The potential competition for preys between Sousa chinensis and the coastal fisheries of western Taiwan
Date Issued
2011
Date
2011
Author(s)
Ko, Meng-Chen
Abstract
The conflict between fisheries and cetaceans has been a universal issue in conservation. The population of Chinese white dolphins (Sousa chinensis) living off the western coast of Taiwan is facing survival challenges due to its small population size, as well as many other anthropogenic impacts including heavy coastal fishing activities. In this study, we investigated (1) the qualitative information from fishermen interviews, (2) the potential overlap in target prey (Pianka’s niche overlap index) between dolphins and fisheries, and (3) the long term trend of prey abundance for Chinese white dolphins, from the aspect of coastal gillnet fisheries. According to 127 fishermen’s interviews from May 2010 to April 2011, we found that 54% of the fishing operation range overlapped with the major habitat of Chinese white dolphins (less than 3 nm off shore or 30 meters water depth). Within this range, the main fishing method was the gillnet (94%). Most of fishermen (91%) said the dolphins had neutral or negative responses toward fishing boats and about half of the fishermen (55%) claimed that dolphin occurrence did not decrease their catches. Many fishermen (42%) claimed the fishery resources had declined over the past 10 years, and 49% of fishermen thought the industrial pollution and illegally trawling within three nautical miles were the main reasons that caused the decline. Most fishermen (72%) said the frequency of occurrence of Chinese white dolphins remain consistent over the years. According to analysis on the data from the 2009 Fishery Yearbook, we found that coastal gillnets and pole and lines showed higher overlap indexes (> 0.80), and the local variation in gillnets showed that Miaoli and Changhwa had higher and more stable overlap indexes than other areas. In addition, both bottom trawls and gillnets showed that Miaoli had a higher resource overlap in major prey (> 0.90). All in all, fewer catch compositions of coastal gillnets were recorded before 1990–1991, but the catch quantities were higher back then; this might indicate that fishermen changed their target preys to smaller fish. In addition, coastal gillnet catches from Fishery Yearbooks showed that Miaoli County had higher catch quantities than other counties. Although fishermen did not express strong averse attitudes toward Chinese white dolphins, half of the fishermen complained about the indirect interference caused by dolphins during operations. Nevertheless, the fish resource has been decreasing yearly, whether referring to fishermen interviews or long term fish logging data. Urgent regulation revisions are required to find a balance between gillnet fisheries and Chinese white dolphins.
Subjects
Chinese white dolphin
fisheries conflicts
resource overlap
fishermen interviews
fishery data bank
Type
thesis
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