PORPOISES in the eastern waters of Hong Kong could be losing their habitat to dredging, much as their cousins, the Chinese White Dolphin, have lost ground in the western waters. Jo Ruxton of the World Wide Fund for Nature (WWF) said the finless porpoises were believed to inhabit the southeast waters, particularly around the Po Toi Islands where dredging has been going on for several months. The porpoises have no dorsal fin and no beak so their faces resemble seals. They are very fat, about 1.8 metres long and dark grey to black, making them difficult to spot. They tend to travel in groups of five. About 10 sightings have been reported to the WWF this year. ''They are still around but they are threatened because the food chain is threatened.'' Ms Ruxton, who used to dive near the Po Toi Islands but has stopped, said the area previously contained many hard and soft corals and small animals which served as food for larger fish. But sedimentation kicked up by dredgers was so bad that visibility was almost zero and the few soft corals and sea fans still alive could be seen only at very low depths, she said. ''We've had three or four dead porpoises washed up this year. They are another group of cetaceans [to which dolphins also belong] likely to be in trouble,'' she said. The dolphins, which are pink, white or grey and have been seen fairly frequently, are feared to have lost feeding grounds to dredging and dumping north of Lantau. The Government recently awarded $2 million for a three-year study of them. The Po Tois were gazetted as a dredging site in 1991. The WWF were unaware of the plan and failed to raise objections within the statutory time limit. Work began this year. Legislator Christine Loh Kung-wai has suggested there be a voluntary 500-metre buffer zone around sensitive sites near dredging areas so corals and other underwater communities could be protected. Ms Ruxton supported the call. The plight of Hong Kong's dolphins and porpoises was raised in the European Parliament last week when a member put forward a motion that should come up for debate within a month. Paul Howell, who represents the English county of Norfolk, has taken on the dolphin and porpoise cause following requests from the local World Wide Fund for Nature office.