ices/nafo decadal symposium 2011, santander 10-12. may barents sea ecosystem: state, climate...
TRANSCRIPT
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