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

Fishing down the food web

From Pauly and MacLean In a perfect ocean. Island Press 2003

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

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

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

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

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)

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

Herring recruitment, SSB, and jellyfish abundance

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

r = -0.61, p = 0.02

Jellyfish do impact on herring survival to age-1

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

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)

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

Jellyfish-herring-climate

Predation/competitionimpact on herring?

Regulation of A. aurita abundance

by C. capillata?

Jellyfish-herring-climate

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

Acknowledgements

Many plates from Aquascope 2000, Strömstad, Swedenand the Sir Alister Hardy Foundation for Ocean Science image library

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

1984

1988

1992

1996

2000

recr

uitm

ent

(mil

lion

s)

observed ricker model

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

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

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

Jellyfish and fish

Whiting secure among C. capillata tentacles

Fish larvae trapped in C. capillata tentacles

Whiting eating A. aurita

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

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

Concomitant changes in North Sea gadoids and plankton

From Beaugrand et al. Nature 2003 Jellyfish survey period