Monitoring Crayfish Populations in Muskoka Lakes
Transcript of Monitoring Crayfish Populations in Muskoka Lakes
Monitoring Crayfish Populations
in Muskoka Lakes
Keith Somers
Dorset Environmental Science Centre
Ontario Ministry of the Environment
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Outline of Presentation
• Using crayfish as indicators
• How we sample crayfish
• Results from spatial surveys
• Results from long-term monitoring
• Exploring cause and effect
• Summary
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Crayfish as Indicators
Why use crayfish as a “bio” monitor?
• Crayfish live for several years
• Crayfish are non-migratory
• There are several crayfish
species with different preferences
and tolerances
• Crayfish are common in Muskoka
• Crayfish are easily sampled
watercolour images © Aleta Karstad 2008 (www.crayfishontario.ca)
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• We assume that:
Crayfish are good indicators of
ecosystem health because their
occurrence and abundance are
linked to physical and chemical
habitat features
Why use crayfish as a “bio” monitor?
Crayfish as Indicators
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What do we know about crayfish?
• There are 7 native and 3
introduced species of
crayfish in Ontario
• Crayfish activity and life
history events (periods of
moulting and reproduction)
are temperature dependent
• Behaviour and habitat
preferences differ among
species (and sexes)
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We also know that:
• There are a number of
different ways to sample
crayfish
• Each method with its own
strengths and weaknesses
• Methods include using SCUBA
or snorkelling to collect crayfish
by hand along transects or
quadrats, using traps,
throw nets, seines, dip nets,
and electrofishing…
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Crayfish Sampling
• 54 baited traps
• when - mid-summer
• traps are set for one night
(or about 24 hours)
• catch identified to species
• catch is expressed as
catch per unit effort – CUE
(number caught per trap
per night)
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Crayfish Sampling
• traps are standard “Gee”
minnow traps with opening
widened to ~3.5 cm
• bait is “canned cat food”
specifically fish or tuna
flavoured
• bait is delivered in 35 mm
film canisters with holes
(6-8) punched in the sides
with one-hole paper punch
• canisters are prepared in
advance, frozen, and used
one per trap
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Crayfish Sampling
• traps are set in groups or traplines
attached to shore
• each trapline consists of 6 traps
attached to a line at 3-m intervals
• the first trap is placed at a depth
of 0.5-1 m and subsequent traps
are lowered to the bottom
• 3 traplines are set in each habitat
(rock, macrophyte, and detritus)
3mUp
to
8m
3m3mUp
to
8m
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. 0 30 60 90 12015Kilometers
Spatial (100 Lake) Crayfish Survey
Brie Edwards
PhD Candidate
University of Toronto
11. 0 30 60 90 12015Kilometers
2HG
2EC
2KD
2HF
2HH
2EA
2KB
2EB
2CF
• Lakes in 9 tertiary watersheds
• Included:
• Sudbury
• Algonquin Provincial Park
• South of the Shield
• Lakes originally surveyed
between 1989 and 1994
• Lakes were re-sampled between
2005 and 2007 using same
methodology.
Spatial (100 Lake) Crayfish Survey
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Comparing Catches from 2 Time Periods
0.00
0.10
0.20
0.30
0.40
0.00 0.10 0.20 0.30 0.40
Historical CUE
Cu
rre
nt
CU
E
• Y axis is current catch
per unit effort (CUE)
• X axis is historical catch
per unit effort (CUE)
• one-to-one line
indicates no change
• above that line – current
CUE is more than
historical CUE
• below 1:1 line – current
CUE is less than
historical CUE
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Catches of Orconectes virilis
0
1
2
3
4
5
0 1 2 3 4 5
Historical CPUE
Cu
rren
t C
PU
E
0.0
0.2
0.4
0.0 0.2 0.4
N = 57
Slope = 0.28
Current CUE is 28%
of historical CUE
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Catches of Orconectes propinquus
0
2
4
6
8
10
0 2 4 6 8 10
Historical CPUE
Cu
rre
nt
CP
UE
0.0
0.3
0.6
0.0 0.3 0.6
N = 39
Slope = 0.09
Current CUE is 9%
of historical CUE
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General Trends in Crayfish Catches
Species Number
of lakes
Slope % of Historical
CUE
O. virilis 57 0.28 28
O. propinquus 39 0.09 9
O. obscurus 9 0.32 32
O. immunis 7 0.38 38
O. rusticus 3 0.09 9
C. bartonii 33 0.10 10
C. robustus 12 0.04 4
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27 lakes – no change
15 lakes – >50% decrease
15 lakes – now absent
10 lakes – new observation
Distribution of Orconectes virilis (57 lakes)
Maintained
≥ 50% Less than Historical
Apparently Lost
Newly Detected
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19 lakes – no change
10 lakes – >50% decrease
10 lakes – now absent
4 lakes – new observation
Distribution of O. propinquus (39 lakes)
Maintained
≥ 50% Less than Historical
Apparently Lost
Newly Detected
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8 lakes – no change
7 lakes – >50% decrease
18 lakes – now absent
2 lakes – new observation
Distribution of C. bartonii (33 lakes)
Maintained
≥ 50% Less than Historical
Apparently Lost
Newly Detected
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Spatial Survey Summary
• Decreases in crayfish trap
catches have been
significant and widespread
• Cambarus spp.
