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132 GREAT BASIN NATURALIST VOI. 45, NO. 1 5 _ tives to nonnatives was 2:1 by density. The distribution of these fish between seining sites •4 and over time was not constant (Fig. 3). Diur- nal movements observed at mile 16.5 were •3 primarily by roundtail chubs. 2 The temporal distribution of fish captured SH 5 at the lower end of the cobbled-riffle area • ~ {SH2 and SH3) was the lowest observed at 0 it Fi 3 It t th t fi h any s e ( g. ). was apparen a s •4 were not moving into or out of this fast riffle area. A comparison of all seining sites be- "•' •3 r tween 1620 and 1745 hours indicates that ~ •~ SH 1 maximum density of fish was found at SH4 ~v •~ }} (0.44 fish/m2 sampled). Subsequent seine o / / hauls at this site showed continuously re- 4 duced densities over the 24 hours sampled. A • comparison of the other sites (Fig. 3) in- `L •3 SH 4 dicates the opposite pattern at the upper site ~ (SH5}, with no change in the intermediate seining location (SHl}. It was believed that :~ the pattern observed resulted from fish mov- ~ ing out of the deep pool (SH4), past the shal- •4 low run (SHl), and towards SH5, which was ~ located at the lower stretch of a riffle area. SH2t3 Macroinvertebrate and larval fish drift .~ samples were taken at each seining site. A • ~ comparison of the drift entering (SH4) and ~ leaving {SH2 +SH3) the riffle area, where squawfish were at their highest observed con- isoo soon oioo oaoo noo boo TIME centrations, indicates that substantial num- bers of macroinvertebrates and larval fish Fig. 3. Distribution of fish captured at five seining originated within this cobble habitat (Fig. 4). sites at river mile 16.5 on the Yampa River over a 24- For example, the diurnal pattern of drift hour period 24-2s Jnly 1981. (macroinvertebrates and larval fish) reached a TABLE 3. Incidence of food in fishes captured on the Yampa River by seining at river mile 16.5 and 18.0 24-26 July lsa1. Fish species Species code Young of the year w/food w/o food Bluehead sucker BH 1 0 Catostomus discobolus Flannelmouth sucker FM 5 1 CCLtOSC0772ZLS latipinnis Fathead minnow FH 0 0 Pimephah~s promelns Red shiner RS 0 0 Notropis hitrensis Redside shiner RD 0 0 Richardsonius balteah~s Roundtail chub RT 38 4 Lila robnsta Sand shiner SS 0 0 N~trop~is stramineus Speckled dace SD 2 0 Rhinichthys oscuulus Channel catfish CC 1 0 Ictalz~n~s punctatus .~, .i