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North Sea

The Barents Sea, physical features:. Large 1.6 mill km 2 High latitude ~70°-80°N Shelf sea Mean depth 230m. Barents Sea. Russia. Norwegian Sea. Norway. North Sea. The Barents Sea, main species:. HADDOCK. POLAR COD. SHRIMP. PHYTOPLANKTON. COPEPODS. OTHER BENTHOS.

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North Sea

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  1. The Barents Sea, physical features: • Large • 1.6 mill km2 • High latitude • ~70°-80°N • Shelf sea • Mean depth 230m BarentsSea Russia Norwegian Sea Norway North Sea

  2. The Barents Sea, main species: HADDOCK POLAR COD SHRIMP PHYTOPLANKTON COPEPODS OTHER BENTHOS

  3. External driving forces: Climate: Fishing: Inflow, ice cover, atmospheric conditions => determine the extent and characteristics of main water masses • Arctic water • Mixed/Frontal water Atlantic water Coastal water • Mainly by Russia and Norway • Demersal fishery • -Mainly cod/haddock • -Shrimp, other demersal fish • Capelin • Harp seals/minke whales

  4. Barents Sea dynamics Pro Mare 1984-1989 : National Research programme Early 1980’s: IMR project ”Lodde på sommerbeite” Skjoldal et al 1992 Blindheim and Skjoldal 1992 Skjoldal et al 1987

  5. How does the climate influence ? • Inflow influences ice distribution, pressure system influence fluxes. • area and volum of water masses • On average atlantic water resides 4 years in the BS, • current condition integrates inflow over several years • Seasonal aspects of inflow? More inflow in winter vs summer? • Climate/inflow influences some important ecosystem components: • Bloom dynamics, match-mismatch copepods and phytoplantkon • Advection of copepods (Calanus finmarchicus) • Strong Recruitement variability (e.g, cod, herring) => Influenced by advective currents

  6. Phytoplankton ~four zones • Coastal current along the coast but goes also quite far into the BS Seasonal dynamics=> always stratification, stable/predictable spring bloom determined by day light • Atlantic water/inflow formation of termocline and stratification: strong internanual variation, timing vary by 6 weeks, can have 2 generations of copepods feeding on the spring bloom during the same season, similar to the Norwegian sea • Seasonally ice covered zone: Shallow melt water, leads to fast but short lived spring bloom, large buid up of phytplankton, copepods unable to reduce it by grazing • Permanently ice covered area (almost disappeared in recent years), partly melted, and has melt water, but light penetration reduced by ice and limits production

  7. Pro mare Phytoplankton Nutrients: Bloom of diatoms reduces silicate and nitrates Bloom of other phytoplankton reduces only nitrates Phaeocystis pouchetii flagelate, geletionous , may form colonies Diatoms better food for copepods, ratio nitrate/silikate at the end of bloom => indicative of grazing pressure from and biomass of copepods

  8. Phytoplankton pelagic bloom • low grazing pressure from copepods • more sedimentation • Indications that Calanus biomass influences the proportion of productions that sinks • Old Russian literature, fast bloom, less grazing, more sedimenation • => Higher organic content in sediments in northern areas • => Still valid?

  9. Zooplankton: Atlantic inflow => fills up the amount of Calanus finmarchicus (BS sink area for Calanus) But a lot of the inflow does not contain Calanus finmarichus and dilutes it. Calanus glacialis shelf species, most important herbivore in arctic BS, l arge and more fexible than C. finmarchicus C. Hyberboreus dominates in the Greenland sea Themisto libelulla; arctic, carnivor amphipods, not as shelf species, transported southwards T. Libellula both prey and competitior of capelin (both feeds on copepods)

  10. Barents Sea dynamics Pro Mare 1984-1989 : National Research programme Early 1980’s: IMR project ”Lodde på sommerbeite” end ofcoldperiod (1970’s), afterthisperiod, large fluctuations and warming trend Dynamics in capelingrowthdeterminecapelinstockdynamics Foodavailability large influenceoncapelingrowth and a strongfeed back ofcapelinonitsprey

  11. Capelin

  12. 1983: strong recruitement of herring and cod • herring predation on capelin larvae • Winter 82-83: large Atlantic inflow during winter, filled the BS with Atlantic water with very low abundance of copepods in central BS • induced reduced growth of capelin • 84/85 capelin stock collapse => increase in krill and amphipods • 1987 year class of capelin had fast growth and matured as 2 year olds due to high abundance of krill and amphipods, fast recovery of capelin

  13. Development in external driving forces: Fishing: 1970’s: High / increasing 1980’s: High on demersal fish High on capelin fishing until collapse 1990’s: Demersals: reduction followed by increase 2000-2009: Decreased on cod => New harvest control rule From Johannesen et al (2012)

  14. Fishing: • Herring: • Collapse of herring in the late 1960’s • Lack of juvenile herring in the BS in the 1970’s • linked to collapse of herring • Cod and haddock: • High fishing pressure: Low levels of cod and haddock in the 1980’s • Altered size/age structure (younger/smaller fish) • ”bottle neck” effect on cod, loss of genetic variability=>Mature younger and smaller ? • Capelin • First capelin collapse, prolonged by fishing? • Shrimp: • Effect on redfish recruitment?

  15. Development in main species: • Demersal fish: • 1970’s: High levels • 1980’s: Historic low levels • 1990’s: Variable • 2000’s: Increasing=>cod comparable to 1950’s • Pelagic fish: • 1970’s: Abundant capelin/Polar cod • No herring • 1980’s: 1. capelin collapse and recovery • Return of herring • 1990’s: 2. capelin collapse and recovery • 2000’s: 3. capelin collapse /recovery • Other pelagics abundant • Zooplankton /Shrimp: • Strong variability, • especially in 1980’s and 1990’s • 2000’s: Shrimp/Krill increasing trend

  16. ”Ecosystem state”

  17. Chronological clustering

  18. Results has not been related to drivers

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