Monitoring Crayfish Populations
in Muskoka Lakes
Keith Somers
Dorset Environmental Science Centre
Ontario Ministry of the Environment
2
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
3
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)
4
• 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
5
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)
6
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…
7
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)
8
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
9
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
10
. 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
12
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
13
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
14
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
15
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
16
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
17
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
18
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
19
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
20
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
21
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
22
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
23
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)
24
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
25
Exploring “cause and effect”
0
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
26
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]
27
15
16
17
18
19
20
21
22
23
24
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
28
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]
29
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
30
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
31
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)