Presented by: Geir Ottersen, Institute of Marine Research, Bergen, Norway

Coauthors: Nils Chr. Stenseth, Kyrre Lekve, and Dag Hjermann University of Oslo, Norway

Responses of fish populations to climate forcing across the North Atlantic

Comparative studies of North Atlantic ecosystems

2nd GLOBEC Open Science Meeting Comparative Ecosystems and Climate Change

15-18 October 2002, Qingdao, P. R. China

2nd GLOBEC Open Science Meeting Comparative Ecosystems and Climate Change

15-18 October 2002, Qingdao, P. R. China

FOCUS

Through examples from the North Atlantic I will show that the response of a fish population to a climate signal may be

To explain these response patterns we must also understand the mechanisms involved. Examples of how Enrichment, Concentration, and Retention processes may affect North Atlantic fish populations will be given.

Unlagged/lagged Linear/nonlinear

Direct/indirect

In interaction with other (non-climatic) factors

Russia

Barents Sea Greenland

80W 40 0 40 80E

80N

60

40

The North Atlantic

North Sea

Newfoundland

Georges Bank

A B A

Climate Climate

Direct response

Indirect response

Ecological response to climate fluctuations I

Through physiology, (metabolic and reproductive processes)

Direct response to climate

Through biotic environment (predators, prey, species interactions, and disease)

and abiotic environment (habitat type and structure).

Indirect response to climate

4 YEARS OLD COD

3,0 3,2 3,4 3,6 3,8 4,0 4,2 4,4 4,6 4,8 5,0

-1,5 -1 -0,5 0 0,5 1 1,5

Temperature anomaly (C)

Mea

n w

eigt

h (k

g)

R2=0.67

Brander and OBrien (2000)

Departure from mean weight at age 4

1960 1970 1980 1990 2000 Year Class

0

-1

+1

Temperature anomaly (C)

Departure from mean weight at age 3

The effect of temperature on weight of North Sea cod

Direct response to climate

Time

Match Peak first feeding of cod larvae

Peak production copepod nauplii

Mismatch Peak first feeding of cod larvae

Peak production copepod nauplii

Time

The match-mismatch hypothesis

Col

d

War

m

Indirect response to climate

Hjort (1914); Cushing (1982)

At At-i

Climatet Climatet-i

Unlagged response

Lagged response

At

Ecological response to climate fluctuations II

NAO and Barents Sea cod abundance Lo

g(ab

unda

nce

age

3)

NAO index spawning year NAO index spawning year

Temperature

Tem

pera

ture

Temperature

Log(

abun

danc

e ag

e 3)

Length yr old cod (mm)

Leng

th

yr o

ld c

od (m

m)

Ottersen and Stenseth (2001)

Temporal delay in ecological response to climate fluctuations

Linear climate signal causes shift in ecological state when climate threshold passed.

Linear ecological response to climate signal

Clim

ate

Time

Ecol

ogic

al

Res

pons

e

Single climate event causes shift in ecological state

A B C

Drinkwater (2002)

A Linear ecological response to climate signal

Growth of Canadian Northern Cod B

ody

mas

s cha

nge

(g)

Climate induced crash in Peruvian anchovy stock

Human and

Single climate event causes shift in ecological state B

El Nio:

Physical processes of importance to marine ecology

Enrichment processes makes more nutrients available to biological productivity

Concentration processes enhances food availability for a predator by increasing the concentration of food particles

Bakun (1996)

Retention processes work towards keeping individual members of a population in the appropriate place during the various parts of the life cycle

Concentration processes:

General example: Encounter-rate increases/decreases as a result of variability in micro-scale turbulence

Rothschild and Osborn (1988)

More specific case: Cod larval feeding success related to turbulence induced contact rate with main prey Calanus finmarchicus nauplii

Sundby and Fossum (1990); Sundby et al.(1994)

Retention processes: Example: Stability of current patterns to which life cycles are adapted Hypothesis: Member-vagrant Sinclair and Iles (1989) Physical features: Wind direction, residual currents, advection Biological feature: Survival through enhanced feeding success and reduced predation risk

Georges Bank case Serchuk et al. (1994); Werner et al. (1993)

Cod and Haddock spawn on the NE corner of Georges Bank and are slowly transported

around the bank as the larvae mature

Dr B. Monger, Cornell University (pers. com.)

Typical recirculation current pattern that retains cod and haddock larvae around Georges Bank

B. Monger

Break in the typical recirculation current pattern, caused by wind events or impinging Gulf Stream Rings, leading

to Advective Loss of cod and haddock larvae

B. Monger

A

B A

Climate Climate

Interactions with other factors

B

Ecological response to climate fluctuations III

Sundby (2000)

Distribution of Atlantic cod and sea temperatures at 100m depth

Atlantic cod

Greenland

UK

Spain

Effects of temperature fluctuations on recruitment to Atlantic cod stocks:

Recruitment to cold-water stocks increases with increasing temperature

Recruitment to warm-water stocks decreases with increasing temperature

Recruitment to stocks in intermediate temperatures shows no clear response to temperature variability.

Ottersen (1996); Planque and Fredou (1999)

A possible mechanism (Sundby 2000): Temperature variability is linked to advection of the cods main food items, Calanus finmarchicus from core production regions.

Norway

Distribution of Calanus finmarchicus

Atlantic water Arctic water Coastal water

Water masses Sundby (2000)

UK

Greenland

Spain

Higher temperatures

Lower temperatures

Schematic view of the North Atlantic

Isotherms

Sundby (2000)

Flow of water masses and Calanus to stocks of lower ambient temperature

Flow of water masses and Calanus to stocks of similar ambient temperature

Temperature-cod link as a proxy for Calanus-cod link

Flow of water masses and Calanus to stocks of higher ambient temperature

Sundby (2000)

2nd GLOBEC Open Science Meeting Comparative Ecosystems and Climate Change

15-18 October 2002, Qingdao, P. R. China

CONCLUSIONS

Through examples from the North Atlantic I have shown that the response of a fish population to a climate signal may be

To explain these response patterns we must also understand the mechanisms involved. Examples of how Enrichment, Concentration, and Retention processes may affect North Atlantic fish populations have been given.

Unlagged/lagged in time Linear/nonlinear

Direct/indirect

In interaction with other (non-climatic) factors

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