1) Fishing has reduced the age diversity of many fish stocks including Atlantic cod, which may make them less robust to climate variability. 2) Studies have found moving correlations between sea temperature in the Kola region and subsequent recruitment of Atlantic cod aged 3, indicating climate impacts early life stages. 3) Models show that survival of Atlantic cod from age 0 to 1 varies spatially according to different environmental regimes.

1. Effects of climate variability on early life
stages of fish (and thus on recruitment)
Geir Ottersen
with input from
Trond Kristiansen
FishExchange Solstrand 19-21 January 2011

2. Fishing has lead to juvenation and loss of age
diversity in many fish stocks, including A-N cod
This may make a stock less robust or
resilient to climate variability/change
1

3. A-N CodMean age in spawning stock
1

4. Moving correlations between Kola sea-temperature
and cod recruitment age 3 (21-year window) A-N cod
1

5. Development of the variance of the population growth rate
explained by temperature and fishing mortality along with
changes in the mean age in the spawning stock
First year of the 30 year temporal windows over which the variance contributions were computed
Rouyer, Ottersen et al., submitted
1
A-N cod

6. Spatial survival patterns
A-N Cod
We modeled cod survival from 0-gr to 1 year olds according to environment
Threshold GAM
2

7. Survival of Barents Sea cod from age 0 to 1 within 4
different environmental regimes
A-N Cod
Spatial survival patterns
2

8. Modelling the Spawning Stock-Recruitment
relationship for North Sea cod
North Sea cod
3

9. Modelling the Spawning Stock-Recruitment
relationship for North Sea cod by a linear relation?
?
?
3

10. Modelling the Spawning Stock-Recruitment
relationship for North Sea cod by a Ricker type relation??
North Sea cod
3

11. Modelling the Spawning Stock-Recruitment relationship
for North Sea cod by a Beverton-Holt type relation??
North Sea cod
3

12. Enhancing the S-R relation by including environmental
effects in a combined Beverton-Holt and Ricker model
Apply a family of recruitment curves depending on
initial larval- and zooplankton densities
Beverton-Holt type relation at high food levels
Overcompensation (Ricker) at limited food levels:
At low food levels the time to metamorphosis is delayed to the
extent that larval mortality accumulates and makes the
recruitment curve overcompensatory
3

13. Model Structure
1 log(R/S) = a + log(exp(-b•S))  log(R)-log(S)=a-bS
2 log(R/S) = a – log(1 + exp(c)•S/maxS)
3 log(R/S = a + log(exp(-b•S)•(1-Z) + 1/(1 + exp(c)•S/maxS)•Z)
4 log(R/S) = a – (a1•T) + log(exp(-b·S)•(1-Z) + 1/(1 + exp(c)•S/maxS)•Z)
1 Traditional Ricker model
2 Traditional Beverton-Holt model
3 Combined Ricker-Beverton-Holt model including a Z effect only
4 Combined Ricker-Beverton-Holt model including Z and T effects
A-priori set of stock (S) and recruitment (R) models
T is sea temperature and Z the zooplankton index developed by Beaugrand et al. (2002)
Sea temperature and Zooplankton are standardized
3

14. North Sea cod
Combined Ricker and Beverton-Holt, dependent
on zooplankton (based upon the data)RECRUITMENT
3

15. North Sea cod
Model # Parameters AIC Support*
1 2 80.4 0
2 2 80.6 0
3 3 64.6 0.24
4 4 62.3 0.76
Model selection
*normalised Akaike weights
(Burnham and Anderson 1998)
The winner is Model 4:
Combined Ricker-Beverton-Holt model
including zooplankton (Z) and temperature (T) effects
3

16. Conclusions
stock-recruitment models for North Sea cod
Our results suggest that the stock-recruitment relationship of North
Sea cod is not stationary, but that its shape depends on
environmental conditions, i.e food (zooplankton) availability and sea
temperature
A full recovery of North Sea cod is not to be expected until the
environment – both food availability and temperature - becomes
more favourable
3

17. The future: Effects of climate change on
the survival of larval cod
Trond Kristiansen, Charles Stock,
Ken Drinkwater, Enrique N. Curchitser
4
Georges Bank
North Sea
Iceland
Lofoten

18. We combine three models:
1) A mechanistic individual-based model for simulating
bioenergetics, behaviour, and feeding of larval cod
2) A general circulation model to simulate ocean dynamics
(the ROMS model)
3) A 3D zooplankton model to simulate the dynamical prey
field
How we model early-life history of fish
4

19. Projected temperature anomalies
Georges Bank North Sea
Iceland Lofoten
4

20. Predicted survival rate in the North Sea
4

21. Predicted survival rate in Lofoten
4

22. • Larval cod survival rates are predicted to increase in
Lofoten and Iceland
• Larval cod survival rates are predicted to decrease in
the North Sea and Georges Bank
• Large phytoplankton is estimated to decrease with
20-30% across all stations, while small phytoplankton
increase or remaine constant
Preliminary conclusions on
Effects of climate change on the
survival of larval cod
4

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