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120 The Southwestern Naturalist vol. 28, no. 1
<br />(H. Tyus and R. Valdez, pers. comm.). Therefore this occurrence is undoubtedly very rare and
<br />probably had little influence on the decline of the Colorado squawfish.
<br />I thank R. Wydoski and C. Reger who participated in the collection. The Utah Cooperative
<br />Fishery Research Unit is jointly supported by the U.S. Fish and Wildlife Service, Utah Division of
<br />Wildlife Resources, and Utah State University.-CHARLES W. McADA, Utah Coop_ Fish. Res. Unit,
<br />UMC-52, Utah State Univ., Logan, UT 84322. (Present address: U.S, Fish and Wildlife Service,
<br />557 25,5 Rd., Suite B113, Grand Junction, CO 81501).
<br />SOUTHWESTERN CACTI GROWING AS EPIPHYTES.-Humphrey (The Boolum and Its
<br />Home, Univ. of Arizona Press, Tucson, 1974) found Opuntia sp. and Ferocactus sp. growing on
<br />Idria columnaris in Baja California Norte, Mexico. He suggests they grow from bird deposited
<br />seed at places on the boojum where soil and debris accumulate. We wish to report here two
<br />instances of cacti growing on alligator juniper (Juniperus deppeana) in moist canyons of the
<br />northern Chihuahuan Desert. Opuntia phaeacantha was seen in August 1981 growing on the end
<br />of a horizontally fractured branch (ca. 50 cm diameter) of a tree in McKittrick Canyon, Guadalupe
<br />Mountain National Park, Culberson Co., TX at an elevation of 1500 m. The cactus is well estab-
<br />lished with 14 joints, and is 2.5 in above the ground in a thicket of canyon bottom vegetation. A
<br />cluster of five 3-6 cm tall Ech.inocereus triglochidialus was seen in October 1978 and January 1982
<br />on a 151 cm dbh tree in Three Rivers Canyon, Otero Co., NM at 2100 in elevation. Much of this
<br />large, old tree is dead, and only 26% of the stern circumference has bark. The cacti ae 3 in above
<br />the ground, and appear to have grown little between observations. They are bedded in decaying
<br />wood in a place that catches moisture and some leaf litter from nearby oaks. Both were left undis-
<br />turbed, and consequently our species indentifications are tentative.
<br />Growth of cacti as epiphytes seems the result of an infrequent combination of circumstances.
<br />There are few large, old trees in the region, and only a fraction of them have platforms to catch
<br />bird or rodent transported seeds, moisture, litter and some sunlight. The first author would appre-
<br />ciate copies of any published or unpublished observations of cacti growing on trees or other
<br />unusual places in the deserts of southwestern North America.-WILLIAM RECD AND RALPH KRAPPA,
<br />Laboratory for Environmental Biology, Univ. of Texas at El Paso, El Paso, TX 79968.
<br />MATURITY AND FECUNDITY OF THE BLUEHEAD SUCKER, CATOSTOMUS DISCO-
<br />BOLUS (CATOSTOMIDAE), IN THE UPPER COLORADO RIVER BASIN, 1975-76.-The blu-
<br />ehead sucker, Catoslomus discobolus, is native to the upper Snake River drainage, Idaho and
<br />Wyoming, Weber and Bear River drainages, Utah and Idaho, and the Colorado River system
<br />above the mouth of the Grand Canyon (Smith, Univ. Mich. Mus. Zool., Misc. Publ. 129:1-133,
<br />1966; Minckley, Fishes of Arizona, Arizona Game and Fish Dept. 293 pp., 1973). Although largely
<br />limited to areas of relatively swift water with cobble or gravel bottom, it is distributed throughout
<br />these rivers and is considered common to abundant in areas of suitable habitat. Information con-
<br />cerning bluehead sucker is generally limited to distribution (Vanicek et al., Southwestern Nat.
<br />98:193-208, 1970; Holden and Stalnaker, Trans. Amer. Fish. Soc. 104:217-231, 1975; Sigler and
<br />Miller, Fishes of Utah, Utah Dept. Fish and Game, Salt Lake City, 204 pp., 1963; Minckley 1973)
<br />or classification (Smith 1966), although Andreasen and Barnes (Copeia, 1975:645-648, 1975) dis-
<br />cussed reproduction of the species in the Weber River, Utah. We studied maturity and fecundity of
<br />bluehead sucker in the Upper Colorado River Basin.
<br />Bluehead suckers were collected using electrofishing gear and trammel nets from the Colorado
<br />River near Grand Junction, Colorado, in April, May, and June 1975; from the Green and Yampa
<br />rivers, near their confluence (Echo Park), in May and June 1975-76; and from the lower Gunnison
<br />River in May 1976. Total lengths were measured to the nearest mm; weight was determined to the
<br />nearest 20 g for fish weighing >200 g and to the neareast g for fish weighing <200 g. Mature
<br />males were identified by presence of tubercles on the anal and caudal fins. Female and immature
<br />fish were dissected to determine sex and maturity. Ovaries were removed from mature females,
<br />identified with a numbered tag, wrapped in cheesecloth, and preserved in 10% formalin.
<br />In the laboratory, ovaries were soaked in water to remove formalin and blotted to remove excess
<br />moisture; eggs were then separated from ovarian tissue. We estimated fecundity gravimetrically,
<br />using a triple-beam balance. Samples from anterior, middle, and posterior sections of the ovary,
<br />totaling about 10% of the entire ovary weight, were weighed to the nearest 0.1 g and counted. The
<br />rest of the ovary was weighed and fecundity estimated by direct proportion. Accuracy of the
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