An industrial purse seine fishery for canning-grade tropical tunas began in the Indian Ocean in the early 1980s, when French and Spanish fishing firms moved vessels into the region from the tropical eastern Atlantic in search of new fishing grounds. There is still exchange of vessels between these two oceans, orchestrated at the level of the firm and based on perceived relative fishing opportunity in either ocean (Fonteneau, personal communication). Early operations were based in Port Victoria, Seychelles, which has remained the primary port of call for landing and transshipping catch, refuelling and resupplying and exchanging crew [38]. The European-owned distant water fishing fleet continues to dominate the fishery in the western Indian Ocean and have established a firm commercial foothold around Seychelles, Mauritius and Mayotte. Asian purse seine fleets are constrained mainly to the eastern Indian Ocean due to proximity to landing sites (e.g. Thailand) despite purse seine fishing generally being much poorer in that region due primarily to the deeper thermocline, which reduces the vulnerability of tunas to surface gears [12]. We did not attempt to anticipate the expansion of the Asian purse seine fleet into the western Indian Ocean in our scenarios as we had very little basis to justify our assumptions of how this would happen.