(C. bartonii and C.
robustus) appear to be
faring the worst
• The cause(s) of the
decreases are unknown0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Historical Overall CPUEC
urr
en
t O
ve
rall C
PU
E Cambarids
Orconectids
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Long-term Monitoring
• Crayfish populations in ~20 Muskoka-area lakes have been monitored for 23 years (1988-2010)
• The same sampling methods (i.e., 54 baited traps) have been used throughout the study
• Original goal was to monitor biological recovery from acid rain
Study Area
Carnarvon
Vankoughnet
35
118
Bracebridge
Dorset
Baysville
117
Dwight
11
Huntsville
Port Sydney
60
1
2
3
4 5
6
7
8
9
1. Harp2. Chub3. Blue Chalk4. Red Chalk5. Red Chalk East6. Dickie7. Heney8. Crosson9. Plastic
79 00'o
45 00'o
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Long-term Monitoring Results
• Some lakes had no
crayfish – other lakes
had 3 species
• Abundances varied a
great deal among
species and over time
• CUE tended to go
down over time (didn’t
suggest recovery)
0
2
4
6
8
10
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Year
CU
E (
No
. p
er
Tra
p)
O. propinquus
C. bartonii
O. virilis
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Long-term Monitoring C. bartonii
-2
0
2
4
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Year
CU
E (
sta
nd
)
• When catches for a
given species are
standardized over time
there is considerable
variation, but an overall
decrease in catch is
evident
• C. bartonii from 9 lakes
revealed 7 significant
decreases in CUE over
time
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Long-term Monitoring O. virilis
-2
0
2
4
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Year
CU
E (
sta
nd
)
• Standardized CUE for
O. virilis from 6 lakes
also decreased (4 of
these trends were
significant)
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Long-term Monitoring O. propinquus
-2
0
2
4
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
Year
CU
E (
sta
nd
)
• Standardized catches
for O. propinquus from
8 lakes were more
variable
• 5 populations
displayed decreases
over time and 3 of
these were statistically
significant
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Exploring “cause and effect”
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2
4
6
8
10
12
0 2 4 6 8 10 12
Historical [Ca++] (mg/L)
Cu
rre
nt
[Ca
++
] (m
g/L
)AW
ME
DE, LC
GV
KA
LWHH
• It is not immediately
clear why crayfish
catches have generally
decreased over time
• One of many
hypotheses focuses on
observed decreases in
calcium concentrations
in Muskoka lakes
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Are Crayfish “limited” by calcium?
• Crayfish were collected
from 19 Muskoka lakes
• Carapaces were dried,
sampled and analyzed
for calcium content
• Crayfish calcium levels
were compared to lake
calcium concentrations
[This is part of Brie Edwards PhD thesis work at the University of Toronto]
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15
16
17
18
19
20
21
22
23
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0.00 10.00 20.00 30.00 40.00 50.00 60.00
Lake [Ca] (mg/L)
Ca
rap
ac
e [
Ca
] (%
dry
ma
ss
)
Correlating Carapace and Lake Calcium
Orconectes virilis
n = 19 lakes, r2 = 0.43, p < 0.01
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Survival and Calcium Availability
• conducted a lab experiment
with juvenile crayfish grown
in tanks with different
concentrations of calcium
[This is part of Brie Edwards PhD thesis
work at the University of Toronto]
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Survival and Calcium Availability
0
20
40
60
80
100
0 10 20 30 40 50 60 70 80
Days
Cu
mu
lati
ve S
urv
ival (%
)
2.5 mg/L (2.58 +/- 0.21)
0.9 mg/L (0.87 +/- 0.05)
0.7 mg/L (0.74 +/- 0.04)
0.5 mg/L (0.51 +/- 0.04)0
20
40
60
80
100
0 10 20 30 40 50 60 70 80
Days
Cu
mu
lati
ve s
urv
ival (%
)
2.5 mg/L (2.42 +/- 0.01)
1.2 mg/L (1.14 +/- 0.01)
0.7 mg/L (0.66 +/- 0.01)
Nonparametric Log-Rank tests
showed significant differences
between Control and Extreme
treatments (p < 0.05)
2009
2010
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Summary
• Crayfish seem to “work” as biomonitors
• Trends over time based on a 100-lake survey and year-to-year monitoring of about 20 lakes indicate crayfish catches are generally decreasing despite ongoing chemical recovery from acid rain
• The cause of these decreases are unknown, but may be related to gradual decreases in calcium – efforts to identify the cause(s) are ongoing
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University of Toronto
- Best in Science Research Grant
- Brie Edwards & Don Jackson
Dorset Environmental Science Centre
- Ron Ingram, Bob Girard, Ron Reid,
Don Evans & Jim Rusak
- many summer students
Field Assistance
- Ellen Fanning & Kraig Picken
Acknowledgements
(watercolour images © Aleta Karstad 2008 - www.crayfishontario.ca)