Scientific presentation on the North sea fish recruitment failure
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Transcript of Scientific presentation on the North sea fish recruitment failure
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
Serial recruitment failure
Sandeel Norway pout
Herring Cod
Increasing sea temperatures
M. Llope
Cod
G. Dingsør, G. Ottersen et al. In prep
Herring
Increasing ambient temperatures IBTS Q1
Switch from C finmarchicus -> C helgolandicus
G. Beaugrand M. Edwards (2008)
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
0 2000 4000 6000 8000
10000 12000 14000 16000 18000 20000
27.0
1.20
05
08.0
3.20
05
19.0
4.20
05
01.0
6.20
05
13.0
7.20
05
13.0
9.20
05
26.1
0.20
05
14.1
2.20
05
12.0
2.20
06
31.0
3.20
06
15.0
5.20
06
01.0
7.20
06
31.0
8.20
06
09.1
0.20
06
07.1
2.20
06
06.0
2.20
07
19.0
3.20
07
03.0
5.20
07
18.0
6.20
07
07.0
8.20
07
18.0
9.20
07
03.1
1.20
07
08.0
1.20
08
04.0
3.20
08
07.0
4.20
08
14.0
5.20
08
27.0
7.20
08
13.0
9.20
08
04.1
1.20
08
16.1
2.20
08
Chel
Cfin
Calanus CV-VI sp
ring
autu
mn
2005 2006 2007 2008 N
umbe
rs/m
2
•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”
Long term changes 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
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.
• 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
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
Enhancing stock-recruitment models for North Sea cod by including climate and zooplankton
Modelling the Spawning Stock-Recruitment
relationship for North Sea cod by a linear relation?
?
?
Modelling the Spawning Stock-Recruitment
relationship for North Sea cod by a Ricker type relation??
Modelling the Spawning Stock-Recruitment
relationship for North Sea cod by a Beverton-Holt type relation??
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)
0 50 100 150 200 250 300
200
400
600
800
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
The future: Effects of climate change on the survival of larval cod (estimated by models)
Trond Kristiansen (IMR) and others
North Sea
Lofoten
Projected temperature development (value today=0.0)
North Sea
Lofoten
Predicted survival rate in Lofoten (distinct increase)
Predicted survival rate in the North Sea (weak decrease)
Thanks, that’s all!