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

The North Fork Flathead Watershed

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

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

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. 2009 TAFS)

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)

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

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)

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

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)

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

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 8 100.635 3.961 (Akaike, 1973; Burnham and Anderson, 1998)

Results: Temperature Modeling Elevation (-) Lake Area (+) R2 = 0.782 AUG Mean = 19.377 – 7.88 x 10 -3 (Elevation) + 1.097 (LM) + 5.026(LH)

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

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%)

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

Westslope Cutthroat Trout Density Y = 1.5492 – 1.8473 (x) R2 = 0.227 Y = -0.6848 + 1.468 (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

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

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

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

Bull Trout Density Key Variables: Y = 0.0604 – 1.4478 (x) Y = -6.7787 + 4.5156x10-3 (x) R2 = 0.56 R2 = 0.46 Key Variables: Stream Width (m) = Negatively associated with density Elevation (m) = Positively associated with density

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

Conclusions Conclusions Bull trout are persisting in cold headwater reaches (8-10.5 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

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

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)

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

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

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