Spatial organization of the pelagic community of the Barents Sea

1. Spatial organization of the pelagic community of the Barents Sea Mette Skern-Mauritzen, Per Fauchald, Edda Johannesen, Ulf Lindstrøm, Elena Eriksen, Nils Øien BarEcoRe project meeting, Herdla, 04.10.2011 NORWEGIAN INSTITUTE FOR NATURE RESEARCH

2. The pelagiccommunity • Capelin – fluctuatingkeyspecies • Repeatedstockcollapses • Adverseeffectsontop predators • Collapse in 2003 – noeffects?

3. The pelagiccommunity Structuring processes, the late summer pelagic community Large scale: • Habitat use; water masses, depth • Migration; ability, motivation • Distribution of prey • Interspecific competition, niche partitioning Small scale: • The predator – prey spatial game; Predators win: positive associations between predators and prey Prey win: negative associations between predators and prey • Positive facilitation: predators seek other predators rather than prey, due to highly elusive prey patches => aggregates predators across space – on few prey patches => many predator free patches => reduce spatial match between predators and prey => reduce predator control of prey populations; prey wins the game

4. Key questions: How was the spatial structure of the pelagic community during the last capelin collapse? • To reveal the trophic structure and major trophic links • Identify the involved processes, and discuss - who is winning the game? - what are the implications for the trophodynamics of this system

5. The pelagiccommunity • The joint Russian – NorwegianEcosystem survey August – September , 2003 – 2007 • Synoptic data on: • Zooplankton • Pelagic fish • 0-group fish • Cod • Seabirds • Marine mammals Study area – Western Barents Sea

6. General additive mixed models (GAMM) GAMM model: Puffin ~ s(depth) + s(X,Y) + random factor(Year) + error Two – stage modelling, zero inflated data Presence/absence Binomial model Presence only Gamma model Distribution Residuals

7. The spatial structureofthepelagiccommunity Late summer, the capelin poor years 2003 – 2007 Lower and mid trophic levels Blue whiting Herring Capelin Polar cod Pelagicfish O-groupfish Zooplankton Southern prey community Fish 0-Herring 0-Cod 0-Capelin 0-Polar cod Northern prey community Zooplankton and fish Krill Amphipods

8. Average late summer distributions, the capelin poor years 2003 – 2007 Top predators Cod age2 Cod imm Cod maturing Cod mature Cod, different size groups Whiteb. dolphin Fin whale Minke whale Humpback whale Cetaceans Atl. puffin Com. guillemot Brün. guillemot Little auk Diving seabirds Kittiwake N. fulmar Surface feeding seabirds

9. The trophic structureofthepelagiccommunity Late summer, the capelin poor years 2003 – 2007 TOP PREDATORS Principal component analyses of averaged distributions Top predators – a wide variety of spatial niches, persistent across years South North

10. The trophic structureofthepelagiccommunity Late summer, the capelin poor years 2003 – 2007 SEABIRDS vs PREY Principal component analyses of averaged distributions Top predators – a wide variety of spatial niches, persistent across years Northern top predators: Associated with krill, amphipods, polar cod, north of the capelin core area Southern top predators: associated with herring, 0-group fish South North Capelin

11. The trophic structureofthepelagiccommunity Late summer, the capelin poor years 2003 – 2007 WHALES VS PREY Principal component analyses of averaged distributions Top predators – a wide variety of spatial niches, persistent across years Northern top predators: Associated with krill, amphipods, polar cod, north of the capelin core area Southern top predators: associated with herring, 0-group fish South North Capelin

12. The trophic structureofthepelagiccommunity Late summer, the capelin poor years 2003 – 2007 COD VS PREY SEABIRDS Principal component analyses of averaged distributions Top predators – a wide variety of spatial niches, persistent across years Northern top predators: Associated with krill, amphipods, polar cod, north of the capelin core area Southern top predators: associated with herring, 0-group fish South North South North Capelin

13. Scalesofdistributions– spatial nichewidth Top predators: 200 – 400 km Correlograms, estimated on distribution data Prey species: 400 – 600 km Top predators confined to narrow niches relative to their prey Distance, km Distance, km Figure 6.

