Demographics of coastal cutthrout troutin Prairie Creek, California

W. G. DuffyUSGS, California Cooperative Fish Research Unit

Humboldt State Universityand

E. P. BjorkstedtNational Marine Fisheries Service

Humboldt State University

Objectives

• Communicate empirical data on the status of coastal cutthroat trout in California.

Outline

• Population abundance and density• Size distribution

Study Area

Reference:Prairie Creek

Recovering: Streelow Creek

Disturbed:Boyes Creek

Stream habitat

650.17

580.24

1170.64

Run narea (ha)

910.26

490.13

1530.68

Riffle narea (ha)

590.15

760.36

1271.25

Pool narea (ha)

4.45.734.4Watershed area (km2)

2.22.16.1Length (km)

BoyesCreek

StreelowCreek

Prairie Creek

Methods

Estimated population abundance during 2000-2004 using modified Hankin and Reeves (1988) sampling.

Area of habitat in pools, runs and riffles measured in July.Population abundance sampling during July and October (except 2004).

Methods (2)Prairie Creek

Single pass diver observations in randomly selected habitat units.

Calibrated diver observationsWhen < 20 coho salmon observed, 3 additional dives.When > 20 coho salmon present, electro-fishing.

Streelow and Boyes CreeksElectrofished all randomly selected habitat units.

Methods (3)Recorded size, fork length (mm) and wet weight (g), of a subsample each season.

Calculated condition (k) as: k = (W/FL3)*10,000

Classified fish < 80 mm FL as cutthroat trout only if maxillary extended beyond posterior of eye and a red/orange slash was visible on the lower jaw.

Data Analysis

GLM used to analyze cutthroat trout density, and size by stream, year, season and habitat type.

ANOVA used when interactions significant.

Linear regression to explore relationships density and size relationships with habitat, area, habitat depth, and “prey”.

Population Abundance

Year

2000 2001 2002 2003 2004

Popu

latio

n Es

t.(+

S.E

.)

0.1

1

10

100

1000

PoolsRunsRiffles

Prairie Creek

Population Abundance

Year

2000 2001 2002 2003 2004

Popu

latio

n Es

t.(+

S.E

.)

0.1

1

10

100

1000

PoolsRunsRiffles

Streelow Creek

Population Abundance

Year

2000 2001 2002 2003 2004

Popu

latio

n Es

t.(+

S.E

.)

0.1

1

10

100

1000

PoolsRunsRiffles

Boyes Creek

Density (no . ha-1)

Year

2000 2001 2002 2003 2004

Den

sity

(No.

ha

)

0

200

400

600

800

1000

1200 Prairie Cr.Streelow Cr.Boyes Cr.

Density (no/ha)

• Stream: Streelow > Prairie & Boyes• Year: 2004 > 2000 & 2001 > 2002 & 2003• Habitat: Runs & Pools > Riffles

Density Distribution

Proportion Distance Upstream

0.0 0.2 0.4 0.6 0.8 1.0

Den

sity

(No

m-2

)

0.0

0.1

0.2

0.3

0.4

0.5

Density = 0.0665 + 0.0054 * Distancer2 = 0.00, p = 0.7958

Density vs. Coho Salmon

Coho salmon m-2

0.0 0.3 0.6 0.9 1.2 1.5

Cut

thro

at tr

out

m-2

0.00

0.03

0.06

0.09

0.12

0.15

0.18Runs

Cutthroat density = 0.0535 + 0.0024 * coho densityr2 = 0.00, p = 0.939

Density vs. Coho Salmon

Coho salmon m-2

0.0 0.1 0.2 0.3 0.4 0.5

Cut

thro

at tr

out

m-2

0.00

0.02

0.04

0.06

0.08

0.10Riffle Habitats

Cutthroat density = 0.0194 + 0.0630 * coho densityr2 = 0.099, p = 0.0606

Density vs. Coho Salmon

Coho salmon m-2

0.0 0.3 0.6 0.9 1.2 1.5

Cut

thro

at tr

out

m-2

0.00

0.05

0.10

0.15

0.20

0.25Pool habitats

Cutthroat density = 0.0213 + 0.1229 * coho densityr2 = 0.424, p = 0.0001

Size Distribution (FL)

Fork Length (mm)

100 150 200 250 300

Perc

ent

0

4

8

12

16

20Prairie Cr.Streelow Cr.Boyes Cr.N = 1,181

Mean = 11095% C.L. = 5.7

Length - Weightlog(Wtg)) = -4.7647 + 2.9027 * log(FL(mm))

r2 = 0.981, p <0.0001

Log (Weight (g))

1.6 1.8 2.0 2.2 2.4 2.6

Log

(For

k Le

ngth

(mm

))

0.0

0.5

1.0

1.5

2.0

2.5

Size Distribution

Proportion of Distance Upstream

0.0 0.2 0.4 0.6 0.8 1.0

Log

(FL(

mm

))

1.6

1.8

2.0

2.2

2.4

2.6

Size (FL)

• Stream: Streelow = Prairie = Boyes• Year: 2002 > 2003 & 2004 > 2000 & 2001• Habitat: Pools > Runs & Riffles

Summary and Conclusions

1) Density relatively stable and similar to that reported by others.

2) Density greatest in smaller, low gradient stream with relatively deep pools.

3) Size did not vary among streams.4) Scale not appropriate for discerning life

history variation.

Thank you