<br />1366
<br />
<br />BESTGEN ET AL,
<br />
<br />TABLE 4,-Abundance estimates, 95% confidence intervals (CIs), coefficients of variation (CVs), numbers of unique
<br />individuals captured (M,+l) and percentages of recruits for Colorado pikeminnow in the Green River basin, Utah and Colorado,
<br />2000-2003, Percent recruits is the abundance of recruits (400-449 mm TL) relative to that of adults (;::450 mm) in the same year
<br />multiplied by 100, Two estimates of adult abundance are shown for 2000, The fust is for the middle Green, Yampa, and White
<br />River reaches only; the second includes estimates for the Desolation-Gray Canyon (N = 699) and lower Green River (N = 355)
<br />reaches in 2001 to account for the lack of sampling in those areas in 2000, The estimate for recruits in 2000 includes only the
<br />middle Green, White, and Yampa river reaches. An estimates for 2001-2003 include those areas and the Desolation-Gray
<br />Canyon and lower Green River reaches.
<br />
<br />Adult
<br />
<br />% Recruits
<br />
<br />Year Abundance SE 95% CI CV Mt+1
<br />2000 3,030 286,8 2,467-3,592 9 910
<br />2000 4,084
<br />2001 3,304 206.1 2,900-3,707 6 990
<br />2002 2,771 282,7 2,216-3,325 10 455
<br />2003 2,142 232,7 1,686-2,598 11 434
<br />2000 150 26,3 98-201 18 39
<br />2001 4]2 51.1 312-512 12 105
<br />2002 130 35,5 61-200 27 17
<br />2003 284 55,8 175-393 20 43
<br />
<br />Life stage
<br />
<br />Recruit
<br />
<br />4,9
<br />12.5
<br />4,7
<br />13.3
<br />
<br />the number of adults present in any given year.
<br />Estimates of Colorado pikeminnow recruit abundance
<br />were significantly higher in 2001 than in 2000 or 2002
<br />but showed no consistent trend over the sampling
<br />period; CVs ranged from 12% to 27%,
<br />
<br />Survival Estimates
<br />
<br />The best model suggested a constant survival rate (S)
<br />over the study period (Figure 4) with the terms TL,
<br />TL2, and TL3. The parameters for the function of logit
<br />S are as follows: intercept = 0.6173 (SE = 0.1370), TL
<br />=0.5606 (0.2373), TL2=-0.2068 (0.1140), and TL3=
<br />-0,1320 (0.0665). Survival was relatively low for fish
<br />about 350 mm TL, increased for fish up to about 600
<br />mm, and then declined for larger fish, The average S
<br />adjusted to the mean TL for Colorado pikeminnow
<br />across all river reaches was 0.65 (95% confidence
<br />
<br />-- 2000-2003 -1991-1999
<br />
<br />
<br /> 0.8
<br />';;j 0,6
<br />;>
<br />';;C
<br />...
<br />::l 0.4
<br />Vl
<br /> 0.2
<br /> 0
<br /> 300 400 500 600 700 800 900
<br />
<br />Colorado pikeminnow TL
<br />
<br />FiGURE 4.-Survival rate of Colorado pikeminnow as a
<br />function of TL (mm) in the Green River basin in 1991-1999
<br />and 2000-2003, The 1991-1999 data were collected during
<br />Interagency Standardized Monitoring Program (ISMP) sam-
<br />pling; data from other periods were collected during
<br />abundance estimation sampling,
<br />
<br />interval [CI] , 0,586-0.708) for the 2000-2003 study
<br />period (Table 5).
<br />The average S for Colorado pikeminnow captured
<br />during ISMP sampling from 1991 to 1999 was 0.82
<br />(95% CI, 0.709-0.891), which was higher than that
<br />observed for 2000-2003. The shape of the survival
<br />relationship was also different, as the best-fit model
<br />included a linear term for the covariate fish TL but not
<br />a quadratic term. An exploratory analysis revealed that
<br />a quadratic term had a positive coefficient, indicating
<br />that the slope continued to rise rather than to decline,
<br />unlike the survival relationship for the 2000-2003 data.
<br />The mean probabilities of capture for the fish used in
<br />the above survival analyses were higher in 2000-2003
<br />than in 1991-1999.
<br />
<br />Probabilities of Capture
<br />
<br />The capture probabilities for Colorado pikeminnow
<br />generated from abundance estimation data also dem-
<br />
<br />TABLE 5.-Estimates of apparent sUlvival and capture
<br />probability and 95% confidence intervals (CIs) for subadult
<br />and adult Colorado pikeminnow captured in the Green River
<br />basin in 1991-1999 and 2000-2003, The data for 1991-1999
<br />were collected as part of a standardized monitoring program to
<br />estimate catch per unit effort indices for Colorado pike-
<br />minnow and were from about 23% of the habitats occupied by
<br />this species in the Green River basin, The data for 2000-2003
<br />were collected during this study to estimate the abundance of
<br />subadult and adult Colorado pikeminnow throughout the
<br />Green River basin; the data for 2000-2001 were from the
<br />middle Green, Yampa, and White river reaches only,
<br />
<br />Variable Period Estimate 95% C1
<br />Survival 1991-1999 0,82 0,709-0,891
<br /> 2000-2003 0,65 0,586-0,708
<br />Capture probability 1991-1999 0.053 0.038-0.074
<br /> 2000-2003 0,090 0,054-0,119
<br />
|