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<br />Report 5- Potamodromy and reproduction of Colorado squawfish in the Green <br />River Basin, Colorado and Utah. (Tyus 1990) <br /> <br />Movements of Colorado squawfish Ptvchocheilus lucius were studied by <br />radiotracking and recapturing tagged fish in the Green River basin of <br />Colorado and Utah, 1980-1988. Of 153 fish tracked, 63% were highly mobile: 41% <br />migrated to known spawning sites, 11% migrated to suspected spawning sites, <br />and 11% moved to other locations. Nonmigratory behavior of tracked fish (18%) <br />was linked with non-annual spawning or sexual immaturity. Contact was lost <br />with 14% of the fish, but five that were lost' one year migrated in subsequent <br />years. Some fish (5%) were radiotagged after the spawning season. Spawning <br />migrations began about 28 days after highest spring flows with water <br />temperatures of 90C or greater. Movement of fish to known spawning areas <br />(N=63) averaged 140.7 km (range 32-372.8 km) in downstream (73%) and upstream <br />(23.8%) directions, and some fish (3.2%) moved downstream in tributaries, then <br />upstream in the mainstream. An autumn-to-spring home range was indicated by <br />radiotelemetry and recaptured fish. Colorado squawfish spawned as summer flows <br />decreased and water temperatures increased, and capture of 13 ripe females <br />indicated that spawning occurred in mean water temperatures of 230C (range 22- <br />250C). Most ripe fish were males, and their mean total length' (Tl) was smaller <br />than females (males, 555 mm, N=194; females, 654 mm, N=14). The possibility <br />of stock differentiation was suggested by radiotracked and recaptured <br />individuals that spawned at the same site for more than one year, and by <br />migrations to a spawning reach from both upstream and downstream areas. <br />Innate and environmental factors influencing reproduction and recruitment <br />should be fully considered in management of this endangered fish. (Abstract) <br /> <br />Report 6- Response of young Colorado squawfish to water flow and light <br />intensity. (Paulin et a1., in prep) <br /> <br />We used an advection-diffusion model to evaluate directional and random <br />movements of 1-, 3-, 6-, and 36-week-old Colorado squawfish Ptvchochei1us <br />lucius with three water flows and two light levels. Fish were placed in the <br />center of a seven-chambered tank and their u~- and downstream locations <br />recorded at water flows of 0, 27, and 237 cm Is. Tank hydraulics represented <br />riverine conditions: a meandering mainstream and associated quiet (backwater) <br />areas. Fish age, flow rate, and light level (light and dark) all influenced <br />the extent and direction of fish movement. larval Colorado squawfish exhibited <br />a diel pattern of downstream movement. Rate of downstream drift was inversely <br />related to fish size, and relative swimming ability was correlated with body <br />length. Juvenile fish tended to move at random through the experimental tank <br />at all flows. A knowledge of drift mechanisms can be used in management and <br />recovery activities for this endangered fish. (Preliminary Abstract) <br /> <br />Report 7- Population size and status of the razorback sucker in the Green <br />River basin, Utah and Colorado. (lanigan and Tyus 1989) <br /> <br />The status of the razorback sucker Xvrauchen texanus in the Green River, <br />Utah, was evaluated with capture-recapture data collected from 1980 to 1988. <br />The razorback sucker population in the upper Green River (river kilometers <br />282-555) was estimated at 948 fish (95% confidence interval, 75B-l,138), based <br />on a total of 410 fish captured (6B recaptured). Razorback suckers in the <br /> <br />10 <br />