7956 - Laserfiche WebLink

Home Browse Search

sand/silt substrate. The lower 10 miles are confined in a low desert canyon, also with a low gradient and fine substrates. ~l~~~ MATERIALS AND METHODS ~ ,~~ ISMP Late juvenile/adult Monitoring Late juvenile/adult monitoring was conducted annually in April and May as river flows began to increase and squawfish began spawning migrations. All sampling procedures complied with guidelines in the Draft ISMP Handbook (FWS 1987). An I8- ft, outboard powered, flat-bottom boat equipped with 2, 14' fiberglass booms extending off the bow was used to electrofish the standardized river reaches. Stainless steel spheres suspended from the booms into the water acted as circuit anodes. -Dropper cables in the middle of the boat acted as cathodes to complete the circuit. Power was supplied by an electric generator with a minimum rated output of 4-kilowatts. A Coffelt Model 15 or equivalent variable voltage pulsator equipped with a lapsed time clock was used to produce a pulsating direct current. Fish were captured with long-handled dipnets and target species placed in live tanks in the boat. An electrofishing crew was comprised of 1 boat driver and 1 or 2 dipnetters. To maximize efficiency and ensure- comparability between years, at Least 2 crew members were required to have previous experience electrofishing large turbid rivers. Each sampling Reach (see Study Area) was subdivided into 2 to 4 subreaches ranging between 2.5 and 6.7 miles in length. Sampling began at the top of each Reach and proceeded downstream at a constant, slow rate along the same shoreline to the end. During sampling, the electrofishing boat proceeded at a constant rate along the shoreline with electrofishing current applied continually to the water column. AIL. shoreline habitat within each Reach was, where possible, eiectrofished including backwaters, tributary mouths and other shoreline features. No attempts were made to concentrate efforts in `good' habitat nor to herd or trap fish. Only rare fishes (Colorado squawfish, razorback sucker, humpback chub, or bonytaii) were targeted, although all fish that could. not be . readily identified were netted. Predatory, non-native fishes including northern pike, walieye, largemouth and smallmouth bass, as well as any uncommon species, were noted on the data sheets. Upon capture of a rare fish, electrofishing was discontinued and data was collected. All rare fishes were weighed and measured and those longer than 200 mm in length were tagged with passively induced transponders (1991-1994). Fish were returned to the river at the site of capture. Additional data collected included water temperature of the capture site and the main river, habitat type, river mile and time of capture. Colorado squawfish which were positively identified but not captured were recorded on 5