Scientific presentation on the North sea fish recruitment failure

1. Centre for Ecological and
Evolutionary Synthesis
ICES/NAFO Decadal Symposium Santander, Spain May 12th 2011
The serial recruitment failure to North Sea fish
stocks during the 2000s, is climate to blame?
Geir Ottersen
E. M. Olsen, T. Falkenhaug, P. Licandro, M. Llope
and others in the RECNOR team

2. Serial recruitment failure
Sandeel Norway pout
Herring Cod

3. Increasing sea temperatures
M. Llope
Cod
G. Dingsør, G. Ottersen et al. In prep
Herring
Increasing ambient temperatures IBTS Q1

4. Switch from C finmarchicus
-> C helgolandicus
G. BeaugrandM. Edwards (2008)

5. Monitoring of plankton at station in the Skagerrak:
Sampling of zooplankton: 2 times per month since 1994
WP2 vertical net tows (180µm), 50 – 0 m
Dynamics of C. finmarchicus (prefered food of larval cod)
and C. helgolandicus co-occuring in the Skagerrak
Calanus finmarchicus
female
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 work in prep.
Calanus helgolandicus
female

6. 0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
27.01.2005
08.03.2005
19.04.2005
01.06.2005
13.07.2005
13.09.2005
26.10.2005
14.12.2005
12.02.2006
31.03.2006
15.05.2006
01.07.2006
31.08.2006
09.10.2006
07.12.2006
06.02.2007
19.03.2007
03.05.2007
18.06.2007
07.08.2007
18.09.2007
03.11.2007
08.01.2008
04.03.2008
07.04.2008
14.05.2008
27.07.2008
13.09.2008
04.11.2008
16.12.2008
Chel
Cfin
Calanus CV-VI
spring
autumn
2005 2006 2007 2008Numbers/m2
•Seasonal variation: >80% C. finmarchicus in spring (Jan-June);
>80% C. helgolandicus in autumn (July-November)
•Interannual variations: The relative proportion of the two species differs
between years: ”finmarchicus years” and ”helgolandicus years”

7. Long term changes 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

8. Conclusions calanus fin vs cal helg
• C. finmarchicus occur in high abundance in spring, while C.
helgolandicus peaks later in the season at lower abundances.
• The annual temperature regime in this region (2-20 ºC) allows
both species to co-occur, but are seasonally separated
through their different temperature optima (niche separation).
• The seasonal increase in temperature triggers a shift from a
system dominated by C. finmarchicus to a system dominated
by C. helgolandcus. This shift occurs in June, at ~13 ºC.
• Higher temperatures, earlier in the season will trigger earlier
shifts from C.fin to C.hel.
• This is bad news for early life stages of cod, which have
Cal.fin. as preferred food.

9. • Year class strength determined from pelagic larval
to juvenile stage (1th winter)
• Low survival through this stage recent years
• YCS of 0-ringers and 1-ringers negative correlated
with bottom temperatures
Nash & Dickey-Collas 2005
North Sea Herring
The reduced herring larval survival does not
appear to be due to the fishery, maybe it is related
to changes in the plankton food of herring larvae?
Payne et al. 2009

10. Since 2001
- Decrease of biomass of small (< 2mm) plankton size
fraction, i.e., the prey of the herring larvae
- Increase of biomass of mesozooplankton > 2mm), i.e.,
potential competitors and predators of herring larvae
Licandro et al. In prep.
Are recent planton changes of significance to herring larvae?
A combined effect of predation (top-down) and
competition for food (bottom-up) could be a possible
cause of the low survival rate of herring larvae

11. Enhancing stock-recruitment models for North Sea cod
by including climate and zooplankton

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

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

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

15. 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 (overcompensation)
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
In combined models Ricker term dominate at low food levels, B-H at higher
Enhancing the S-R relation by including environmental
effects in a combined Beverton-Holt and Ricker model
Model 4 best model as selected by the Akaike Information Criteria (AIC)

16. 0 50 100 150 200 250 300
200400600800

17. 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

18. The future: Effects of climate change on the
survival of larval cod (estimated by models)
Trond Kristiansen (IMR) and others
North Sea
Lofoten

19. Projected temperature development (value today=0.0)
North Sea
Lofoten

20. Predicted survival rate in Lofoten
(distinct increase)

21. Predicted survival rate in the North Sea
(weak decrease)

23. Thanks, that’s all!