浙江东部牛蛙的自然种群及潜在危害

牛蛙(Rana catesbeiana)的入侵已成为一些本地两栖类种群数量下降或灭绝的主要因素之一。1959年牛蛙被引入中国大陆，但直到1990年才开始在国内大范围饲养。牛蛙的自然种群在国内一直未见报道。我们于2003年9—11月调查了浙江省东部5区3县的牛蛙种群，发现在岱山、秀山、六横及佛渡岛上有牛蛙分布，共捕获23只牛蛙，包括4只成年个体，18个亚成体和1只蝌蚪。于2004年1月和2月在岱山捕获28只蝌蚪。结果显示：(1)牛蛙的蝌蚪能在当地越冬成活，说明牛蛙在上述4岛成功地建立了自然种群；(2)牛蛙主要分布于水库、池塘和溪流，牛蛙的生境与6种当地蛙有部分重叠；(3)养殖时管理不善造成的牛蛙逃逸，以及牛蛙价格过低而导致养殖户将牛蛙弃置野外可能是牛蛙入侵的主要原因。牛蛙对当地蛙的潜在威胁很大，开展牛蛙的分布、食性和种群动态研究是当务之急。

Natural populations of bullfrog (Rana catesbeiana) and their potential threat in the east of Zhejiang Province

The invasion of bullfrog (Rana catesbeiana) has become one of the main factors leading to population decline and extinction of some native amphibians. Although bullfrogs were introduced into mainland China in 1959, they were not wildly raised until 1990. Natural populations of the species in China have never been reported. We investigated bullfrogs in Zhoushan Archipelago and Ningbo area in the east of Zhejiang Province, China. Bullfrogs were found on Xiushan, Liuheng, Daishan and Fodu island. A total of 23 individuals of bullfrogs were captured on these islands from Sep. to Nov. 2003, including 4 adults, 18 juveniles and 1 tadpole. Twenty-eight tadpoles of bullfrogs were captured from Daishan between Jan. and Feb. 2004. This clearly shows that tadpoles of bullfrogs can over-winter and bullfrogs have successfully established their populations in the wild on these islands. Bullfrogs were mainly found in reservoirs, ponds and rivers, and share habitats with 6 indigenous frog species in this area. Escape from farms and release of live bullfrogs abandoned by bullfrog farmers due to falling profits are the main sources of the bullfrog invasion. There will be a great potential threat of bullfrogs to indigenous amphibians in the area. There is an urgent need for greater understanding of the diet, distribution and population dynamics of the bullfrog in China.