Spatial management of Indian Ocean tropical tuna fisheries: potential and perspectives

Effective use of spatialmanagement in the pelagic realm presents special challenges due to high fish and fishermobility, limited knowledge and significant governance challenges. The tropical Indian Ocean provides an ideal case study for testing our ability to apply existing data sources to assessing impacts of spatialmanagement on tuna fisheries because of several recent controversial spatial closures.We review the scientific underpinnings of pelagicMPAeffects, spatio-temporal patterns of IndianOcean tunacatch, bycatch andfishmovements, and the consequences of these for the efficacy of spatial management for Indian Ocean tropical tuna fisheries. The tropical Indian Ocean is char-acterized by strong environmental fluctuations, regular seasonal variability in catch, large observed tuna displacement distances, relatively uniform catch-per-unit-effort and bycatch rates over space, and high fisher mobility, all of which suggest significant variability and move-ment in tropical tuna fisheries that are simply not well adapted to static spatial closures. One possible exception to this overall conclusion would be a large time/area closure east of Somalia. If closed for a significant fraction of the year it could reduce purse-seine bycatch and juvenile tuna catch. Dynamic closures following fishmigratory patterns are possible, butmore focused information on fishmovements will be needed for effective implementation. Fortunately, several recent improvements in conventional fisherymanagement and reporting wil