Gyre Index and blue whiting: Environment and recruitment Jan Arge - PowerPoint PPT Presentation

Gyre Index and blue whiting: Environment and recruitment Jan Arge Jacobsen & Hjálmar Hátún

The basis – currents and fronts!

The Subpolar Gyre and the marine climate Subpolar Gyre Labrador Sea convection Subtropical Gyre (Hatun et al ., Science 2005)

Source flows to the Rockall Region

(Canadian Journal of Fisheries and Aquatic Science, 2009) 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 !

The Subpolar Gyre I and the marine climate R Record high T and S Weak. Salinity at Rockall (obs.) Gyre index (GI) Salinity in the Irminger Current (obs.) Strong

The Subpolar Gyre and the marine climate Warm Cold Simulated temperature Large mid-1990s changes!

Blue whiting: Spawning-feeding distributions/migrations Herring Feeding Blue whiting Mackerel Spawning

Pre-1995 Blue whiting (cold and low-saline) spawning distribution Catches Scotland

Post-1995 Blue whiting (warm and saline) spawning distribution Catches Scotland

Blue whiting Migration

Cold years – Faroe-Shetland Ch.

Warm years – Iceland-Faroe region Stronger prim. production and probably more food

A threefold blue whiting stock size increase SST (in Rockall Area) Stor endringer i kolmule bestanden Stock size (<- shifted 3 years)

Spatial Shift (Blue whiting catches – all nations) 1997 Cold (1990-1996) Warm (1998-2003) Post-spawning migration (Hátún et al . 2009a) Spawning distribution (Hátún et al . 2009b)

Need to understand the processes North Atlantic Sub-polar gyre Atmospheric forcing Gyre Index alone cannot explain recruitment Recruitment (Payne et al., 2011, in press)

Curl ( ws ) Wind stress curl 2 [N/m ] Green- Wind stress ( ws ) - arrows land (NCAR/NCEP) Cyclonic (Curl >0) UK 0 Anticyclonic (Curl <0)

WSC = 0 Subpolar Subtropical Gyre Gyre

WSC = 0 ”Inter-gyre region” ’Window’ Subpolar Subtropical Gyre Gyre

Subpolar Gyre Subtropical Gyre Varying proportions “drifting” south-/northwards from Porcupine Bank due to environment?

R Recruitment and wind stress curl Spain Recruitment WSC vs.

Recruitment and wind stress curl

Northward transport Recruitment? Improved Recruitment and wind stress curl, shifted on year ahead

Blue whiting May 2011 Improved recruitment? 30 60 25 50 20 40 % 15 30 % 10 20 5 10 0 0 10 15 20 25 30 35 40 2 4 6 8 10 12 15+ Length in cm age i n years

So is the recruitment predictable? Not with certainty - But certainly not if the marine climate is ignored

History soon ?!