台灣離島旅遊對硨磲貝的衝擊

本研究目的在探討台灣離島觀光旅遊是否會對硨磲貝野外族群造成影響，野外調查研究於2019年10月至2021年5月期間，以水肺潛水方式在澎湖七美望安、綠島及南沙太平島沿岸共33個測站進行硨磲貝的現況調查，記錄種類、數量及殼長大小等資料。同時蒐集澎湖群島與綠島海域歷年來的硨磲貝調查報告，以及旅遊人口數量資料以進行後續比對與分析。台灣過去硨磲貝種類有7種，本研究現況調查結果顯示，三海域共記錄到5種硨磲貝，分別為菱硨磲（Hippopus hippopus）、長硨磲（Tridacna maxima）、諾亞硨磲（T. noae）、鱗硨磲（T. squamosa）和圓硨磲（T. crocea）。數量方面，於澎湖七美望安海域記錄到53顆硨磲貝，平均密度為0.27顆/100 m2；綠島記錄到194顆，密度為2.43顆/100 m2，太平島海域記錄到259顆，密度為3.7顆/100 m2。澎湖七美望安海域硨磲貝密度顯著低於綠島與太平島海域，且遠低於其他研究於台灣鄰近海域所調查之結果。根據先前文獻顯示，過低的族群密度可能影響澎湖七美望安海域硨磲貝的繁殖成功率。然而綠島海域的硨磲貝平均殼長卻顯著低於其他海域，原因可能與綠島地區所設立之硨磲貝禁採之法規有關，只保育15 cm以下幼貝，卻可以採集成貝有關聯。分析結果也表明不同區域隨著離島旅遊人數下降，該地區的硨磲貝密度似乎有上升的趨勢，與本研究預期相符。綜合本研究之結果，建議將硨磲貝科種類即早列入台灣野生動物保育名錄，加強宣導硨磲貝在珊瑚礁生態系的重要性與保育觀念，以及強化執法力道保護台灣近岸現存的硨磲貝資源，甚至可以透過種苗培育和放流來補充野外的族群量。

關鍵字

硨磲貝密度；硨磲貝科；保育；種苗復育；種苗放流

並列摘要

In order to investigate whether the offshore islands tourism in Taiwan could have impacts on population of giant clams, several field survey were conducted by SCUBA diving to assess the species composition, abundance and shell length of giant clams in 33 stations around Penghu Qimei, Wangan, Green Island and Nansha Taiping Island water from October 2019 to May 2021, meanwhile, this study collected the historical survey reports of giant clams and tourist data in Penghu and Green Island for further comparison and analysis. In the past, there were 7 species of giant clams in Taiwan; 5 of them were found during the field survey, i.e., Hippopus hippopus, Tridacna maxima, T. noae, T. squamosa and T. crocea. In terms of giant clam abundance, we observed 53 clams in Penghu Qimei and Wangan, with the density of 0.27 clam/100 m2; 194 clams in Green Island, with the density of 2.43 clam/100 m2; 259 clams observed in Nansha Taiping Island, with the density of 3.7 clam/100 m2. The density assessed in Penghu Qimei and Wangan was significantly lower than those of Green Island and Nansha Taiping Island, even far below the density assessed in nearby area by other studies. Previous study stated that the low giant clams density may affect the fertilization probability or reproduction rate of giant clams population of Penghu Qimei and Wangan. However, the average size class of giant clams around Green Island were significantly smaller than the other area, this may attribute to the local giant clam harvesting regulations in Green Island, that is, protecting the juvenile clams whose shell length smaller than 15 cm but not prohibiting from collecting adult clams. The analysis of this study also showed that the density of giant clams seemed to have an increase trend as the number of tourists from offshore islands declined in different regions, which was in line with the expectations of this study. Based on evidence of this study, it is recommended that all the species of family Tridacnine should be listed in Catalogue of Taiwan Wildlife Protected Species as soon as possible, further to reinforce the advocacy about the importance of giant clams to the coral reefs ecosystem and about giant clams conservation cogitation and also strengthen the law enforcement in order to protect the remaining clam resources around Taiwan, even to replenish the wild population through clam restoration and seedling releasing.