Distribution Prediction and Ranging Pattern of Indo-Pacific Humpback Dolphins (Sousa chinensis) in Taiwan
Date Issued
2011
Date
2011
Author(s)
Yeh, Chih-Huey
Abstract
Indo-Pacific humpback dolphins (hereafter Chinese White dolphins) inhabit in shallow coastal waters, almost within 25 m depth. Due to the proximity to areas of human activity, Chinese white dolphins have encountered tremendous threats caused by many anthropogenic activities. In Taiwan, the population size is no more than 100 individuals and the population has been listed as “Critically Endangered” (CR) by IUCN since 2008. With a view to providing practical information to conservation management, the purpose of this research is to identify critical regions within habitat, including finding key factors that influenced the distribution pattern in population level and investigating differences in ranging patterns among age classes and breeding statuses in individual level as described in the following two parts.
In the first part, habitat modeling techniques were applied to build prediction models. The environmental raster data within 2006-2010 survey coverage and occurrence of dolphins including sighting and tracking positions (n=2289) were input to ArcGIS 9. Three models were applied, including Generalized Additive Models (GAMs), MaxEnt (Maximum Entropy Modeling) and GARP (Genetic Algorithm for Rule-set Prediction). The appropriate models were selected, containing key factors including maximum water depth, standard deviation water depth, standard deviation salinity and distance to shore. An ensemble models was generated by overlaying these three models to obtain map of suitable areas for Chinese white dolphins in Taiwan. Predicted suitable areas were limited inshore, with the probability of occurrence was higher in coastal area of southern Miaoli County to Dadu River and coastal area of Yunlin County to Waisanding Sandbar.
In the second part, individual ranging pattern was investigated and comparisons were made between age classes and breeding statuses. For the range estimate, 57 individuals with more than ten sightings were selected from 71 identified dolphins. Minimum Convex Polygon (MCP) method and latitudinal length were the two estimators for the range size. The average MCP size was 192.6 km2, and the average latitudinal length was 69.1km. Old individuals tended to have smaller ranges despite non-significant result.
As for site fidelity, individuals were divided into residents and transients to north and south region respectively based on cluster analysis in range use, but the monthly sighting rate didn’t show clear stratification. Sighting rates of transients were close to those of residents in southern region, where most individuals tended to utilize as intensively as residents, but visited other areas on occasion. On the other hand, many dolphins tended to be either residents or transients that visited other areas frequently. In addition, females who have been observed calving have significantly higher sighting rates.
To sum up, the result of distribution prediction, ranging patterns and site fidelity revealed two suitable areas that were occupied by residents. Moreover, dolphins who used to be mothers used these regions more frequently. Specific research in habitat use should be carried out in future to obtain detailed information about habitat preference and possible functions of regions within habitat.
Subjects
Chinese white dolphins
distribution pattern
GAMs
MaxEnt
GARP
ranging pattern
site fidelity
Type
thesis
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