Assessing Crayfish Habitat

Dan O’Brien

John Meredith

Leroy Mims

• Scientists are observing invasive crayfish displacing indigenous crayfish in the Lake Mendota Watershed.

• Invasive crayfish are thought to disrupt aquatic habitat for native fish and plants species.

• This project assesses the relationship between crayfish and their surrounding environmental variables. Are there trends in environmental habitat?

Problem Statement

Project Overview

Aquatic Vegetation

Sinuosity

Floodplain Width

Riverbed

Proportion Of Watershed Development

•Native Crayfish •Invasive Crayfish

EVALUATE

Data Sources

FloodplainWidth

AquaticVegetation

Proportion of WatershedDevelopment

Riverbed

River Sinuosity

Crayfish

•Methods

•Results

•Improvements

Methods: Aquatic Vegetation

MethodsAquatic Vegetation

MethodsAquatic Vegetation

MethodsAquatic Vegetation

MethodsAquatic Vegetation

(1) Determine stream segments within each Dane County subwatershed

(2) Measure river-miles for each stream segment

(3) Compare this length to the minimal distance from source to mouth

MethodsSinuosity

Methods

(1) Determine

field sites

(2) Measure

floodplain width

perpendicular

to the river channel

Floodplain

1.Create a buffer around the sampled sites.2. Select the Length Slope Factors found in proximity to the sites.3. Determine if there is a difference in tolerance to erosion.

SoilsMethods

1. Create a buffer around the sampled sites.2. Select the land use types found in proximity to the crayfish.3. Determine if there is a difference in suitable habitat between the two species.

Land-useMethods

Results

No significant difference (p=.84)

0.001.002.003.004.005.006.007.008.00

CRAYFISH

Perc

enta

ge

CATCH NO CATCH

No basis for comparison

0.00

2.00

4.00

6.00

8.00

CRAYFISH

Perc

enta

ge

NATIVE INVASIVE

ResultsAquatic Vegetation as a Percent of Surface Area within 100 meters of Field Sites

No significant difference in sinuosity (p=.16)

Results

Difference in Average Sinuosity

1.25

1.3

1.35

1.4

1.45

1.5

1.55

CRAYFISH

Sin

uo

sity

NATIVE

INVASIVE

Significant difference in Floodplain width (p=.049)

Results

Difference in Average Floodplain Width

0

100

200

300

400

500

600

CRAYFISH

Wid

th (

m)

NATIVE

INVASIVE

Results

Length-slope factor

NATIVE INVASIVE

A: HIGHEST 0 3

B 12 5

C 5 1

D 1 0

E: highest 0 1

X2 Analysis (p-value is ~.20)

Number of field sitesfor each species containing any soil-type

with the following classification.

Results

AGRICULTURAL AND MIXED URBAN OCCURENCES

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Ag

ricu

ltu

re a

nd

mix

ed U

rban

Per

cen

t

NATIVE

INVASIVE

Land-use (p-value=.002)

Conclusion

For aquatic vegetation, results are inconclusive.

Results for sinuosity and riverbed substrate were promising, but not significant.

However, for floodplain width and proportion of 200-m buffer in agriculture or mixed-urban land-use, we observed a difference in the habitat for invasive crayfish.

Conclusion

Floodplain width and proportion of 200-m buffer in agriculture or mixed-urban land land-use:

• Invasive crayfish inhabit wider floodplains, implicating different watershed hydrologies.

• Native crayfish inhabit regions with less erodible soil-types - suggests particulate flow may be a factor.

Data Challenges

Tree canopy obstructing rivers at the onesite with Invasive Crayfish

Data Challenges• Decision to pursue Aquatic Vegetation from

Panchromatic QuickBird not made in light of field site locations

• Satellite images cut-off too far south tocompare Invasive against Native Crayfish

• Images only a snapshot of time (July 31, 2004), while aquatic vegetation, the riverbanks and

crayfish vary throughout the season• Inherent errors built into digitization process• Manual digitization• Upstream vegetation

Data Challenges

•River velocity

•Land-use classification

•Flood-plain

Questions?

Assessing Crayfish Habitat

Dan O’Brien

John Meredith

Leroy Mims