This document discusses competition among native and invasive fish species in a lake ecosystem. The key points are: 1) The invasive roach species was introduced over 100 years ago but only recently increased in population, coinciding with declines in the native Arctic charr and some decrease in pike populations. 2) As the roach population increased, diet analyses found the native perch and Arctic charr shifted from eating more macroinvertebrates and zooplankton to becoming more zooplanktivorous. 3) In contrast, the roach diet has remained stable, dominated by macroinvertebrates and predatory zooplankton. This suggests the roach increase

1. Competition among native and
invasive fish
Ian J Winfield 1, Peter M Smyntek 2,
Janice M Fletcher 1, J Ben James 1
& Jonathan Grey 2
1
2
Lake Ecosystems Group, Centre for Ecology &
Hydrology, Lancaster LA1 4AP, U.K.
School of Biological and Chemical Sciences, Queen
Mary University of London, London E1 4NS, U.K.

2. Introduction
Carnivores
Planktivores
Perch
Changes in
Pike diet
Increase in
roach
Reduction in
zooplankton
Zooplankton
Increase in
Phytoplankton
phytoplankton
Increased
internal Pload
Chemistry
Climate
change
Reduction in
Arctic charr
Warmer
water
Prolonged
stratification
Reduction
in oxygen
at depth
Physics

3. Structure of presentation
•
Introduction
•
Roach arrival and expansion (reprise)
•
Methods
•
Population trends of native species
•
Diet shifts and competition
•
Summary

4. Introduction
(1986)
(1991)
(2013)
(1899)
(2009)

5. Introduction
Arctic charr (Salvelinus alpinus)
Atlantic salmon (Salmo salar)
Common bream (Abramis brama)
Brown trout (Salmo trutta)
Bullhead (Cottus gobio)
European eel (Anguilla anguilla)
European perch (Perca fluviatilis)
Minnow (Phoxinus phoxinus)
Pike (Esox lucius)
River lamprey (Lampetra fluviatilis)
Roach (Rutilus rutilus)
Rudd (Scardinius erythrophthalmus)
Sea lamprey (Petromyzon marinus)
Stone loach (Barbatula barbatula)
Tench (Tinca tinca)
Three-spined stickleback (Gasterosteus aculeatus)

6. Roach arrival and expansion (reprise)
2n -1
t a
e d
y
-1
)
50
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

7. Roach arrival and expansion (reprise)
6000
-1)
5000
4000
3000
h
s
i
f
(
e
c
a
d
n
u
b
A
2000
1000
0
1990
1995
2000
Year
2005
2010

8. Methods
Pike
Gill nets
1944+
Arctic charr
Gill nets
1940+
Perch
Traps
1943+
Roach
Gill nets
1995+
Population trends by CPUE (etc.)
Arctic charr
Fishery records
1966+
Hydroacoustics
1990+

9. Methods
Pike
Gill nets
1944+
Arctic charr
Gill nets
1940+
Arctic charr
Fishery records
1966+
Gut contents analysis
Perch
Traps
1943+
Diet compositions
Roach
Gill nets
1995+
Stable Isotopes Analysis
(SIA) of C, N

10. Population trends of native species
-1 w
k
e
-1)
Perch
90
60
p
a
r
t
h
s
i
f
(
E
U
P
C
30
0
1981
1986
1991
1996
2001
2006
2011

11. Population trends of native species
Arctic charr

12. Population trends of native species
Pike
-1 d
y
a
-1)
2.0
1.5
1.0
t
e
n
h
s
i
f
(
E
U
P
C
0.5
0.0
1981
1986
1991
1996
2001
2006
2011

13. Population trends of native species
Pike
5250
Weight (g) 4750
of 75cm pike
4250
3750
3250
1981
1986
1991
1996
2001
2006
2011

14. Diet shifts and competition
Perch
Zooplanktivores
1.0
Macroinverts
Daphnia
Chironomids
North Basin
0.8
0.6
0.4
0.2
0.0
1982
1987
Zooplanktivores
1.0
1992
1997
Macroinverts
2002
Daphnia
2007
2012
Chironomids
South Basin
0.8
0.6
0.4
0.2
0.0
1982
1987
1992
1997
2002
2007
2012

15. Diet shifts and competition
Arctic charr
Zooplanktivores
1.0
Macroinverts
Daphnia
Chironomids
North Basin
0.8
0.6
0.4
0.2
0.0
1982
1987
Zooplanktivores
1.0
1992
1997
Macroinverts
2002
Daphnia
2007
2012
Chironomids
South Basin
0.8
0.6
0.4
0.2
0.0
1982
1987
1992
1997
2002
2007
2012

16. Diet shifts and competition
Roach
1.0
Predatory zooplankton
Macroinverts
Daphnia
Chironomids
North Basin
0.8
0.6
0.4
0.2
0.0
1982
1987
1992
Predatory zooplankton
1.0
1997
Macroinverts
2002
Daphnia
2007
2012
Chironomids
South Basin
0.8
0.6
0.4
0.2
0.0
1982
1987
1992
1997
2002
2007
2012

17. Diet shifts and competition
Zooplankton
Macroinvertebrates*
October-March Adult Eudiaptomus abundance, long-term
8000
0.8
6000
0.2
0.4
0.6
4000
0.0
Numbers per litre
1.0
1.2
North Basin
1991
1994
1997
2000
Year
2003
2006
Total
macroinverts.
caught (3 min.
kick sampling)
2009
2000
0
6000
4000
2000
0
* Environmental Change Network data from Iain D M Gunn

18. Summary
•
Roach introduced to Windermere over 114 years ago, but quiescent
until 1990s despite significant eutrophication
•
Recent increase coincident with population trends in perch (little
change), Arctic charr (decrease) and pike (some decrease)
•
Diet changes alongside roach increase:
•
•
Arctic charr decreases in macroinvertebrates and Daphnia,
increase in zooplanktivores
•
•
Perch decreases in macroinvertebrates and Daphnia, increase
in zooplanktivores
Roach remarkably stable and dominated by macroinvertebrates
and predatory zooplankton
Interpretation of roach competitive impact on perch and Arctic charr,
forcing greater food niche overlap between these native species

19. Acknowledgements
•
They say they want to help me but with the stuff they keep on sayin’,
I think those guys just wanna keep on playin’