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Alfonso Pérez-Rodríguez, Mariano Koen -Alonso*, Fran Saborido -Rey

Study of the demersal fish community of the Flemish Cap (NAFO Div. 3M): Changes in community structure and common trends during the period 1988-2008. Alfonso Pérez-Rodríguez, Mariano Koen -Alonso*, Fran Saborido -Rey. Institute of Marine Research, CSIC, Spain.

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Alfonso Pérez-Rodríguez, Mariano Koen -Alonso*, Fran Saborido -Rey

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  1. Study of the demersal fish community of the Flemish Cap (NAFO Div. 3M): Changes in community structure and common trends during the period 1988-2008. Alfonso Pérez-Rodríguez, Mariano Koen-Alonso*, Fran Saborido-Rey Institute of Marine Research, CSIC, Spain. *Northwest Atlantic Fisheries Centre, DFO, Canada. FisheriesEcology ICES/NAFO Symposium on the variability of the North Atlantic and its marine ecosystems during 2000-2009 Santander, Spain, May 10-12 2011

  2. Introduction: Flemish Cap.

  3. Aims of thestudy 1.- Study of the whole demersal fish community: common trends in time series of biomass of both commercial and non commercial species from 1988 to 2008. 2.- Evaluation of the importance of: - Oceanographic conditions - Fishing. - Post-larval predation.

  4. Material & methods • 1.- Material: • Index of Biomassbysweptarea and temperaturefromthe EU (IEO, IIM-CSIC, AZTI-Tecnalia and IPIMAR)Julysurveys in Flemish Cap fortheperiod 1988-2008. • NAO indexfromthe NOAA website: http://www.cpc.noaa.gov • Declared and estimatedcatchesfromthe NAFO websiteand scientific assessments: http://www.nafo.int/about/frames/about.html • 2.- Methods: • Dynamic Factor Analysis (DFA) (Zuur et al, 2003). • MDS and PERMANOVA.

  5. Groups of demersal species • Groups of species: • Group 1: >0.05% total biomass • Group 2: <0.05% total biomass & > 15 years • Group 3: <0.05% total biomass & < 15 years

  6. DFA models. Groups I and II 1.- Modelswithoutexplanatory variables, onlycommontrends 2.- Modelswithexplanatory variables: - NAO index: averagevalue of 4,5,6 and 7 previousyears - Index of Fishingpressure: AEF=Total catches/Total fishbiomass - Predation: Piscivorous abundance

  7. Results: Group of species I

  8. Results: Group of species I Modelfit Residuals AIC values AIC values

  9. Results: Group of species II

  10. Results: Group of species II AIC values AIC values

  11. Values of coefficients in groups I and II: NAO index

  12. Values of coefficients in groups I and II: AEF and Piscivorous Group I Group II

  13. Group I Analysis of obtainedcommontrends Group II

  14. Results: Group of species III

  15. Results: Group of species III PERMANOVA: significantdifferencesbetween “positive” and “negative” groups of years. MDS:

  16. Recruitmentormigration? • Forspecies of group III, Flemish Cap presentsuboptimumconditions. • As thethermalconditionschange, the “rare” speciescompositionchanges. • No migration: previousworkspointedtotheisolation of theshallowestpopulations. • Thetwoyearsoverlap of cold and warmperiodspointstowards a recruitmentprocess: • Larval “immigration”? • “Ghost” adults?

  17. Conclusions 1.- The NAO index seems to be a good predictor for the dynamic of the fish demersal community in Flemish Cap due to its correlation with oceanographic conditions (mainly temperature). 2.- Fish predation is a key driver in the changes observed in the demersal community and its relative importance in relation to the other forcing factors is higher in the group of species II than in the group I. 3.- Fishing activity has shown a significant effect, although it was more important in the group of commercially important species (group I). Deviance from the expected negative effect could be ascribed to indirect effects (e.g. trophic cascades). 4.- In the group of rare species, changes could be related with variations in recruitment in relation with temperature preferences. Larval “immigration” is possible, although the existence of “ghost” adult individuals is a plausible hypothesis. 5.- The aim of this study are the global effects and global responses. Individual species studies, considering the spatial dimension are necessary in order to go deeper in the relationship of each particular species dynamics with the biotic and abiotic conditions surrounding it.

  18. Specialthanksto: • Stafffromthe NAFC-DFO. • AZMP programe • Staffinvolved in the EU annualsurvey (IEO, IPIMAR, AZTI-Tecnalia and IIM) • NEREUS program. Alfonso Pérez-Rodríguez, Mariano Koen-Alonso*, Fran Saborido-Rey Institute of Marine Research, CSIC, Spain. *Northwest Atlantic Fisheries Centre, DFO, Canada. FisheriesEcology ICES/NAFO Symposium on the variability of the North Atlantic and its marine ecosystems during 200-2009 Santander, Spain, May 10-12 2011

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