archives and isotopes: changes afoot in the food web of windermere
TRANSCRIPT
Archives and isotopes: changes afoot in the
food web of Windermere
Jonathan Grey, P Smyntek, S Maberly & I Winfield et al
Long term research on the fish of Windermere
1940+ Arctic charr gill net survey
1943+ Perch traps
1944+ Pike gill nets
1966+ Arctic charr fishery record scheme
1990+ hydroacoustic survey
1995+ Roach gill nets
Long term fish abundance
General increase since late 1990s, especially in the south basin
data from Winfield et al
0
1000
2000
3000
4000
5000
6000
1990 1995 2000 2005 2010
Ab
un
dan
ce (
fish
ha
-1)
Year
Decrease in Arctic charr
Marked decline since 2000; 2010 CPUE lowest recorded
data from Winfield et al
0
1
2
3
4
5
6
1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
CP
UE
(fi
sh
h-1
)
Year
Increase in roach
data from Winfield et al
0
10
20
30
40
50
1995 2000 2005 2010
CP
UE
(F
ish
100 m
2n
et-
1 d
ay
-1)
Year
Fishy Conflict
English Lake District
Stable isotope ‘mapping’
Isotopes and archives
Grey et al 2009
Defatted muscle 13
C (‰)
-30 -28 -26 -24 -22 -20 -18 -16 -14 -12
Acid
ifie
d s
ca
le
13C
(‰
)
-30
-28
-26
-24
-22
-20
-18
-16
-14
-12
y = 0.99x + 0.64; r2 = 0.92; P<0.0001
A
Hypotheses testable using SIA
1. Roach populations have increased as a result of warming surface water
2. The recent reduction in summer zooplankton is causally linked to increased
predation pressure by planktivorous fish
3. The increased abundance of summer phytoplankton, and associated
changes in the lake such as increased ratio of phytoplankton chlorophyll a to
total phosphorus, is causally linked to the reduction in grazing pressure
4. The decline in Arctic charr in the lake is causally linked to competition for food
with other planktivorous fish, particularly the introduced roach in recent years
5. Invasion by a generalist consumer (roach) has also affected the top predator
in the lake (the pike) by shortening the food chain, further influencing food-
web interactions.
Windermere isotopic food web…. then
Offshore (Pelagic) Near shore (Littoral)
Tro
ph
ic L
eve
l In
dic
ato
r 1
5N
13C (‰)
15N
(‰
) ?
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
2000 2005 2009 2010
Pro
po
rtio
n in
Die
t
Cyclops
Daphnia
Macroinverts
Chironomids
Isotope mixing model of dietary contribution
Importance of littoral prey; greater importance of
primary consumers
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
2000 2005 2009 2010
Pro
po
rtio
n in
Die
t
Cyclops
Daphnia
Macroinverts
Chironomids
Isotope mixing model of dietary contribution
Increase in pelagic and possibly profundal prey
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1985-1987 1992-1994 2000-2002 2003-2005 2009-2010
Pro
po
rtio
n in
Die
t
Cyclops
Daphnia
Macroinverts
Chironomids
Isotope mixing model of dietary contribution
Slight shift from littoral toward profundal prey
2000 2005 2009 2010 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Pro
po
rtio
n in
Die
t
Roach
Perch
Charr
Isotope mixing model of dietary contribution
Shift from charr to roach
Windermere isotopic food web….. now
Offshore (Pelagic) Near shore (Littoral)
Tro
ph
ic L
eve
l In
dic
ato
r 1
5N
13C (‰)
15N
(‰
)
Change in trophic position?
Shift from charr to roach
Year
2000 2002 2004 2006 2008 2010
Ch
an
ge
in
tro
ph
ic p
ositio
n f
rom
1
5N
da
ta
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Pike - Roach
Pike - Charr
Pike
Charr Pike
P-zoop Roach
H-zoop M-inverts
Basal Res
2000 2010
Summary
• Long term collections and archived tissues / samples from the FBA / CEH has
provided material for food web reconstruction
• Stable isotope analysis of carbon and nitrogen can be conducted on such
material with confidence
• Roach diet comprises mostly littoral prey; trophic overlap with perch appears
to have pushed perch toward reliance on pelagic and profundal resources
• Knock on effect to charr pushing them toward reliance on more profundal
resource. Cautionary note: we do not know what YOY fish are doing
• Shift in pike diet from charr to roach and consequent shift in ‘routing’ of energy
through the foodweb from the pelagic to the littoral zone
• Subtle shift in trophic position – increasing efficiency within food web?
http://www.windermere-science.org.uk/home [email protected]