9330 - Laserfiche WebLink

Home Browse Search

20001 XYRAUCHEN TEXANUS IN LAKE MOHAVE 183 TABLE 1. Individual tracking summaries for sonic telemetry of 10 wild adult Xyrauchen texanus in Lake Mohave, Ari- zona and Nevada, November 1994 to July 1997. Fish are individually identified by tag code; number of observations, average and total distance (m d-t) traveled, days tracked, and range (km) of each fish are presented. Fish ID TL (mm) Weight (kg) No. of obs. Distance traveled Min. Max. Avg. - - - - - - (m d-t) - - - - - - - s Total distance traveled (km) Days tracked Range (WPa) FEMALES 88 615 2.70 65 0 6,703 603 1322 250.4 974 32-66 276 654 3.61 71 21 3,502 606 708 352.5 953 24-67 339 665 3.33 62 9 10,108 767 1413 417.4 981 27-99 375 680 3.35 54 4 2,368 417 544 249.7 540 16-64 384 631 2.76 36 0 6,886 614 1133 18310 466 26-65 465 614 2.94 65 9 6,558 485 851 2643 969 5-34 x 643 3.12 59 7 6,021 582 996 286.2 814 MALES 2228 558 2.40 51 3 15,607 788 2280 231.5 540 39-90 366 588 2.29 57 0 1,986 243 509 167.7 974 31-62 348 526 1.75 65 0 17,353 509 2154 181.7 960 32-71 258 595 2.26 57 0 1,635 242 334 120.9 540 29-47 X 567 118 58 1 9,145 446 1319 175.5 754 eWP = way-point where cold Hoover Dam releases mix with warmer Lake Mohave waters. We observed 9 X. texanus (nontagged) near the surface at the mixing zone on 8 June 1997 (9 fish per 1.5 km). Movements Fish movements were variable and distinc- tive by sex and among individuals. Both males (> 17.4 km d-1) and females (10.1 km d-1) trav- eled substantial distances in short periods of time, while some fish remained sedentary for days. Fish on average moved 527 in d-1 (u = 242-788 in d-I), and while there was no statis- tical difference between sexes, females tended to be slightly more active (ac = 582 in d-I) than males (x = 446 in d-1; Table 1). Hourly movement rates were statistically examined, and although no significant trends were iden- tified, apparently fish might be slightly more active during summer at midmorning hours (0900-1000 h), supporting previous observa- tions (McAda and Wydoski 1980). Movement rates were examined both for nondirectional (m d-I) and directional (linear km month-1) activities. Monthly averages near the end of, or shortly after, spawning (March, April, May) exceeded 1000 in d-1 for 1995, 1996, and 1997 (Table 2). Linear distances traveled (km month-1) peaked following spawning for all 3 yr (March 1995, May 1996, April 1997 [Table 2]). Linear ranges for indi- viduals (N = 10) averaged 39 km (18-72 km) during the course of the study. Females on average ranged 42 km (29-72 km) compared to 35 km (18-51 km) for males. All study fish returned to spawning sites used in previous years, but they also visited other spawning sites. Spawning (31 Janu- ary-15 March 1995, 1996) females were signif- icantly (ANOVA/Fl g = 6.79, P = 0.0314) more active (460 vs. 87 m d-1) than males. During peak spawning (1-28 February 1995, 1996), the majority of females crossed the reservoir to visit other spawning sites while males typi- cally remained at a single site (Fig. 2). Habitat Use Xyrauchen texanus exhibited a significant association with inshore (<50 in of shore) habi- tats (P < 0.001, chi square test). This affinity was most pronounced during spawning when distance from shore averaged <30 in. Fish moved offshore during summer (July-Novem- ber), possibly to avoid warmer water tempera- tures (Fig. 3). During warmer months the reservoir pre- sented fish a wide range of thermally stratified habitats. Temperatures up-reservoir were cold (12°-16°C), regardless of season or depth, due to hypolimnetic releases from Lake Mead. During summer the reservoir thermally strati- fies further downstream presenting tempera- tures ranging from 30°C (surface) to 15°C