The turbid yellow-brown waters of the Strait of Malacca lap up against the mudflats of the east coast of Sumatra in a blur of earth and sea, with the two almost indistinguishable from the vantage point of our small hired boat. Beyond the shore, mangrove forests stretch up and down the coast for as far as our eyes can see, though not far behind the mangroves, are the oil palm plantations.