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18 Gila species. often receive periods. If placed in moderate current, however, the fish would much external abrasion if left in the trap for long Physical Measurements An assemblage of compact, durable, time efficient equipment was procured to collect physical and chemical data to permit the compilation of as much data as possible with the highest possible level of accuracy. Probably the most time-saving device utilized relative to traditiona' equipment and methods was the Marsh-McBirney Model 201 portable water velocity meter. This was a direct-reading device which reduced the time of taking water velocity measurements by 70-80% from the older methods of counting the rotations of a water wheel. Velocity measurement, were taken at 0.6 the distance from the surface (Bovee and Milhous 1978). Distances between shorelines were measured using a hand-held range finder and depths were recorded with a collapsible stadia rod and a Lowrance Model LRG l5l0A depth finder. The Lowrance depth- finder has a strip chart which provides an opportunity to enter notations relative to station location and descriptive notes pertaining to important features on the printout. Total dissolved solids, salinities and conductivities were measured with a Yellow Springs Model 33 meter which has a combined conductivity and temperature probe. Conductivity is expressed as micromhos per centimeter. Salinity is temperature compensated and recorded in grams per kilogram. A Hach Model DRIl colorimeter was used to measure pH, dissolved oxygen and turbidity. Turbidites were measured in forazin turbity units (FTU) which are equivalent to Jackson turbidity units. Fish weights were taken with Chatillon 2g x 1000 g or 20 g x 5 kg platform scales. Fish Collection Gears As pointed out earlier, rivers present a variety of fluvial conditions that require unique sampling methods. Some areas such as the swift, deep canyons present an almost insurmountable obstacle to procuring representative fish samples with current technology. There was no single technique which efficiently salnpled all habitats for all sizes of fish. We strived to use the gear or combinati( of gears that would provide a good, cross-section of the fish population in each habitat. Table 3 presents the general habitat types within the primary gear types employed. The gear probably utilized to the greatest extent were seines. While a variety of seine sizes and meshes were used, the two utilized most were 15 x 4 ft, 1/8 in mesh and 30x 6 ft, 1/4 in mesh nets.