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

Outline

-Background on Windermere &

stable isotope analysis of food webs

-Archived samples: diet shifts-Archived samples: diet shifts

-Wider effects on the ecosystem

11

12

9.8 °C

10.7 °C

Increase in water temperature of Windermere

Tem

pe

ratu

re o

C

8

9

10

1940 1950 1960 1970 1980 1990 2000 2010

9.8 °C

Year

Tem

pe

ratu

re

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)

Windermere fish

Glacial relic species

Minnow (Phoxinus phoxinus)

Northern 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)

Invasive species

Arctic charr – near southernmost edge of its distribution

Roach – historically a southern distribution but expanding northwards

English Lake District

Arctic charr

Gill nets

1940+

Northern pike

Gill nets

1944+

Arctic charr

Fishery records

1966+

Windermere long-term fish research

Perch

Traps

1943+

Hydroacoustics

1990+

Roach

Gill nets

1995+

3000

4000

5000

6000

Ab

un

dan

ce (

fish

ha

-1)

Long-term fish abundance

Start of roach expansion

0

1000

2000

1990 1995 2000 2005 2010

Ab

un

dan

ce (

fish

ha

Year

• Increase since late 1990s, particularly in south basin

30

40

50

CP

UE

(F

ish

100 m

2n

et-

1 d

ay

-1)

Roach increase

0

10

20

1995 2000 2005 2010

CP

UE

(F

ish

100 m

Year

2

3

4

5

6

CP

UE

(fi

sh

h-1

)Arctic charr decrease

0

1

1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

CP

UE

(fi

sh

h

Year

• Since early 2000s, particularly in south basin; 2010 values are the lowest on

record

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Nu

mb

ers

pe

r li

ter

Summer zooplankton abundance 1985 - 2010

3.0/L

2.0/L

Decline in Zooplankton Abundance

0.0

0.5

1.0

1.5

2.0

1980 1985 1990 1995 2000 2005 2010

Nu

mb

ers

pe

r li

ter

Decrease in summer zooplankton by 33% following

roach expansion (1985-1995 vs. 1996 – 2010)

Windermere Food Web – A Stable Isotope Picture

Pike

Perch Arctic charrRoach

Tro

ph

ic L

ev

el

Ind

ica

tor

15N

Zooplankton

Phytoplankton

Offshore

(Pelagic)

Near shore

(Littoral)

Macroinvertebrates

Energy Source

Tro

ph

ic L

ev

el

Ind

ica

tor

δδ δδ1

5

δδδδ13C

Benthic Algae

& Detritus

Methods

Measured δδδδ13C & δδδδ15N 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

0.5

0.6

0.7

0.8

0.9

1

Pro

po

rtio

n i

n D

iet

Proportions of Prey in Charr Diet

Cyclops

Daphnia

Calculated from δδδδ13C & δδδδ15N

Predatory

zooplankton

Herbivorous

zooplankton

0

0.1

0.2

0.3

0.4

1985-1987 1992-1994 2000-2002 2003-2005 2009-2010

Pro

po

rtio

n i

n D

iet

Macroinverts

Chironomids

Macroinverts

Chironomids

Period of Years

0.5

0.6

0.7

0.8

0.9

1

Pro

po

rtio

n i

n D

iet

Proportions of Prey in Roach Diet

Cyclops

Daphnia

Calculated from δδδδ13C & δδδδ15N

Predatory

zooplankton

Herbivorous

zooplankton

0

0.1

0.2

0.3

0.4

0.5

2000 2005 2009 2010

Pro

po

rtio

n i

n D

iet

Macroinverts

Chironomids

Macroinverts

Chironomids

Year

0.6

0.7

0.8

0.9

1

Pro

po

rtio

n i

n D

iet

Proportions of Prey in Perch Diet

Cyclops

Daphnia

Calculated from δδδδ13C & δδδδ15NPredatory

zooplankton

Herbivorous

zooplankton

0

0.1

0.2

0.3

0.4

0.5

0.6

2000 2005 2009 2010

Pro

po

rtio

n i

n D

iet

Macroinverts

Chironomids

Macroinverts

Chironomids

Year

0

0.2

0.4

0.6

0.8

1

1985-1987 1992-1994 2000-2002 2003-2005 2009-2010

Pro

po

rtio

n i

n D

iet Proportions of Prey -

0.6

0.8

1Cyclops

Daphnia

Predatory

zooplankton

Herbivorous

zooplankton

Calculated from δδδδ13C & δδδδ15N

0

0.2

0.4 Macroinverts

Chironomids

0

0.2

0.4

0.6

0.8

1

2000 2005 2009 2010

zooplankton

Macroinverts

Chironomids

0.5

0.6

0.7

0.8

0.9

1

Pro

po

rtio

n i

n D

iet

Proportions of Prey in Pike Diet

Roach

Perch

Calculated from δδδδ13C & δδδδ15N

2000 2005 2009 20100

0.1

0.2

0.3

0.4

0.5

Pro

po

rtio

n i

n D

iet

Charr

Year

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• 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

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• QMUL: Ian Sanders, Nicola Ings and Michelle Jackson

• CEH Lancaster: Helen Grant

• Freshwater Biological Association

& Queen’s University Belfast

• Natural Environment Research Council (NERC)