1. Abiotic and Biotic Factors Influencing the Distribution of Bull Trout and Westslope Cutthroat Trout West of the Continental Divide in Glacier National Park
Vin D’Angelo, Department of Environmental Studies, UM, Missoula
Clint C. Muhlfeld, Aquatic Ecologist, USGS NOROCK West Glacier, MT
Vicki Watson, EVST Dept.,
UM, Missoula

2. The North Fork Flathead Watershed

3. Westslope Cutthroat Trout, Oncorhynchus clarkii lewisi
A species of special concern in Montana
Stream resident, adfluvial, fluvial
Flathead River
Insert Lake Photo
Commerce Creek, BC

4. Bull Trout, Salvelinus confluentus
GNP’s top native piscivore
Listed as threatened under ESA in 1998
Insert Lake Photo

5. Threats: Hybridization
Westslope cutthroat trout and introduced rainbow trout (O. mykiss sp.) produce fertile offspring but hybrids are less fit
Hybridization is more common in warm, degraded streams and has been spreading throughout upper Flathead system
(Muhlfeld et al TAFS)

6. Threats: Lake Trout, S.namaycush
Lake trout may have fully displaced bull trout in some western GNP lakes
(Meeuwig et al., 2008; Fredenberg et al., 2007)

7. Project Objectives
Determine the geographic distributions of westslope cutthroat trout and bull trout in tributaries to the North Fork Flathead within GNP
Examine the occurrence and density of these species in relation to abiotic and biotic factors using logistic and linear regression models

8. Methods: Fish and Habitat Survey
78 Sample Sites
Presence/absence
Density (fish/100m2)
Stream width (m)
Gradient (%)
Woody debris (LWD/100m2)
Elevation (m)
Lake trout effect (Y/N)
Estimated August mean temperature (oC)

9. Methods: Temperature Modeling
24 HOBO thermographs
Temperature (oC)
Elevation (m)
Gradient (%)
Lake Area Above Site (ha)
HOBO Loc Fig

10. Data Analysis: Temperature
Predictive Model: Multiple Linear Regression
August Mean Temperature = Constant + Elevation + Gradient + Lake Area Moderate + Lake Area High
Lake Effect Categories
Low (<5ha)
Moderate (5-100ha)
High (>100ha)

11. Data Analysis: Fish Presence and Density
Presence-Absence
Logistic regression models
P (presence) = e Bo+ B1x+ Bix
1 + e Bo + B1x+ Bix
Fish Density (fish/100m2)
Linear regression models
Density = B0 + B1x + Bix
Independent Variables:
Stream width, elevation, gradient, large woody debris, lake trout presence, estimated August mean temperature

12. Model Selection k AICc An Information Theoretic Approach
(AICc) = Akaike’s Information Criterion adjusted for small sample size
ΔAICc = models within 2.0 of lowest AICc are equally plausible k
AICc
ΔAICc 5
96.674
0.000 6
97.419
0.745 7
98.647
1.973 8
3.961
(Akaike, 1973; Burnham and Anderson, 1998)

13. Results: Temperature Modeling
Elevation (-)
Lake Area (+)
R2 = 0.782
AUG Mean = – 7.88 x (Elevation) (LM) (LH)

14. Westslope Cutthroat Trout Presence Models
Number of Parameters
ΔAICc
% Correct
Lake Trout, Temp, LWD 3
0.000
75.6
Elevation, Lake Trout, Temperature, LWD 4
0.816
78.2
Elevation, Width, Lake Trout, Temp, LWD 5
2.435
79.5
LWD, Temp 2
2.675
Elevation, LWD, Gradient, LKT, Temp, Width 6
4.894
Lake Trout, Temp
7.592
73.1
Temp 1
9.108
62.8

15. Westslope Cutthroat Trout Presence
Westslope cutthroat trout are widely distributed but are most likely to occur in reaches with complex habitat in streams with no lake trout influence
Present in 47 of 78 sites
(60.3%)

16. Westslope Cutthroat Trout Density Models
Number of Parameters
ΔAICc
Adj. R2
Gradient, Width, Lake Trout 3
0.000
0.665
Elevation, Gradient, Width, Lake Trout 4
0.769
0.671
Elevation, Gradient, Width, Temp, Lake Trout 5
1.786
0.676
Gradient, Width 2
3.617
0.578
Width, Lake Trout
4.302
0.616
Elevation, Gradient, Width, Temp, Lake Trout, LWD 6
4.821
0.667
Width, Lake Trout, Elevation
6.597
0.449

17. Westslope Cutthroat Trout Density
Y = – (x)
R2 = 0.227
Y = (x)
R2 = 0.559
Key Variables:
Stream width (m) = negatively associated with density
Gradient (%) = positively associated with density
Lake Trout Presence = negatively associated with density

18. Bull Trout Presence Models
Number of Parameters
ΔAICc
% Correct
Gradient, Elevation 3
0.000
98.6
Gradient, Width, Elevation
0.027
Elevation, Gradient, Width, Temp 2
1.064
Gradient, Width, Temp
1.456
97.1
Width, Temp
3.297
88.5
Elevation, Gradient, LWD, Temp, Width 5
3.397
89.7
Gradient, Temp
4.374

19. Bull Trout Presence
Present in 9 of 78 sites (11.5%)

20. Bull Trout Density Models
Number of Parameters
ΔAICc
Adj. R2
Elevation, Stream Width 2
0.000
0.843
Stream Width 1
4.558
0.503
August Mean Temperature
6.105
0.286
Elevation
6.436
0.387
Lake Trout
8.676
0.215
Elevation, Width, Temp 3
10.072
0.869
Width, Temp
11.421
0.441

21. Bull Trout Density Key Variables:
Y = – (x)
Y = x10-3 (x)
R2 = 0.56
R2 = 0.46
Key Variables:
Stream Width (m) = Negatively associated with density
Elevation (m) = Positively associated with density

22. Conclusions
Westslope cutthroat trout are widely distributed in western GNP
They are most prevalent and abundant in reaches with complex habitat
Lake trout may negatively affect their distribution and abundance

23. Conclusions Conclusions
Bull trout are persisting in cold headwater reaches ( oC) that are often isolated by barriers to non-native species
Populations are depressed and may be at high risk of extirpation due to the invasion and establishment of nonnative lake trout
These data are in agreement with documented declines in bull trout numbers in GNP over the last 50 years

24. Conservation and Management
Inform Monitoring
New locations for future bull trout surveys
Delineate critical habitat for recovery projects

25. Conservation and Management
Non-native species are a continuing threat
Barrier installation may be critical
Suppression/eradication
(Dan Kotter, USGS, 2009)
(Clint Muhlfeld, USGS, 2009)

26. Conservation and Management
Climate change will likely exacerbate current threats
W.C. Alden, GNP Archives, 1913
Greg Pederson, USGS, 2005

27. Upcoming Projects Bull trout translocation study WCT genetics survey
Vin D’Angelo, USGS, 2008
Vin D’Angelo, USGS, 2009

28. Acknowledgements Co-advisers: Field Crew: Vicki Watson Clint Muhlfeld
Carter Fredenberg
Terra Marotz
Ben Galloway
Dan Kotter (GIS)