Evidence for impacts by jellyfish on herring recruitment in the North Sea
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Transcript of Evidence for impacts by jellyfish on herring recruitment in the North Sea
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Evidence for impacts by jellyfish on herring
recruitment in the North Sea
Chris Lynam1, Andrew Brierley1, Mike Heath2 & Steve Hay2
1 Gatty Marine Lab. University of St Andrews2 Marlab, Aberdeen
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Fishing down the food web
From Pauly and MacLean In a perfect ocean. Island Press 2003
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Sardine Sardinops sagax(also known as pilchard)
Boyer et al. SA J Mar Sci 2001
High fish landings
Fishery collapse& 1st reports of jellyfish
Rise of the jellyfish
No jelly?
Benguela
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Anecdotal evidence from the Benguela Many tonnes of jellyfish but only 1 sardine caught in 66 trawls.~1/2 of whichcontained >80% by mass jellyfish
• 12m diameter circular mouthopening.
• Mesh sizereducing from 400 to 36 mm
• Towed for ~5 min at 3 knots
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Interactions between fish and jellyfish
• Top down, medusae prey on fish eggs/larvae
• Bottom up effect, medusae prey on zooplankton which regulate fish survival
• Dietary overlap (Purcell & Sturdevant 2001)
50%73%
Pacific herring(Clupea pallasi)
Aurelia labiata Cyanea capillata
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North Sea Jellyfish
Aurelia aurita Cyanea capillata Cyanea lamarckii
C. capillata feeding on A. aurita
C. capillata feeding on C. lamarckii
Fish larvae trapped in C. capillata tentacles
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Predatory impact by jellyfish on herring larvae
Aurelia aurita is predatory on Atlantic
herring larvae in the Baltic Sea (Möller
Science 1984).
Aequorea victoria is predatory upon Pacific
herring larvae in British Columbia
(Purcell & Grover MEPS 1990)
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Our data• Jellyfish by-catch from IYGPT nets, during ICES
International 0-Group Gadoid surveys of the North Sea.• 15 years (1971-86, not 1984) • >430000 medusae
from 2030 IYGPT trawls
• ICES Autumn-spawning herring data, for North Sea, Eastern English Channel, Skagerrak and Kattegat combined
Survey area
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Herring recruitment, SSB, and jellyfish abundance
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The residual survival, i.e. the difference between the observed and the expected
(Ricker-modelled) survival = ln(R) – ln(SSB), is a measure of external impacts on
larval survival.
Residual survival = observed survival -expected survival
Residual survival = ln(Robserved) - ln(Rmodelled)
Herring residual survival
residuals (survival-ricker)
-1.50
-1.00
-0.50
0.00
0.50
1.00
1.50
1960
1964
1968
1972
1976
1980
1984
1988
1992
1996
2000
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r = -0.61, p = 0.02
Jellyfish do impact on herring survival to age-1
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1971-86
The North Atlantic OscillationA climatic phenomenon that contributes greatly to the variability in the
weather system over the North Sea and Europe.
The NAO impacts on the sea level pressure, turbulence, sea surface
temperature, ocean heat transport and deep ocean convection and has the
potential to influence profoundly the pelagic environment.
+ NAO leading to strong westerlies, high turbulence, and warmer SSTin the North Sea.
From Hurrell 2003
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Jellyfish: links to the NAOThe abundance of A.aurita in the North Sea
is negatively correlated with the winter
North Atlantic Oscillation Index
(Lynam et al. Limnol. Oceanogr. 2004)
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Herring: links to the NAO
Climate variation governs alternating periods of herring and sardine (Sardina
pilchardus) dominance in the English Channel (Alheit & Hagen Fish Oceanogr.
1997).
• low NAO, herring dominate over sardines in English Channel
The NAO is linked to herring year-class-strength in the Baltic Sea (Axenrot &
Hansson Limnol. Oceanogr. 2003) (r2 = 0.35 p < 0.03 n = 10)
• low NAO, weak year class of herring in the Baltic Sea
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Jellyfish-herring-climate
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Predation/competitionimpact on herring?
Regulation of A. aurita abundance
by C. capillata?
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Jellyfish-herring-climate
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Summary
A. aurita are detrimental to North Sea herring recruitment and survival to age-1, via
• Predation on herring larvae by medusae, and
• Competition between larvae and medusae for zooplankton food.
This impact is mediated by the climate, as quantified by the NAO, through
• Increased predation/competition between herring and C. capillata in low NAO years.
> reduced herring recruitment
• Regulation of A. aurita by C. capillata in high NAO years.
> enhanced herring recruitment
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Acknowledgements
Many plates from Aquascope 2000, Strömstad, Swedenand the Sir Alister Hardy Foundation for Ocean Science image library
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The Ricker model estimates recruitment from the Spawning Stock Biomass
RRicker = (a.S).exp(-b.S)
where, RRicker = numbers (millions) age-1 for year class y,
S = SSB (tonnes) in year y. The constants a = 1.16 x 10-1, b = 8.53 x 10-7 were fitted by non-linear least-squares estimation using the Gauss-Newton algorithm.
Removal of long-term trend due to SSB from recruitment
020000400006000080000
100000120000
1960
1964
1968
1972
1976
1980
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recr
uitm
ent
(mil
lion
s)
observed ricker model
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The survival of herring to age-1 was calculated from the difference between the
natural logarithms of the SSB and recruitment level (R):
Survival = ln(R) – ln(SSB)
Herring survival index
-6.00
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1960
1964
1968
1972
1976
1980
1984
1988
1992
1996
2000
surv
ival
to a
ge-1
survival ricker fitted survival
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The difference between the observed and the expected (Ricker-modelled)
survival, the residual survival, is a measure of external impacts on larval survival.
Survival residuals = observed survival -expected survival
Herring residual survival
residuals (survival-ricker)
-1.50
-1.00
-0.50
0.00
0.50
1.00
1.50
1960
1964
1968
1972
1976
1980
1984
1988
1992
1996
2000
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In each spawning ground analysed the
abundance of jellyfish was positively
correlated with the herring larval abundance.
Aurelia aurita
Buchan
(r2 = 0.44 p = 0.04 n = 10)
Central
(r2 = 0.61 p = 0.02 n = 8)
C. capillata
Orkney/Shetland region
(r2 = 0.48 p < 0.01 n = 14)
Spawning groundsOrkney/Shetland
Buchan
Central
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Jellyfish and fish
Whiting secure among C. capillata tentacles
Fish larvae trapped in C. capillata tentacles
Whiting eating A. aurita
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Low NAO
NADW
NAC
weak CSJ
GS
++
GS
High NAO
LSIW
strong CSJNAC
+
Possible North Atlantic Oscillation (NAO) driven changes in Atlantic currents influencing the North Sea showing the four regions of the North Sea where jellyfish data were analysed. NAC = North Atlantic Current, GS = Gulf Stream, CSJ = Continental Shelf Jet, LSIW = Labrador Sea Intermediate Water, NADW = North Atlantic Deep Water, and + signifies a positive effect on jellyfish abundance, adapted from Reid et al. (1998).
Currents
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Long-term series of a combined index of Candacia armata and Metridia lucens in the NW North Sea. Reproduced from Corten 1999.
The abundance of zooplankton Atlantic water indicator species Candacia armata and Metridia lucens EoS
Regime Shift 1983 linked to Atlantic Inflow
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Concomitant changes in North Sea gadoids and plankton
From Beaugrand et al. Nature 2003 Jellyfish survey period