|
<br />~
<br />/
<br />,,~-
<br />. j
<br />
<br />
<br />l
<br />,
<br />1
<br />1
<br />1
<br />1
<br />l
<br />1
<br />1
<br />\
<br />j
<br />.
<br />I
<br />j
<br />l
<br />\
<br />;
<br />I
<br />
<br />228
<br />
<br />TRANS. AME.R. FISH. SOc., 1975, NO.2
<br />
<br />is common in the upper, cold water parts
<br />of the basin (Beckman 1952).
<br />
<br />Hybrids
<br />
<br />Flannelmouth sucker X humpback sucker
<br />hybrid. Hybrids between the flannelmouth
<br />and humpback suckers were collected
<br />throughout the range of the humpback
<br />sucker, usually in quiet, backwater areas
<br />in association with humpback suckers.
<br />They were readily distinguished by an in-
<br />tennediate lateral line scale number and a
<br />much abbreviated, although distinct, keel
<br />behind the occiput. This hybrid was rare,
<br />40 being collected during the study, but
<br />was nearly as numerous as the humpback
<br />suckers collected during the study.
<br />Hubbs and Miller (1953) described this
<br />hybrid from eight specimens, two from the
<br />upper Colorado River system and six from
<br />the upper Green River. Jordan (1891) col-
<br />lecteJ one of the above specimens in 1889
<br />from the Delta, Colorado, area. Banks
<br />(19640) reported this hybrid from area 3 be-
<br />fore closure of Flaming Gorge Dam.
<br />Vanicek, Kramer, and Franklin (1970) col-
<br />lected 16 hybrids from the same area after
<br />closure of the dam. No fertile hybrids have
<br />been reported even though hybrids have
<br />been known for over 75 years.
<br />Bluehead sucker X lvhite Slicker hybrid.
<br />The hybrid between the bluehead and
<br />white suckers was found only in the
<br />Yampa River. It is extremely abundant in
<br />area I and rare in area 2, as is the white
<br />sucker. Hubbs, Hubbs, and Johnson (194::~)
<br />described this hybrid from the upper Col-
<br />orado and Gunnison Rivers. Baxter and
<br />Simon (1970) reported it from a tributary of
<br />the Little Snake River in Wyoming. It ap-
<br />pears to be distributed in the npper parts
<br />of the basin following the range of the
<br />white Slicker.
<br />Flannclmouth -sucker X white sucker hy-
<br />brid. The fbnnelmuuth X white sucker hy-
<br />brid is rare to cOlllmon ill area 1, rare in
<br />2, and rare (one spccimen) in 10. It was
<br />collected in 1969. ]970, and ]971. Baxter
<br />and Simon (1970) reported this hybrill hUlIl
<br />Big Savery Creek. tributary of the Little
<br />Snake River, \Vyoming, hut no description
<br />has been published.
<br />
<br />
<br />DISCUSSION
<br />Twenty-nine species were collected dur-
<br />ing the study, of which 19 were intro-
<br />duced. All native species previously re-
<br />ported from the study area were collected
<br />except one. Taba, Murphy, and Forst
<br />(1965) reported the mountain sucker
<br />(Catostomus platyrhynchus) from the Col-
<br />orado River below Moab. They distin-
<br />guished it from the bluehead sucker by the
<br />presence of notches at the side of the
<br />mouth. Smith (1966) reported side notches
<br />as a characteristic of the subgenus
<br />Pantosteus, and that they were well de-
<br />veloped on both the bluehead and moun-
<br />tain suckers. Also, the mountain sucker is
<br />characteristically found in small, cold
<br />mountain streams. Therefore, the above
<br />report is probably a case of mistaken iden-
<br />tification.
<br />The diversity of species is greater in the
<br />more heterogeneous high gradient, rocky
<br />bottom hahitats than low gradient, sandy
<br />bottom areas. For example, high gradient
<br />areas 2 and 3 Crable 1) had 23 and 23
<br />species present" respectively, whereas low
<br />gradient areas ;) and 6 had only 13 and 12.
<br />Total fish Hum hers are also considerably
<br />higher in rocky areas.
<br />Areas 7 and 8 are exceptions to this
<br />generalization. Each of these high gradient
<br />areas support only 15 species, compared
<br />with 25 frol11 similar areas in the Green
<br />Hiver basin. Total fish numbers are similar
<br />in both areas, although native species
<br />dominated the Green and introduccd
<br />species the Colorado Hiver. This was pro-
<br />nounced among juvcnile fishes. Areas 11
<br />and 12 were sampled less inlensely than
<br />other sections of the study area, which
<br />might account for the low diversity found
<br />lllcre. Red shiners and green sunfish are
<br />also known from area 12 (l{. R. Miller,
<br />personal communication).
<br />Flannelmouth and bluehead suckers are
<br />I he dominant fish in the st udy area. Col-
<br />orado sfJuawfish, honytail chub, humpback
<br />clmb, and humpback sucker are very rare
<br />and undoubtedly are threatened with ex-
<br />tind ion if man cont inues to alter their
<br />habitat. The Yampa Hiver, particularly the
<br />lower portion, and the middle and lower
<br />
<br />'J< -"::'-" ,_,-_.' ~r~:""> _' ':'-"i~,,"'''',:',~~>~: '''''''', "7~''D'":'''"~;''~,,;''~W'~''' ":-0", ';<:':"~r-~;l "<-_,~,~""""''''''''?_>,,,, - _c" - -
<br />
|