There are a few taxis-brousses on Île Sainte Marie. A ride north along the road from Ambodifotatra to the northern tip is Ar15,000 (two hours). Private taxis are more common, though disproportionately expensive. They usually hang out by the harbour in Ambodifotatra. You have a reasonable chance of flagging one down along the airport road. Tariffs are fixed and posted at the tourist office and hotel receptions: it’s Ar20,000 to the airport, Ar35,000 to Loukintsy.