Conservation implications of the genetic structure and habitat use of green turtles (Chelonia mydas) in the South China Region and baseline contaminant levels in green turtles and Burmese pythons (Python bivittatus)

Abstract

Sea turtles and Burmese pythons (Python bivittatus) are globally endangered and vulnerable species. Their survival is at risk as they face daily anthropogenic threats of all kinds. Current research efforts on sea turtles in South China mainly focus on captivity and husbandry, hematology and blood chemistry, while the Burmese python has been studied very little in its native range. This situation creates a pressing need for comprehensive scientific research on these free-ranging species. The primary objective of this study is to generate essential baseline biological and ecological information for development of scientifically-sound conservation and management measures for green turtles (Chelonia mydas) in South China, including Hong Kong, Guangdong and Taiwan, and for Burmese pythons in Hong Kong. The study consisted of three major parts: (i) Genetic stock composition of green turtles, (ii) Habitat use and movement of green turtles and (iii) Levels of contaminants in green turtles and Burmese pythons. Findings of studies on genetic structure and habitat use help identify connectivity between nesting and foraging grounds of green turtles for spatial management. Specimen collection was conducted in collaboration with the Gangkou National Sea Turtle Nature Reserve of mainland China, and the National Museum of Marine Biology and Aquarium and the Penghu Marine Biology Research Centre of Taiwan. Blood and skin samples of nesting, by-catch and stranded green turtles in South China were genetically analysed in collaboration with the Southwest Fisheries Science Center of the United States National Oceanic and Atmospheric Administration (NOAA). Mixed stock analysis based on the 760 bp mitochondrial (mt) DNA control regions of the specimens (n=110) revealed that major source rookeries contributing to the foraging aggregations in South China were Peninsular Malaysia, Yap in the Federated States of Micronesia, the Turtle Islands in the Philippines and Malaysia, the central Ryukyu, Yaeyama and Ogasawara islands of Japan, and Wan-an Island of Taiwan. Habitat use and oceanic movement of green turtles were determined by satellite tracking (n=34) coupled with home range analysis, and analysis of a database of live and stranded sea turtles. Foraging grounds of several sea turtle species (green turtle, hawksbill turtle Eretmochelys imbricata and loggerhead Caretta caretta) were mainly distributed along the coasts of Hainan Island and Leizhou Peninsula of Guangdong Province, mainland China, as well as of Taiwan and the Philippines, and outlying islands in the South China Sea and East China Sea. Activity hotspots and migratory corridors of green turtles, in particular nesting green turtles, in South China were identified. Coastal waters near Wanning City of Hainan Island, eastern Leizhou Peninsula, Iriomote-jima and Ishigaki-shima of the Ryukyu Islands of Japan and Dao Bach Long Vi of Vietnam serve as foraging grounds for nesting green turtles from different origins in South China. Moreover, the Paracel (Xisha) and Pratas (Dongsha) Islands in the South China Sea, Huidong Gangkou and its vicinity, Liouciou Island and Penghu Island of Taiwan contain both nesting sites and foraging grounds for green turtles. These sites that are associated with the migratory corridors, in particular Hainan Island, eastern Leizhou Peninsula and Liouciou Island, currently lack conservation plans for sea turtles, and therefore should be given higher priority for habitat and species protection. In the third part of the study, scute, liver and muscle tissues of stranded green turtles in South China and liver tissues of Burmese pythons collected in Hong Kong were analysed for the levels of 17 trace elements including As, Ag, Ba, Cd, Cu, Cr, Co, Cs, Fe, Mn, Pb, Ni, Se, Sr, Tl, V and Zn, methylmercury (MeHg) and polybrominated diphenyl ethers (PBDEs). This study revealed the first baseline tissue burdens of PBDEs and MeHg in green turtles