|
<br />lq~ G~-k.rMMi+h e.,+o.l.
<br />
<br />i<6L\ 1
<br />
<br />Reprinted from THE SOUTHWESTERN NATURALIST
<br />Vol. 39, No, 4, December 1994
<br />Made in United States of America
<br />COLLECTION OF AGE-O RAZORBACK SUCKERS
<br />(XYRAUCHEN TEXANUS) IN THE LOWER
<br />GREEN RIVER, UTAH
<br />
<br />t
<br />
<br />F. BRANDT GUTERMUTH, LEO D, LENTSCH, AND KEVIN R, BESTGEN
<br />
<br />Utah Division of Wildlife Resources, Native Wildlife Section,
<br />1596 West North Temple, Salt Lake City, UT 84776 (FBG, LDL)
<br />Larval Fish Laboratory, Department of Fishery and Wildlife Biology,
<br />Colorado State University, Fort Collins, CO 80523 (KRB)
<br />Present address of FBG: United States Fish and Wildlife Service,
<br />Lincoln Plaza Suite 404, 145 East 7300 South, Salt Lake City, UT 84775
<br />
<br />I
<br />
<br />Historically widespread and abundant
<br />throughout warm water reaches of the Colorado
<br />River basi , the endemic razorback sucker (Xy-
<br />rauchen lex nus) is now rare and listed as en-
<br />dangered ( nited States Fish and Wildlife Ser-
<br />vice, 1991) Mainstem dams that alter habitat
<br />and in trod ction of non-native fishes which prey
<br />upon or co pete with early life stages are among
<br />the large-s ale ecological disturbances that have
<br />negatively ffected the razorback sucker (Tyus,
<br />1987; Minc ley et ai., 1991), Rarity oflarval and
<br />especially j venile razorback suckers in collec-
<br />tions, and resence of only aged adults in re-
<br />maining p pulations indicates recruitment fail-
<br />ure (McCa thy and Minkley, 1987; Lanigan and
<br />Tyus, 1989' Minckley et ai., 1991),
<br />Adult ra orback suckers are abundant only in
<br />Lake Moh ve in the lower Colorado River basin
<br />(Minkley, 983; Minckley et ai., 1991), and the
<br />largest rem ining riverine population is in the
<br />upper Gree River, near Jensen, Utah (Lanigan
<br />and Tyus, 1989; Tyus and Karp, 1990; Minckley
<br />et aI., 1991), In Lake Mohave, razorback suckers
<br />spawn ann ally and produce large numbers of
<br />larvae, but juvenile recruitment has been rare
<br />since the 1950s (Marsh and Minckley, 1989;
<br />Minckley et ai., 1991), Juvenile razorback suck-
<br />ers were historically rare in collections from the
<br />Colorado River basin, and most juveniles caught
<br />since 1980 were collected from canals and ponds
<br />downstream of Lake Havasu and Parker dam in
<br />the lower Colorado River (Minckley et ai., 1991),
<br />In the Green River, near Jensen, Utah, ripe ra-
<br />zorback suckers annually congregate over gravel
<br />bars, but prior to this record, the only recent
<br />evidence of successful reproduction was limited
<br />to a 1984 collection series of larvae tentatively
<br />identified as razorback suckers by D, E. Snyder
<br />(Tyus, 1987; Tyus and Karp, 1990), Although
<br />Holden (1980) reported capture, in 1977, of two
<br />
<br />..
<br />I.
<br />
<br />approximately 50-mmjuvenile razorback suckers
<br />from below the confluence of the White and Green
<br />rivers, further analysis of these specimens (e,g"
<br />low gill raker and high lateral line counts) by
<br />other researchers suggests that they were more
<br />likely razorback x flannelmouth sucker (Catas-
<br />tamus latipinnis) hybrids (P, Holden, pers, comm,),
<br />Unfortunately, these specimens have been lost
<br />and were not analyzed, Thus, only two substan-
<br />tiated collections of razorback sucker juveniles
<br />have been made in the Upper Colorado River
<br />basin, Smith (1959) reported two young razor-
<br />back suckers, each about 38 mm total length (TL),
<br />from a pre-impoundment Lake Powell survey of
<br />the Colorado River in Glen Canyon, and Taba
<br />et ai. (1965) reported eight specimens (90 to 115
<br />mm TL) from backwaters of the Colorado River
<br />downstream of Moab, Utah, during surveys in
<br />1962 to 1964,
<br />Our 30 July 1991 collection of two early ju-
<br />venile razorback suckers (LFL catalog #2725;
<br />36,6 and 39,3 mm TL) in the lower Green River
<br />near Hell Roaring Canyon (89,5 km above con-
<br />fluence with the Colorado River) is the first ver-
<br />ified evidence of razorback sucker survival beyond
<br />the larval period in the upper Colorado River
<br />basin since that reported by Taba et ai. (1965),
<br />Specimen identity was verified by G, R, Smith
<br />and D, E, Snyder using morphological, meristic,
<br />and osteological characters, The latter characters
<br />were revealed by radiographs and included the
<br />fan-shaped neural complex bones diagnostic for
<br />juvenile razorback sucker (Snyder and Muth,
<br />1990),
<br />The specimens were captured at 1325 h by
<br />seine (3,2 mm mesh; 1.2 by 4 m) in a 3,5 m wide
<br />by 24,5 m long, silt-bottom backwater which
<br />opened to 12 m in width at the mouth, Slightly
<br />turbid water and a large boulder were the only
<br />cover, Maximum water depth was 0,7 m, but
<br />
|