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Last modified
7/14/2009 5:02:35 PM
Creation date
5/20/2009 10:17:31 AM
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UCREFRP
UCREFRP Catalog Number
9404
Author
Douglas, M. E. and P. C. Marsh.
Title
Ecology and Conservation Biology of Humpback Chub (Gila cypha) in the Little Colorado River.
USFW Year
1996.
USFW - Doc Type
Tempe.
Copyright Material
NO
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also differed significantly among reaches, with greatest overall <br />va, as at Confluence (F = 4.19; P < 0.01; SAS, 1985). <br />P-. lation estimates adjusted for fishing effort.---Differences <br />i:-. rmalized population estimates could result from increased <br />e::- --t. To test our estimates with fishing effort fixed, we first <br />::ted two specifications: (a) that slopes of the between-camp <br />regressions of population estimate vs effort were homogeneous <br />(i.e., regression lines parallel; see Somers and Jackson, 1993), <br />and (b) th-t interaction between fishing effort and population <br />estimates was nonsignificant. Based upon a priori statistical <br />contrasts, estimated populations in Confluence and Salt Canyon <br />reaches were similar, but each was significantly larger than at <br />Powell Canyon reach, irrespective of fishing effort (Table 1--1). <br />Population estimates for each reach and for the entire river.--- <br />Three-dimensional plots of adjusted population estimates by reach <br />are presented in Figure 1--3. Powell Canyon exhibited lower <br />e,-•timates than either Confluence or Salt Canyon, particularly in <br />1991 (Fig. 1--3a). In 1992 (Fig. 1--3b), increased activity at <br />confl%enc- during early March was reflected in elevated estimates <br />at `'owell in late March-April, followed by elevated estimates at <br />Canyon April-t}_ourh-June. Estimates at confluence again <br />increased in Ar-ii-June. Raw population estimates by reach per <br />sampling periou, and estimates normalized by river km, are in <br />Appendix 1--1. Raw population estimates per sampling period for <br />the entire LCR are presented in Appendix 1--2. This appendix also <br />contains a second population estimate for the entire river, <br />derived by summing estimates calculated over reaches for each <br />sampling period (as recorded in Appendix 1--1). An ANOVA <br />comparing these two estimates for the entire LCR (i.e., monthly <br />vs summed by month over reaches) was nonsignificant (F = 1.15; df <br />= 1,36; P > 0.7; Proc GLM, SAS, 1985). Both estimates are plotted <br />in Figure 1--4. In 1991, highest estimates were recorded for <br />early August (3157 vs 5390), while lowest were for December (745 <br />vs 1285) (Fig. 1--4). In 1992, highest estimates were for April <br />(5555 vs 5683), while lowest were for August (635 vs 408). A <br />December sampling trip in 1992 was cancelled due to inclement <br />weather. Both techniques indicated elevated population estimates <br />from early March through June of 1992 (Fig. 1--4). Also, both <br />techniques demonstrated an upswing in estimated population size <br />in autumn of both years. The average estimate summed over reaches <br />was larger (but not significantly so) than that calculated by <br />month (2993 vs 2434; N = 19; Sidak's multiple range test; SAS, <br />1985). <br />Five best-fitting population estimates were retained from <br />analysis of a CH-matrix for the entire 19 month study (Table 1-- <br />2). The highest criterion (0.61) was Pollock and Otto's estimator <br />(Mbh), which assumes that capture probabilities vary by individual <br />animal and by behavioral response to capture (i.e., behavior and <br />5
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