ICES CM2010/Q:07 (abstract 1524) “Not to be cited without prior reference to the author”

Trophic structure and fisheries interactions in the gulf of Lions (north-western Mediterranean)

D. Almarcha-Bănaru, C. Mellon-Duval, D. Roos, J.-L. Bigot, A. Souplet, A. Jadaud, J.-P. Beaubrun, J.-M. Fromentin

ABSTRACT The gulf of Lions system was described using Ecopath mass-balance model of trophic interactions, with the aim of characterising its structure and functioning and to understand the effects of the multi-specific fisheries operating in this area.

KEYWORDS: gulf of Lions, Ecopath with Ecosim, fisheries impact, food web

INTRODUCTION The gulf of Lions represents an important feeding area for fishes, birds and mammals, for both resident and migratory . Its productivity is related to the Rhone river inputs, bottom morphology and water circulation. Fishing has been proposed as the main major human disturbance to coastal areas, within an ecosystem context where target and non-target species interact establishing complex relationships. In the gulf of Lions many species of commercial interest are intensively exploited on the continental shelf and upper slope by French and Spanish fleets using multi- specific artisanal gears like trawlers, purse seines, gillnets and other small gears.

METHODS The present Ecopath model represents an average annual situation (2000-2009) of the gulf of Lions system from 0 to 2500 m covering a total area of 20400 km 2 (Fig. 1).

N

50 km

Figure 1. Study area situated in the south of France.

The Ecopath and Ecosim (EwE) modelling approach version 6 (Christensen et al., 2005; www.ecopath.org) was used to ensure energy balance of the model. EwE divides the production of biomass of each functional group of the ecosystem into predation mortality caused by the biomass of the other predators, exports from the system both from fishing activity and other exports, biomass accumulation in the ecosystem and other mortality. For each trophic group the energy balance is given by the basic equation: consumption = production + respiration + unassimilated food. Inputs data were based on landings databases, aerial, acoustic and bottom trawl surveys, stock assessment working groups, stomach analyses and published information.

1 RESULTS AND DISCUSSION The model is composed of 39 compartments, including seabirds, 2 groups of cetaceans, 17 groups of fish, 12 groups of invertebrates, 5 groups of primary producers, detritus and discards (Table 1). It includes more than 99% of the exploited fish and invertebrate species in the gulf of Lions. The pedigree index of the model (0,67) ranks within the highest values when compared with other similar models. European pilchard and represented the main species in terms of biomass and landings in the gulf of Lions. Other fishes like: Atlantic mackerel, fishes (feeding on benthic ), hake, poor cod, Atlantic bluefin tuna and fishes (feeding on polychaetes), as well as some invertebrates (bivalves-gastropods and octopuses) showed also high values in the catches. Functional groups of the food web were organised into five trophic levels with the highest one represented by dolphins, anglerfishes, Atlantic bluefin tuna, European hake and (Fig. 2).

Trophic level pelagic demersal benthic

33% 83% 6% 8%

5%

9%

Figure 2. Structure of the pelagic, demersal and benthic food web. The links between the different compartments are proportional with the trophic flows. Large arrows show coupling between pelagic, demersal and benthic compartments through consumption.

Fishes like Atlantic mackerel, blue whiting, European pilchard, fishes (feeding on benthic crustaceans), as well as some invertebrates (bivalves - gastropods, benthic crustaceans, mesozooplankton, macrozooplankton and echinoderms) had high relative total impact on the entire food web. Important coupled pelagic-demersal-benthic interactions through consumption were observed (Fig.2). The most consumed groups of the food web were (53%), (21%), detritus (12%) and worms (9%). The biomass produced by the exploited fish species is mainly consumed in the food web by fishes (77%) and cephalopods (5%) and secondary exploited by fisheries (18%). Among fishes the most consumed in the food web are European pilchard (32%), other planctonophagous fishes (19%), blue whiting (16%), European anchovy (15%), Atlantic mackerel (7%), and fishes (feeding on benthic crustaceans) (5%). The 7 different analysed fisheries were operating at mean trophic level situated between 2.5 for small artisanal boats, 3.2 - 3.8 for gillnets, 3.3 - 3.4 for trawls, 3.0 for purse seine (12-24 m) for and 4.1 for purse seine (24-40 m). Large trawl (24-40 m) had the highest impact on most of the considered groups, while purse seine (> 24 m) had the lowest one (Fig. 3).

