Jo King:Jo King:

The Implications of Warming Climate for the Management of North Sea Demersal Fisheries

R.M. Cook and M.R. HeathFRS Marine Laboratory, P.O. Box 101, 375 Victoria Road, Aberdeen, AB11 9DB, UK

Very Important People

• Net Benefits: A sustainable and profitable future for UK fishing. Cabinet Office Prime Minister’s Strategy Unit, London, UK

• Inquiry into the future of the Scottish Fishing Industry. Royal Society of Edinburgh, Edinburgh, UK

• Concluded fishing the main cause of decline in demersal stocks

A well informed press

Fishing News March 2004: Natural changes affect stocks- maybe more than fishing

Nature 2004. Climate findings let fishermen off the hook

Temperature Effects

• High temperature associated with lower recruitment in cod (O’Brien et al, Planque and Frédou, Clark)

• Temperature affects biology of plaice and sole (van der Veer and Witte, Wegner et al)

What is the relative contribution of temperature and spawning stock biomass to recruitment?

Stock-Recruit Model

)/( bSSBcTaSSBeR

R = recruitsSSB = spawning stock biomassT = temperature index

a=proportionality constantb=density dependence coefficientc=temperature coefficient

Assumed gamma errors

North Sea Stocks

• Cod

• Haddock

• Whiting

• Saithe

• Plaice

• Sole

• Herring (honorary demersal fish)

Spawning biology

• Demersal fish spawn in spring (Feb-April)

• Eggs are pelagic• Temperature may be proxy for

environmental effects in early life stages

• Herring spawn in autumn, benthic eggs- not obvious that SST is relevant

North Sea Temperature Index

• IBTS data for February SST

• 10 fixed stations

• Performed single factor analysis

• Factor explains about 80% of variance

• Used factor as index of temperature

North Sea Temperature index

-3.00

-2.00

-1.00

0.00

1.00

2.00

3.00

1957

1960

1963

1966

1969

1972

1975

1978

1981

1984

1987

1990

1993

1996

1999

Te

mp

era

ture

Ind

ex

1957-1987 - cool - mean index= -0.371988-2002 - warm- mean index= +0.7

Temperature Coefficient

-0.8

-0.4

0

0.4

0.8

Par

amet

er v

alu

e

Cod

Saithe

Plaice Sole

Haddock

Herring

Whiting

Performance Indictors

• MSY- Maximum sustainable yield• Fmsy- Fishing mortality to produce MSY• Bmsy- Spawning stock biomass as MSY• Bpa- ICES minimum ‘safe’ spawning stock

biomass (usually calculated in ‘cold’ regime)• Fpa- ICES maximum ‘safe’ fishing mortality

(usually calculated in ‘cold’ regime)

Equilibrium Calculations

• Age structured production model

• Used temperature modified Ricker S-R model

• Fixed growth, natural mortality, maturity and selection pattern

• Calculated values for cool and warm regime

• Assumes annual temperature anomalies are consistent with equilibrium

Warm versus Cold Regime

0.00

0.50

1.00

1.50

2.00

Cod Saithe Plaice Sole

Ra

tio

Fmsy

MSY

B(Fpa)(h)/Bpa

Recent catch vs MSY in warm regime

0

50

100

150

200

250

300

350

Cod Saithe Plaice Sole

[000

t]

MSY(h)

mean catch

Bmsy(h)

Conclusions

• Detectable effect of temperature on cod, saithe, plaice and sole recruitment

• In warm regime, cod, plaice and sole cannot reach their minimum safe biomass (Bpa) if fished at current agreed Fpa

• Cod can sustain a larger catch even in warmer regime provided recovery is possible

• Long term yields of flatfish expected to decline• Saithe appears to benefit from warmer

temperatures