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<br /> <br /> <br /> <br /> <br /> <br />1 <br /> <br /> <br /> <br />1 <br /> <br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br />METHODS <br />Field collections--The three sampling sites for Colorado squawfish larvae were the <br />Yampa River just upstream (RK 1) of its confluence with the Green River in Echo Park within <br />Dinosaur National Monument (1990-1996), the Green River near Jensen, Utah (1990, 1994, and <br />1995), and the Green River about 15 km upstream of Green River, Utah (1991-1996). Sampling <br />started in late-June to early-July each year, two to six weeks after peak spring discharge when <br />daytime water temperature exceeded about 16°C (Kesler et al. 1988, Tyus and Haines 1991). <br />Sampling continued for four to nine weeks after the first Colorado squawfish larvae were <br />captured and ended when none were captured for three to five consecutive days, usually by mid- <br />August. <br />Colorado squawfish larvae were sampled daily at dawn (ca. 0600 hr) with conical drift <br />nets (0.15 m2 mouth diameter, 4 m long, 560 µm mesh) set nearshore in water 30 to 40 cm deep. <br />Three nets were set on each sampling occasion for up to 2 hr, but sampling stopped if debris load <br />exceeded 3.8 L/sample. Water depth at which a white object disappeared from sight was <br />recorded as a measure of water turbidity. General Oceanics flow meters (mode12030) suspended <br />in each net mouth recorded water velocity during the net-set. <br />To evaluate whether dawn-nearshore-samples represented the abundance, age, and size of <br />larvae transported downstream past sampling sites, additional diel and cross-channel sampling <br />was conducted. Diel and cross-channel sampling was conducted at the Yampa River collection <br />site in 1992 (9, 10, 13, 15, 17, 18, 23, 24, 25, 27, and 29 July). This sampling consisted of <br />standard dawn-nearshore-samples supplemented with three dawn-samples collected at each of <br />midchannel-surface and midchannel-bottom locations. Samples were also collected at those <br />same locations at noon (1200 to 1400 hr), dusk (1900 to 2100 hr) and midnight (0000 to 0200) <br />and resulted in 36 samples/d (3 locations x 4 times x 3 replicate samples). Samples could not be <br />collected at all positions during all periods on 15 and 23 July, 1992. In addition to 1992 diel and <br />cross-channel sampling, diet-only sampling was conducted on at least four but up to 14 occasions <br />annually from 1992-1996. Each diel sampling occasion consisted ofnearshore-samples collected <br />at each of the four time periods (12 samples/d). <br />Samples were fixed immediately in 100% ethanol and fish were removed from debris <br />within 4 hr and preserved in 100% ethanol. Rapid sample processing prevented fish from being <br />5 <br />