in South China. It also updates the baseline levels of 17 trace elements in green turtle tissues based on a larger sample size over a broader geographical coverage than previous reports, and is the first study to report baseline levels for 17 trace elements in Burmese pythons in their native range. Relative to other studies reported over 10 years ago in the same region, 10-fold higher levels of the toxic elements Pb, Ba, V and Tl and 40-fold greater Cd levels were measured. PBDE levels measured in liver tissues of green turtles in South China were 27-fold and 50-fold greater than those reported in Australia and Japan. These very high pollutant levels warrant further investigations of their potential toxicological risks to green turtles in South China and their source rookeries spanning Southeast Asia to Micronesia in the western Pacific. The measured trace element levels in Burmese pythons in this study were generally within the range observed in other snake species elsewhere, indicating hat trace element pollution is unlikely an imminent threat to Burmese pythons in Hong Kong. The outcomes of the above studies, combined with cultural considerations, serve as a foundation for recommendations for conservation and management strategies for reen turtles in South China. Research priorities should be given to expand themonitoring of potential and existing nesting sites, as well as tracking and/or genetic tudies on nesting green turtles to advance our knowledge of migratory corridors and habitat connectivity. Studies on quantification and mitigation of threats, namely direct take and bycatch of sea turtles, at activity hotspots should also be pursued. In addition to habitat protection, conservation actions compatible with local cultural practices and involvement, such as incorporating proper religious release, should also be explored. Considering the broad geographic coverage and connectivity of habitats used by green turtles, it is necessary to promote networking and cooperation among stakeholders for regional collaboration in habitat protection and threat mitigation to conserve green turtles more effectively in the South China Region. 海龜及緬甸蠎蛇(Python bivittatus)是全球瀕危的物種，牠們每天面對著各色各樣的人為威脅。南中國海龜的研究集中在人工飼養、血液學及血液生化學的範疇，而有關緬甸蠎蛇在其原生棲息地的研究則缺少，因此我們必須對這些野外物種進行全面的科學研究。本研究的主要目的是為南中國(包括香港、廣東及台灣)綠海龜(Chelonia mydas)及香港的緬甸蠎蛇制定以科學基礎的保育及管理措施，得到針對這些物種的重要而基本的生態資料。本研究包括三部份: (一) 綠海龜的基因結構; (二) 綠海龜的生境分布及活動動向; 及(三) 綠海龜與緬甸蠎蛇體內的基線污染物量。 綠海龜的基因結構及生境分布可找出產卵地與覓食地的連繫，這有助確定綠蠵龜群種相互的關聯，從而為地域層面上保育海龜的合作定下科學性的基礎。本研究作者與中國惠東港口海龜國家級自然保護區、台灣國立海洋生物博物館及澎湖海洋生物研究中心合作，為南中國混捕或擱淺的綠海龜採樣進行研究。有關綠海龜基因結構的研究，本研究作者與Southwest Fisheries Science Center of the United States National Oceanic and Atmospheric Administration 合作分析南中國內產卵、混捕或擱淺綠海龜血液及皮膚組織樣本(n=110)中mtDNA control region 的單倍體頻率(haplotype frequency)，透過 Mixed Stock Analysis與其他地區群種的比較及統計，顯示南中國地區的覓食綠海龜與馬來西亞、菲律賓(包括馬菲的Turtle Islands)、密克羅尼西亞聯邦的雅浦州、日本的中央琉球、八重山和小笠原群島，及台灣望安島地區的繁殖種群有連繫。通過衛星追蹤(n=34)、活動範圍分析(home range analysis)及分析活體和擱淺海龜的個案，加上以前的研究，指出綠海龜、玳瑁(Eretmochelys imbricata)及赤蠵龜(Caretta caretta)的覓食地集中分布於中國海南島、廣東雷州半島及台灣、菲律賓沿岸，以至於南中國海的島嶼與東海一帶。本研究也確定綠海龜(尤其是產卵母龜)於南中國的活動熱點及遷移路線範圍。中國海南島萬寧市、東雷州半島、日本琉球的西表島和石垣島，及越南白龍尾島的沿海一帶均是源自南中國不同產卵地的綠海龜的覓食地。此外，南海的西沙及東沙群島、惠東港口一帶、台灣小琉球島及澎湖群島具備綠海龜的產卵地及覓食地。這些地點位於綠海龜遷移路線上，須要加強保護海龜及其生境; 尤其是現時缺乏全面保育海龜措施的海南島、東雷州半島及台灣小琉球島。 在本研究的第三部分環境污染物的風險評估，共取得南中國擱淺或混捕綠蠵龜的背甲角質層(n=86)、肝組織(n=14)和肌肉組織(n=11)及香港緬甸蠎蛇的肝組織(n=20)，用作測量17種微量元素(包括砷As、銀Ag、鋇Ba、鎘Cd、銅Cu、鉻Cr、鈷Co、銫Cs、鐵Fe、錳Mn、鉛Pb、鎳Ni、硒Se、鍶Sr、鉈Tl、釩V和鋅Zn)、甲基汞 (MeHg)及持久性有機污染物中多溴聯苯醚Polybrominated diphenyl ethers (PBDEs)。本研究是首次報告南中國綠海龜體內的PBDEs及MeHg量，也根據較以前研究更大的樣本數量及地理範圍更新綠海龜體內的17種微量元素。是次研究亦首次報告原生棲息地的緬甸蠎蛇體內的17種微量元素。結果發現相對於10年前相同地區的數據，南中國地區的覓食綠蠵龜體內的鉛(Pb)、鋇(Ba)、釩(V)、鉈(Tl)高出10倍，鎘(Cd)高出40倍。南中國的綠蠵龜肝組織的PBDEs量較日本及澳洲的研究數據分別高27倍及50倍。綜合而言，將來須要對這些較高污染物量對南中國綠蠵龜群種及其連繫的繁殖種群的生態毒理學影響進行更深入的評估研究。本研究蠎蛇體內的微量元素量與其他地區蛇類的相關研究數據相近，指出重金屬污染並未對香港蠎蛇造成明顯威脅。 綜合是次研究的結果及本土文化的考慮，可為制定針對南中海綠海龜保育及管理措施奠定基礎。未來的研究重點須聚焦於現存及潛在產卵地的監測，進行更多對產卵母龜的追蹤及基因結構以深化遷移路線和生境聯繫方面的知識，以及針對量化與緩和對綠海龜在其活動熱點的威脅，包括捕殺及混捕。在保護生境以外，亦可嘗試推行與本土文化相容的保育行動，如正確地進行宗教野放等。正因為綠海龜廣大的活動範圍及生境聯繫，我們須聯合各地域各方利益相關者的力量及合作，使之更有效地保護南中國綠海龜生境及緩和牠們所面對的威脅。

Date of Award	2 Oct 2015
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Margaret Burkhardt MURPHY (Supervisor)