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METHODS Movement, Spawning and Rearing Investigations The movement of adult Colorado squawfish was followed using radiotelemetry. Fish were collected using electrofishing, gill nets, trammel nets, and traps. !Colorado squawfish longer than 500 mm total length (TL) were surgically implanted with radio transmitters following procedures outlined by Tyus (1982). Transmitters weighed about 10-11 grams in air and had a life expectancy of approximately 6 months. All rare fishes collected were weighed (grams) and measured (TL, mm). River reaches where radio-equipped Colorado squawfish were released were searched for the presence of these radiotagged fish at least bi- weekly. A larger area was searched at times when fish could not be located in the immediate tudy area. The majority of the search effort was conducted using boatsi however, airplanes and helicopters were also, employed. Location and movement of fish was identified by river mile (RF1) with the confluence of the Green and Colorado rivers starting as RM 0. Other tributary mileage was calculated using the tributary mouth as RM 0. Possible spawning areas for Colorado squawfish were identified using radiotelemetered fish, and by analyzing collections of larval fish. The radio tracking effort was intensified during the suspected Colorado squawfish spawning season, July-August. When more than one radiotagged fish were found at a particular location--a possible indica- tion of pre-spawning or spawning activities in that area--trammel nets were actively fished (drifted) there to determine if other Colorado squawfish night be present; Collected Colorado squawfish were measured in the usual runner, and observations were made for sexual products and any external reproductive characteristics of the fish. Larval fishes were collected during July and August from backwaters, shorelines, and mid-channel. Samples taken in the Colorado and Green rivers included backwater and shoreline seine and dip net samples. In addition, a special pilot study of larval drift was conducted in the Green River by the use of 121 diameter ichthyoplan?ton nets. These nets were constructed of 0.03 in mesh wall and 0.02 in mesh cod end. Each net was suspended in mid-channel from a cross-channel guy-wire attached to metal fence posts driven into the shorelines. The nets were weighted fore and aft and floated with plastic bottles. The nets were set for 10 minute duration at 0600, 1200, 1800 and 2400 hours. Samples were preserved in 5% formaldehyde and sent to the Larval Fish Laboratory, Fort Collins, • Colorado for identification. Larval drift sampling was done at: 1. Green River immediately above the mouth of the Yampa River (RIN1 345). 2. Yampa River near the mouth (RM 0.3). 3. Green River below Split Mountain Canyon (RM 314.9). 4. Green River immediately above the mouth of the White River (RM 246.3). - 5. Green River below the mouth of the White River (RM 245.5). - 3 -