OMJ-98 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 Skreslet 1, Angel Borja 2, Luca Bugliaro 3, Georg Hansen 4, Ralf Meerkötter 5, Ketil Olsen 1 and Jean Verdebout 3 1 Bodø Regional University (Norway), 2 AZTI (Spain), 3 EC-JRC Space Applications Institute (Italy), 4 NILU (Norway), 5 German Aerospace Center. ICES Symposium The Influence of Climate Change on North Atlantic Fish Stocks Bergen May 2004 UVAC European Commission Contract N o EVK3-CT (Mare Cognitum, TASC)

OMJ-98 NE Arctic Cod abundance forced by natural vernal fershwater discharge Estimated 0-group index 1 year lag behind discharge Norwegian landings of Barents Sea juveniles 3 year lag behind discharge P=0.05 P=0.01 P = 0.05 Lofoten Islands Barents Sea Larval survival lag 1yr Catch juveniles lag 3yr P > 0.05 (Data from Skreslet 1976, 1986) The few non-regulated rivers in Norway no longer represent the seasonal and interannual variation in freshwater discharge to the sea

OMJ-98 Planktonic components of the Vestfjord in late winter and spring Advection of cod eggs from spawning grounds in Lofoten. (Ellertsen et al. 1984) Wintering (black) and reproduction (hatched) habitats of C. finmarchicus (Sømme 1934) Annual sampling 1983-present

OMJ-98 Calanus finmarchicus generation shift in the Vestfjord area  First generation was produced locally but disappeared in July.  Second generation was imported from the mid- Norwegian shelf in September-October. Copepodite stage abundance in m depth in the Saltfjord basin

OMJ-98 Wintering habitats for Calanus finmarchicus in the eastern Norwegian Sea Current velocities > 40 cm s -1 (Poulin et al 1996) Accumulated stocks NCC NAC Average N m -2 sea surface in Saltfjord in October N=5 Salt- fjord (Data from Skreslet & Borja 2003)

OMJ-98 NAO Tropo- spheric AO Strato- spheric Calanus sp Seasonrp rp finmar- chicus Mar-Jul Jul-Sep hyper- boreus ---Jul-Sep Atmospheric pressure gradients vs copepod abundance in the Saltfjord (Data from Skreslet & Borja 2003)

OMJ-98 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 H H Geophysical effects of NAO (North Atlantic Oscillation) (Greene & Pershing 2000) NAO positive NAO negative H H

OMJ-98 S N Boreal species Arctic species North America Eurasia 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) Norway + _ 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

OMJ-98 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 Nauplii I-VI 95% Conf. N = 7 Y = X r = p < 0.001

OMJ-98 Abundance of wintering C. finmarchicus as function of parental UVR exposure in May P < 0.01 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 1 st generation: a) ontogeny b) sexual maturation c) ovulation d) mating

OMJ-98 r = 0.53, p < 0.01 O-gr index UVR 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

OMJ-98 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 1 st generation of C. finmarchicus reproduce during summer in the NCC, under influence of meltwater outflow and solar radiation of UV.  The 2 nd 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

OMJ-98 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

OMJ-98 Forcing of trophic energy flow in the food-web of juvenile NE Arctic Cod (Modified from Skreslet, 1997) + (UVR) -