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the main objectives pursued.

Understanding the coupling between small pelagic fishes and marine top predators using ecosystem-based surveys.

Certain G1, Masse J2, Van Canneyt O3, Petitgas P2, Doremus G3, & Ridoux V3

1Norwegian Institute for Nature Research (NINA), NO-7485 Trondheim, Norway.

2Ecology and Model for Halieutic (EMH), IFREMER Nantes, France.

3Center for Research on Marine Mammals (CRMM), Université de La Rochelle, France

Achieving a good understanding of the “vertical” relationships existing between marine prey and predator community, as well as of “horizontal” relationships existing within each of these two communities, is a great step toward an integrated understanding of the functioning of pelagic ecosystems. The PELGAS (PELagique GAScogne) scientific cruises in the Bay of Biscay, France, are systematic ship-based surveys that focus on the whole pelagic ecosystems, with a particular attention paid to acoustic sampling of small pelagic schooling fishes. They are led each spring (in May) since 2000 under the direction of IFREMER (EMH team, Nantes). Since 2003, a systematic visual census of top predators (seabirds and cetaceans) has been simultaneously conducted on board by the CRMM (Center for Research on Marine Mammals). Between 2003 and 2008, near 24 000 km of transects have been covered, along which both small pelagic fishes and marine predators have been sampled simultaneously. To summarise the relationships existing within the upper-part of the pelagic food web in the Bay of Biscay in spring, we carried out a classical multivariate analysis of a series of k-tables using PELGAS data, in order to capture the most stable part of the sampled spatio-temporal pattern. Our analysis reveals several prey-predator-fisheries associations that can be understand as functional groups in the Bay of Biscay Ecosystem.

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