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habitat use, movement, and habitat needs related to spawning. Starting in 1989, stomach content analysis for ingestion of fish prey was included in the processing of gamefish specimens collected downstream of Craig. The post-runoff period was defmed as two parts: a baseflow period from July to October in each year; and a winter period of ice-on condition in the river from November to February each year. The pre-runoff period was defmed as starting in March each year. The break in the hydrograph separating pre-runoff from runoff periods was defmed as the point of inflection in the ascending limb of the hydrograph leading to peak flow. This occurred at the start of May in 1988 and 1991, and the runoff period in these years was considered to be May and June. Runoff started at mid-April and ran through June in 1989, and started on May 20 and ran through June in 1990. (See Figure 2) Hydrologic data, including daily flow in cubic feet per second (cfs) and water temperatures were acquired from U.S. Geological Survey (USGS) Water Resources data for Colorado to compare between year differences and correlate with fish population trends (Ugland et al. 1989-1992). Due to varying flow level from May-November, sampling techniques had to be varied to accommodate habitat conditions. During pre-runoff and runoff flows, sampling was conducted using a flat-bottomed john boat powered by an outboard jet unit for radiotracking and sampling gear transport. Another similar john boat outfitted with electrofishing capability was also used when flows were sufficient to enable this heavier craft to negotiate the short, rocky gradients and potentially shallow riffles present in the study area. A "block and shock" technique was developed in conjunction with CSU Larval Fish Lab personnel. The gist of the technique was to place either trammel or gill nets in low-flow river habitats that appeared suitable for the target fish species, and subsequently create a disturbance in these habitats to initiate fish movement, thereby increasing the capture potential of the passive nets. The technique appeared particularly effective in the spring when rising river flows created side channel and tributary backwaters that could be completely blocked from the main channel with nets. If the river current permitted, oars were used to move the boat and minimize premature disturbance of the fish when setting the net across the mouth of the backwater. Northern pike, channel catfish, and Colorado squawfish appeared quite susceptible to this technique compared to our sampling experience with these species from continuous shoreline electrofishing employed during the Interagency Standardized Monitoring Program (ISMP) annual endangered fish sampling efforts. Nets used in this process included 30.5 m trammel nets, 1.8 or 2.4 m deep with 150 nun mesh outside walls and 25 nun mesh inner wall; or a 38 m monofilament gillnet, 1.8 m deep with five experimental mesh panels ranging from 13 to 44 mm mesh size. The electrofishing equipment included a Coffelt VVP-15, 5000 watt generator, and 25 cm diameter stainless steel sphere anodes suspended from shielded dropper cables made of 9.5 nun steel cable. Output power during block and shock efforts was set initially at 200-400 volts and 2-10 amps at the head end of the backwater. During the approach to the blocked mouth of the backwater, power was decreased to minimize electrofishing injuries to fish already captured in the blocking net. Commonly during this process, voltage was below 100 v and amperage was less than 0.5 amps at the time the boat neared the blocking net. 5