9533

• UCREFRP Catalog Number: 9533
• Author: Muth, R. T. and E. Wick.
• Title: Field Studies on Larval Razorback Sucker in Canyonlands National Park and Glen Canyon National Recreation Area, 1993-1995.
• USFW Year: 1997.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

existing laboratory techniques for marking otoliths in live razorback sucker larvae with
fluorescent chemicals, and (4) evaluate survival and growth potentials of larval razorback
sucker placed in enclosures free of nonnative predators or competitors located in nursery
habitats at selected locations in the lower Green River within CANY.

METHODS

Description of Study Areas, Sampling Periods, River Flow/Temperature Regimes

Sampling in 1993 was conducted inside Millard Canyon (river km, RK, 53.6; distance
from the confluence of the Green and Colorado rivers, RK 0.0) and in the Anderson
Bottom-Bonita Bend area (RK 50.4-49.6) on the lower Green River, and in the lower 47 km of
the Colorado River inflow to Lake Powell (Imperial Canyon, RK 320.3, to Hite Bridge, RK 273.3;
distance from Lee's Ferry, Arizona, RK 0.0). In 1994, sampling was conducted in Millard
Canyon and the Bonita Bend area on the lower Green River, in the Gooseneck area (RK 58.4)
and inside Shafer and Lathrop canyons (RK 55.8 and 37.6, respectively) on the middle
Colorado River, and in the lower 47 km of the Colorado River inflow to Lake Powell. The study
area in 1995 included the Millard Canyon-Holeman Canyon reach (RK 53.6-44.8) on the lower
Green River and the lower 47 km of the Colorado River inflow to Lake Powell. In 1993,
sampling occurred on 17-19 June in the lower Green River and 20-22 June and 3-6 August in
th.e Colorado River inflow to Lake Powell. Sampling in 1994 occurred on 4-5 and 17-18 June
in the lower Green River, 2-4 and 16-17 June in the middle Colorado River, and 9-12 June,
19-20 June, and 16-18 July in the Colorado River inflow to Lake Powell. Field work in 1995
occurred on 16-17 May, 2-8 and 20-24 June, and 7-10 July in the lower Green River, and
11-13 July in the Colorado River inflow to Lake Powell.
Habitats sampled had negligible water velocity and included flooded side canyon
shorelines, flooded washes, side- and mainchannel backwaters, and mainchannel shorelines
and mud flats. Many of these habitats are dry or isolated from the mainchannel during late
summer-winter. As river flows increase in April-June, these habitats reconnect to the
mainchannel, fill with water, and are passively or actively invaded by fish. As flows begin to
recede in late June-early July, fish either move out of these habitats and back into the
mainchannel or are eventually trapped inside and possibly die. Although these habitats are
typically ephemeral under present flow regimes and riparian conditions, they serve as primary
nursery areas in CANY and GLCA for young native and nonnative fishes.
Flows and temperatures recorded by the U.S. Geological Survey during April-July in
1993-1995 for the middle and lower Green River at the Jensen (middle) and Green River
(lower) gages, Utah, and middle Colorado River at the Cisco gage, Utah, are presented in
Appendices A (Green River) and B (middle Colorado River). Annual peak mean daily
discharges (m3/s) were 710 (on 31 May 1993), 331 (22 May 1994), and 803 (19 June 1995) for
the lower Green River, and 1,347 (23 May 1993),424 (21 May 1994), and 1,455 (19 June 1995)
for the middle Colorado River. Although magnitude of peak mean daily discharges for the lower
Green and middle Colorado rivers was similar in 1993 and 1995, temporal occurrence of peak
flows was 19 (lower Green River) to 27 d (middle Colorado River) later in 1995 than in 1993.
Mainchannel water temperatures were similar in 1993 and 1995 and comparably higher in 1994
for the lower Green River but were considerably lower in 1995 compared to 1993 and 1994 for
the middle Green River during late April through July. Nursery habitats sampled on the lower

3