Transcript Slide 1

Towards an understanding of Bonneville
cutthroat trout responses to riparian grazing
exclosures
Scott Miller1,2 and Phaedra Budy1,3
1Intermountain
Center for River Rehabilitation and Restoration,
Department of Watershed Sciences, Utah State University
2Bureau
of Land Management
3USGS Utah Cooperative Fish and Wildlife Research Unit
Introduction
Habitat Degradation
Invasive Species
Disease
Bonneville cutthroat trout (BCT)
Introduction
• Livestock grazing is leading cause of riparian and instream
habitat degradation in western U.S.
• > 80% of western riparian areas affected
Introduction
Grazing
Habitat Degradation
Invasive Species
Disease
Bonneville cutthroat trout (BCT)
Introduction
• Riparian grazing exclosures widely
implemented on public lands
• UT public lands: > 150 riparian
exclosures
• Goals: Restore degraded habitat
and facilitate the coexistence of
grazing and native fish
populations
Source: ICRRR Restoration Database
Introduction
• Despite widespread implementation,
few studies assess restoration
efficacy
• Cutthroat: Equivocal or conflicting
results
• What factors contribute to
differential responses among
system?
Introduction
Grazing
(-)
Riparian vegetative
cover/biomass
(-)
Terrestrial arthropod
inputs
(-)
Salmonid biomass
Saunders and Fausch 2007
Introduction
Questions:
1. Do BCT populations differ between grazed and ungrazed
reaches?
2. What reach-scale factors are related to differences in
BCT populations between grazed and ungrazed reaches?
3. Do recovery patterns vary as a function of grazing
regime, exclosure age, or exclosure size?
Site selection
• 10 paired grazed and ungrazed
reaches
-
BCT
2nd & 3rd order reaches
Maintained exclosure
Active grazing
Minimize geomorphic differences
between pairs
• System characteristics
- Grazing regime: season long vs.
rotational
- Age: 4 – 39 years
- Size: 0.06 – 96%
Sampling
Paired study design
Upstream: Grazed
Downstream: Ungrazed
Min. 1 km buffer
• Reach lengths: 20x bankfull
• Sampled once: summer 2008 or 2009
Response variables
• Fish assemblages
- 3-pass depletion
- Reaches: 20x bankfull
- Response variables: Density,
biomass, condition, composition
• Diet
- Stomach contents - gastric lavage
- Stable isotopes (δ13C and δ15N)
Response variables
• Physical habitat measurements:
Continuous
Undercut banks
Overhanging vegetation
Habitat units (e.g., riffle, run, pool)
Response variables
• Physical habitat measurements:
Continuous
Undercut banks
Overhanging veg.
Habitat units (e.g., riffle, run, pool)
Point
Depth
Velocity
Substrate
Temperature*
Width
Response variables
• Prey availability
- Terrestrial arthropod prey
- 5 pan traps/reach
- 48 hours
- Aerial aquatic insects
- 5 pan traps/reach
- 48 hours
- Benthic aquatic arthropod prey
- 8 composite Surbers/reach
Results
Do BCT populations differ
between grazed and
ungrazed reaches?
% Change: BCT Density
700
600
500
400
300
200
100
NA NA
0
-100
Statistical Test
Wilcoxon signed rank test
700
% Change: BCT Biomass
Response Variable
% change =
100* ((Ungrazed-Grazed)/Grazed)
600
500
400
300
200
100
0
-100
NA NA
Results
• Consistent directional
changes, while magnitude
of change highly variable
• No differences in condition,
age structure, or
assemblage composition
600
W+ = 34.0, P = 0.030, df =8
500
400
300
200
100
NA NA
0
-100
700
% Change: BCT Biomass
• On average, density and
biomass significantly
greater within exclosures
% Change: BCT Density
700
600
W+ = 33.0, P = 0.042, df =8
500
400
300
200
100
0
-100
NA NA
Results
What reach-scale factors are related to differences in BCT
populations between grazed and ungrazed reaches?
