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148 The Southwestern Naturalist vol. 34, no. 1 ~ March 1989 Notes 149 "~
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<br />NEV UTAH
<br />CALIF °LaM•
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<br /> LEGEND
<br />10 0 10 20 30
<br />DEPTH
<br />SCALE OF METERS '
<br /> ----- VELOCITY
<br /> ~ SPAWNING
<br /> DEPRESSIONS
<br />FIG. 1-Spawning depression distribution, water depth, and velocity profiles for razorback suckers
<br />(Xyrauchen texanus) in the Colorado River, Lake Mohave, Nevada-Arizona.
<br />1
<br />location. Spawning activities appeared to be restricted to a 300-mz area of scoured sands and gravels
<br />deposited in the river channel From a dry wash located 4.6 km downstream of Hoover Dam. Substrate
<br />size in this area was different from the larger armored material or fine sands observed in other areas
<br />of the river. `
<br />Additional dives were conducted over the spawning area on 11 February, 25 February, and 11
<br />March 1984 with suckers (1 to 37) observed on each occasion. All observations, measurements, and
<br />underwater sampling were accomplished using scuba equipment. The spawning site was mapped with
<br />water depth and velocity profiles shown in Fig. 1. Scuba observations revealed that vigorous and
<br />repeated spawning activities disturbed the substrate and resulted in obvious depressions. Activities
<br />Rushed finer materials from the substrate leaving depressions lined with larger gravels and cobble.
<br />Within the spawning area, i8 depressions measuring 0.25 to 1 mz were identified and occurred at
<br />depths of 1.2 to 2.0 m (28 January). Mean water velocities (Marsh McBirney Row meter, Mod. 201)
<br />ranged from 0.00 to 0.37 m/s. Nose velocities (10 cm from substrate) at Rve specific sites where
<br />spawning was observed averaged 0.15 m/s (range of 0.12 to 0.18 m/s).
<br />Twenty-three Surber samples yielded 103 eggs and 34 larvae. Eggs and larvae were collected during
<br />January and February, but none were found during March. Samples (n = 19) taken directly from
<br />spawning depressions yielded 10.5 to 16.7 eggs/m2 and 0.7 to 5.7 larvae/m2. Samples (n = 3) taken
<br />from finer material outside of depressions did not yield any eggs or larvae. One sample collected from
<br />large-cobble substrate located immediately downstream from the spawning site yielded 52 eggs (273.7
<br />eggs/mz) and 21 larvae (110.5 larvae/mz), suggesting a high degree of drift.
<br />Fecundity of adult female razorback suckers has been found to average nearly 1,800 ova/cm standard
<br />length, and most females are >50 cm standard length (=about 100,000 ova/female; Minckley, 1983).
<br />Based on maximum observed density of 274 eggs/m2, it appears females deposit only a few eggs at a
<br />time.
<br />Spawning behavior was similar to that reported for populations in reservoirs. However, spawning
<br />males appeared to be less mobile in the river. The majority of fish, which appeared to be "small"
<br />(approximately 40 cm total length) males, maintained stationary positions on the downstream end of
<br />the site. This behavior was different from the roving nature previously observed and reported for
<br />reservoir-spawning groups (Minckley, 1983). Larger fish, presumably females, periodically moved into
<br />the area from the adjacent river, attracting some of the otherwise stationary males to form spawning
<br />groups of three to eight fish. These groups, composed of one female and several males, would spawn
<br />over depressions or swim around the area before dispersing. The spawning act only took a few seconds
<br />and, other than orienting with the current, was similar to that reported elsewhere. However, on several
<br />occasions spawning groups appeared to seek shelter downstream of large boulders and, while maintaining
<br />their position, would roll in mass for several seconds.
<br />These observations illustrate that razorback suckers can and do spawn in lotic environments down-
<br />stream from major impoundments. Possibly, these riverine spawning conditions more closely resemble
<br />the structural habitats utilized by razorback suckers in the Colorado River prior to man's influence on
<br />the system.
<br />I thank P. Marsh and R. Leutheuser for critical review of the manuscript.
<br />LITERATURE CITED
<br />HOLDEN, P. B., AND C. B. STALNARER. 1975. Dis[ilbu[IOn and abundance Of mainstream fishes Of
<br />the middle and upper Colorado River basins, 1967-1973. Trans. Amer. Fish. Soc., 104:217-
<br />231.
<br />MARSH, P. C., AND D. R. LANGHORST. In press. Feeding and fate of wild larval razorback sucker.
<br />Environ. Biol. Fishes.
<br />HINCKLEY, C. O., AND S. W. CAROTHERS. 1979, Recent collections of the Colorado squawfish and
<br />razorback sucker from the San Juan and Colorado rivers in New Mexico and Arizona.
<br />Southwestern Nat., 24:686-687.
<br />HINCKLEY, W. L. 1983. Status of the razorback sucker, Xyrauchen texanus (Abbott), in the lower
<br />Colorado River basin. Southwestern Nat., 28:165-187.
<br />ULMER, L. ] 980. Movement and reproduction of razorback sucker inhabiting Senator Wash Reservoir,
<br />California. Proc. Desert Fishes Council, 12:106.
<br />GORDON MUELLER, Bureau of Reclamation, Boulder City, NV 89005.
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