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