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Gyre Index and blue whiting: Environment and recruitment
Jan Arge Jacobsen & Hjálmar Hátún
Gyre Index and blue whiting: Environment and recruitment Jan Arge - - PowerPoint PPT Presentation
Gyre Index and blue whiting: Environment and recruitment Jan Arge - - PowerPoint PPT Presentation
Gyre Index and blue whiting: Environment and recruitment Jan Arge Jacobsen & Hjlmar Htn The basis currents and fronts! The Subpolar Gyre and the marine climate Subpolar Gyre Labrador Sea convection Subtropical Gyre (Hatun
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Subtropical Gyre Subpolar Gyre Labrador Sea convection (Hatun et al., Science 2005)
The Subpolar Gyre and the marine climate
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Source flows to the Rockall Region
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Here we show that the spawning distribution of blue whiting is variable, regulated by the hydrography west of the British Isles. When the North Atlantic subpolar gyre is strong and spreads its cold, fresh water masses east over Rockall Plateau, the spawning is constrained along the European continental slope and in a southerly position near Porcupine Bank. When the gyre is weak and conditions are relatively saline and warm, the spawning distribution moves northwards along the slope and especially westwards covering Rockall Plateau ! (Canadian Journal of Fisheries and Aquatic Science, 2009)
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R I
Salinity in the Irminger Current (obs.) Salinity at Rockall (obs.) Gyre index (GI)
Record high T and S
The Subpolar Gyre and the marine climate
Weak. Strong
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Simulated temperature Cold Warm
The Subpolar Gyre and the marine climate
Large mid-1990s changes!
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Blue whiting
Blue whiting: Spawning-feeding distributions/migrations
Spawning Mackerel Herring Feeding
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Pre-1995
(cold and low-saline)
Blue whiting spawning distribution
Catches
Scotland
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Catches
Post-1995
(warm and saline)
Scotland
Blue whiting spawning distribution
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Blue whiting Migration
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Cold years – Faroe-Shetland Ch.
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Warm years – Iceland-Faroe region
Stronger prim. production and probably more food
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Stor endringer i kolmule bestanden
A threefold blue whiting stock size increase
SST (in Rockall Area)
Stock size (<- shifted 3 years)
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Warm (1998-2003) Cold (1990-1996)
Spatial Shift
(Blue whiting catches – all nations)
1997
Spawning distribution (Hátún et al. 2009b) Post-spawning migration (Hátún et al. 2009a)
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Need to understand the processes
(Payne et al., 2011, in press) North Atlantic Sub-polar gyre
Recruitment
Gyre Index alone cannot explain recruitment
Atmospheric forcing
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Wind stress curl
UK
Green-
land
Anticyclonic (Curl <0) Wind stress (ws) - arrows (NCAR/NCEP)
Curl (ws)
[N/m ]
2
Cyclonic (Curl >0)
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WSC = 0 Subtropical Gyre Subpolar Gyre
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Subpolar Gyre ”Inter-gyre region” ’Window’ WSC = 0 Subtropical Gyre
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Subtropical Gyre Subpolar Gyre
Varying proportions “drifting” south-/northwards from Porcupine Bank due to environment?
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Recruitment and wind stress curl
Spain
R
Recruitment vs. WSC
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Recruitment and wind stress curl
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Recruitment and wind stress curl, shifted on year ahead
Northward transport Improved Recruitment?
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Blue whiting May 2011
10 20 30 40 50 60 5 10 15 20 25 30 10 15 20 25 30 35 40 2 4 6 8 10 12 15+
% %
Length in cm age i n years
Improved recruitment?
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So is the recruitment predictable?
Not with certainty - But certainly not if the marine climate is ignored
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