7726

• UCREFRP Catalog Number: 7726
• Author: Stanford, J. A. and J. V. Ward.
• Title: Fish of the Colorado System.
• USFW Year: 1986.
• USFW - Doc Type: 385-403
• Copyright Material: YES

a vary in morphometry, meristic characters and ecology (Hubbs et al., 1974); four
B
-;; subspecies are present in the Lower Basin and two in the Upper Basin (Deacon
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~ et at. 1979; Williams 1978; Behnke & Benson 1980). The Colorado River
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OJ OJ cut-throat trout (Salmo clarkipleuriticus) is native to the headwaters of virtually
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c. 0 ~ 0 a all Upper Basin tributaries, and is one of 15 subspecies in the western United
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ell B Ef 3 S -;; States tentatively recognised by Behnke (198 I). An undescribed Catostomus
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'" E ell a related to C. latipinnis is isolated in the Little Colorado River (Minckley 1973).
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:3 .0 '5 .; I:l::
:9 "5 E E 'S: E 3 In all, 46 native fish (including subspecies) existed in the Colorado drainage
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a a i:i: :a a prior to regulation; based on present taxonomy, thirty-eight (85%) are endemic.
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_ 0 '" i:i5 l:ll<l) High endemism is a salient biogeographic feature of Colorado River fish,
'" .- l:ll I:l:: l:ll '" OJ '" ...
t.) ~ -;; ...
._ ;::I ~ ... ~ ~ ... a c. OJ OJ
....0 ... a OJ ." ~ OJ 0 '" 'S: ~ '" ~ reflecting diverse habitats from alpine streams to desert springbrooks (Miller
3 'C OJ OJ C. ~ ~
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ell ~ ... ~ i:i: ....J<I) ....J 1958). The endemism is a result of the Quaternary history of fluctuating pluvial
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and interpluvial episodes in the intermountain area of western North America.
'" E ell Many genera and several extant species were present in Pliocene times, and
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~ OJ '" ~ radiated in Pleistocene drainages to the Colorado River (Smith 1978). Mainly
;: ~ OJ ~ ... ~
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ell OJ OJ ell subspecific differentiation occurred as populations were isolated by desertifi-
ell .0 c ell ell > OJ
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E ;::I 0 C ell ~';:: ;::I
ell ... E cation in the Southwest (e,g. Pluvial White and Moapa rivers, Meadow Valley
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"'" :a -5 ~ .0 i:' OJ Wash, Las Vegas Wash and Little Colorado River). Smith (1978) evoked the
t.) eIl,- OJ
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E ... ,5 ...
... -5 c ell ell a 0 concept of island biogeography (MacArthur & Wilson 1967) to illuminate the
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~ .~ OJ ell -5 S ~ 'S: impact of isolation on pluvial fish in the intermountain area of western North
IE a ell
,5 ell .;:: ;::I :a ~ ~ ~~ C America, including the Great Basin and the Colorado River. He noted that 51
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OJ C. ell OJ goO a ,5 <l.l.o OIl", of the 81 intermountain native fish occurred in only one sub-basin, and con-
'" .... <l.l ell .;:: .... 0:1 '82
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..c ." OJ c.~ 5:< c. "'..c
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<l.l <l.l ~ IE . ell ell ~ t.) OJ OJ eluded that the present fauna is mainly a consequence of local extinctions within
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t: ~ >> ell a a .... .... = 0:1 a Pleistocene fauna, rather than recent colonisation. Thirty-five percent of the
., "'" <l.l .::: 't: 0:1 a ~ ~ '" ;::I '" t.)
<2 "0 .3 t.) IE '~ ~~~ OJ <l.l ..c 0" ~~
<l.l 0 0 i:2 r./'J. t; 0 0 0 <Il 0:1 Colorado River fauna is found only in the Virgin-Pluvial White system, and
.... 0' I:l:: <Il
i:l. i:l.
Z another 20% is endemic in the Gila drainage. However, only nine of 38 endemic
Z Z ~ Z Colorado River fish are found upstream of the Little Colorado River. Most of
ell ~ o' ~
;::I en ~ <Il @ 0 the Upper Basin fish (eight of 14 taxa) Occur in adjacent drainages (e.g. Snake
;;; ~ ~ j~ ~ ~ ~ ~
ill ~ ~ River), or were distributed into the Lower Basin at various times; one subspecies
..c is endemic (Rhinichthys osculus thermalis: Behnke & Benson 1980). The dichot-
ell ~ omy between the diverse Lower Basin fauna and a comparatively depauperate
.... 'So >> 0
<l.l a ~ c ]
<l.l "'" 'is.. ..c a Upper Basin fauna (cf. Stanford & Ward 1986a: Fig. 1) reflects the influence of
S .... t.) a ell 't: -;; a ;3
<l.l ;::I ;3 <.: c. >..c '8
'" "'" .... ell t.) . is.. c. ell S the Pleistocene Lake Hau1apai, near the mouth of the Grand Canyon (Smith
a t.) <l.l a ell ;3 ;::I .,,<E
~ "'" c. ~ c.
a t.) .; ." t.) 0:1 I:>ll B ."
0 ;::I c ~ ell ~ 3 o a OJ 1978). Isolating barriers were most prevalent in the xeric Lower Basin (Naiman
E ~ ell .... .... ,- .!!l c.
.... <l.l ~ - .... .t:
E ~ .!!l ;::I 0 ~ :a ,- c. 1981 ).
0 OJ ~ ~ ell 0 cil
0 OJ 0 ~ ~ i:l: 0
u 0 The fossil record also reflects a gradient (due to latitude and altitude) from
~ * the Upper to Lower basins (e.g. Cottus in the north, cyprinodontids in the
,"
-< " ] south; Smith 1978), Clines in species distributions are evident in Upper (Lanigan
-d O'L: * ~~
..... '" .;:,.
OJ f-o- & Berry 1981; Stanford & Ward 1984) and Lower Basin tributaries (LaBounty
;::I z~." ~ .- ....
.s "E ""0 ~ ~ <.; '" ~ .,
.... ~ o '" ; '" <.; .... <:~ & Minckley 1972; Cross 1976), However, high-altitude headwater streams in the
C 0:1 E! ..., o E.:: -<:l <: c.-
.... <.; ~~ a a 0.;:)0 0"" '"
0 0 ,,0 '" 0",0 ~ '" north (e.g. Gunnison River: Fig. la) contain a more stenothermic fauna than
u '" -< .!:: '- a a ::l ~~ ..... "-:l
..., gJ5." 00 0:1 '" Z~~ "S'2~ ....J '" "
>- 11~ .., Od ... .S S S ~ 2 ~ $ ~ -
..... c U75] G~~ the south (cf. Gila River: Fig. 1 b). For example, Salmo gilae survives late-
....; ....J .~ ." "'~ ~ C t:: ~ .5 "E
... "0 - OJ f-o " .... 's:::== ~-g
i ell <:I .... " .... <:I C. ;:s '" '" OJ OJ i:l. ....- ~ <.; '" ;:J " ,-
~ ;::I --C 'C; '" .- - 0 f-o :::: .:: ~ .!?;.D.~ >- ~d3 ~ 0 .::r:: o "'l:ll ~~...I summer temperatures up to 27"C in the Gila drainage (Lee & Rinne 1980),
-<:l a '- '" "'u 8aO (j~~ i:l.ce'-"
~ <: OJ '(jl:ll (jl:ll (j'-" uu \.)'-"\.) whereas S. clarki pleuriticus in the Upper Basin inhabits waters well below 20oC.
u.. I:>ll
388 A, 389