14. The large scaledstructureofthepelagiccommunity • In late summer, with low capelin abundance (2003 – 2007): • Northward zooplankton gradient • Pelagic fish – partitioning the Barents Sea • Top predators – wide diversity of niches • Narrow niches relative to prey

15. The large scaledstructureofthepelagiccommunity • In late summer, with low capelin abundance (2003 – 2007): • Generalist top predators – including the capelin predators Brünnichs guillemots and baleen whales: • Inhabited the northern BS, in association with macro-zooplankton, polar cod, and capelin • Cod – inhabited the frontal areas with capelin, increasingly north with age • Piscivorous top predators - the common guillemots, puffins, white- beaked dolphins: • Inhabited the front / southern BS, in association with herring and 0- group fish

16. General additive mixed models (GAMM) GAMM model: Puffin ~ s(depth) + s(X,Y) + random factor(Year) + error Two – stage modelling, zero inflated data Presence/absence Binomial model Presence only Gamma model Distribution Residuals

17. Scalesofpatches– spatial nichewidth Top predators: 100 – 200 km Correlograms, estimated on residuals Prey species: 200 – 400 km

18. Species associations at patch scale Correlations between residuals Pink cells: r ≥ 0.15, Red cells: r ≥ 0.30 • Few sign. correlations • Stronger between predators than between predators and prey • Predator – prey corrs. may and may not reflect the large scaled associations

19. Species associations at patch scale • At patch scale: • Strong associations between predator species • positive facilitation a significant process • Weak associations between predators and prey • Due to positive facilitation; aggregating predators on few prey patches, most patches without predators • Prey avoidance behaviour: krill and sampling? • The predator-prey associations that were present; did not necessarily reflect the large scale associations • Suggest feeding on what is present within habitat?

20. Implications for the trophodynamics • The late summer system; • - maximum extent of the pelagic community • - high top predator diversity • - low capelin abundance • Omnivorous (capelin) predators – occupied northern areas with polar cod, macro-zooplankton, and low densities of capelin • Piscivorous predators – occupied southern areas with a fish prey community • Omnivorous predators more prone to perform seasonal foraging migrations following the MIZ and a two-trophic prey community

21. Implications for the trophodynamics • Top predators: • Diverse and narrow spatial niches – associated with e.g. banks • Limited associations with specific prey species, varying with scale • => diverse diet within habitats? • Positive facilitation • Are the predators loosing the game? • => Reduced spatial match between predators and prey • => Reduce the predator control of prey; • Pair-wise predator – prey interactions not likely to be strong; • spatial prey refuges, availability of alternative prey species within habitats • Implications for trophic control – i.e. strength of top-down control? • Winter system: • Simple; low species diversity, low habitat diversity • Dynamic, overlapping predator distributions • Strong spatial and dietary responses of predators to prey • => Stronger top-down control in this season?

22. Nils Øien Thankyou for yourattention

23. Top predator responses to thecapelinrecovery Baleenwhales – spatial responses Late summer Capelin distribution 2010 Whale observations 2010 Fin wh. Humpb. Green backgroundshades: Meandistribution 2003 - 2007 Minke • Stable late summer / autumn distributions • - independent of changing capelin abundance • - Increasing overlap with capelin due to northern capelin distribution shift Skern-Mauritzen et al 2011. MEPS

24. Cod –dietaryresponse The trophic structureofthepelagiccommunity Late summer, the capelin poor years 2003 – 2007 Preygroups capelin polar cod herring krill amfipods shrimp otherfish otherinv Average individual consumption (weight) for cod (50-75 cm length) Edda Johannesen et al. In prep.

25. Top predator responses to thecapelinrecovery Cod –dietaryresponse Late summer Preygroups capelin polar cod herring krill amfipods shrimp otherfish otherinv Average individual consumption (weight) for cod (50-75 cm length) Edda Johannesen et al. In prep.

26. Top predator responses to thecapelinrecovery Cod –dietaryresponse Late summer Preygroups capelin polar cod herring krill amfipods shrip otherfish otherinv More capelin in the diet with more capelin in the system Edda Johannesen et al. In prep.

27. Top predator responses to thecapelinrecovery Late summer Seabirds – spatial responses • Seabird distributions • - Persistent spatial niches • - Strong habitat selection • What determines year-to-year • changes in distribution • (in 50 km grid cells) • Local density of prey? • Abundance of prey within the system? Thick-billed murre Yeart Thick-billed murre Yeart+1 Per Fauchald et al. In prep.

