9330

• UCREFRP Catalog Number: 9330
• Author: Mueller, G., P. C. Marsh, G. Knowles and T. Wolters
• Title: Distribution, Movements, and Habitat Use of Razorback Sucker ‎(Xyrauchen Texanus)‎ in a Lower Colorado River Reservoir, Arizona-Nevada
• USFW Year: 2000
• USFW - Doc Type: Western North American Naturalist
• Copyright Material: YES

182 WESTERN NORTH AMERICAN NATURALIST [Volume 60
Survey Design
We conducted weekly surveys by boat
using a global positioning system (GPS) and a
preestablished survey grid composed of 71
way-points or "listening stations" programed
into a CPS navigational system (Fig. 1). Sites
were at <1600-m intervals to standardize
search effort and ensure systematic coverage
of the reservoir. Transmitter signals were
detected using a DH-2 hand-held, directional
hydrophone, a USR-5W ultrasonic receiver,
and headphones. When signals were detected
from way-points, we searched out the exact
location and further triangulated using the
hydrophone and GPS. A digital readout pro-
vided time interval measurements between
signals that correlated to tag (fish) tempera-
ture. Recorded data included fish location (lat-
itude and longitude), body temperature, and
estimated distance (<10 in, 10-50 in, 50-100 m,
> 100 m) from shore. Vertical water tempera-
ture profiles were measured using a Hydro-
labTM temperature profiler between May and
October 1995.
Surveys were scheduled biweekly for the
14-month transmitter life and were conducted
in 2 shifts: 0200-1000 h and 1400-2200 h.
Transmitter life greatly exceeded manufac-
turer estimates, allowing us to collect addi-
tional intermittent information between April
and August 1996 and from April through July
1997,
was determined through observations and the
collection of newly emergent larval X. texanus
by an independent program (Mueller 1995).
Movement rates (m d-I) during active spawn-
ing (31 January-15 March 1995, 1996) for both
sexes were examined for differences in move-
ment patterns and distances using an analysis
of variance (P < 0.05; Sokal and Rohlf 1981). To
compare male and female movement patterns
when spawning observations and larval sucker
densities were most prevalent, we mapped
individual fish movement during peak spawn-
ing (1-28 February).
RESULTS
A total of 20 X. texanus (10 males and 10
females) were surgically implanted with sonic
transmitters. Six females and 4 males were
tracked during the entire 14-month study
period and were used in this analysis (Table 1;
see Mueller et al. 1998). Remaining fish were
excluded from analysis because either we lost
contact during the study period or transmit-
ters became immobile (shed tag or mortality).
An expanded description can be found in
Mueller et al. (1998). Study fish averaged 609
mm (555-680 mm) total length and 2.78 kg
(1.75-4.21 kg). More than 1000 contacts were
recorded representing 580 daily fish sightings,
300 hourly sightings, 800 body temperatures,
and 100 vertical water temperature profiles.
Data Analysis
Using digitized shoreline profile maps of
Lake Mohave and the geographical informa-
tion system (GIS) program ARCINFOTM, we
created movement maps and calculated dis-
tances (m) and movement rates (m d-I) be-
tween detection locations. Rate measurements
and distances from shore were transformed
into single classification frequency distribu-
tions, and observed data were summarized by
classes. Shoreline use was examined by com-
paring percentiles of available surface habitat
to the percentile of fish use within specific
zones via a chi square test (P < 0.001; Sokal
and Rohlf 1981). Comparisons of shoreline habi-
tat utilization, movement rates, and area affin-
ity were divided into spawning (November-
April) and nonspawning (May-October) peri-
ods as defined by reports for X. texanus in
Lake Mohave (Minckley 1983, Bozek et al.
1990, Minckley et al. 1991). Active spawning
Distribution
Fish distribution was distinctly seasonal.
Some areas of the reservoir were occupied
year-round, while other locations were used
specifically for spawning or as summer sanctu-
aries. Big Basin and Owl Point areas (Fig. 1)
were used year-round; Tequila and Yuma coves
and the warm/cold mixing zone were used
seasonally. Fish were seldom detected in up-
or down-reservoir canyon habitats. Detection
numbers were highest between way-point
(WP) 30 and WP 37. Fish found in Big Basin
typically were along the Nevada shoreline be-
tween Nine Mile and Six Mile coves (Fig. 2).
This area was used by 3 fish during spawning
and by 5 during summer. Tequila Cove (WP 39)
was visited by all but 1 fish during spawning.
Owl Point (WP 32) was visited by all
spawners and by 4 fish during summer and
autumn. Following spawning, 7 suckers moved
into the area between WP 12 and WP 24