Smyntek et al 2011 presentation at the Symposium for European Freshwater Sciences

1. One pressure too many?
Diet shifts in a declining Arctic charr population
& the implications for the lake food web
Peter Smyntek & Jonathan Grey
School of Biological and Chemical Sciences
Queen Mary University of London

2. Outline
-Background on Windermere &
stable isotope analysis of food webs
-Archived samples: diet shifts
-Wider effects on the ecosystem

3. Increase in water temperature of Windermere
12
10.7 °C
11
Temperature oC
9.8 °C
10
9
8
1940 1950 1960 1970 1980 1990 2000 2010
Year

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

5. Arctic charr – near southernmost edge of its distribution
English Lake District
Roach – historically a southern distribution but expanding northwards

6. Windermere long-term fish research
Arctic charr
Fishery records
1966+
Northern pike Arctic charr
Gill nets Gill nets
1944+ 1940+
Perch Roach
Traps Gill nets
1943+ 1995+
Hydroacoustics
1990+

7. Long-term fish abundance
6000
5000
Abundance (fish ha-1)
4000
Start of roach expansion
3000
2000
1000
0
1990 1995 2000 2005 2010
Year
• Increase since late 1990s, particularly in south basin

8. Roach increase
50
CPUE (Fish 100 m 2 net-1 day-1)
40
30
20
10
0
1995 2000 2005 2010
Year

9. Arctic charr decrease
6
5
CPUE (fish h-1)
4
3
2
1
0
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year
• Since early 2000s, particularly in south basin; 2010 values are the lowest on
record

10. Decline in Zooplankton Abundance
Summer zooplankton abundance 1985 - 2010
5.0
4.5
Numbers per liter
4.0
3.5
3.0/L
3.0
2.5
2.0/L
2.0
1.5
1.0
0.5
0.0
1980 1985 1990 1995 2000 2005 2010
Decrease in summer zooplankton by 33% following
roach expansion (1985-1995 vs. 1996 – 2010)

11. Windermere Food Web – A Stable Isotope Picture
Pike
Perch Arctic charr
Trophic Level Indicator
Roach
δ15N
Macroinvertebrates Zooplankton
Benthic Algae
Phytoplankton
& Detritus
Near shore Offshore
(Littoral)
δ13C (Pelagic)
Energy Source

12. Methods
Measured δ13C & δ15N of archived samples
(1985 – 2010):
- zooplankton (predatory & herbivorous)
- macroinvertebrates (nearshore/littoral)
- chironomids (deep offshore/profundal)
-fish scales & opercular bones (gill cover)
-Dietary mixing model: proportions of potential
food items consumed

13. Proportions of Prey in Charr Diet
Calculated from δ13C & δ15N
1
Predatory
Proportion in Diet
0.9 Cyclops
zooplankton
0.8
0.7
Herbivorous
0.6 Daphnia
zooplankton
0.5
0.4
0.3 Macroinverts
Macroinverts
0.2
0.1
0 Chironomids
Chironomids
1985-1987 1992-1994 2000-2002 2003-2005 2009-2010
Period of Years

14. Proportions of Prey in Roach Diet
Calculated from δ13C & δ15N
1
Cyclops
Predatory
0.9
zooplankton
0.8
Proportion in Diet
0.7
Herbivorous
Daphnia
0.6 zooplankton
0.5
0.4
Macroinverts
0.3 Macroinverts
0.2
0.1
Chironomids
Chironomids
0
2000 2005 2009 2010
Year

15. Proportions of Prey in Perch Diet
Calculated from δ13C & δ15N Predatory
1 Cyclops
zooplankton
Proportion in Diet
0.9
0.8
Herbivorous
0.7 Daphnia
zooplankton
0.6
0.5
0.4 Macroinverts
Macroinverts
0.3
0.2
0.1 Chironomids
Chironomids
0
2000 2005 2009 2010
Year

16. Proportions of Prey - Calculated from δ13C & δ15N
Proportion in Diet
1
0.8
0.6
0.4
0.2
0
1985-1987 1992-1994 2000-2002 2003-2005 2009-2010
1 Predatory
Cyclops
0.8 zooplankton
0.6 Daphnia
Herbivorous
zooplankton
0.4 Macroinverts
Macroinverts
0.2
Chironomids
Chironomids
0
1
0.8
0.6
0.4
0.2
0
2000 2005 2009 2010

17. Proportions of Prey in Pike Diet
Calculated from δ13C & δ15N
1
0.9 Roach
0.8
Proportion in Diet
0.7
0.6
Perch
0.5
0.4
0.3
0.2
Charr
0.1
0
2000 2005 2009 2010
Year

18. Conclusions
• Diet of charr included more deep water & less near shore food
sources after roach expansion
• Roach feed on near shore food sources
• Perch diet shifted: near shore to offshore
• Pike diet shifted: offshore-based (charr) to near shore-based
(roach)
• Change in carbon/energy flow through the ecosystem following
roach invasion

19. Acknowledgements
• CEH Lake Ecosystem Group - especially: Ian Winfield, Steve
Thackeray, Stephen Maberly, Ian Jones, Mitzi DeVille, Ben James,
Janice Fletcher, Alex Elliott, Jack Kelly & Heidrun Feuchtmayr
• QMUL: Ian Sanders, Nicola Ings and Michelle Jackson
• CEH Lancaster: Helen Grant
• Freshwater Biological Association
& Queen’s University Belfast
• Natural Environment Research Council (NERC)