Scientific talk on effects of climate variation and young fish - general ideas about climate effects on marine ecosystems - variations in temperature-zooplankton-North Sea cod - spatial population structure and detecting climate effects

1. 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

2. How Does Climate Affect Fish?
Prey
Modified from slide by Ken Drinkwater, IMR Disease
Physiological Effects
•Metabolic processes
•Growth
Recruitment
Distribution and
migration
Predators

3. 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
Climate
Time
Ecological
Response
Ecological response to climate signal
Ottersen, Stenseth, Hurrell 2004
Climate fluctuations…. Oxford Univ. Press

4. Linear ecological response
to climate signal
10
12
14
16
18
20
22
1950 1960 1970 1980 1990 2000
Ln(Recruitment)
Cod at West Greenland
Recruitment
8
9
10
1950 1960 1970 1980 1990 2000
SST
Year
Temperature
Stein and Borovkov

5. Climate induced
crash in Peruvian anchovy stock
Human and
Single climate event causes
shift in ecological state
El Niño:

6. 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?

7. 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

8. 0
500
1000
1500
2000
1963 1968 1973 1978 1983 1988 1993 1998 2003 2008
Recruitmentinmillions
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

9. 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

10. 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

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

12. 0 50 100 150 200 250 300
200400600800

13. 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.

14. 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

15. 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.sst
With population structure
Lauren Rogers, CEES UiO

16. Larval SST
Estimated mean and 95% Credible
Intervals for β.sst:
β.sst
Ignoring population structure!
With population structure
Lauren Rogers, CEES UiO
Temperature effect appears weaker and becomes
harder to detect if we ignore population structure.

17. Image: Glynn Gorick for ICES
WG Cod and Climate Change
Thanks, that’s all