A Comparison of Sika Deer Population Conditions between the Hidaka and Akan Districts in Hokkaido, Japan

Abstract

The sika deer (Cervus nippon yesoensis) population in Hokkaido was near threatened due to heavy snow and overexploitation for meat and fur between the 1890s and 1940s (Inukai 1952). At least three or four populations (Akan, Hidaka, Taisetsu, and Ishikari lowland) occur in the area, all of which have different mitochondrial DNA haplotype compositions and have survived a bottleneck (Nagata et al. 1998; Nabata et al. 2007). The Akan population, distributed mainly in the eastern part of Hokkaido, irrupted during the 1980s and 1990s (Kaji 1995; Uno et al. 2009). The population density estimated by aerial surveys have decreased from 1999 to 2008 in the Akan district (Uno et al. 2006; Inatomi et al. 2012). Mass mortality occurred in 1996 in Akan National Park (Uno et al. 1998) and in 1999 in Shiretoko National Park (Kaji et al. 2004), and a density effect on the recruitment rate was reported for the Akan population in the 1990s (Ueno et al. 2010). In contrast, the Hidaka population is distributed across the southwestern part of Hokkaido around the Hidaka mountain area (Nabata et al. 2007) and has increased dramatically during the 2000s (Uno et al. 2007). Population condition parameters, such as reproductive rate, body size, and nutrition, are fundamental for population management (Hanks 1981). Several studies on the conditions of the Akan sika deer population have been reported, such as pregnancy rate and sexual maturity (Suzuki and Ohtaishi 1993), growth rate (Suzuki et al. 2001), nutritional condition (Yokoyama et al. 2000b, 2001), and causes of natural mortality (Uno et al. 1998). However, no study of the Hidaka population has been conducted, and quantitative data are lacking for body mass and pregnancy rates. The objectives of this study were to characterize the condition of the Hidaka sika deer population and to identify the differences of the female body mass and the pregnancy rate between the Hidaka and Akan districts, which are in different phases of population dynamics.