Research Paper

Rapid changes in environmental factors could affect the distribution of Taiwanese humpback dolphins (Sousa chinensis taiwanensis) off the coast of Yunlin, Taiwan

Chi-Hung Lin, Lien-Siang Chou

Published on: 18 April 2021

Page: 184 - 192

DOI: 10.6165/tai.2021.66.184


A small population of fewer than 80 Sousa chinensis taiwanensis inhabit the western coast of Taiwan. To explore the relationship between environmental factors (water depth, temperature, salinity, turbidity, and pH) and distribution patterns of dolphins, this study was conducted in Yunlin, which has been one of the population’s core areas despite being subject to heavy industrial development. 242 day-surveys were conducted along four parallel transect lines between 2008 to 2018, during which sightings of 274 dolphin groups of this species were recorded. The standardized dolphin sighting rate (groups/100km) was used as an index for comparison. Contrasting to the roughly steady distribution in east-west gradient, the north-south gradient exhibited substantial and varied temporospatial changes among three sections (north, middle, and south) off the coast of Yunlin and among three periods. Dolphin sighting rate during spring-summer was significantly higher than that during Autumn-winter. Taking data from inshore surveys for long term comparison, we found that sighting rates at the middle section remained high and relatively stable (around 2-4.6), whereas the rates in the other two sections exhibited opposite trend with high fluctuations, e.g. drastically fluctuated between 0-3.4 in the northern section, while from 3.36 declined to 0.35 in the southern section. We further discovered that rapid changes in three environmental factors, including turbidity, pH, water depth and construction disturbance, could play key roles on dolphin distribution patterns, and can serve as good indicators for habitat suitability for this vulnerable subspecies.

Keyword: distribution, environmental factors, pH, turbidity, Sousa chinensis taiwanensis, Taiwanese humpback dolphins

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