Mitigating impacts of fishing on pelagic ecosystems
15-18 Oct 2012 Montpellier (France)
Thursday 18

› 13:45 - 14:05 (20min)
› Auditorium
Can the fishing time at FADs be adjusted to reduce bycatch by purse seiners?
Fabien Forget  1, 2, 3, *@  , John David Filmalter  1, 3, 4@  , Rodney Govinden  5@  , Marc Soria  6@  , Paul Cowley  2@  , Laurent Dagorn  7  
1 : Institut de Recherche pour le Developpement  (IRD)
Mahe -  Seychelles
2 : South African Institute of Aquatic Biodiversity  (SAIAB)
Private Bag 1015, Grahamstown, 6140 -  South Africa
3 : Rhodes University
Private Bag 1015, Grahamstown 6140 -  South Africa
4 : South African Institute for Aquatic Biodiversity  (SAIAB)
Private Bag 1015, Grahamstown, 6140 -  South Africa
5 : Seychelles Fishing Authority   (SFA)
Mahe  -  Seychelles
6 : Institut de Recherche pour le Développment  (IRD)  -  Website
Université de la Réunion. 15, Avenue René Cassin 97 400 Saint Denis -  Réunion
7 : Institut de Recherche pour le Développement  (IRD)
Institut de Recherche pour le Développement
sete -  France
* : Corresponding author

Fish aggregations at FADs are multi-specific in nature and comprise both targeted tuna species and several bycatch species. We acoustically tagged the three major tuna species - yellowfin tuna (Thunnus Albacares), bigeye tuna (T. obesus), skipjack tuna (Katsuwonus pelamis) - and some major bycatch species - silky sharks (Charcharinus falciformis), oceanic triggerfish (Canthidermis maculatus) and rainbow runners (Elagatis bipinnulata) - at the same drifting FADs (10 FADs). We investigated the temporal and spatial dynamics of the different species simultaneously to assess a potential time-dependent vulnerability. We specifically explored the fine scale diel patterns of association of the tagged species to determine if there are specific times of the day when only certain species are present at the FAD. Additionally, we used depth data (transmitted by pressure sensitive acoustic tags) to determine whether distinct diel patterns exist in the vertical distribution of the various species. These data are discussed in the light of a mitigation approach where the fishing time of tuna purse seiners could potentially be adjusted to reduce the capture of bycatch.

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