Existing laws in Hong Kong and mainland China make it illegal to harvest, disturb, or harass white dolphins, Porter said. Dolphin habitat areas are also protected.
But those statutory safeguards have done little to shield the shallow-water mammals from significant and harmful effects of water pollution, she added.
The Pearl River watershed includes an area containing one-eighth of mainland China's population. It spills agricultural runoff, industrial chemicals, and other pollutants into the muddy estuary favored by the dolphins. Coastal cities add to the problem, dumping factory and household waste into the waterway.
Hong Kong alone is said in recent years to have dumped some 120 million gallons (450,000 cubic meters) of semi-processed sewage a day into its harbors.
The effluent could fill 200 Olympic-size swimming pools.
Despite their name, white dolphinsas they are known locally in Hong Kong and mainland Chinaappear bubble-gum pink.
They belong to the Indo-Pacific humpback dolphin (Sousa chinensis) species, which inhabits waters spanning western Africa, India, and Australia.
Along the West African coast, the dolphins appear black and sport large, namesake humps.
In Indian waters the marine mammals display spotted skin and grow smaller humps. In Australia the animals are gray.
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES