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METHODS Six sample trips were conducted through Cataract Canyon between 10 July and 13 October 1985. Each trip consisted of 5 to 6 days on the river. Launch sites were alternated between Potash on the Colorado River and Mineral Bottom on the Green River, after the second trip. This was done to sample for YOY squawfish and radiotrack on the lower Green River above the confluence, and to radidtrack on the lower 50 miles of the Colorado River. This effort was coordinated with the ongoing programs of the U.S. Fish and Wildl ife Service (USFWS), which samples for YOY on the Colorado River down to the confluence and down to river mile (RM) 30 of the Green River. Three rafts were used on each sample trip. An 18-foot Riken Havasu was used as an electrofishing raft~, and a 16-foot Avon Professional was used to set gill and trammel nets and for seining. The rafts were equipped with a 25 and 15 horsepower outboard motor, respectively. A 23-foot motorized IIJ_ Rigll, provided by Tag-A-Long Tours (TAG), was used to carry camp gear and additional sample equipment. The core crew consisted of 2 USBR biologists, 2 ERI biologists, and 2 support TAG boatmen. Ten different fish sample gears were used in this investigation. DC el ectrofishlng was conducted from the l8-foot raft with a Honda EMS4500 generator and a Coffelt VVP-15. Gill nets, 100 x 6 feet with 2 and 2.S-inch mesh, were used as well as trallllel nets, 50 x 5 feet with 1. 5 and 12-; nch mesh. The trammel nets were either tied to shore or floated between brailes. Hand seines, 15 x 4 feet with 1/4-inch mesh and 10 x 3 feet with 1/16-inch mesh were used to sample shallow areas for small fishes. Drift nets made of 560 micron Nitex plankton netting, 10 feet long with a 1 x 1.5- foot opening, were used to sample the ichthyoplanton. Long-handled dip nets and fine mesh kick screens were also used for sampling small fishes in shallow habitats. All endangered fi sh were wei ghed and measu red, and equ i pped with a serially-numbered red Carlin dangler tag. Young fish that could not be identified afield were preserved in 10% buffered formalin and forwarded to the Larval Fish Laboratory in Fort Collins, Colorado. A concerted effort was made to minimize mortal ity to endangered fishes, incl uding, short-term sets on all gill and trammel nets, and immediate return of all identifiable young fishes. Catch per unit captured by seining. each seine haul, and time or area. Hauls computation. effort (CPE) ~as computed for YOY Colorado squawfish Catch per 10m of surface area seined was computed for a mean computed for all hauls taken within a specified that did not yield squawfish were also included in the 3