利用雷射照相技術及體色分級判斷台灣東部海域瑞氏海豚之年齡與性別

Abstract

野生動物的型態學及生物學資料是了解其族群動態、生活史(成長)、族群結構的重要參數。生活在海洋的鯨豚因不易接近或捉放，這類型資料大多來自於擱淺或誤捕的死亡個體。為取得野生族群的即時的生態資料，利用鯨豚的型態及體表顏色變異來進行推估型態學及生活史相關資訊已成另類方法。瑞氏海豚(Grampus griseus)是台灣東岸常見的鯨豚種類之一，其體表逐漸累積的白色疤痕可視為判斷年齡的指標，然而尚未被系統化的數據證實。本研究嘗試利用雷射照相技術(Laser-metrics)操作來測量台灣東部海域野生瑞氏海豚的背鰭大小進而推估體長（第二章）。另外，並嘗試以數值量化瑞氏海豚之背鰭白色疤痕程度，來探索白色疤痕程度與性別、年齡及體長的關係（第三章）。研究結果顯示，雷射光點距離的估算會受與目標物距離、目標之垂直角度差異及投射目標之位置的不同而有顯著差異。量測長度的最小誤差百分比(%Mean error)是在目標物垂直角度改變20度以內，其值小於1%。利用54隻擱淺/混獲死亡瑞氏海豚製作背鰭型質與體長之相關曲線。透過雷射技術蒐集的15隻野生個體，同個體推估的背鰭寬與高最大差值分別為0.5至4.9公分，及0.2至3.5公分。另外，體長推估值在方程式內與方程式間的最大差值分別為42.9及49.5公分。疤痕程度量化方面，顯示疤痕程度之多寡較適合用於推估年齡，並初步顯示有雌性體色較黑(79%)，雄性體色較白(86%)之趨勢，但仍需要更多雄性樣本以支持性別二型性。本研究方法未來能應用於推估野生鯨豚之基本型態學資料，尤其是本研究的目標物種-瑞氏海豚。

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.