydraulic modeling the physical attributes of each polygon will be

determined for the analysis between fish and habitat characteristics.

On the Yampa River a different mark was used for each run-rime sequence, which

allowed for determining if recaptured fish had moved up, down or had not moved between

captures. Fish sampling was later in 2000 than previous years because flows were too low to

float the shocking boat during most of September. In general it was found that the boat could

be floated for most of the river at flows over 150 cfs. Flows under 120 cfs are problematic for

electrofishing due to long reaches of shallow habitat. Flow was down to 65 cfs on September

21, but rose to 797 cfs on September 24, following 2 days of rain (Figure 3). Most sampling

was completed after that.

Three mark and recapture electrofishing passes were made at Sevens on the Yampa

River in 2000 on September 28, October 4 and 9 and mean daily flow on those dates (Maybell

gage) were 400 cfs, 240 cfs, and 210 cfs, respectively. Three passes were made for the entire

station at Duffy on September 12, 26 and October 10 and flows on those dates were 69 cfs,

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