An assessment is made of the Indian Ocean yellowfin tuna (Thunnus albacares ) stock, using data from a sport fishery in the Pemba Channel off the Kenya-Tanzania border in conjunction with commercial catch figures for theIndian Ocean. The long-term maximum sustainable yield is estimated to be around 113,000 tons/annum; dataindicate that catch levels of yellowfin tuna in the Indian Ocean exceed the MSY by a dangerous amount.