Potamodromy and Reproduction of Colorado Squawfish in the Green River Basin, Colorado and Utah
Abstract
Movements of Colorado squawfish Ptychocheilus lucius were studied by radio-tracking and recapturing tagged fish in the Green River basin of Colorado and Utah, 1980–1988. Of 153 fish tracked, 63% were highly mobile: 41% migrated to known spawning sites, 11% migrated to suspected spawning sites, and 11 % moved to other locations. Nonmigratory behavior of tracked fish (18%) was linked with non-annual spawning or sexual immaturity. Contact was lost with 14% of the fish, but five that were lost one year migrated in subsequent years. Some fish (5%) were radio-tagged after the spawning season. Spawning migrations began about 28 d after highest spring flows when water temperatures were 9°C or greater. Movement offish to spawning areas (N = 63) averaged 140.7 km (range, 32–372.8 km) in downstream (73%) and upstream (23.8%) directions, and some fish (3.2%) moved downstream in tributaries, then upstream in the mainstream. An autumn-to-spring home range was indicated by radiotelemetry and recaptured fish. Colorado squawfish spawned as summer flows decreased and water temperatures increased, and capture of 13 ripe females indicated that spawning occurred in mean water temperatures of 23°C (range, 22–25°C). Most ripe fish were males, and their mean total length was smaller than that of females (males, 555 mm, N = 194; females, 654 mm, N = 14). The possibility of stock differentiation was suggested by radio-tracked and recaptured individuals that spawned at the same site for more than 1 year, and by migrations to a spawning reach from both upstream and downstream areas. Innate and environmental factors influencing reproduction and recruitment should be fully considered in management of this endangered fish.
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