Jo King: The Implications of Warming Climate for the Management of North Sea Demersal Fisheries R.M. Cook and M.R. Heath FRS 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 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 R=recruits SSB=spawning stock biomass T=temperature index a=proportionality constant b=density dependence coefficient c=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 cool - mean index= warm- mean index= +0.7

Temperature Coefficient

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

Recent catch vs MSY in warm regime

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