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Field experiments using mylar shielding were conducted to determine the impacts of UV-B on food quality in four western boreal toad breeding ponds located in central Colorado. The breeding ponds were located at elevations ranging from 2971 m to 3272m, an elevational range associated with at least a 5% change in UV-B exposure. The protein concentration in algae decreased with increased exposure to UV-B, chlorophyll a concentration was not affected by UV-B exposure, and community composition of algae was affected. Densities of Chlorophyta and Xanthophyceae increased and densities of Diatomaceae and Cyanophyta decreased under mylar shielding. Not all members of taxonomic groups reacted in the same way. These data are...
This study was conducted to describe the distributions of both native and nonnative fishes and to identify spatial patterns in fish assemblage stucture of Muddy Creek in the upper Colorado River basin of Wyoming using data collected from 77 reaches during 1999-2004. Fish assemblages in high-elevation reaches were characterized by brook trout (Salvelinus fontinalis) and represented a coldwater faunal zone. Reaches at lower elevations were characterized by warmwater fish species. The upper segment of the warmwater faunal zone contained four native (i.e., bluehead sucker [Catostomus discobolus], flannelmouth sucker [C. latipinnus], speckled dace [Rhinichthys osculus], roundtail chub [Gila robusta]) and two nonnative...
Habitat use and movements of young Colorado squawfish Ptychocheilus lucius were determined by seining 1,194 of the fish in shoreline areas. A total of 922 of these was fin-clipped in selected habitats and 230 (25%) were subsequently recaptured. Most young Colorado squawfish were captured in shallow shoreline embayments (backwaters; 85% of captures), where they were most abundant in spring (April; 68%). Some individuals used more than one habitat and moved between backwaters, shoreline eddies, and main-channel runs. A diel pattern of backwater use was associated with warmer water temperatures, especially in spring (April) when backwater temperatures exceeded river temperatures. Published in Journal of Freshwater...
Native as well as some non-native fishes in the upper Colorado River were found drifting during their larval and early juvenile stages of development. Five native fishes (flannelmouth sucker, bluehead sucker, roundtail chub, speckled dace, and mottled sculpin) dominated the drift with about 87 percent of the catch. The only 3 non-native species found in the drift (white sucker, fathead minnow, and green sunfish) occurred in very low numbers. Significantly greater numbers of drifting fishes were found along the shoreline than in the midchannel surface zone. Larval fish were first caught in the drift when the water temperature reached 16°C during a rapid warming trend in mid-to-late July. About 65 percent of the...
We studied the effects of three flow regimes on the activity patterns and movements of one-, three-, six-, and 36-week old Colorado pikeminnows (Ptychocheilus lucius) and two-week old razorback suckers (Xyrauchen texanus) in an experimental tank under light and dark conditions. The seven-chambered tank simulated a system of backwater habitats, which are used by the young fishes in nature. Water flows through the tank were slow, and velocities were discernable only in the vicinity of surface ports that connected each chamber. Fish movements were related to light or dark condition and activity tended to increase with age. Larvae, relatively active in daylight, moved little at night with no flow, but flow stimulated...