The document summarizes research on the expansion of roach populations in the UK and locally. It finds that roach presence has increased significantly since the 1970s, with the species now found in over 40% of UK sites. Through ecological niche modeling using temperature data, the study predicts roach habitat may continue expanding rapidly this century as air temperatures increase. The model estimates roach presence in the UK could rise to over 70% of sites with a 2°C warming and over 90% of sites with a 4°C warming. This suggests temperature has been a key factor limiting roach distribution previously.

1. Expansion of roach populations in
the UK & locally
J.A. Elliott, I.J. Winfield, P. Henrys, M. Tanguy, B.
James, J. Fletcher, J. Cooper & S.C. Maberly
Centre for Ecology & Hydrology,
Lancaster & Wallingford

2. The Roach (Rutilus rutilus)
• Fourth most recorded fish species in the UK Database and Atlas
of Freshwater Fish (DAFF)
• Eurythermal cyprinid (4 to >30 oC)
• Preference for warmer temperatures: growth occurs only >12 oC
• Omnivorous
• Known to have significant impacts on ecosystems

3. Roach in the UK
Red=Roach presence pre-1973
Yellow=Roach presence post-1973
*Data from DAFF
Salmonids (e.g. Arctic charr)
Cyprinids (e.g. roach)

4. Windermere: Roach expansion
2n -1
t a
e d
y
-1
)
50
Gill nets
40
30
20
m
0
1
h
s
i
F
(
E
U
P
C
10
0
1995
‘It is not unlikely that these had
been brought as live-bait for
pike, as live-baiting is
occasionally done by strangers.’
(Watson, 1899)
2000
Year
2005
2010
Pike prey

5. Roach and temperature

6. Predicting UK expansion
• Aim: To use ecological niche modelling to examine how roach
habitat in the UK may change over this century
• Method:
DAFF data
(1973-89)
Compare to
DAFF data
(1990-2006)
GLM with
binominal
response
Validate
Seasonal air
T oC grid means
(Met Office)

7. Creating the model
DAFF data
(1973-89)
Seasonal T oC
grid means
(Met Office)
GLM with
binominal
response
Need a
probability
threshold
Compare to
DAFF data
(1973-89)??

8. Probability threshold
True positives
0.876
Probability threshold to
define a presence value (1)
False positives

9. Compare to observed 1990-2006 DAFF
Model
Grids
tested
EncRoach-S* All
Changed
AUC
% Match
FPE
FNE
0.867
82%
7%
11%
48%
25%
26%
*EncRoach-S = Environmental Change & Roach (Seasonal)

10. Sensitivity to increasing air temperature
Air temperature increase (°C)
Probability of
presence
1
2
3
4

11. Sensitivity to increasing air temperature
Area of
UK
No. of
(total no. grids
grids)
All UK
(2470)
0
Increase in air temperature (oC)
1
2
3
4
Presence
842
1005
1214
1509
1810
% cover
Presence
34.1
817
40.7
958
49.1
1083
61.1
1202
73.3
1279
% cover
Presence
61.2
25
71.8
47
81.2
93
90.1
153
95.9
211
% cover
Scotland Presence
(903)
% cover
10.7
0
20.2
0
39.9
38
65.7
154
90.6
320
0
0
4.2
17.1
35.4
England
(1334)
Wales
(233)

12. Next steps & Conclusions
• Test the model using UKCIP climate change scenarios
• But, if temperature has been restricting Roach habitat range,
we could see over this century a rapid increase in the
distribution of this ecologically significant fish