Yadav Ramesh Kumar, Lamichhane Saneer, Thanet Dol Raj, Rayamajhi Trishna, Bhattarai Santosh, Bashyal Ashish, Lamichhane Babu Ram
Department of National Parks and Wildlife Conservation Kanchenjunga Conservation Area Tapethok Nepal.
National Trust for Nature Conservation Ratnanagar, Chitwan Nepal.
Ecol Evol. 2022 Oct 18;12(10):e9425. doi: 10.1002/ece3.9425. eCollection 2022 Oct.
Gharial () is a Critically Endangered crocodilian species whose abundance in Nepalese rivers is low due to the threat they face. We estimated gharial abundance in the Rapti River, one of the major rivers in Chitwan National Park (CNP) holding the largest numbers of gharials in Nepal. The Rapti River, running across the CNP, was divided into 18 segments, each measuring ~4 km, and gharials were counted directly with three replicates. Gharial count data were analyzed using an N-mixture model (negative binomial) and the overall occupancy of gharials was estimated using a single season occupancy model. Covariate effects were also investigated on gharial abundance. Our findings revealed that the Rapti River is home to 150 gharials (119-181), with a mean abundance of 8.3 (SD = 3.45) across each segment. The presence of humans and square of Rapti River depth were the significant covariates that had a negative and positive impact on gharial abundance, respectively. Similarly, the number of sandbank present influenced the detection probability of gharials. Our study shows that gharial population estimation can be improved using the N-mixture model. The overall gharial occupancy estimated using single season occupancy model was 0.84 (SD = 0.08), with a detection probability of 0.37 (SD = 0.02). The management authority should concentrate on segments to minimize human disturbance (e.g., fishing, washing clothes, extraction of riverbed materials). If the gharial population in this river declines, their population in central Nepal will be threatened. Hence, we suggest designating the Rapti River section that passes across the CNP as a "no extraction zone."
印度食鱼鳄（Gharial）是一种极度濒危的鳄类物种，由于面临威胁，它们在尼泊尔河流中的数量稀少。我们估算了拉普提河（Rapti River）中印度食鱼鳄的数量，拉普提河是奇特旺国家公园（Chitwan National Park，CNP）的主要河流之一，尼泊尔境内数量最多的印度食鱼鳄就栖息于此。流经CNP的拉普提河被划分为18个河段，每个河段长约4公里，并对印度食鱼鳄进行了三次重复的直接计数。使用N混合模型（负二项分布）分析印度食鱼鳄的计数数据，并使用单季占有率模型估算印度食鱼鳄的总体占有率。还研究了协变量对印度食鱼鳄数量的影响。我们的研究结果显示，拉普提河中有150只印度食鱼鳄（119 - 181只），每个河段的平均数量为8.3只（标准差 = 3.45）。人类的存在和拉普提河深度的平方是分别对印度食鱼鳄数量产生负面和正面影响的显著协变量。同样，沙洲的数量影响了印度食鱼鳄的探测概率。我们的研究表明，使用N混合模型可以改进印度食鱼鳄种群数量的估算。使用单季占有率模型估算的印度食鱼鳄总体占有率为0.84（标准差 = 0.08），探测概率为0.37（标准差 = 0.02）。管理部门应集中关注各河段，以尽量减少人为干扰（如捕鱼、洗衣服、开采河床材料）。如果这条河流中的印度食鱼鳄种群数量下降，尼泊尔中部的印度食鱼鳄种群将受到威胁。因此，我们建议将穿过CNP的拉普提河段指定为“禁采区”。
