Stig Skreslet 1 , Angel Borja 2 , Luca Bugliaro 3 , Georg Hansen 4 ,

1. ICES Symposium The Influence of Climate Change on North Atlantic Fish Stocks Bergen 11-14 May 2004 Some roles of climate in the population ecology of Calanus finmarchicus (Copepoda) in mid-Norwegian shelf water and in the year-class formation in NE Arctic cod (Gadus morhua) Stig Skreslet1, Angel Borja2, Luca Bugliaro3, Georg Hansen4, Ralf Meerkötter5, Ketil Olsen1 and Jean Verdebout3 1 Bodø Regional University (Norway), 2 AZTI (Spain), 3 EC-JRC Space Applications Institute (Italy), 4NILU (Norway), 5German Aerospace Center. UVAC European Commission Contract No EVK3-CT-1999-00012 (Mare Cognitum, TASC)

2. Barents Sea Estimated 0-group index 1 year lag behind discharge Catch juveniles lag 3yr P=0.01 P > 0.05 Larval survival lag 1yr P = 0.05 Lofoten Islands P= 0.05 P=0.05 P = 0.05 Norwegian landings of Barents Sea juveniles 3 year lag behind discharge P = 0.01 P = 0.05 P = 0.05 (Data from Skreslet 1976, 1986) NE Arctic Cod abundance forced by natural vernal fershwater discharge The few non-regulated rivers in Norway no longer represent the seasonal and interannual variation in freshwater discharge to the sea

3. Planktonic components of the Vestfjord in late winter and spring Advection of cod eggs from spawning grounds in Lofoten. (Ellertsen et al. 1984) Annual sampling 1983-present Wintering (black) and reproduction (hatched) habitats of C. finmarchicus (Sømme 1934)

4. Calanus finmarchicusgeneration shift in the Vestfjord area Copepodite stage abundance in 0-370 m depth in the Saltfjord basin 1997-98. • First generation was produced locally but disappeared in July. • Second generation was imported from the mid-Norwegian shelf in September-October.

5. Wintering habitats for Calanus finmarchicus in the eastern Norwegian Sea Average N m-2 sea surface in Saltfjord in October N=5 Accumulated stocks Salt- fjord NCC NAC (Data from Skreslet & Borja 2003) Current velocities > 40 cm s-1 (Poulin et al 1996)

6. Atmospheric pressure gradients vs copepod abundance in the Saltfjord (Data from Skreslet & Borja 2003)

7. Geophysical effects of NAO (North Atlantic Oscillation) NAO positive NAO negative H H (Greene & Pershing 2000) H H H H • Storms follow northerly tracks • Westerly winds in Norwegian Sea • Increased NAC advection • Much precipitation in Scandinavia • Storms follow southerly tracks • Northerly winds in Norwegian Sea • Decreased NAC advection • Little precipitation in Scandinavia

8. North-East Atlantic population system of Calanus finmarchicus • Observations • Abundance negatively correlated with • NAO in the North Sea • (Fromentin & Planque 1996) • Abundance positively correlated with • NAO in northern Norway • (Skreslet & Borja, 2003) Eurasia North America Arctic species • Hypothetical causal relationships • Population shifts latitudinal distribution • with winds in the NE Atlantic • and/or • Population size is a function of • precipitation and river discharge + N S Norway _ Boreal species

9. Nauplii I-VI 95% Conf. N = 7 Y = - 10803X + 371383 r = 0.709 p < 0.001 Summer reproduction of C.finmarchicus in the Norwegian Coastal Current Argo drifter velocities > 40 cm s-1 (Poulin et al 1996) Lofoten Summer reproduction habitat

10. Biologically weighted doses of lethal UVR on eggs in the G1 reproduction habitat, calculated from satellite data on ozone and cloudiness in May October abundance of G2 copepods in the Saltfjord (CFSO) Significant negative correlation before the summer reproduction in June-August may indicate potential effects on 1st generation: a) ontogeny b) sexual maturation c) ovulation d) mating Abundance of wintering C. finmarchicus as function of parental UVR exposure in May P < 0.01

11. O-gr index UVR r = 0.53, p < 0.01 ICES 0-group abundance of NE Arctic Cod as function of average UVR in Lofoten in March-May • Speculation: UVR disinfects the aquatic environment of eggs and larvae • Kills bacteria • Trigger viral attacks on bacteria

12. Summary • Freshwater outflow from Norway probably forces recruitment to the NE Arctic cod stock via food-web interactions that are not clear. • The population system of Calanus finmarchicus plays a key role in the transfer of the troposphere’s hydrological forcing of cod recruitment. • The 1st generation of C. finmarchicus reproduce during summer in the NCC, under influence of meltwater outflow and solar radiation of UV. • The 2nd generation of C. finmarchicus and a generation of C. hyperboreus invade north Norwegian fjords in October. • The stock abundance of C. finmarchicus in October is negatively correlated with UVR in May, but positively correlated with NAO in March-July, and AO in July-September. • UVR is not detrimental for juvenile cod biology but may interact with the microbial environment of cod eggs and larvae in Lofoten in favourable ways

13. Future challenges • The complex forcing of climate on cod population systems cannot be solved by only disciplinary field-work, and time-series analyses • Modern models for numerical marine ecosystem analyses allow for simulation of zooplankton production, but fail to assimilate the relevant forcing of river discharge • The lack of functions that couple zooplankton production and fish population models is an obstacle for understanding how climate forces fish production

14. Forcing of trophic energy flow in the food-web of juvenile NE Arctic Cod (UVR) + (UVR) - (Modified from Skreslet, 1997)