Proportion overhanging vegetation
Aquatic benthic prey biomass
Terrestrial prey biomass
Aerial aquatic prey biomass
Width-to-Depth ratio
Proportion undercut banks
Residual Pool Depth
Habitat Diversity
Temperatue
Substrate (D16)
Kendall’s tau: % Change
BCT Density
BCT Biomass
0.57
0.46
0.21
0.43
0.50
0.57
0.28
0.36
0.21
0.14
0.71
0.5
-0.07
0.14
0.21
-0.14
-0.21
0.29
-0.43
-0.36
BCT density responses
scaled with increases in
cover availability
Percent change: BCT density
BCT biomass responses
proportional to increases in
terrestrial prey availability
Percent change: BCT biomass
Results
600
R2 = 0.53
500
400
300
200
100
0
-100
-200
-100
700
600
-50
0
50
100
Percent change: Terrestrial prey inputs
150
R2 = 0.41
500
400
300
200
100
0
-100
-10.00
0.00
10.00
20.00
30.00
Percent change: Undercut banks
40.00
Results
25
50
20
40
15
30
10
20
*
5
Percent change
• Terrestrial prey comprised
only 11% of prey availability
by biomass
Proportion terrestrial biomass
Ungrazed
Grazed
10
0
Huff
1.2
• 50% of ingested prey
Dry
Big
Big2
C.
Rock
Rock2 Randolph LMC
All Sites
-100
Ungrazed
Grazed
1.0
0.8
-60
0.6
-40
0.4
-20
0.2
0.0
0
Huff SpawnTemple Dry
Big
Big2 Rock Rock2
All Sites
Average Percent change
-80
Chesson's Alpha (Terrestrial)
• BCT foraging behavior:
strong preference of
terrestrial prey
Spawn Temple
Results
Do recovery patterns vary as a function of grazing regime,
exclosure age, or exclosure size?
Aquatic benthic prey biomass
Terrestrial prey biomass
Aerial aquatic prey biomass
Width-to-Depth ratio
Proportion undercut banks
Proportion overhead vegetation
Residual Pool Depth
Habitat Diversity
Substrate
Temperature
BCT Density
BCT Biomass
Averages
Kendall’s tau: % Change
Grazing regime Exclosure Age Exclosure Size
0.06
0.05
0.28
0.46
0.18
0.11
0.09
-0.3
-0.03
-0.43
-0.1
0.63
0.12
-0.32
-0.14
0.43
0
0.13
0.06
0.14
-0.04
0.43
0.41
0.17
0.37
0.18
-0.2
-0.3
-0.1
-0.21
-0.47
-0.07
-0.14
-0.47
0
-0.07
0.33
0.17
0.19
Results
Weak relationships with age…
1978 (SL)
1978 (SDR)
Grazed
Overriding influence of grazing practices
Ungrazed
Results
Differential responses between grazing regimes and
among abiotic and biotic variables
400
Average % Change
Rotational
Season-long
300
Grazed: SL
Ungrazed: SL
200
100
0
s
ity
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CT
W
dV
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H
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Ov
Results
Differential responses between grazing regimes and
among abiotic and biotic variables
400
Average % Change
Rotational
Season-long
300
Grazed: SDR
Ungrazed: SDR
200
100
0
s
ity
ion
pth
s
as
t
rey
r
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a
P
e
m
t
iv
io
h:D
ge
ial
t
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B
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t
d
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CT
W
dV
rre
bit
B
a
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H
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Ov
Results
BCT Density (fish/km)
Passive restoration bang for your buck: BCT responses
500
560%
*% Change relative to Grazed - SL
400
300
200
100
312%
95%
0
Grazed - Ungrazed - Grazed - Ungrazed SL
SL
SDR
SDR
Results
BCT Density (fish/km)
Putting responses in a regional context
800
600
400
200
0
Median
population level
Take home points
• Variable fish responses to grazing management are likely
predictable
• Both habitat and prey resource availability (terrestrials)
likely facilitate BCT recovery
• Grazing management at larger spatial scales will greatly
increase efficacy of passive restoration efforts
• Landscape versus local-scale processes in facilitating
abiotic and biotic recovery trajectories
Future questions
• What factors control the recovery of terrestrial
arthropod assemblages
• Do exclosures facilitate increased growth and survival =
source populations
• Identify interactions among grazing regime, exclosure
age, and size
• How robust are these patterns
Acknowledgements
Funding
• UDWR Endangered Species Mitigation Fund (# 0809)
• Intermountain Center for River Rehabilitation and
Restoration
• Bureau of Land Management
Field and lab assistance
• Paul Mason, Gary Thiede, Reed Chaston, Dave Fowler,
Katrina Langenderfer, Ben Marett, Ellen Wakeley, and Hilary
Whitcomb
Logistics and permitting
• Wyoming Game and Fish Department, Idaho Fish and Game,
Utah Department of Wildlife Resources