spawning stock and recruitment relationship in north sea cod shaped by food and climate

3rd GLOBEC Open Science Meeting

Victoria, BC, Canada 22-26 June 2009

Spawning stock and recruitment relationship in North Sea cod shaped by food and climate

Geir Ottersen

Based on a submitted paper by

E. M. Olsen1,2, G. Ottersen1,2, M. Llope2, K.-S. Chan3, G. Beugrand4 & N. C. Stenseth1,2

1Institute of Marine Research, Norway 2Centre for Ecological and Evolutionary Synthesis, University of Oslo, Norway 3University of Iowa, USA 4National Center for Scientific Research (CNRS), France

Image: Glynn Gorick for ICES WG Cod and Climate Change

Centre for Ecological and Evolutionary Synthesis

THE NORTH SEA

Edwards et al. (2006)

Switch from C finmarchicus -> C helgolandicus

Marcos Llope, CEES, UiO

Increasing sea temperatures

Decline in cod abundance and biomass

North Sea Cod Juvenile Biomass

SSB 1-year old

Modelling the Spawning Stock-Recruitment

relationship for North Sea cod


relationship for North Sea cod by a linear relation?


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


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

Beverton-Holt or Ricker or both?

Modeling an environmental effect on recruitment in gadoids: Apply a family of recruitment curves depending on initial larval- and zooplankton densities Overcompensation (Ricker) at limited food levels. Beverton-Holt type relation at high 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

Based upon theoretical work by R. Johansen (2007): A model for the interaction between gadoid larvae and their nauplii prey. Math. Bios. 208:177-192

North Sea cod

Our approch to enhance the S-R relation: Apply temperature, annual average values for the region from COADS Apply zooplankton from G. Beaugrand’s CPR based index

Data sets

1960 1970 1980 1990 2000

5010

015

020

025

0

a

SSB

(100

0 t)

1960 1970 1980 1990 2000

200

400

600

800 b

Rec

ruitm

ent (

mill)

1960 1970 1980 1990 2000

-4-2

02

4

c

Zoop

lank

ton

inde

x

1960 1970 1980 1990 2000

9.5

10.0

10.5

11.0

d

Sea

surfa

ce te

mpe

ratu

re (C

)

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 zooplankton effect only 4 Combined Ricker-Beverton-Holt model including zooplankton (Z) and temperature (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 is standardized to a mean of zero and a standard deviation of one. Zooplankton is standardized to range from 0 to 1

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)

Model 4: log(R/S) = a – (a1•T) + log(exp(-b·S)•(1-Z) + 1/(1 + exp(c)•S/maxS)•Z)

Combined Ricker-Beverton-Holt model including zooplankton (Z) and temperature (T) effects

Beverton-Holt with temperature (based upon the data)

REC

RU

ITM

ENT

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

REC

RU

ITM

ENT

0 50 100 150 200 250

0.0

0.2

0.4

0.6

0.8

1.0

Spawning stock biomass

Zoop

lank

ton

abun

danc

e

Spawning stock biomass

Zo

opla

nkto

n Red dots = recruitment

Data points sponsored by Disney?

0 50 100 150 200 250 300

200

400

600

800

Conclusions 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