Two main corridors
Most dolphins are either gray or black in color, but as the Indo-Pacific humpback matures it turns either white or pink, with dark speckles, and features a camel-like hump under its dorsal fin. Its unique appearance sets it apart from all other types of dolphins.
After four years of surveying, Chou has found that Taiwan's humpback dolphins range from the Miaoli County fishing port of Longfeng in the north to Tainan County's Jiangjun fishing port in the south, and spend their time in water averaging 7.6 meters deep and three kilometers from shore. Their range is thus a narrow band extending some 200 kilometers from north to south, including two main "hotspots" for hunting and social activity. One hotspot extends from southern Miaoli to northern Changhua, while the other runs from Yunlin to the Waisanding barrier island at the border of Yunlin and Chiayi counties (Fig 1).
Says Chou, "We've conducted 70 surveys per year in recent years and taken a total of over 40,000 photos, which we use to identify individual dolphins. On that basis, we estimate a population of 84 to 86 humpback dolphins on the west coast."
Chou explains that the standard international practice in surveying small dolphin populations is to take a photo whenever one is spotted and note the place and time of the sighting and the dolphin's behavior at the time. The photos are then used to identify individuals and analyze how they behave in different areas.
Having compared the overall sighting rate for Taiwan's humpback dolphins (three populations per 100 kilometers) and the sighting rate along the Changhua coast (0.46 populations per 100 kilometers), and based on analysis of Changhua coastal behavior records, Chou has concluded that the humpback dolphins off the Changhua coast are mostly just passing through. In the waters near the proposed Kuokuang Petrochemical complex, she has only once spotted a dolphin feeding.
"Our last two years of surveys indicate that most of the dolphins stay generally put in one of two 'hotspots,' one north and one south, while only about 30% of them, or some 25 dolphins, roam north and south. Southern Changhua is an important passageway for them."
Tsai Chia-yang, director of Changhua Coast Conservation Action and a long-term observer of the Changhua coastal ecology, is less than sold on the idea that dolphins are mere passersby off the southern part of the Changhua coast (site of the proposed Kuokuang Petrochemical complex). Tsai points out that the intertidal zone is fully six kilometers wide at this part of the coast, and it is quite possible that humpback dolphins may take advantage of the tides to herd fish into the shallows and feed on them, which wouldn't be observable to someone on a boat six or seven kilometers away. Moreover, the mouth of the Zhuoshui River is rich in nutrient salts, and ought by all rights to be an ideal feeding ground for the humpback dolphins. Further study is needed to determine whether humpback dolphins feed and live at the mouth of the Zhuoshui River.
Projected site of Kuokuang Petrochemical plant