Emma Orlova, Polar Research Institute of Marine Fisheries and Oceanography, Murmansk, Russia

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1 Eastern Scotian Shelf and Barents Sea intercomparison: climate fluctuation, human impact and system resilience Brian Petrie, Ken Frank, Jon Fisher, William Leggett and Nancy Shackell, Bedford Institute of Oceanography, Darthmouth, Canada Emma Orlova, Polar Research Institute of Marine Fisheries and Oceanography, Murmansk, Russia Edda Johannesen, Mette Skern-Mauritzen, Randi Ingvaldsen and Jan Erik Stiansen, Institute of Marine Research, Bergen, Norway

2 Eastern Scotian Shelf and Barents Sea intercomparison: climate fluctuation, human impact and system resilience ICES Annual Science Conference, Nantes September 2010 Session S Joint ICES/PICES Theme Session on: Climate variability: responses and comparison of northern hemisphere marine ecosystems

3 Motivation: Ecosystem intercomparison: Eastern Scotian Shelf ntercomparison Barents Sea Collapsed cod stock Largest cod stock in the world ntercomparison To shed light on: why some fisheries collapse and others do not in the face of similar exploitation regimes why some stocks recover after collapse

4 Outline: Temporal development in ecosystem state Extrinsic forcing Climate Fishery Ecosystem processes Stock resilience Trophic forcing Predator-prey role reversal

5 Eastern Scotian Shelf Barents Sea Comparing temporal development: Eastern Scotian Shelf Barents Sea s.d. units Rapid shift in many time series around 1990 when the groundfish stocks collapsed Principal component analysis on time series

6 Temporal development Eastern Scotian shelf collapsed groundfish stocks changes at all trophic levels Barents Sea larger groundfish stock warmer

7 Extrinsic forcing: climate variation Cold => warm cool period around 1990 high variability thereafter overall an increasing trend with shorter period variability

8 Extrinsic forcing: fishing pressure Long term mean cod fishing mortality higher in BS compared to ESS ( ) Temporal variation: Eastern Scotian shelf Barents Sea Around 1990: F increased strongly causing stock collapse, fishing banned in 1993 remains in effect At the same time: Strong reduction in fishing pressure =>management response (Norway and Russia) to declining survey indices and commercial catch rates

9 Ecosystem processes: stock resilience ESS cod stock recovered after release in fishing pressure in late 1970 failed to recover after release in fishing pressure after 1993 BS cod responded to the release in fishing pressure 1990 s and in mid 2000 s

10 Ecosystem processes: trophic forcing TL 4 TL 3 TL 2 # # # # Negative correlation between Positive correlations abundance between time of series adjacent for all trophic trophic levels levels in food chain = Trophic levels unbalanced Trophic Level 1 Time

11 Correlation groundfish and forage fish abundance Ecosystem processes: trophic forcing Eastern Scotian Shelf 15 y time window sliding correlations Barents Sea Prey biomass Prey biomass + Predator biomass - Predator biomass Bottom-up (balanced) prior to cod collapse Top-down (unbalanced) after collapse Mostly balanced Short periods with top-down

12 Ecosystem processes: predator prey role reversal Outburst of forage fish following decline in predator fish set the stage for predator prey role reversal predators become prey Biomass Time Can explain the lack of recovery of collapsed groundfish stocks

13 Juvenie cod Survival rate Ecosystem Southern processes: Gulf Predator of St. Lawrence prey Cod role reversal Southern Gulf of St. Lawrence Barents Sea Juvenile cod survival rates strongly related to pelagic fish biomass (Swain and Sinclair 2000) Similar relationship observed in other systems (Baltic Sea, NW Atlantic areas) No relationship between juvenile cod survival and forage fish abundance

14 Summary: Temporal development: Synchronous but different development in the two systems External forcing: Climate: Temporal variation not synchronous Fishing pressure: Overall higher fishing pressure on cod in BS Strong reduction in fishing pressure in the BS co-occurred with the period with very high fishing pressure and stock collapse in ESS Ecosystem processes: Stock resilience: BS cod more resilient to fishing than ESS cod Trophic forcing: BS mostly balanced, ESS changed for balanced (pre-cod collapse) to un-balanced (after collapse) Predator-prey role reversal Important in the ESS and can explain lack of recovery Unimportant in the BS - Fishing on forage fish -Large spatial scale (BS>13 x ESS), less overlap between juvenile predators and forage fish

15 This work is supported by: Thank you for your attention!

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17 Barents Sea Warm inflow + NAO: Large transport of warm Atlantic water, large melting of polar ice Eastern Scotian Shelf Cold inflow + NAO: Colder, fresher and more inflow water

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19 - By-catch in other groundfish fisheries (Shelton et al Seal predation

20 1.2 Fiskedødelighet torsk (alder 5-10) F Flim Fpa