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North American Journal of Fisheries Management 23:270-275, 2003
<br />© Copyright by the American Fisheries Society 2003
<br />ft.
<br />Factors Influencing Poststocking Dispersal of
<br />Razorback Sucker
<br />GORDON A. MUELLER'
<br />U.S. Geological Survey, Box 25007,
<br />D-8220, Denver, Colorado 80225, USA
<br />PAUL C. MARSH
<br />Arizona State University, Department of Biology,
<br />Tempe, Arizona 85287, USA
<br />DEAN FOSTER
<br />4221 South Kolb Road,
<br />Tucson, Arizona 85730, USA
<br />MANUEL ULIBARRI'
<br />Willow Beach National Fish Hatchery, HC37 Box 17,
<br />Willow Beach, Arizona 86447, USA
<br />TOM BURKE
<br />Bureau of Reclamation, Box 61470,
<br />Boulder City, Nevada 89006, USA
<br />Abstract.-Efforts to reintroduce razorback suckers Xy-
<br />rauchen texanus to specific river reaches have been
<br />plagued by downstream drift and poor survival, which
<br />have been attributed to stress, disorientation, predation,
<br />and poor conditioning. Poststocking dispersal of eight test
<br />groups (15 fish each) of razorback suckers was examined
<br />for 28 d with telemetry equipment. Fish were released in
<br />three different locations in the Colorado River basin of
<br />Utah, Arizona, and Nevada: (1) a 65,000-ha reservoir, (2)
<br />a small (<1-ha) backwater, and (3) a large (30-ha) back-
<br />water on the mainstem river. At each location, subgroups
<br />were released immediately (reference) or held to accli-
<br />mate them to the site (3-7 d) before release. Two of four
<br />subgroups for the large-backwater test were precondi-
<br />tioned to flow. Dispersal from the stocking sites was rapid
<br />and declined with time for all tests, as fish appeared to
<br />seek and find cover. Downstream drift was most pro-
<br />nounced (x = 69.5 km) from the small backwater and
<br />significantly (Kruskal-Wallis test, P < 0.01) greater than
<br />either the reservoir (x = 3.7 km) or large-backwater sites
<br />(x = 7.7 km). Site-acclimation tests were inconclusive,
<br />but downstream movement was significantly (Wilcoxon
<br />two-sample test, Z = -2.298, P < 0.01) less for fish
<br />preconditioned to flow (x = 1.9 km) compared with pond-
<br />reared fish (x = 7.7 km). We concluded that poststocking
<br />dispersal may decrease if razorback suckers are precon-
<br />ditioned to flow.
<br />Though once common, the razorback sucker
<br />* Corresponding author: gordon_a_mucllerCn)usgs.gov
<br />Present address: Dexter National Fish Hatchery
<br />Dexter, New Mexico 88230, USA.
<br />Received April 24, 2000; accepted May 2, 2002
<br />Xyrauchen texanus has declined in distribution
<br />and abundance and now is represented only by
<br />small populations of old adults in the Colorado
<br />River basin (Minckley et al. 1991; USFWS 1998).
<br />The fish was federally listed as endangered in
<br />1991 (USFWS 1991). Over 12 million razorback
<br />suckers, mostly fry or juveniles, have been
<br />stocked in the lower Colorado River basin
<br />(Minckley et al. 1991). Efforts to repopulate spe-
<br />cific river reaches have been plagued by down-
<br />stream drift and poor survival (Marsh and Lan-
<br />ghorst 1988; Marsh and Brooks 1989), factors
<br />commonly attributed to stress, disorientation,
<br />starvation, and predation (Wedemeyer et al.
<br />1990). As a result, larger fish (>25 cm) are being
<br />released to reduce predation (Mueller 1995), fish
<br />are being stocked further upstream anticipating
<br />drift (Burdick and Bonar 1997) or stocking pro-
<br />grams are simply being terminated.
<br />Researchers have recommended that site accli-
<br />mation (Minckley et al. 1991), physical condi-
<br />tioning (Wydoski 1994), and winter releases
<br />(Marsh and Brooks 1989) be tested to determine
<br />whether performance and survival improve. How-
<br />ever, reintroduction programs have yet to test these
<br />hypotheses. Consequently, we examined the ef-
<br />fects of site acclimation and rearing environment
<br />on dispersal of hatchery-reared razorback suckers
<br />released at three different locations in the Colorado
<br />River basin of Utah, Arizona, and Nevada.
<br />270
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