Evaluation of relative density indices for sika deer in eastern Hokkaido, Japan

Abstract

We evaluated relative density indices of sika deer (Cervus nippon) to aid in population management. We monitored sika deer population trends from 1992 to 2002 in the eastern part of Hokkaido Island, northern Japan, using spotlight surveys, aerial surveys, catch per unit effort (CPUE), sighting per unit effort (SPUE), and cost of damage to agriculture and forestry. We assumed that the artificial bias in the spotlight index would be lower than in other indices, and compared temporal patterns of other indices to those produced using spotlight surveys using model II regression. There was a significant correlation between the damage cost index and the spotlight index, and both indices indicated consistent population trends. Managers used CPUE as a tool to determine hunting quota efficiency. The SPUE index had the smallest standard error among the indices, and the spotlight survey index had the second smallest standard error. Overall, the spotlight survey was the most useful index because its estimate error was small and it was precise in showing population trends; however, spotlight surveys did lead to underestimation once in 1994. The SPUE index seems to be effective in checking the validity of the spotlight index, but there are so many environmental and demographic uncertainties that several independent indices should be used and crosschecked for accurate evaluation of population trends.

It counts who counts: an experimental evaluation of the importance of observer effects on spotlight count estimates

“…If a population survey programme only aims to obtain abundance information in the form of count indices (e.g. Winchcombe and Ostfeld 2001;Uno et al 2006;Garel et al 2010), varying ability of observers to estimate distance are of course of minor importance.…”

“…Spotlight counts have been used for estimating density and abundance indices or even density estimates of nocturnal animals, such as several species of deer (Winchcombe and Ostfeld 2001;Koganezawa and Li 2002;Uno et al 2006;Garel et al 2010), Eurasian rabbit Oryctolagus cuniculus (Caley and Morley 2002;Barrio et al 2009), red fox Vulpes vulpes Communicated by Dr. C. Gortázar…”

Effects of deer abundance on broad-leaf tree seedling establishment in the understory of Abies sachalinensis plantations

“…The island is divided into 12 deer management units (Hokkaido Institute of Environmental Sciences 1994; Uno et al 2006; Fig. 1).…”

Management approach using simple indices of deer density and status of understory vegetation for conserving deciduous hardwood forests on a regional scale

“…The number of records reported each year during this period ranged from 18,068 to 26,642. Based on these data, the mean number of sika deer sighted per hunting day in a mesh, which is generally called the sighted per unit effort (SPUE), was calculated (Uno et al 2006).…”

“…The advantages of this method are its small measurement errors (Uno et al 2006) and its high efficiency in terms of cost and labor force, because the original data needed to calculate SPUE can be collected by hunters if the researcher can organize assistance from hunters (Roseberry and Woolf 1991).…”