2 Trawls 12-24m, Purse seine <12m Trawls 24-40m Purse seine 12-24m Purse seine >24m Gillnet <12m <3nm Gillnet <12m, 12-18m >3nm Other small gears <12m, <3nm

100% 80% Positive 60% impact 40% 20% 0% -20% -40% -60% Negative -80% impact -100% 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

Figure 3. Impact of the fisheries on the different functional groups induced by direct or cascade effect.

CONCLUSION A high number of multi-species models directed at fisheries questions developed in the last decades, each of which has benefits and limitations. The mass-balance approach incorporated in the EwE software has been widely used for constructing food web models of marine ecosystems and to address issues to fisheries management (Christensen et al., 2005). The present model constitutes the first mass-balance model constructed to characterise the structure and the functioning of the exploited system of the gulf of Lions from the lowest to the highest trophic levels and it represents an important effort to integrate the available data. Deficiencies in the available biological and landings data sources have been identified. Preliminary results also highlighted the importance of data sources for further Ecosim and Ecospace scenarios.

ACKNOWLEDGEMENTS D. Almarcha-Bănaru is titular of a post-doc fellowship co-funded by the ANR “AMPED” and IFREMER, France.

REFERENCES Christensen V., Walters C. J., Pauly D., 2005. Ecopath with Ecosim: a user’s guide [online]. Fishery Centre, The University of British Columbia, Vancouver, B. C. Available from http://www.ecopath.org/modules/Support/Helpfile/EwEUserGuide51.pdf. www.ecopath.org

Contact author : Daniela Almarcha-Bănaru, Post-doc IFREMER, Centre Halieutique Méditerranéen et Tropical, Laboratoire Ressources Halieutiques, B.P. 171 - Avenue Jean Monnet, 34203 Sète, France. Phone : +33 (0)499573251 ; Fax : +33 (0)499573295 ; E-mail : [email protected]; [email protected].

