The smooth-coated otter (SMO) and small-clawed otter (ASCO) are both globally threatened species important for the stability of riverine ecosystems. However, their current distribution status in southeast Asia is still unclear and thus difficult for conservation management planning. This project aims to (1) assess their current distribution status in coastal areas of southern Thailand, (2) evaluate distribution change and the factors influencing the changes, and (3) identify hotspot areas for otter conservation. We conducted surveys using both local fishermen interviews and field surveys (direct sighting, track and sign, camera-trap). During the first six months (July-December 2016), surveys covered 29 grids (725 km2). Each grid contained at least 10% mangrove forest. In total, 125 line-transects were surveyed and 123 camera-traps were set (2,165 trap-nights). Based on interview (n = 50), most (50%) local fishermen believe that the populations of both otter species have declined during the past 30 years due to hunting, persecution, being kept as pets and prey depletion, respectively. Combining all survey methods, SMO appears to occupy two times larger area than ASCO (21 vs 9 grids). From camera-trap data, SMO has occupancy estimate at 72% (95%CI = 33-93%), with detection probability at 25% (95%CI = 14-40%). Camera-trapping is the most suitable method for confirming species presence in these habitats. Persecution and opportunistic hunting remain a threat, and thus require more attention.