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20001 XYRAUCHEN TExANUS IN LAKE MOHAVE 181 <br />has a maximum width of 6 km (Fig. 1). Lake <br />Mohave has no tributaries other than the Col- <br />orado River, which enters as cold, hypolim- <br />netic releases (Lake Mead) from Hoover Dam. <br />Flows are discernible for the first 20-30 km, at <br />which point the river exits Black Canyon and <br />the reservoir broadens and depth increases. <br />Maximum depth at Davis Dam is 35 m. <br />Construction of Davis Dam in 1954 repre- <br />sented the last mainstem reservoir built on the <br />lower Colorado River. It is believed the reser- <br />voir population of X. texanus originated from <br />an initially high period of recruitment from <br />individuals trapped upstream during the clo- <br />sure of Davis Dam (Minckley 1983, Marsh <br />1994). <br />METHODS <br />Collections <br />A trammel net (2 m x 3.7 cm x 50 m) was <br />used to capture wild adult X. texanus on 6-7 <br />Hoover Dam <br />Waypoint 1 <br />2 <br />3 <br />0 <br />4 <br />STUDY AREA 5 6 <br />Nevada Utah <br />alifornia) A-na <br />7 <br />8 <br />Fish Detections = <20 20-39 ® 40-59 0 >60 <br />37, <br />Cottonwood <br />Cove <br />'`1 38 <br />b <br />c <br />November 1994 from Lake Mohave at Yuma <br />and Tequila coves. Each fish was measured for <br />total length (mm), weighed (g), anesthetized <br />with tricaine methanesulfate (125 mg L-1), <br />and surgically implanted (after Tyus 1987) <br />with a sonic transmitter. A 30- to 40-mm <br />medio-lateral incision was made slightly ante- <br />rior and dorsal to the left pelvic fin, and the <br />transmitter was inserted into the abdominal <br />cavity so that it rested on the pelvic girdle. <br />The incision was sutured with 4-5 knots using <br />3-0 Ethilon black monofilament nylon and an <br />FS-1 cutting needle. We allowed the fish to <br />recover 1-10 min after surgery and then <br />released them at capture sites. Transmitters <br />weighed 6 g, measured 16 x 55 mm, had a 14- <br />month life expectancy, and were individually <br />coded. Transmitters had an average detection <br />range of 1 km and logged the transmitter (fish) <br />temperature (± 0.25°C) that was compared <br />with water temperature profile data to deter- <br />mine fish depth. <br />a b <br />m <br />Tequila Cove <br />to (Release site) <br />0 (21 <br />6-Mile <br />24 Cove <br /> <br />25 <br />R26 9 -mil" <br />Cove <br />9 <br />10 fflWillow Beach <br />, , Marina <br />? 12 <br />13 <br />14 <br />ra <br />15 N <br />16 <br />17 <br />v° <br />18 <br />19 <br />a <br />30 <br />r! 31 <br />Owl Point <br />k 33 <br />c <br />39 • 69 <br />70 <br />i <br />X41• 42 • 71 <br />44 43 <br />Davis Dam <br />• <br />47 48 49 <br />3 ?- 1 0 Big Basin <br />4 Si5 a <br />56 <br />958 <br />• <br />N o? <br />61 <br />62 <br />• <br />64 <br />• <br />0 5 km 6: <br />1 I • <br />66 <br />Yuma Cove <br />(Release site) <br />Fig. 1. Segmented map of Lake Mohave, Arizona-Nevada, showing numbered GPS way-point locations and place <br />names mentioned in the text. Shaded areas reflect total number of fish detections per way-point from November 1994 <br />through July 1997.