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Last modified
8/11/2009 11:34:21 AM
Creation date
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UCREFRP
UCREFRP Catalog Number
8105
Author
Haines, G. B., D. W. Beyers and T. Modde.
Title
Estimation of Winter Survival, Movement and Dispersal of Young Colorado Squawfish in the Green River, Utah.
USFW Year
1998.
USFW - Doc Type
Recovery Program Project 36,
Copyright Material
YES
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<br />SUBADUL T HUMPBACK CHUB IN THE COLORADO RIVER <br /> <br />273 <br /> <br />90 data points: three variables (depth, velocity and cover), three distances from shore at lO-m intervals <br />along 100 m of shoreline. With these data, mean transect depth, velocity and total cover were derived for <br />reaches 1 and 2 and for all six shoreline types. A total of 69 longitudinal transects among all shoreline <br />types were measured: 40 in Reach 1, and 29 in Reach 2 (Table II). Discharge at the time transects were <br />obtained from the gauge station located above the confluence of the LCR. <br />Fish sampling. We used electrofishing catch rates to estimate relative densities of subadult humpback <br />chub ( < 200 mm TL) within all three geomorphic reaches and each of the six shoreline types (Table III). <br />Electrofishing was conducted from Achilles SU-16 research boats equipped with Mark XX@ Complex <br />Pulse Systems, as described in Valdez and Ryel (1995). The time required to sample each shoreline was <br />recorded, and catch per unit effort (CPE) was expressed as the number of fish caught per 10 h of fishing. <br />AI: 1 time:area fish-sampling ratio was assumed and thus the catch data were used as a measure of <br />relative density. Time of day and turbidity were recorded for each sample (Valdez and Ryel, 1995). Only <br />samples from high turbidity, nighttime or crepuscular periods were used to reduce confounding effects of <br />light on catch rates (Valdez and Hugentobler, 1993). <br />Flow duration curves. We used mean daily discharge data from the Lee's Ferry gauge to derive pre- and <br />post-dam flow duration curves. Flow duration curves characterize the temporal flow regime by showing <br />the temporal flow distribution as a discharge occurring over a percent of time for a period of record <br />(Leopold et al., 1964). Data from 1922 and 1960 were used to construct the pre-dam curve and from 1965 <br />and 1994 to construct the post-dam curve. To construct these curves, discharge was ranked from highest <br />to lowest and plotted against cumulative percent time. <br /> <br />Analyses <br />Physical differences among geomorphic reaches and shoreline types. Our first objective was to quantify <br />physical differences among reaches and shoreline types. To determine how reaches were geomorphically <br />different, the availability of shoreline types, width-to-depth ratio and total riffle area of the three reaches <br />were examined. To determine if depth, velocity and cover varied between reaches (blocks) and among <br />shoreline types (treatments) and to determine if shoreline conditions depended on reach (interaction), a <br />generalized randomized block multiple analysis of variance was used (GRB MANOV A) (Neter and <br />Wasserman, 1974). Because we were specifically interested in physical differences among only these <br />reaches and our inferences would be limited to this system, we considered the reach effect as fixed. This <br />assumption allowed us to use the residual error term as the mean square error when calculating F-ratios <br />(Neter and Wasserman, 1974). Mean transect depth and velocity were 10glO-transformed to correct for <br />heteroscedasticity in the MANOV A (Zar, 1984). We used an a priori a value of 0.1 (10% chance of type <br />I error) for all statistical analyses due to low sample size and probable low power. <br />Relationships between subadult humpback chub and geomorphology. To determine if subadult humpback <br />chub were associated with reach and shoreline differences (objective 2), associations of fish with specific <br />depth, velocity and cover conditions were examined and relative densities of fish among reaches and <br />cf shoreline types were compared. Initially, we wanted to determine if the longitudinal distribution of <br />subadult humpback chub could be explained by something other than habitat selection (e.g. passive <br />dispersion). We therefore examined how densities varied throughout the three reaches for each shoreline <br />type. Downstream distributions of subadult humpback chub densities within each shoreline type were <br />fitted with a LOWESS line-of-best-fit (SYSTAT, Inc., 1992). A monotonic decline in density would be <br />consistent with the distribution expected from passive dispersion. A flat line with large differences in <br />magnitude of densities among shoreline types would imply local habitat selection was occurring. <br />Discriminant functions analysis (DF A) was used to determine if the presence of fish within sample units <br />was associated with differences in mean depth, velocity and cover. For this analysis, only fish samples that <br />were spatially concurrent with a longitudinal transect (n = 173) and thus had associated habitat informa- <br />tion were used. <br />To determine if variation in fish densities was associated with differences among reaches or shoreline <br />types, a GRB ANOV A was conducted with reaches as blocks and shoreline type as the treatment. An <br />interaction term between reach and shoreline type was included in this model. Block effects were also <br /> <br />~ 1998 John Wiley & Sons, Ltd. <br /> <br />Regul. Rivers: Res. Mgmf. 14: 267-284 (1998) <br />
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