Transcript PowerPoint-presentasjon - Havforskningsinstituttet

The Response of Atlantic Cod
(Gadus morhua) to Future
Climate Change
Ken Drinkwater
Institute of Marine Research, Bergen, Norway
Bjerkenes Center Climate Research
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Presentation focuses upon temperature effects and uses
what we know from past studies to predict the future
Outline
•Temperature-Cod Relationships
•Future Climate Change
•Predicted Cod Responses
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Temperature-Cod Relationships
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Cod Stocks
Cod presently
inhabit many of
the continental
shelf areas of the
northern North
Atlantic,
bordering the
subpolar gyre.
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Cod Recruitment and Temperature
Warm Temperatures
Warm Temperatures
increases Recruitment
decreases Recruitment
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6
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4
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Recruits
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3
Temp
Mean Annual Bottom Temperature
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Planque and Fredou (1999)
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Growth Rates
Temperature accounts for most of the differences in
growth rates between stocks (Brander 1994, 1995).
Temperature accounts not only for stock
differences but also for interannual variability
within stocks
West Greenland
Faroe Islands
Brander 1995
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Field estimate of growth rate
Specific growth rates from Brander (2003).
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Further on Temperature Effects
• Individual growth and production of Atlantic
cod is found to increase with temperature (Dutil
and Brander, 2004).
•In spite of this, population abundance tends to
be maximum in colder water stocks, e.g.
Northeast Arctic cod and until recently,
Northern cod off Newfoundland.
•There are no cod stocks found at average
bottom temperatures exceeding 12°C.
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1.2
From Rätz and Lloret 2003
IR
The condition of the
fish as measured by
Fulton’s K (higher
values means better
condition) also
shows an increase
with increasing
temperature.
Fulton's condition
1.1
GB
SC
1.0
NS
SL
NO
0.9
IC
SB
NE
GR
0.8
0
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2
3
4
5
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8
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Temperature (°C)
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10
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3.5
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Temperature
appears to
affect age of
maturity of
Atlantic Cod
Combining age of maturity of different cod stocks
from Hutchings and Myers (1993) with bottom
temperatures from Brander (1994).
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R2=0.65
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Age (yrs)
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5
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3
2
1
0
0
2
4
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Mean Annual Bottom Temperature (°C)
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Future Climate Change
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Future changes in global mean temperature for six
different emission scenarios using several different
climate models (IPCC; 200 ).
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The multi-model ensemble annual mean change of the temperature
(color shading), its range (thin blue isolines) (°C) and the multi-model
mean change divided by the multi-model standard deviation (solid green
isolines, absolute values) for 2071-2100 relative to 1961-1990.
Summary of Temperature Changes in Cod Regions
Predicted temperature changes range from 2° to 5°C.
Multi-model variability varies from ±1.5°C at lower
values to ±3°C.
Maximum temperatures and uncertainty ranges in the
north (e.g. Barents Sea, Greenland) and minimum in the
south (e.g. North Sea, Celtic Sea, Georges Bank).
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Cod Responses to Temperature Scenarios
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Cod Recruitment and Temperature
Warm Temperatures
Warm Temperatures
increases Recruitment
decreases Recruitment
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6
8
4
9
Recruits
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3
Temp
Mean Annual Bottom Temperature
2
Planque and Fredou (1999)
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2
d(Recruitment)/dT
1.5
R2 = 0.75
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GB
0.5
0
-0.5
-1
-1.5
0
2
4
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Bottom Temperature
If BT < 5° and T warms stock recruitment generally increase
If BT between 5° and 8.5°C little change in recruitment
If BT >8.5°C recruitment generally decreases
If BT 12°C we do not see any cod stocks
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Effect on abundance of 1°C increase
Increase
No change
Decrease
Collapse
?
2°C Temperature Increase
3°C Temperature Increase
4°C Temperature Increase
Northward Expansion
In addition to the changes in the present stocks, under
warming temperatures the cod with expand northward.
This will include establishing new spawning sites.
How far north?
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?
Northward Expansion
Growth – With increasing temperatures both individual
growth (Brander 1995) and stock production (Dutil and
Brander 2003) should generally increase.
Condition – With increasing temperatures and
improved growth rates the cod should be in better
condition.
Maturity – With increasing temperatures age of
maturity will likely decrease.
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Summary
With increasing temperatures:
•Overall Atlantic cod production should generally
increase both due to individual growth and stock
production and better condition.
•The cod will expand northward, which will include the
establishment of new spawning grounds.
•However, we expect some of the present warmer water
stocks will decrease substantially and the stocks in the
warmest waters may disappear altogether.
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Caveats
•Only considered temperature effects on cod.
•The temperature changes will be linked to what happens to
the circulation changes, e.g. to the thermohaline circulation
and wind forcing.
•There is high uncertainty in the future temperature scenarios
and few regional climate models are available.
•Cod is not independent of the ecosystem and can not be
considered separately, i.e. its food.
•Fishing will play a major role in the response and must be
included in future .
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Observational Support for Conclusions
• In spite of the uncertainties and general nature of the
results, there is support for the conclusions.
1. During the 1920s and 1930s warming, cod spread
northward (see Drinkwater poster).
2. There is evidence that spawning sites move northward
under warming conditions (see Sundby and Nokken
poster).
3. Cod production and biomass was high in most regions
during the last warm period from the 1920s to the
1960s or so.
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1.2
From Rätz and Lloret 2003
IR
Fulton's condition
1.1
GB
SC
1.0
NS
SL
NO
0.9
IC
SB
NE
GR
0.8
0
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4
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Temperature (°C)
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