Monitoring Crayfish Populations in Muskoka Lakes

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)

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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

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…

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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

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

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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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Distribution of O. propinquus (39 lakes)

Maintained


Apparently Lost

Newly Detected

18





Distribution of C. bartonii (33 lakes)

Maintained


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

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

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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”

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

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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)

Monitoring Crayfish Populations in Muskoka Lakes

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