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<br />I <br />fl <br />I <br /> <br />[I <br /> <br />[I <br />fl <br /> <br />' . . <br /> <br /> <br /> <br />fI <br />fI <br />rl. <br /> <br />I <br /> <br /> <br /> <br />il <br />:_1 <br />fl <br />~ <br />l.. <br /> <br /> <br /> <br />~I <br />il <br /> <br />\_'---' <br /> <br /> <br /> <br />:.1 <br />:1 <br />II <br /> <br />'--... <br /> <br /> <br />,I <br />'I <br /> <br />1. Fish Surveys: Davis Dam to Lake Havasu <br /> <br />Introduction <br /> <br />The Colorado River bordered by Davis and Parker dams supports a diverse and impressive recreational <br />fishery. Rainbow trout have been stocked in the cool tail waters of Davis Dam for over 50 years. Lake Havasu <br />supports an economically important black bass fishery. During the past decade, more than 875 acres of habitat <br />structures were placed throughout the reservoir as part of the Lake Havasu Fisheries hnprovement Program. A <br />recent economic report estimated the project is generating more than $18 million annually by nonresident <br />anglers to the local economy (Anderson, 2001). <br />Historically, this section of river contained the last remnants of the main stem native fishes in the lower <br />basin. Topock Marsh and other associated backwaters located between Fort Mohave and Needles, California <br />provided nearly 1,740 ha of off-channel nursery habitat (Beland 1953). While Davis Dam was being <br />constructed (1950-1954), Jonez and Sumner (1954) observed both bonytail and razorback sucker young in the <br />vicinity of the new dam and a large number of young were collected at Cottonwood Landing in 1950 (Miller <br />1961). This represented the last documentation of significant numbers of young for either species in a river <br />environment. The last Colorado pikeminnow taken from the lower main stream was captured from Lake <br />Mohave by an angler in 1962; anglers continued to take bonytail from the river near Bullhead City until the <br />mid-1970's (Minckley, 1979; Mueller and Marsh, 2002). A few razorback suckers lingered in the area until <br />the late 1990's, possibly dating back to the prepdredging era (1950's). <br />Closure of Davis Dam and the filling of Lake Mohave Gaused a brief resurgence ofbonytail and razorback <br />sucker production. The new reservoir trapped native fish and initial flooding apparently mimicked conditions <br />necessary to sustain young. Bonytail and razorback sucker communities rapidly expanded in the early years <br />until nonnative predators over whelmed their progeny (McCarthy and Minckley, 1987). The resulting native <br />community numbered in the tens of thousands (Minckley, 1983). This community has been the topic of study <br />for nearly four decades by faculty from Arizona State University and the University of Nevada-Las Vegas. <br />Assisted by other state and federal agencies, wild populations have heen monitored and hatchery-reared fish <br />have been stocked to augment declining wild stocks. More than 55,000 razorback sucker and similar numbers <br />ofbonytail (as of2003) have been stocked in Lake Mohave to augment those populations. The objective of the <br />razorback sucker stocking program is to maintain the community through artificial production by using <br />innovative methods designed to maintain the genetic diversity of the population (Mueller, 1995). <br />Natives found in the river between Parker and Davis Darns have received less scrutiny. In 1976, 611 <br />tlannelmouth suckers were stocked and during the past decade, 30,000-razorback sucker and 18,000 bonytail <br />were also introduced. During the past 3 years, FWS and other agencies have conducted an annual, one-week <br />survey of Lake Havasu. However, there has not been an intensive effort to assess these specific introductions. <br />In recent years, state biologists reported collecting multiple year classes of tlannelmouth sucker during annual <br />fish surveys. It was hoped the factors that allowed the survival of tlannelmouth juveniles may also benefit <br />razorback sucker. The objectives of this study included: <br />1. describe the fish community found in the 80 kIn portion of the river downstream of Davis Dam, with <br />special interest in bonytail, tlannelmouth sucker, and razorback sucker, <br />2. determine what factors contributed to the successful colonization of the tlannelmouth sucker, <br />3. identify spawning locations used by the natives, and <br />4. determine the survival rate of stocked fish. <br /> <br />2 <br />