Indian fishermen hauled ashore only half of the country's marine potential, estimated to be 4 million tonnes per annum. So, the question before the department of ocean development was how best the fishermen can make use of the potential fishing zone (PFZ) maps sent by remote sensing satellites.PFZ maps - generated by the National Remote Sensing agency, Hyderabad - are sent to directors of fisheries, who communicate them to fishermen. Shoals of fish located by the satellites are marked out on a map, and since fish shoals remain in the same place for at least two days, they use a mariner's compass to reach the location.