中国野生东北虎数量监测方法有效性评估

虎数量监测是虎保护的核心内容之一。野生虎现存数量少、领域宽广,加之习性机警,很难对其数量和种群变化趋势做出准确的评估。合适的虎数量监测方法随着监测目标、监测尺度、虎密度、猎物密度、气候及其它环境因素的变化而不同。2002—2011年,用东北虎信息收集网络法,样线调查法,猎物生物量和捕食者关系法,对东北虎数量进行监测。(1)用老虎信息收集网络法研究2006年完达山东部地区东北虎的种群现状,结果显示东完达山地区2006年东北虎数量为6—9只,由1只成年雄虎,2—3只成年雌虎,2—4只亚成体虎和1只小于1岁的幼体虎组成;(2)用猎物生物量和捕食者关系法得到东完达山地区2002年东北虎的密度为0.356只/100 km2,能容纳22—27只东北虎;(3)用样线法在黑龙江的老爷岭南部和吉林省大龙岭北部面积1735.99 km2的区域内设置样线64条,总长609 km,没有发现东北虎足迹链。样线调查的结果表明,在2011年2—3月该调查区域东北虎的数量为0只。监测结果表明,用猎物生物量和捕食者关系得到东北虎数量远远超过现实数量,人们对有蹄类的盗猎和猎套对老虎的伤害可能是其主要原因;样线法调查得出的结果低于现实种群,主要原因是老虎数量极低和调查者对野生虎行为学了解甚少,较难在野外有效的发现虎信息;且样线法监测仅应用于当东北虎以一定的密度(即有定居虎)存在的情况下(多数监测样线能发现虎信息)。虽然和样线法一样存在着诸如专家估计密度和真实密度之间的关系,老虎足迹数量和老虎真实密度间关系不确定,保守估计等内在缺点,在目前中国东北地区野生东北虎种群密度极低,且多是穿越于中俄边境地区的游荡个体的现状下,信息收集网络法是一种高效,可行东北虎监测方法。因此,建议建立更广泛的监测信息收集网络,培训监测人员,严格执行信息收集程序,减少专家估计误差以完善此监测方法。此外,其他监测方法,如占有法、基于标志重捕远红外照相法、粪便DNA法、足迹数码信息法、警犬法等,应根据各种方法的理论前提、误差来源、适用范围和老虎是否定居及密度等具体情况有选择地加以应用,且有些方法可能成为未来中国野生东北虎种群的有效监测工具。

Assessment of monitoring methods for population abundance of Amur tiger in Northeast China

Information on abundance and variation in abundance are bases for the effective wildlife management. Accurate survey methods are necessary to monitor the status and dynamics of endangered population of Amur tiger. The tigers are notoriously hard to monitor because they are secretive, occur at low density, wander widely, and are very rarely observed. Suitable monitoring methods vary in their reliability depending on the monitoring objectives, the spatial and temporal scale, tiger population density, prey density, climate, terrain and other environmental parameters. The accuracy and feasibility of three methods (Information collecting networks, traditional transect survey and tiger-prey biomass relationships) for monitoring Amur tiger population abundance were assessed in the eastern Wanda Mountains, Heilongjiang Province and 8 bordering forest area between the southern Laoye Mountains in Heilongjiang Province and the northern Dalong Mountains in Jilin province during 2002-2011.The results showed that: 1) there were at least 6-9 wild Amur tiger in the eastern Wanda Mountains (1 male, 2-3 adult females, 2-4 sub-adults and 1 cub), in 2006 by using an information network for tigers; 2) there were 22-27 wild tigers in the eastern Wanda Mountains in 2002-2004 based on the prey biomass relationship method, which obviously exaggerated the tiger population size; and 3) 0 tigers in 8 bordering forestry areas between the southern Laoye mountains in Heilongjiang Province and the northern Dalong Mountains in Jilin province, in 2011 by using traditional transect method, which underestimated the true tiger population size. The reasons for exaggeration of the tiger population using the biomass method could be previous losses of tigers from the area due to snares and competition with another carnivore, especially with people for ungulates. The transect method may have underestimated tiger densities in the survey areas because it was based on little prior knowledge of tiger behavior. It could only be usefully applied when tigers exist in at least moderate densities (i.e., when there is a high probability of encountering tiger tracks along a suite of routes). Although there is inherent potential error and bias, such as the unclear relationships of "expert estimates" and the true density, and between tiger track densities and actual tiger densities, same as the transect method, the monitoring of tiger populations using information networks provides a record of minimum tiger presence, and may be an appropriate approach when tiger presence is extremely rare, transitory and unstable, such as in northeast China. This approach is economically efficient and should be further improved by established a wider network across the landscape to encompass all potential tiger habitat using better trained monitoring staff. An occupancy survey would be an ideal method to monitor tigers at the landscape scale when tigers are determined to be permanently present in some areas of northeastern China. Camera traps, DNA identification, dog identification, track identification, monitoring methodology based on capture-recapture systems may only work when tiger densities are high enough to provide ample capture-recapture data. They may be appropriate for future use in China. The density overestimates as determined by the large ungulate biomass method indicated that tiger numbers might be stabilized if strict measures were taken to alleviate the factors threating both the tigers and their prey. We should also monitor populations of large ungulates and threat factors to those ungulates while at the same time make efforts to monitor abundance trends in the tiger population itself.