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. Llopeand 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

Changes in

North Sea

temperatures

Switch from C finmarchicus

-> C helgolandicus

G. Beaugrand

Changes in

North Sea

plankton

M. Edwards (2008)

Monitoring of plankton at station in the Skagerrak:Sampling of zooplankton: 2 times per month since 1994WP2 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

sprin

g

autu

mn

2005 2006 2007 2008N

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)

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Cold

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Average

0 50 100 150 200 250 300

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WarmRec

ruitm

ent

0 50 100 150 200 250 300

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Very warm

Spawning stock biomass

North Sea cod: Effects of spawning stock biomass, food availability (zooplankton index), and sea surface temperature on recruitment at age 1

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 SeaNorth Sea

LofotenLofoten

Projected temperature development (value today=0.0)

North SeaNorth Sea

LofotenLofoten

Predicted survival rate in Lofoten(distinct increase)

Predicted survival rate in the North Sea(weak decrease)

MAIN CONCLUSIONS (that partly answer our initial question)

Temperatures increased, also ambient winter temp of herring and cod

Changes in zooplankton community both in the NS proper (CPR) and the Skagerrak (WP2 net tows )

In particular decrease in Cal fin and increase in Cal hel abundance shift to Cal hel dominance earlier in year with higher temp (Skagerrak)

Decrease in biomass of small plankton, increase of mesozooplankton: Shift from prey of herring larvae towards more competitors and predators unfavorable for herring recruitment

Shape of stock-recruitment relationship of North Sea cod depends on zooplankton availability and temperaturePresent situation unfavorable for cod recruitment

IBM predicts higher future temperatures and lower survival for larval cod

Thanks, that’s all!