3 Table 1. Description of the functional groups of the model

Functional group Common and latin names of species/groups and their percentages

1 Pico-nanophytoplankton autotrophe bactéria, pico-eucaryotes ( Synechococcus ), autotrophe nanophytoplancton ( Mesodinium ) 2 Microphytoplankton diatoms, dinoflagellates 3 Microphytobenthos Spp 4 Posidonie Posidonia oceanica leaf (blade and sheath) 5 Benthic macrophytes and Spp epibionts 6 Nano-microzooplankton ciliats, eggs and nauplii of , small cladocerans, pteropods, euphausids, mysids 7 Mesozooplankton copepods, cladorerans, pteropods, euphausids, mysids, amphipods, ostracods, fish and invertebrate eggs and larvaes 8 Macrozooplankton krill, fish and invertebrate eggs and larvaes, pteropods, euphausids, mysids, amphipods 9 Gelatinous zooplankton siphonophorae, tunicate (salpida, doliolida, appendicularia), hydromedusae, ctenophora, chaetognatha 10 Worms nematods and annelids 11 Bivalves and gastropods Spp 12 Octopuses Octopus spp, Eledone cirrhosa, E. moschata 13 Cuttlefish and squids Sepia spp, Sepietta spp, Sepiola spp, Ilex coindettii, Loligo spp, Todarodes spp, Allotheuthis spp, Histioteuthis spp. 14 Suprabenthic and benthic mysids, amphipods, isopods, cumaceans, benthic copepods, crustaceans euphausids, pagurids, shrimps , brachyurids 15 Lobsters Nephrops norvegicus , Palinurus spp, Homarus vulgaris 16 Echinoderms echinids, asterids, ophiurids, crinoids, holothurians 17 Other benthic invertebrates cnidarians, sponges, tunicats, siponcles, etc 18 European pilchard Sardina pilchardus (W., 1972) 19 European anchovy Engraulis encrasicholus (L., 1758) 20 Other planctonophagous 28% round sardinella- Sardinella aurita V., 1847; 20% European fishes sprat- Sprattus sprattus (L., 1758); 50% picarel- Spicara spp.; 2% red bandfish- Cepola macrophthalma (L., 1758); <1% big- scale sand smelt- Atherina boyeri R., 1810 21 Fishes (feeding on plants) 90% bogue- Boops boops (L., 1758); 10% salema- Sarpa salpa (L., 1758) 22 Atlantic mackerel Scomber scombrus L., 1758 23 Mediterranean horse mackerel Trachurus mediterraneus (S., 1868) 24 Blue whiting Micromesistius poutassou (R., 1827) 25 Atlantic bluefin tuna Thunnus thynnus (L., 1758) 26 European hake (L., 1758) 27 Atlantic horse mackerel Trachurus trachurus (L., 1758) 28 Anglerfish 67% Lophius budegassa S., 1807; 33% L. piscatorius L., 1758 29 European conger Conger conger (L., 1758) 30 Poor cod Trisopterus minutus (L., 1758) 31 Fishes (feeding on fishes) 47% Chub mackerel- Scomber japonicus H., 1782; 19% swordfish- Xiphias gladius L., 1758; 15% small-spotted catshark- Scyliorhinus canicula (L., 1758); 15% raies- Raja spp.; 3% East Atlantic red gurnard- Aspitrigla cuculus (L., 1758); 1% megrim- Lepidorhombus whiffiagonis (W., 1792); 1% brill- Scophtalmus rhombus (L., 1758)

4 32 Fishes (feeding on benthic 45% European seabass- Dicentrarchus labrax (L., 1758); 22% crustaceans) gurnards- Trigla spp., Lepidotrigla spp., Eutrigla gurnardus (L., 1758); 10% scorpion fish- Scorpaena spp., Helicolenus dactylopterus dactylopterus (D., 1809); 9% red mullets- Mullus barbatus barbatus L., 1758, M. surmuletus L., 1758; 8% axillary seabream- Pagellus acarne (R., 1827); 2% fourspotted megrim- Lepidorhombus boscii (R., 1810); 2% greater forkbeard Phycis blennoides (B., 1768); 2% gobies- Gobius spp.; <1% mullets- Mugil spp., Liza spp. 33 Gilthead seabream Sparus aurata L., 1758 34 Fishes (feeding on 85% soles- Solea spp.; 9% common pandora- Pagellus polychaetes, bivalve and erythrinus (L., 1758); 4% striped seabream- Lithognathus gastropods) mormyrus (L., 1758); 2% sars- Diplodus spp.; < 1% Mediterranean rainbow wrasse- Coris julis (L., 1758) 35 Sea birds 90,9% gulls- Larus michahellis; shearwaters- 6,4% Calonectris diomedea diomedea, 0,1% Puffinus yelkouan yelkouan, 0,5% P. yelkouan mauretanicus; 1,2% t erns- Sterna hirundo; 0,9% Northern Gannet - Morus bassanus 36 Dolphins bottlenose dolphin- 12,4%Turpsios truncatus, 17,3% striped dolphin- Stenella coeruleoalba , 3,4% Risso's dolphin- Grampus griseus; 5,1% sperm whale- Physeter macrocephalus; 61,8% pilot whale- Globicephala melas 37 Whales fin whale- Balaenoptera physalus 38 Detritus and associated hétérotrophe bactéria 39 Discards 20% of total landings of Sardina pilchardus , 60% of total landings of Trachurus spp.

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