Investigating coastal ecosystem structure and dynamics using Ecopath/Ecosim ecosystem models and stable isotope data

Transcription

1 Investigating coastal ecosystem structure and dynamics using Ecopath/Ecosim ecosystem models and stable isotope data Torstein Pedersen Einar M. Nilssen Silje Ramsvatn, PhD student Trond Ivarjord, vit. Ass. Fredrikke Museæus, tech. Marianne Nilsen, IRIS Lyne Morissette, ISMER, Canada Anita Maurstad, TMU Håvard Fause, master student Ina Kolsum, master student Christer Michalsen, master student Geir Helge Systad, NINA

2 Background Main objective: which biotic and abiotic factors affect dynamics and structure of coastal ecosystems in northern areas? Is it possible to advocate management regimes that enhance fishery yield, resilience, resistance and biodiversity? Use models that integrate data from classical sampling methods and stable isotope data?

3 Comparative ecosystem approach; local (Sørfjord vs Ullsfjord), regional, intercontinental scale General large decline in costal cod after 1995 Cascade effects of decline in cod? Ullsfjord warmer and more diverse than Sørfjord Reference ecosystem for king crab effect studies

4 Barents Sea Ullsfjord & Sørfjord Norwegian Sea Russia Sweden Finland Norway Ullsfjord, a deep, outer and relatively warm fjord (400 km 2 ), and Sørfjord which is shallower and colder (55 km 2 ) Ullsfjord has higher biodiversity

5 Mass-balance approach Ecological groups (n = 40 in Ullsfjord) Input data are Biomass, P/B, Q/B, Ecotrophic efficiency (need 3 of 4), catches and diet Diet data input are essential Ecopath -> Ecosim -> Ecospace 6 Combine with 5

6 Unique approach; uses Ecopath-model structure as framework for strategic sampling of groups that are necessary and important to estimate ecosystem model

7 Structure in Ullsfjord 40 group model, new groups shown in bold, multistanza groups in colour Gr. No. Gr. No. 1 Mammals 21 Heterotrophic nanoflagellates birds & mammals (5) 2 Pisciivore benthic bird 22 Schypomedusae 3 Pelag diving birds 23 Chaetognaths 4 Surface feeding birds 24 Other shrimps 5 Benthic invertebrate f. birds 25 Pelagic shrimps 6 Large cod 26 Other large zooplankton 7 Small cod 27 Large crustacea 8 Large saithe 28 Predatory benthos 9 Small saithe 29 Detrivore polychaetes 10 Large haddock 30 Small benthic crustacea Fish (10) 11 Small haddock 31 Small molluscs 12 Small gadoids 32 Large bivalves 13 Large other fish 33 Detrivore echinoderms 14 Small other fish 34 Herbivore echinoids 15 Small pelagic fish 35 Other benthic invertebrates 16 Herring 36 Bacteria 17 Small krill 37 Phytoplankton 18 Large krill 38 Macroalgae zooplankton/ crustaceans 19 Small zooplankton 39 Discard and offal 20 Microzooplankton 40 Detritus zooplankton/ cr.nekton (10) benthos (9)

8 Field/Survey Literature data Commercial catch data Diet analysis

9 Large sampling effort, challenge to sample all groups and diets representatively

10 How to represent; top-predators, fish and pelagic groups (WP1), benthic invertebrate groups (WP2)? How to assess and incorporate data from stable isotopes into an Ecopath model (WP3)? How to evaluate effects of trophic control mechanisms and exploitation regimes using Ecopath/Ecosim modelling (WP4)?

11 Stable isotopes (SI) Trophic level (TL) Carbon δ 13 C= 13 C / 12 C Primary source of carbon

12 SI can be used to investigate ontogenetic diet shifts Haddock less than 20 cm in length feed pelagic and then change to a more benthic signature/diet at larger size Ullsfjord Small haddock (< 20 cm)

13 How to compare Ecopath models with diet data input from gut content analysis (GCA) and stable isotopes (SI)? Use MIXSIR, a bayesian source mixing model, to estimate diet prey proportions for a predator from the SI of the predator, SI of potential prey groups and trophic enrichment factors for delta13c and delta15n. Uses individual data.

14 GCA Ecopath Comparison of trophic levels estimated directly from SI data and Ecopath model based on stomach/literature data input 1:1 line regression SI data

15 SI Ecopath Comparison of trophic levels directly from SI data and Ecopath model based stable isotope data diet input Trophic level increased with new diet data SI data

16 Fish species Invertebrate bentic predators Invertebrate benthos Detrivore echinoderms

17 whiting Trophic redundancy long rough dab (fish with length cm) witch haddock

18 Fish species Invertebrate bentic predators Invertebrate benthos Detrivore echinoderms

19 Conclusions SI SI can be used to estimate diet input to Ecopath models More local data can be used SI can be also used to improve diet data from benthic invertebrates, need sufficient diversity of groups

20 Comparative Ecosystem approach

21 Group Fish and shrimp Pelagic shrimp Shrimps Herring Small pelagic fish Small other fis Large other fis Small gadoids Small haddock Large haddock Small saithe Large saithe Small cod Sørfjord Ullsfjord Large cod Biomass (g C m -2 )

22 Group Group Benthic invertebrate groups Biomass P/B Other benthic i Other benthic i Herbivore echin Herbivore echin Detrivore echin Detrivore echin Large bivalves Small molluscs Large bivalves Small molluscs Sørfjord Ullsfjord Small benthic c Detrivore polyc Predatory benth Large crustacea Sørfjord Ullsfjord Small benthic c Detrivore polyc Predatory benth Large crustacea Biomass (g C m -2 ) P/B (per year)

23 Regional comparison Mammals Seabird Norwegian Sea/Barents Sea Sørfjord Ullsfjord North Sea Cod Haddock Saithe Prawns Small gadoids Small pelagic fishes and herring Biomass g C m -2

24 Intercontinental: Sørfjord versus Northern Gulf of St Lawrence, Canada Who are the main predators? Morissette et al In Sørfjord, fishing mortality is minimal, and cod is the dominant predator In the Gulf of St. Lawrence, fishing is 10X higher, and since cod is collapsed, marine mammals became the main predators

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26 Annual catch (tons) Fangst per fartøy (kg per fatøy) Fishery regimes. Annual catches of deep sea shrimp in Ullsfjord and Lyngen (source Råfisklaget) 600 Fangst Ullsfjord 500 Fangst Lyngen År

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