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

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

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A-N Cod Mean age in spawning stock

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

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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

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A-N cod

Spatial survival patterns A-N Cod

We modeled cod survival from 0-gr to 1 year olds according to environment

Threshold GAM

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Survival of Barents Sea cod from age 0 to 1 within 4 different environmental regimes

A-N Cod Spatial survival patterns

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Modelling the Spawning Stock-Recruitment

relationship for North Sea cod North Sea cod

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Modelling the Spawning Stock-Recruitment

relationship for North Sea cod by a linear relation?

?

?

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Modelling the Spawning Stock-Recruitment

relationship for North Sea cod by a Ricker type relation?? North Sea cod

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Modelling the Spawning Stock-Recruitment relationship

for North Sea cod by a Beverton-Holt type relation?? North Sea cod

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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

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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

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North Sea cod

Combined Ricker and Beverton-Holt, dependent on zooplankton (based upon the data)

REC

RU

ITM

ENT

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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

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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

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The future: Effects of climate change on the survival of larval cod

Trond Kristiansen, Charles Stock, Ken Drinkwater, Enrique N. Curchitser

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Georges Bank North Sea

Iceland

Lofoten

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

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Projected temperature anomalies

Georges Bank North Sea

Iceland Lofoten

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Predicted survival rate in the North Sea

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Predicted survival rate in Lofoten

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• 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

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Image: Glynn Gorick for ICES WG Cod and Climate Change

Thanks, that’s all