28. Top predator responses to thecapelinrecovery Late summer Seabirds – spatial responses Thick-billed murre Yeart Thick-billed murre Yeart+1 Per Fauchald et al. In prep.

29. Top predator responses to thecapelinrecovery Late summer Seabirds – spatial responses Whales – spatial responses - Persistent spatial niches - Independentofcapelinabundance Per Fauchald et al. In prep.

30. Top predator responses to thecapelinrecovery Late summer Seabirds – spatial responses • Seabird distributions • - Persistent spatial niches • - Strong habitat selection • What determines year-to-year • changes in distribution • (in 50 km grid cells) • Local density of prey? • Abundance of prey within the system? Thick-billed murre Yeart Thick-billed murre Yeart+1 Per Fauchald et al. In prep.

31. Top predator responses to thecapelinrecovery Late summer Seabirds – spatial responses Thick-billed murre Yeart Thick-billed murre Yeart+1 Per Fauchald et al. In prep.

32. Top predator responses to thecapelinrecovery Late summer Seabirds – spatial responses Whales – spatial responses - Persistent spatial niches - Independentofcapelinabundance Per Fauchald et al. In prep.

33. Top predator responses to thecapelinrecovery Late summer Seabirds – spatial responses • Seabird distributions • - Persistent spatial niches • - Strong habitat selection • What determines year-to-year • changes in distribution • (in 50 km grid cells) • Local density of prey? • Abundance of prey within the system? Thick-billed murre Yeart Thick-billed murre Yeart+1 Per Fauchald et al. In prep.

34. Top predator responses to thecapelinrecovery Late summer Seabirds – spatial responses Thick-billed murre Yeart Thick-billed murre Yeart+1 Per Fauchald et al. In prep.

35. Top predator responses to thecapelinrecovery Late summer Seabirds – spatial responses Whales – spatial responses - Persistent spatial niches - Independentofcapelinabundance Per Fauchald et al. In prep.

36. Top predator responses to changingcapelinabundance – in winter The winter system: simple, species poor, contracts in the southern Barents Sea Lower and mid trophic levels X Blue whiting Herring Capelin X Polar cod X X X X X X 0-Herring 0-Cod 0-Capelin 0-Polar cod Krill Amphipods

37. Top predator responses to changingcapelinabundance – in winter Cod age2 Cod imm Cod maturing Cod mature Top trophic levels ? ? ? Whiteb. dolphin Fin whale Minke whale Humpback whale X X X Atl. puffin Com. guillemot Brün. guillemot Little auk Kittiwake N. fulmar

38. Top predator responses to changingcapelinabundance – in winter Preliminary results from winter surveys - Cod: Stomach fullness in capelin rich and poor years => Cod consumption more dependent on capelin abundance in winter than in summer Capelin rich Capelin poor Michalsen et al. 2008. ICES J Mar Sci

39. Top predator responses to changingcapelinabundance – in winter • Preliminary results from winter surveys • Seabirds: spatial responses • Highly dynamic distributions • Low niche segregation • Stronger spatial responses to capelin Per Fauchald et al. In prep.

40. To summarize: • The late summer system: • Large geographic extent, complex system • Persistent predator niches; niche partitioning • Large diversity of prey species • Few positive, few negative, mostly no strong responses to changing capelin abundance and distribution • The winter system: • Limited geographic extent, simple system • Dynamic and overlapping predator niches • Strong dietary and spatial responses to capelin

41. Implications for ecosystem monitoring Monitoring of dynamic trophic interactions requires • Ecosystem surveys with synoptic coverage of the different trophic levels • Monitoring across seasons • Improved monitoring techniques of species of trophically high importance but economically low importance, such as the zooplankton • Adaptive monitoring; reduced time for large-scaled, regular surveys to allow for more process-oriented surveys in certain areas / at certain scales

42. Implications for ecosystem management The top predators’ susceptibility to fluctuations in key prey species (and to fisheries) varies • with availability of alternative prey species • across seasons Seasonal variation in effects of top predators on prey? • In summer: diverse niches, weak responses of top predators to prey => weak predator (top-down) control - In winter: strong top predator responses to prey => stronger predator (top-down) control New project: Adapting the Atlantis ecosystem model to the present results - Explore effects and success of various management regimes