Bio-economic modelling of Fishing Agregation Devices (FADs) and management issues

Transcription

1 Bio-economic modelling of Fishing Agregation Devices (FADs) and management issues Olivier Guyader*, L. Reynal**, Jean Boncoeur*** * Ifremer UMR AMURE ** Ifremer Lesser Antilles fisheries unit *** University of Brest UMR AMURE

2 1. Context

3 More than 50% worldwide tuna catches under FADs (Fonteneau et al. 2000) LARGE (capital intensive) purse seiners using DRIFTING man-made FADs in OFFSHORE AREAS

4 MOORED COASTAL FADs operated by SMALL SCALE FLEETS 18 0'N 17 0'N Activité en nombre de mois : [0] ]0-25[ [25-50[ [50-75[ [75-100[ 600 vessels in FADs fisheries (Martinique and Guadeloupe) 16 0'N [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ [ 30 nm [ [ >= 'N 14 0'N Système géodésique: Projection Mercator Ellipsoïde WGS 'O 62 0'O 61 0'O

5 Geographical distribution of yellowfin catch by major gears Contribution to total fishing mortality is low Lesser Antilles as «resource takers»

6 2. A simple model of FADs-Vessels interactions

7 a) FAD interactions An area i (size=1) B: Biomass available in the area for a period t F: Number of FADs in the area β : Agregation capacity / attractivity of FADs Biomass under FADs vs Number of FADs Biomass per FAD vs Number of FADs β=0.05 β=0.1 β=0.3 β=0.5 β=0.9 Biomass in the area j β=0.05 β=0.1 β=0.3 β=0.5 β= Biomass available under the FADs B F = B.( 1 e βf ) Biomass available per FAD Number of FADs Number of FADs

8 b) Vessels interactions Catch function under FADs K: Number of vessels in the area K/F : number of vessels per FADs q m : Catchability coefficient δ m : Index of interaction around FAD which depend on fishing techniques/targeted species Evidence of interactions - Dolphinfish in Guadeloupe - Drifting longlines (Lesser Antilles) - Purse seiners (?) Total Catches per FAD vs number of vessels per FADs Total Catches Delta=1 Delta=2 Delta=0.5 Delta= Number of vessel on FAD

9 3. Implications for fisheries management 1. Open access 2. TURFs (Spatial allocation) 3. Collective regulated FADs

10 Number of FADs Total catches Fleet profit Fleet profit (incl. FAD cost) Profit per vessel Effort shift to coral reef fisheries 2. TURF 1. Open Access Equilibrium Biomass FAD Vessel

11 Aerial survey of the FADs density in Guadeloupe (open access FADs fisheries OVERCAPACITY)

12 3. Collective set of FADs (organized network) Optimal number of FADS and Vessels per FAD given different levels of interaction Given a number of vessel, what is the best number of FADs given FAD unit cost?.. Delta=1 Delta= Net Profit Net Profit Vessels per FAD Number of FADs Vessels per FAD Number of FADs

13 4. Conclusion FADs regulation required including access regulation (individual fishing permits, ) On going / future work on : Fish and Fishermen dynamics around FADs and between FADs Interactions between FADs fisheries and coral reef fisheries.

14 Analysis of fishing strategies through GPS tracking

15 Current 2008 average gross margin per gear type ( /trip) Gros ss Margin per fishing trip ( ) Trolling line Hook and line FADs Traps Gillnet Trammel net Hand line Longline Snorkeling Large pelagic species Coral-reef ecosystem species

16 Répartition spatiale de l activité (en nombre de mois métiers) Casier DCP! 18 0'N 18 0'N Activité en nombre de mois : [0] 17 0'N 17 0'N ]0-25[ [25-50[ [50-75[ [75-100[ [ [ [ [ [ [ [ [ [ [ 16 0'N 16 0'N [ [ [ [ [ [ [ [ [ [ [ [ [ [ >= 'N 15 0'N 14 0'N Système géodésique: Projection Mercator Ellipsoïde WGS 'N Système géodésique: Projection Mercator Ellipsoïde WGS 'O 62 0'O 61 0'O 63 0'O 62 0'O 61 0'O

17 Allocation of effort between coral reef fisheries and pelagic (FADs) fisheries

18 FAD unit cost Optimal numb ber of FADs Plus la capacité d agrégation augmente, plus l écart entre le nombre optimal de DCP se réduit FADs agregation capacity