Scientific talk on effects of climate variation and young fish

Effects of climate variation on young fish

Geir Ottersen

Nordic Climate-Fish 2nd Conference: “Latitudinal changes in marine resources, exploitation and society within the Nordic and adjacent Seas”

15-17 August 2012 in Risør, Norway

general ideas about climate effects on marine ecosystems variations in temperature-zooplankton-North Sea cod spatial population structure and detecting climate effects

How Does Climate Affect Fish?

Prey

Modified from slide by Ken Drinkwater, IMR Disease

Physiological Effects •Metabolic processes

•Growth

Recruitment Distribution and migration

Predators

Single climate event causes shift in ecological state

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

Ecological response to climate signal

Ottersen, Stenseth, Hurrell 2004 Climate fluctuations…. Oxford Univ. Press

Linear ecological response to climate signal

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22

1950 1960 1970 1980 1990 2000

Ln

(Rec

ruit

men

t)

Cod at West Greenland

Recruitment

8

9

10

1950 1960 1970 1980 1990 2000

SS

T

Year

Temperature

Stein and Borovkov

Climate induced crash in Peruvian anchovy stock

Human and

Single climate event causes shift in ecological state

El Niño:

Increasing sea temperatures

M. Llope, Instituto Espanol de Oceanografia Cadiz

Variations in temperature-zooplankton-North Sea cod

M. Edwards, SAHFOS (2008)

Changes in plankton composition May this gradual change cause a shift in ecological state when threshold passed?

Higher temperatures leading to an increase in the abundance of phytoplankton earlier in the year has changed the food web structure through competitive exclusion of holozooplankton by meroplankton (i.e., less organisms that are planktonic for their entire life cycle, more that are planktonic only during larval stages, thereafter benthic). The result is significantly diminished transfer of energy towards top pelagic predators (e.g. fish) and increased transfer to the benthos.

Shift in transfer of energy from pelagic fish to benthos

ICES STATUS REPORT ON CLIMATE CHANGE IN THE NORTH ATLANTIC (eds. P.C. Reid and L. Valdes) September 2011

0

500

1000

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2000

1963 1968 1973 1978 1983 1988 1993 1998 2003 2008

Recr

uitm

ent in

milli

ons

Recruitment (age 1)

North Sea cod

G. Dingsør, G. Ottersen et al. In prep

Increasing ambient temperatures for cod IBTS Q1

Mean temperature in region

Age-2 ambient temperature

Age-4 ambient temperature

ICES

Switch from C. finmarchicus (prefered food of larval cod) towards C. helgolandicus in the North Sea

Edwards et al. 2011. Ecological Status Report, SAHFOS, UK

Calanus finmarchicus female

Calanus helgolandicus female

Monitoring of plankton at station in the Skagerrak, off Arendal: Sampling of zooplankton: 2 times per month since 1994 WP2 vertical net tows (180µm), 50 – 0 m

Samples recently reanalysed for identification of C. fin and C. hel Aims: - To describe the seasonal and interannual variation in relative proportions of the two species. - Reveal possible causes for the observed variations.

T. Falkenhaug, E. Bagøien, C. Broms, IMR work in prep.

Switch from C. finmarchicus towards C. helgolandicus in the Skagerrak

Seasonal and interannual variations in ratio of C. finmarchicus/ C. helgolandicus 1= 100% C. finmarchicus (blue) 0=100% C. helgolandicus (red) M

onth

Year

The period of C. helgolandicus dominance (ratio>0.5) has appeared earlier in the season in recent years (2004-2008).

CVI females

T. Falkenhaug, E. Bagøien, C. Broms, IMR work in prep.

0 50 100 150 200 250 300

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Conclusions • occur in high abundance in spring, while

peaks later in the season at lower abundances.

• The seasonal increase in temperature triggers a shift from a system dominated by to a system dominated by

This shift occurs in June, at ~13 ºC.

• Higher temperatures, earlier in the season will trigger earlier shifts from to

• The stock-recruitment relationship of North Sea cod is not stationary, its shape depends on food (zooplankton) availability and sea temperature

• The change in calanus is bad news for early life stages of cod, which have as preferred food, and is thus negative for recruitment.

Including spatial population structure helps detect effects of climate on population dynamics

Stocks, i.e. management units, need not be real biological units (populations) but may consist of distinct spawning units with low levels of inter-mixing

Spatial population structure is increasingly recognized in marine fishes: e.g., cod, yellowtail flounder, herring

Climate effects are expected to be more difficult to detect if spatial structure is unaccounted for

Example from current research on Skagerrak coastal cod (using beach seine data on 0-group)

Larval SST

Estimated mean and 95% Credible Intervals for β.sst:

β.ss

t

With population structure

Lauren Rogers, CEES UiO

Larval SST

Estimated mean and 95% Credible Intervals for β.sst:

β.ss

t

Ignoring population structure!

With population structure

Lauren Rogers, CEES UiO

Temperature effect appears weaker and becomes harder to detect if we ignore population structure.

Image: Glynn Gorick for ICES WG Cod and Climate Change

Thanks, that’s all