1 1

Ken DrinkwaterInstitute of Marine Research, Bergen, Norway

Bjerkenes Center Climate Research

The Response of Atlantic Cod (Gadus morhua) to Future

Climate Change

2 2

Outline

Presentation focuses upon temperature effects and uses what we know from past studies to predict the future

•Temperature-Cod Relationships

•Future Climate Change

•Predicted Cod Responses

3 3

Temperature-Cod Relationships

4 4

Cod Stocks

Cod presently inhabit many of the continental shelf areas of the northern North Atlantic, bordering the subpolar gyre.

Cod Recruitment and TemperatureCod Recruitment and Temperature

Mean Annual Bottom Temperature11

10

9

8

7

6

4

3

2

Temp

Warm Temperatures

decreases Recruitment

Warm Temperatures

increases Recruitment

Recruits

Planque and Fredou (1999)

Temperature accounts for most of the differences in growth rates between stocks (Brander 1994, 1995).

Growth Rates

7 7

Temperature accounts not only for stock differences but also for interannual variability within stocks

Brander 1995

West Greenland Faroe Islands

8 8

Field estimate of growth rate

Specific growth rates from Brander (2003).

9 9

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.

10 10

0.8

0.9

1.0

1.1

1.2

0 1 2 3 4 5 6 7 8 9 10 11

Temperature (°C)

Fulto

n's c

ondi

tion

GB

NS

IC

SLNO

SBGR

NE

SC

IRFrom RFrom Rätz and Lloret 2003ätz and Lloret 2003 The condition of the fish as measured by Fulton’s K (higher values means better condition) also shows an increase with increasing temperature.

7

7

7

63.5

2

Temperature Temperature appears to appears to

affect age of affect age of maturity of maturity of

Atlantic CodAtlantic Cod6

0

1

2

3

4

5

6

7

8

0 2 4 6 8 10 12Mean Annual Bottom Temperature (°C)

Ag

e (

yrs

)

R2=0.65

Combining age of maturity of different cod stocks from Hutchings and Myers (1993) with bottom temperatures from Brander (1994).

13 13

Future Climate Change

14 14

Future changes in global mean temperature for six different emission scenarios using several different climate models (IPCC; 200 ).

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.

16 16

Summary of Temperature Changes in Cod RegionsPredicted temperature changes range from 2° to 5°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).

Multi-model variability varies from ±1.5°C at lower values to ±3°C.

17 17

Cod Responses to Temperature Scenarios

Cod Recruitment and TemperatureCod Recruitment and Temperature

Mean Annual Bottom Temperature11

10

9

8

7

6

4

3

2

Temp

Warm Temperatures

decreases Recruitment

Warm Temperatures

increases Recruitment

Recruits

Planque and Fredou (1999)

19 19

R2 = 0.75

-1.5

-1

-0.5

0

0.5

1

1.5

2

0 2 4 6 8 10 12

Bottom Temperature

d(R

ecru

itm

ent)

/dT

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

GB

Effect on abundance of 1°C increase

Increase

No change

Decrease

Collapse

?

2°C Temperature Increase

3°C Temperature Increase

4°C Temperature Increase

24 24

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?

?

Northward Expansion

26 26

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.

27 27

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.

Summary

28 28

•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 .

Caveats

29 29

• 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.

Observational Support for Conclusions

30 30

0.8

0.9

1.0

1.1

1.2

0 1 2 3 4 5 6 7 8 9 10 11

Temperature (°C)

Fulto

n's c

ondi

tion

GB

NS

IC

SLNO

SBGR

NE

SC

IRFrom RFrom Rätz and Lloret 2003ätz and Lloret 2003