9532

• UCREFRP Catalog Number: 9532
• Author: Anderson, R. and G. Stewart.
• Title: Riverine Fish Flow Investigations.
• USFW Year: 2000.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

METHODS

FISH SAMPLES

Fish were electro-shocked and netted from an Achilles raft using a Smith-Root electro-

fisher powered by a 5000-watt generator with the anode mounted on a forward boom. The

boat was maneuvered by either oars or by a battery powered 40 pound trolling motor. Two

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. The Darroch multiple mark method (Everhart

and Youngs 1981) was used to estimate abundance with ninety-five percent confidence

intervals.

".
Sections of river both up and downstream of the mapped site were electrofished on the

Yampa and Colorado Rivers. Fish were measured and released at specific locations in each

study reach. The stops were typically above each riffle. This allowed for a qualitative

assessment for species composition and relative abundance in each riffle-run sequence in the

sample reach. On the Yampa River a different mark was used for each run-riffle sequence,

which allowed for determining if recaptured fish had moved up,.down or had not changed

sequences between captures. Four total passes were made at the Sevens stations, on August

30, September 1, 14 and 16. Flow on those dates (MaybeU gage) were 315 cfs, 280 cfs, 219

cfs and 201 cfs, respectively. The reach from the Duffy run above the launch to the lower end

was electro-fished on August 25, Septembe,r.~, 15 and 17. The flows on those dates were 302

cfs, 347 cfs, 293 cfs and 265. The upper section and the run directly upstream of the launch

site were electro-fished on August 23, 24, September 1, and September 7 at flows of340 cfs,

302 cfs, 318 cfs and 370 cfs.

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