ICES/NAFO Decadal Symposium 2011, Santander 10-12. May

Barents Sea ecosystem: State, climate fluctuations,

and human impact

E. Johannesen, R. Ingvaldsen, P. Dalpadado, M. Skern-Mauritzen, J. E. Stiansen, E. Eriksen, H. Gjøsæter, B. Bogstad and T. Knutsen

Institute of Marine Research, PO Box 1870, 5817 Bergen, Norway

Aim:

- To assess the state of the Barents Sea ecosystem 2000-2009 in comparison with earlier decades

• Main biological components─ Top predators─ Pelagic fish─ Zooplankton/benthos─ Primary production

• Ecological process

• External driving forces − fishing− climate

And all this in only 20 minutes!

North Sea

Barents Sea

Nor

weg

ian

Sea Russia

Nor

way

• Large1.6 mill km2

• High latitude ~70°-80°N

• Shelf seaMean depth 230m

The Barents Sea, physical features:

The Barents Sea, main species:

HADDOCK

COPEPODS

POLAR COD

SHRIMP

OTHER BENTHOS

PHYTOPLANKTON

External driving forces:

Mainly by Russia and Norway• Demersal fishery

-Mainly cod/haddock-Shrimp, other demersal fish

• Capelin• Harp seals/minke whales

Climate: Fishing:Inflow, ice cover, atmospheric conditions=> determine the extent and characteristics of main water masses

Atlantic water

Arctic water

Mixed/Frontal water

Climate

Fishing

Demersal fish

Pelagic fish

Shrimp

Zooplankton

Below average

Missing value

~Long term averageAbove average

Normalized time series

BARENTS SEA1970-2009

Our data:

OTHER BENTHOS

SHRIMP

POLAR COD

COPEPODS

HADDOCK

PHYTOPLANKTON

FishingClimate

The ecosystem state described with PCA on 20 time series

Hig

h C

ape

lin

Bio

mas

s Lo

wH

igh

Sh

rim

p s

tock

Lo

w

Low Temperature HighLow Haddock Biomass HighHigh Fishing mortality cod Low

Most im

portant factors P

C1

Most important factors PC2

Development in main species:

0123456789 Blue whiting (from 2004) Herring 1-2 years

Polarcod (from 1986) Capelin (from 1973)

1000

000

t

19701974

19781982

19861990

19941998

20022006

-3

-2

-1

0

1

2

3 Krill Zooplankton biomass Shrimp

Ano

mal

ies

Demersal fish:1970’s: High levels1980’s: Historic low levels1990’s: Variable2000’s: Increasing=>cod comparable to 1950’s

Pelagic fish:1970’s: Abundant capelin/Polar cod

No herring1980’s: 1. capelin collapse and recovery

Return of herring1990’s: 2. capelin collapse and recovery2000’s: 3. capelin collapse /recovery

Other pelagics abundant

Zooplankton /Shrimp:Strong variability,

especially in 1980’s and 1990’s

2000’s: Shrimp/Krill increasing trend

19701972

19741976

19781980

19821984

19861988

19901992

19941996

19982000

20022004

20062008

0

0.2

0.4

0.6

0.8

1

1.2

0

0.1

0.2

0.3

0.4

0.5

0.6

Cod Haddock Capelin

Fish

ing

mor

talit

y (F

bar

5-10

)

Rela

tive

fishi

ng m

orta

lity

cape

lin

Development in external driving forces:

1970’s: High / increasing

1980’s: High on demersal fishHigh on capelin fishing until collapse

1990’s: Demersals: reduction followed by increase

2000-2009:Decreased on cod=> New harvest control rule

Fishing:

Development in external driving forces:Climate:

1970’s-1990’s

Increasing trend Strong variabilityVariation correlated with NAOVariation correlated across water masses

2000-2009:

Warmest on record (since 1900)Increase in mixed water Reduction in Arctic waterCorrelation with NAO breaks (~1997)

Development in interactions:

Demersal fish:

Pelagic fish

ShrimpKrill

Correlations betwen trophic levels by decade

Development in interactions:

1970-1979:

Demersal fish:

Pelagic fish

ShrimpKrill

0.6-0.4 0.1

0.6

=> Mostly positive= bottom up

Development in interactions:

1980-1989:

Demersal fish:

Pelagic fish

Shrimp Krill

-0.3-0.2 -0.6

0.3

Zooplankton biomass

-0.6

Mainly negative: top-down

Development in interactions:

1990-1999:

Demersal fish:

Pelagic fish

Shrimp Krill

-0.3-0.2 -0.0

-0.9

Zooplankton biomass

-0.6

Negative: top-down

Development in interactions:

2000-2009:

Demersal fish:

Pelagic fish

Shrimp Krill

-0.10.5 0.8

0.1

Zooplankton biomass

-0.2

Positive/weak negative: bottom-up

Effect of key prey on predators:

Development in interaction strength:

Weight age 5 ~ log (capelin biomass y-1)

ns * *** ns

=> Temperature ns

Seperate regressions by decade and species:

Summary last decade:2000-2009:

• Warmest on record• Decreasing/low fishing pressure on cod• High demersal stocks=> cod stock comparable to the 1950’s• Capelin collapse and recovery, other pelagic fish abundant• Krill and shrimp increased• Trophic forcing changed from top down to mostly bottom-up • No clear effect of capelin collapse on predators (e.g. haddock/cod weight)

Þ High temperature = high production/biodiveristy of alternative prey?Þ High Temperature=> large feeding area

200619961986

Bottom temperatures during the three capelin collapses

Pelagics abundance

Summary:

Barents Sea 1970-present:1970’s High stocks, bottom up regulation

1980’s : Pertubations causing strong variability and top-down control in the1980-90’sÞ Return of herring, collapse of capelinÞ Heavy fishing pressureÞ Cold

2000-2009: Þ Bottom upÞ Weaker interactions/Less effect of capelin on predators

??

=> Return to the 1970’s?Or something not previously observed?

Thank you for your attention!

Temperature FB

Krill /Zooplankton biomass1970’s na /0.21980’s -0.2/-0.51970’s -0.7/-0.51970’s 0.1/0.4