Trophic models: What do we learn about Celtic Sea and Bay of Biscay ecosystems?

Type Article
Date 2017-08
Language English
Author(s) Moullec Fabien1, 2, Gascuel Didier1, Bentorcha Karim1, Guenette Sylvie3, Robert MarianneORCID4
Affiliation(s) 1 : UBL, Agrocampus Ouest, UMR Ecol & Ecosyst Hlth 985, 65 Rue St Brieuc,CS 84215, F-35042 Rennes, France.
2 : Univ Montpellier, MARBEC, UMR 248, IRD, Pl E Bataillon, F-34095 Montpellier, France.
3 : EcOceans, 12 St Croix, St Andrews, NB E5B 2K5, Canada.
4 : IFREMER, Unite Sci & Technol Halieut, Lab Technol & Biol Halieut, 8 Rue Francois Toullec, F-56325 Lorient, France.
Source Journal Of Marine Systems (0924-7963) (Elsevier Science Bv), 2017-08 , Vol. 172 , P. 104-117
DOI 10.1016/j.jmarsys.2017.03.008
WOS© Times Cited 27
Keyword(s) Ecosystem Approach to Fisheries Management (EAFM), Bay of Biscay, Celtic Sea, Ecopath with Ecosim, EcoTroph, Trophic indicators
Abstract Trophic models are key tools to go beyond the single-species approaches used in stock assessments to adopt a more holistic view and implement the Ecosystem Approach to Fisheries Management (EAFM). This study aims to: (i) analyse the trophic functioning of the Celtic Sea and the Bay of Biscay, (ii) investigate ecosystem changes over the 1980–2013 period and, (iii) explore the response to management measures at the food web scale. Ecopath models were built for each ecosystem for years 1980 and 2013, and Ecosim models were fitted to time series data of biomass and catches. EcoTroph diagnosis showed that in both ecosystems, fishing pressure focuses on high trophic levels (TLs) and, to a lesser extent, on intermediate TLs. However, the interplay between local environmental conditions, species composition and ecosystem functioning could explain the different responses to fisheries management observed between these two contiguous ecosystems. Indeed, over the study period, the ecosystem's exploitation status has improved in the Bay of Biscay but not in the Celtic Sea. This improvement does not seem to be sufficient to achieve the objectives of an EAFM, as high trophic levels were still overexploited in 2013 and simulations conducted with Ecosim in the Bay of Biscay indicate that at current fishing effort the biomass will not be rebuilt by 2030. The ecosystem's response to a reduction in fishing mortality depends on which trophic levels receive protection. Reducing fishing mortality on pelagic fish, instead of on demersal fish, appears more efficient at maximising catch and total biomass and at conserving both top-predator and intermediate TLs. Such advice-oriented trophic models should be used on a regular basis to monitor the health status of marine food webs and analyse the trade-offs between multiple objectives in an ecosystem-based fisheries management context.
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