A 25-years population dynamics of sika deer in Kyushu Island, Japan: Estimation using vector autoregressive spatiotemporal model and evaluation of a large-scale management

Abstract

Regional management of large herbivore populations is known to be effective in reducing local economic damages and conserving local endemic plants. However, herbivores often move across management areas, and the effect of population management on a large spatial scale is poorly understood, even though it is necessary to use a large-scale approach across multiple management units to implement appropriate management. In this study, to better understand large-scale management and improve management efficiency, we evaluated effects of large-scale management of a sika deer (Cervus nippon) population on Kyushu Island (approximately 36,750 km2) in Japan. We estimated the population dynamics and spatial distributions of the deer and evaluated the effects of harvests, density dependence, and climatic conditions on the population dynamics both across Kyushu Island and in smaller prefectural management units. Fecal pellet count surveys conducted from 1995 to 2019 and results from a vector autoregressive spatio-temporal model showed relatively stable population dynamics and four high-density core areas. No increasing or decreasing trends were observed in the population dynamics, even though harvesting increased annually until it reached about 110,000 in 2014, indicating that harvesting was not related to the population dynamics. In addition, although no effects of density dependence were confirmed, maximum snow depth during winter decreased deer density at the management unit scale. Harvesting represents a major source of mortality in the Kyushu Island population because of the absence of predators. Although, approximately 110,000 sika deer were harvested annually after 2014, it is surprising that the effect of harvesting on population dynamics was not significant. A main cause of no reduction of the population was that the population used to determine the harvest number was underestimated. In addition, it was indicated that multi-management units need to manage the core areas because the high-density core areas were located across a few management units. This study highlights the difficulties involved with wide-area management of large herbivores and points out the importance of accurate stock assessment, reduction of the risk of management failure, and cooperation among management units. Our research is an important contribution to the study of the effects of large-scale harvesting in a large geographic area.

Spatially biased reduction of browsing damage by sika deer through culling

“…High regional culling pressure decreased browsing damage in that region. In contrast, Suzuki et al (2021a) reported there was little effect of culling on deer abundance at the prefectural scale. These findings highlight the importance of spatial scale in the management of large herbivores.…”

“…Hunters report the locations of culled deer to the Kumamoto prefectural government, which tallies these data by grid meshes (5 km latitude × 5 km longitude). The annual number of culled deer has increased, with a 4‐fold increase between 1999 (4,335 deer) and 2017 (17,360 deer; Suzuki et al 2021 a ).…”

“…The size of each site was 50 × 200 m and the number of survey plots at each site was 110 (1 × 1 m). We reported locations of the survey sites in Suzuki et al (2021a). We used the GAM formula:…”

“…The climate is mild, with an average winter (Dec–Feb) temperature of about 6°C and sparse snowfall in recent years (Suzuki et al 2021 a ). Climate effects on the population dynamics of the deer are presumed to be minimal (Suzuki et al 2021 a ). Annual precipitation is approximately 2,000 mm, with about 60% of the precipitation occurring during summer (Jun–Sep).…”

“…Kumamoto Prefecture has a subtropical climate. The climate is mild, with an average winter (Dec–Feb) temperature of about 6°C and sparse snowfall in recent years (Suzuki et al 2021 a ). Climate effects on the population dynamics of the deer are presumed to be minimal (Suzuki et al 2021 a ).…”