Scotland’s Crayfish Crisis
Zara Gladman
[email protected]
Overview
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Scotland’s crayfish crisis: some background
Tackling the crisis
Biodiversity and environmental change
Scotland’s crayfish crisis:
some background
American signal crayfish
(Pacifastacus leniusculus)
Scotland’s crayfish crisis:
some background
American signal crayfish
(Pacifastacus leniusculus)
Scotland’s crayfish crisis:
some background
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Large, freshwater, decapod crustacean
Native to western North America
Imported to Britain in 1970s for aquaculture
First recorded in Scotland in Galloway, 1995
Scotland’s crayfish crisis:
some background
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Non-native invasive species cited as one of the top
5 drivers of ecosystem change
Serious threat to biodiversity  listed under
‘Species Action Framework’ in 2007
Tackling the crisis
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Where is it?
How can we get rid of it?
What is it doing?
Tackling the crisis
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Where is it? 1. Distribution
How can we get rid of it? 2. Control
What is it doing? 3. Impact
3 broad aims of PhD
Tackling the crisis
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Where is it? 1. Distribution
How can we get rid of it? 2. Control
What is it doing? 3. Impact
3 broad aims of PhD
1. Distribution
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Fine-scale distribution of
signal crayfish largely
unknown
For effective
control/containment, we must
know where it is!
First aim: develop a protocol
for detecting crayfish 
applied across Scotland
1. Distribution
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Compared the crayfish detection ability of four active
sampling techniques
30 riffles on upper River Clyde
1. Hand searching
2. Electrofishing (1, 2, 3 runs)
3. Kick sampling
4. Surber sampling
1. Distribution
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Results: combination of kick sampling and 3
runs of electrofishing  best chance of
detecting signal crayfish (Gladman et al., accepted)
1. Distribution
• Protocol
Location
River Catchment
Fishery Trust Undertaking the Survey
Upper Clyde
Clyde
Clyde River Foundation
River North Esk (ponds); Lugar Burn/main stem
North Esk
Esks DSFBs
Pow Burn
South Esk
Esks DSFBs
Rankeillour Burn (Fife)
Eden
Forth Fisheries Trust
River Teith (pond and ditches)
Forth
Forth Fisheries Trust
River Tyne (stillwater fishery, East Lothian)
East Lothian Tyne
Forth Fisheries Trust
Tiel Burn (Fife)
Tiel
Forth Fisheries Trust
Murray Burn
Water of Leith
Forth Fisheries Trust
Kirkcudbrightshire
Dee
Galloway Fisheries Trust
Skyre Burn
Fleet
Galloway Fisheries Trust
River Nairn
Nairn
Ness and Beauly Fisheries Trust
Dighty Water (Dundee)
Dighty
Tay DSFB
River Earn
Earn
Tay DSFB
River Ardle (pond and small stream)
Ericht
Tay DSFB
Shee Water (pond and small stream)
Ericht
Tay DSFB
Rivers Ettrick and Till
Tweed
Tweed Foundation
Kirkbank (Teviot Water)
Tweed
Tweed Foundation
1. Distribution
. . . So where is it?
Sinclair, CA (2009). Fine scale mapping of
signal crayfish distribution in Scotland, Scottish
Natural Heritage Commissioned Report,
Project 26686.
2. Control
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Physical
Chemical
Biological
Case study: Loch Ken’s crayfish crisis
2. Control
Loch Ken’s crayfish crisis
Cray
fish c
r
isis '
l
oomi
n
g' on
loch
2. Control
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Summer 2009: Marine Scotland
funded an intensive 4-month
trapping programme:
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Loch Ken’s crayfish crisis
Assess the scale of the infestation
Assess the feasibility of control
Opportunity for research:
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Effect of intensive trapping on the
population
Two mark-and-recapture projects: one
before and one after the trapping
programme
2. Control
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Loch Ken’s crayfish crisis
Crayfish sampled at 3
sites (transects of 15
creels, 400 m apart)
during two sessions:
before (May/June) and
after (September) the
trapping programme
2. Control
Loch Ken’s crayfish crisis
2. Control
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Loch Ken’s crayfish crisis
Total catch
3879 crayfish before trapping programme
3205 crayfish after trapping programme
. . . very little effect?!
2. Control
Loch Ken’s crayfish crisis
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. . . Sex is important!
Site 1
Site 2
Site 3
Before
After
Before
After
Before
After
1 M :
0.42 F
1 M :
1.04 F
1 M :
0.37 F
1 M : 1.54 F
1 M :
0.40 F
1 M :
0.85 F
Numbers of males and females caught during the two mark and recapture sessions before (May/June) the removal programme and after (September) the removal programme Denotes within‐sex pairwise comparison with statistically significant difference p<0.01
2. Control
Loch Ken’s crayfish crisis
. . . Sex is important!
Due to:
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Bias of trapping towards
large males
Changes in reproductive
state of females:
 berried females in May
are trap shy; egg release in
summer
Numbers of males and females caught during the two mark and recapture sessions before (May/June) the removal programme and after (September) the removal programme Denotes within‐sex pairwise comparison with statistically significant difference p<0.01
2. Control
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Loch Ken’s crayfish crisis
Density estimates
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Population estimates from mark and recapture
data were used to make estimates of density
(based on a trapping radius of 100 m2, Accosta &
Perry, 2000)
Range 1.06 – 9.05 crayfish per m-2
Very high densities compared with other lakes:
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Lake Billy Chinook: 0.24 c.p.m-2 and 1.13 c.p.m-2
Lake Donner: 0-1.15 c.p.m-2
Lake Tahoe: 0.53-8.38 c.p.m-2
2. Control
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Loch Ken’s crayfish crisis
Other observations
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Mean size of crayfish reduced
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Significant for males
Movements
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At least 800m in two weeks; 3 km in 6 months
2. Control
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Loch Ken’s crayfish crisis
Summary
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Trapping significantly reduced males; effect on
females complicated by trap bias/reproductive
status  sex ratio skewed towards females
Mean size of crayfish reduced
Crayfish capable of significant movements
High densities mean loss to biodiversity likely
to be significant
Biodiversity and environmental change
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Alien species are a major threat to biodiversity
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Very difficult (impossible?) to reverse changes

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Research is important in helping us understand ecological
problems . . . and deal with them!
Prevention is preferable!
Thanks to . . .
Colin Adams
Colin Bean
Jo Long
Willie Yeomans
[email protected]