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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