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<br />summer. The river becomes relatively clear at about the same time it
<br />reaches 68-80F.
<br />More than 90% of the squawfish collected during this sharp in-
<br />crease in abundance \\"ere ripe males. A few immature squawfish ilnd
<br />suspected females were also taken. No ripe females (extruding eggs)
<br />were taken. The data indicate squawfish apparently move into tlH~
<br />Yampa from the Green Hiver as waters clear and warm to 60-70 Fin
<br />July and early August. The assumed reason for movement is spawning.
<br />The causes, origin and extent of this migration arc unknovvn.
<br />Abundance of juvenile squawfish in lower Yampa Canyon has de-
<br />creased since 1968. Small squawfish could be readily seined from
<br />several areas in lower Yampa Canyon in 1968. Very few were found
<br />in 1969 and none could be found ill many attempts in 1970. This Wih
<br />undobutedly a reflection of poor spawning success but whether this is
<br />common for Colorado squawfish is not known. Vanicek and KnmlCi"
<br />(1969) found a few \"veak year classes in Colorado sq uawfish but suc-
<br />cessful spawlling was the rule. "Whether the decrease in abundance of
<br />juvenile fish was natural or man-influenced is not clear. Ne\"erthele~';.
<br />the Yampa Hiver appears very important as a spawning area for Colo,
<br />rado squawfish and maintains a relatively small population.
<br />The humpback chub was taken in such small numbers that littk
<br />can be said about it. It should be noted that this species is not very
<br />common any place in the Colorado River basin. Its presence in tll"
<br />Yampa River is important to our kno'v\"ledge and preservation of thi,
<br />specIes.
<br />The bony tail chub also was very rare. Vanicek, et al. (1970) fOllnd
<br />this species to be common at Echo Park on the Grecn Hiver in 10GI-
<br />1966. Our study has found the bony tail to be rare at Echo Park. TIll'
<br />hon)'tail chuh i, nut common ehe\\'hNe ill the basin, thus as with Iii.
<br />humpback chub, its presence in the Yampa I\iver is important to olll"
<br />knowledge and preserva tion of this species.
<br />The humpback sucker was rare ill the area studied. The reporl("\
<br />concentration in spring ancl filII appeilrs to be in response to the }>Olllld"
<br />ed, silty conditions at the mouth of the Yampa, which is the fayorl'd
<br />habitat ft'I" the species.
<br />Introducecl carp (CypriTlllS carpio), sand shiner (No/ropis s/r([lI:
<br />inells), channel catfish (lc/alllrlls pWlc/allls), and largemolll1l 1><1"
<br />(lHicrop/cr/lS salmoides) were found only in the lower, larger sl'di(lll'
<br />of the Dolores Hiver. These species are generally considered llH'd ill!: I
<br />Jilrge stream fishc's so prohably did nol find the middle, drier sccli,'11
<br />of the river favorable hnbitat. The red shiner (Notropis lulrcTlsis\ \\.1'
<br />
<br />j
<br />
<br />410
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