Non-native fish monitoring activities in Glen and Grand Canyons during 2000
Dave Speas, AGFD
Carl Walters, UBC
Scott Rogers, AGFD
Bill Persons, AGFD
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
Dis
char
ge
(cfs
)
6000
10000
14000
18000
22000
26000
30000
34000
Mar Apr May Jun Jul Aug Sep Oct
Glen Canyon/Lees Ferry Grand Canyon
*December Glen Canyon trip not shown
2000 Hydrograph and Fishery Survey Trips
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.
A Typical Depletion/M-R Site
Depletion Theory
A Typical RBT Depletion Sample
Example: No 98 fish (x intercept). Likelihood of No maximized given observed depletion data
0
100
200
300
400
500
40 60 80 100
Cumulative Catch
CP
E
0
1E-23
2E-23
3E-23
4E-23
5E-23
6E-23
90 95 100 105
Estimated # at start of experimentL
ikel
iho
od
• 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
Species-specific q Bias with Fish Density
Rainbow Trout
0
0.2
0.4
0.6
0.8
1
0 50 100 150
Est. # present
q
Brown Trout
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50
Est. # present
q
First pass CPE vs. Nearshore Fish Abundance
Rainbow Trout
0
1000
2000
3000
4000
0 50 100 150
Est. # present
CP
E
Brown Trout
0
200
400
600
800
1000
0 10 20 30 40 50
Est. # presentC
PE
Longitudinal Distribution of Rainbow Trout in Grand Canyon, 2000
N 743,000 RBT
0
5000
10000
15000
20000
25000
30000
0 50 100 150 200 250
River Mile
# F
ish
/RM
Data Best Fit 95% CI
Longitudinal Distribution of Brown Trout in Grand Canyon, 2000
N 57,000 BNT
0
1000
2000
3000
4000
5000
0 50 100 150 200 250River Mile
# Fi
sh/R
M
Best Fit Data 95% CI
Caveat of Population Estimates from Electrofishing
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 18-225, occurring mostly in first 100 miles of river
• Approximately 20,000-100,000 BNT in RM 18-225, occurring mostly in upper-middle Granite Gorge
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
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)
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 (Kn=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%)
Length Frequencies of Rainbow Trout in Glen Canyon, 2000
Fre
qu
ency
March
0
23
46
69
92
115
138
161
184
50 100 150 200 250 300 350 400 450 500
June
50 100 150 200 250 300 350 400 450 500
September
0
23
46
69
92
115
138
161
184
50 100 150 200 250 300 350 400 450 500
December
50 100 150 200 250 300 350 400 450 500
RBT Length Frequencies During April-June
1995-1999
Re
lati
ve
Fre
qu
en
cy
50100
150200
250300
350400
450 500
2000
Re
lati
ve
Fre
qu
en
cy
50100
150200
250300
350400
450 500
Synthesis Model Predictions for Juvenile RBT
0
1
2
3
4
5
1994 1996 1998 2000
CP
E
020004000600080001000012000
CF
S
Pred <235 Obs <235 Flow Flux
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
Number of brown trout captured in Glen Canyon during 1991-1998: 1
Number of brown trout captured in Glen Canyon during 1999-2000: 5