Biological and ecological traits of non-targeted species caught by the tuna purse seine fishery in the western Indian Ocean

Tuna purse seine fishery in the western Indian Ocean is estimated to have relatively low bycatch species, representing about 3.4 % of the total catch. Yet, with the recent implementation of a yellowfin tuna quota and the new discard ban policy, removal of non-targeted species is expected to be higher in the next few years. Thanks to observer programs, it is possible to monitor incidentally catches in terms of biomass and composition estimates; nevertheless little quantitative information exists on the biology and ecology of those non-targeted species, particularly in the western Indian Ocean. Thus it is very difficult to assess their removal effect on the role and function of the pelagic ecosystem. Within this context three objectives have been defined for this paper. First the main biological and ecological traits available in the literature for those bycatch species were reviewed. Secondly, the new biological sampling launched in Seychelles was presented. Finally, some length-weight relationships were updated for the western Indian Ocean, using morphometric data collected on board and at landing.