Using Laser-metric and color quantification to estimate age and sex of Risso’s dolphin (Grampus griseus) in eastern Taiwanese waters.
Date Issued
2013
Date
2013
Author(s)
Au, Ka-Yuan
Abstract
Morphology and biological information including age and sex of wild animals is important to know population dynamic, ecological and life history issue of the animals. The data of cetaceans are mostly from stranded or by-caught carcasses due to the difficulty of capturing and approaching the individuals. However, these data from free-ranging cetaceans are important to reflect ecological issue in time. The methods for speculating the life history information from the animal’s morphology and color patterns provide an alternative. Risso’s dolphins (Grampus griseus) are one of the most common species in Taiwanese waters. The accumulated white scars could be a potential age indicator and could be seen to reflect sexual dimorphism. But, these have not been proven systematically. In this research, a laser-metrics device was adopted to measure dorsal fin base length (DBL), dorsal fin height (DH), and the total body length (TBL) of wild Risso’s dolphins in Taiwan (see Chapter 2). Furthermore, with the quantitative scar-color pattern, the relationships between the color, age, sex and TBL (see Chapter 3) were been explored. Results showed that the distance between laser dots (DLD) varied significantly with the distance from target, the vertical angles of target, and the shooting positions of target. The mean error in length is below 1% when the vertical angle of target was under 20°. Data of 54 stranded/by-caught individuals were used to construct the correlation between dorsal fin morphology and TBL. Results of 15 sighted individuals in the wild shows the variations for estimated DBL and DH ranged from 0.5cm to 4.9cm and 0.2cm to 3.5cm, respectively; the maximum variations for estimated TBL were 42.9cm and 49.5cm within and between regressions, respectively. Results of quantitative scar-color patterns showed that it was more appropriate to estimate age rather than estimate TBL. Furthermore, there was potential trend on sexual dimorphic coloration of Risso’s dolphins, with 79% of the females were blackish and 86% of the males were whitish. This trend needed to been confirmed with more samples, especially male samples. This research can be applied to advance the morphological information of wild cetaceans, and the Risso’s dolphins in particular.
Subjects
瑞氏海豚(Risso’s dolphins)
雷射照相技術
體色
背鰭型態
體長
性別
Type
thesis
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