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Methods Subadult-adult Colorado squawfish monitoring was conducted in April and May, prior to peak runoff. All sampling was conducted from rigid-bottom, outboard-powered electrofishing boats equipped with 4- or S-kilowatt generators and WP-15's (or equivalent) to adjust the voltage transmitted to the water. Electrofishing boats used two spherical anodes suspended from booms in front and two cathodes (usually stainless steel cables) suspended from each side of the boat. Investigators used direct current and tried not to exceed 300 volts or 12 amps (usually held on or below 6 amps).- Electrode size and shape, and voltage and amperage output were adjusted regularly to minimize the possibility of injuring a rare fish, while maximizing electrofishing effectiveness as much as possible. Investigators began at the top of each reach and electrofished downstream at a constant rate with electrical current applied constantly to the water column. Investigators did not make judgements about locations that might hold Colorado squawfish and attempt to 'sneak up' on fish. Right and left shorelines of all sampling reaches were each sampled once. Backwaters, tributary mouths, and other habitat features along the shoreline were also sampled. Because the sample reaches had different lengths (5 to 22 miles), they were divided into at least two, but no more than five subreaches ranging between 2.5 and 6 miles long. These subreaches remained constant after being established in the first year of ISMP. Sampling began at the top of each subreach and proceeded to the bottom. If a rare fish was captured within a subreach, sampling was stopped and the fish was processed and released as near to the capture site as possible. Sampling began again at the location where the fish was captured and continued downstream until another rare fish was captured or the end of the subsection was reached. At the top of the next subreach, data sheets were completed and the elapsed-time clock was reset before sampling-began again. Elective reaches were sampled using the same sampling design. Only rare fishes (Colorado squawfish, razorback sucker, humpback chub, or bonytail) or fish of special interest (e.g. northern pike or roundtail chub) were captured for the monitoring program. Other introduced species (walleye, largemouth bass, smallmouth bass, and green sunfish) that could be identified when shocked were counted but not always captured. Rare fish attracted to the cathodes that were identifiable, but that could not be netted, were also counted. All captured rare fish were measured (total length [mm]), weighed (g), and tagged internally with uniquely-numbered PIT tags (Burdick and Hamman 1993) before release. Capture data were analyzed as number of Colorado squawfish collected per hour of electrofishing effort (CPE). CPE calculations were done using two methods-1. (Colorado squawfish collected/sampling time) and 2. ([Colorado squawfish collected + Colorado squawfish observed]/sampling time). One sample consisted of the electrofishing done along one shoreline of one subreach, with at least two samples (range, 2-8) taken in each monitoring reach. CPE was calculated for all subreaches and then mean CPE was calculated for each monitoring reach and for each river. CPE was not calculated for fishes other than Colorado squawfish. However, total numbers of the species mentioned above were tallied for each sampling reach. Simple comparisons of total numbers captured or observed while shocking were made in reaches or rivers where most of these species occurred. Size distributions of all Colorado squawfish collected were summarized by river. Mean and median lengths and other summary statistics were calculated for the 13 reaches and four rivers sampled. 10