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Warming climate alters the biogeography of the southeast Bering Sea. Franz Mueter 1 * and Mike Litzow 2. 1 Joint Institute for the Study of the Atmosphere and the Oceans, University of Washington 2 Alaska Fisheries Science Center, Kodiak; [email protected]

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Warming climate alters the biogeography of the southeast bering sea l.jpg

Warming climate alters the biogeography of the southeast Bering Sea

Franz Mueter1* and Mike Litzow2

1 Joint Institute for the Study of the Atmosphere and the Oceans, University of Washington

2 Alaska Fisheries Science Center, Kodiak; [email protected]

* Current address: Sigma Plus, Fairbanks; [email protected]



Winter sea ice drives summer bottom temperatures l.jpg

0

0

20

20

40

40

60

60

Winter sea ice drives summer bottom temperatures

High-ice year (1997)

Depth (m)

Low-ice year (1998)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Redrawn from Stabeno et al. 2001. Fisheries Oceanography 10:81-98

°C

-2 0 2 4 6 8 10 12 14


The problem persistent climate forcing l.jpg

Summer bottom temperature

°C

P = 0.04

Winter ice extent

P = 0.01

Ice cover index

The problem – persistent climate forcing


Objectives l.jpg
Objectives

  • Use NMFS bottom trawl survey (1982-2006) to describe community response to warming

  • Identify outstanding questions for predicting response to future warming


Northward shift in biomass l.jpg

2

1

0

-1

-2

Northward shift in biomass

Change in total CPUE

1982-1986 to 2002-2006

Change in biomass (CPUE0.25, tons / km2)

°N

°W

51 taxa consistently identified through time series:

9 Arctic taxa / 42 subarctic taxa, 10 crustaceans / 41 fishes


Slide7 l.jpg

Shifts in North-South gradients, averaged among 51 taxa

P = 0.0095

P < 0.001

CPUE-where-present

Probability of occurrence

North

0.10

0.03

0.00

0.01

Latitudinal gradient

-0.10

-0.01

-0.20

-0.03

South

1985

1990

1995

2000

2005

1985

1990

1995

2000

2005

Year

Year


Shifts in center of distribution for 45 taxa 1982 2006 l.jpg

Snow crab

Rock sole

Halibut

Pollock

Mean shift = 31 km

One-sample t = 3.50

P = 0.0005

Rate similar to North Sea (Perry et al. 2005)

2-3 times faster than terrestrial mean (Parmesan and Yohe 2003)

Shifts in center of distribution for 45 taxa, 1982-2006


Retreat of the cold pool l.jpg

0 2 4 6 8

Retreat of the cold pool

1982-1986

55 57 59 61

°N

175 170 165 160

°W

Summer bottom temperature (°C)


Retreat of the cold pool10 l.jpg
Retreat of the cold pool

Predictions: Increased subarctic:Arctic community biomass

Increased diversity

Increased average trophic level


Changing community structure in the cold pool l.jpg
Changing community structure in the cold pool

Ratio Arctic:subarctic biomass

0.30

P < 0.01

0.25

0.20

Arctic CPUE:subarctic CPUE

0.15

0.10

0.05

1985 1990 1995 2000 2005

Year


Changing community structure in the cold pool12 l.jpg

16

15

14

13

12

Changing community structure in the cold pool

Diversity (species richness)

P < 0.01

Species / haul

1985 1990 1995 2000 2005

Year


Changing community structure in the cold pool13 l.jpg
Changing community structure in the cold pool

Mean trophic level

3.76

P < 0.01

3.74

3.72

Trophic level

3.70

3.68

3.66

1985 1990 1995 2000 2005

Year



Climate biogeography links15 l.jpg
Climate – biogeography links

Arctic and subarctic biomass in cold pool area

R2 = 0.70

Subarctic taxa

R2 = 0.08

Arctic taxa

Mean bottom temperature (° C)


Climate biogeography links16 l.jpg
Climate – biogeography links

Mean trophic level of survey catches in cold pool area

R2 = 0.39

Mean bottom temperature (° C)


Climate commercial fisheries links l.jpg

16

12

8

4

0

Climate – commercial fisheries links

Commercial snow crab catch, 1982-2005

R2 = 0.59

Catch (104 t)

Ice cover index (3-yr running mean)


Climate commercial fisheries links18 l.jpg
Climate – commercial fisheries links

Mean trophic level of total commercial catch, 1982-2004

R2 = 0.36

Trophic level

Ice cover index (3-yr running mean)


Slide19 l.jpg

What we don’t know, #1: what else besides direct temperature effects is driving distribution shifts?

20

20

b) Residual trend

a) Direct temp. effect

10

10

Latitudinal displacement (km)

0

0

-10

-10

-20

-20

1.0

2.0

3.0

4.0

1985

1995

2005

Average bottom temperature (oC)

Year

Even after temperature effects removed, significant northward displacement remains

Center of distribution averaged over 45 taxa


Slide20 l.jpg

What we don’t know, #2: what explains variability in distribution shifts?

Change in center of distribution for 45 taxa, 1982-2006

General Linear Model to explain variability among taxa:

Effect P

Commercial status (fished vs. non-fished)

Temperature preference (from survey)

Trophic level

Maximum length (for fish)

0.80

0.67

0.12

0.83


Conclusions l.jpg
Conclusions distribution shifts?

Warming of the Bering Sea since 1982:

Community-wide northward shift

Community reorganization in cold pool area

Change in fisheries


Conclusions22 l.jpg
Conclusions distribution shifts?

Continued warming:

Loss of Arctic species, increase in subarctic species

Variability in shifts = potential for new community state

Need to understand:

How biotic interactions constrain response to warming

Emergent effects


Acknowledgements l.jpg
Acknowledgements distribution shifts?

Everyone who has participated in the annual Bering Sea survey for the last 25+ years

Claire Armistead, Bern Megrey and Jeff Napp for their assistance


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