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Non-native fish monitoring activities in Glen and Grand Canyons during 2000 Dave Speas, AGFD Carl Walters, UBC Scott Rogers, AGFD Bill Persons, AGFD.

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Presentation on theme: "Non-native fish monitoring activities in Glen and Grand Canyons during 2000 Dave Speas, AGFD Carl Walters, UBC Scott Rogers, AGFD Bill Persons, AGFD."— Presentation transcript:

1 Non-native fish monitoring activities in Glen and Grand Canyons during 2000 Dave Speas, AGFD Carl Walters, UBC Scott Rogers, AGFD Bill Persons, AGFD

2 Objectives: Grand Canyon Obtain population estimates of salmonids in Grand Canyon for use in assessing predation risks to humpback chub Evaluate strengths and weaknesses of longitudinal CPE/depletion/mark-recapture methods

3 *December Glen Canyon trip not shown 2000 Hydrograph and Fishery Survey Trips

4

5 Population Estimate Approach Theory: CPE=q(N), or catch rate is result of catchability coefficient (q) times local fish population. Q derived through depletion electrofishing (multiple passes) and/or mark recapture experiments conducted at selected sites Calibration of CPE to local fish population via q method applied to index (single pass) electrofishing samples collected throughout entire canyon Resulting longitudinal curve and confidence bands were then integrated to obtain system-wide population estimates.

6 A Typical Depletion/M-R Site

7 Depletion Theory A Typical RBT Depletion Sample Example: N o  98 fish (x intercept). Likelihood of N o maximized given observed depletion data

8 560 index electrofishing samples collected between SWCA and AGFD AGFD conducted 76 depletion and 20 mark/recapture experiments. Only 9 experiments were conducted in turbid water (information need). 877 salmonid stomach samples were collected (pending analysis) Results

9 Species-specific q Bias with Fish Density

10 First pass CPE vs. Nearshore Fish Abundance

11 Longitudinal Distribution of Rainbow Trout in Grand Canyon, 2000 N  743,000 RBT

12 Longitudinal Distribution of Brown Trout in Grand Canyon, 2000 N  57,000 BNT

13 Caveat of Population Estimates from Electrofishing

14 Summary and Conclusions I: Grand Canyon Longitudinal electrofishing surveys likely adequate for system wide salmonid population estimates, but variations in catchability need to be evaluated Minimum annual sample size for salmonids approximately 240 samples to detect 20% change in brown trout CPE over 5 years; 2 trips/yr likely depending on importance of seasonal variance in q Approximately 500,000-1,000,000 RBT in RM , occurring mostly in first 100 miles of river Approximately 20, ,000 BNT in RM , occurring mostly in upper-middle Granite Gorge

15 Summary and Conclusions II: Grand Canyon Estimates are likely biased negatively by depletion method (M/R estimates approximately 1.5X greater), but extrapolation assuming uniform fish density in river channel likely biases estimate positively “Order-of-magnitude” estimates Information needs: variations in catchability with high brown trout density, turbidity, seasons; cross-sectional fish distribution; reconciliation of depletion and M/R estimates

16 Glen Canyon Objective: Monitor rainbow trout relative density, relative condition, size distribution and proportional stock density Methods: Standardized electrofishing at 9 transects/trip, 4 trips (March, June, September, December)

17 Status of Rainbow Trout Fishery in Glen Canyon CPE for all fish in 2000 (4.7 fish/minute) greater than 1999 (3.7 fish minute), but significance is marginal (P=0.0733) CPE for age 2+ fish in 2000 (2.89 fish/minute) unchanged from 1999 Mean relative condition unchanged from 1999 (K n =77.9), peaked during June (slightly earlier than long term average) (MO: 0.90) PSD (# >=406 mm/# >=305 mm) in 2000 (0.14) up slightly from 0.12 in 1999 (MO undetermined) Percent age-0 and age-1 among highest on record (35-40%)

18 Length Frequencies of Rainbow Trout in Glen Canyon, 2000

19 RBT Length Frequencies During April-June

20 Synthesis Model Predictions for Juvenile RBT

21 Summary and Conclusions: Glen Canyon Relative condition and PSD largely unchanged from 1999, seasonal variation normal High survival of YOY/juvenile RBT, though partially biased by electrofishing conditions (low, steady flows) High persistence of YOY trout during 31K, although gear saturation possible

22 Number of brown trout captured in Glen Canyon during : 1 Number of brown trout captured in Glen Canyon during : 5


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