Article ID: 2425
Since the 1980s, population and distribution expansions of sika deer (Cervus nippon) in Japan have caused serious damage to agriculture, forestry and the natural environment. Deer population dynamics are affected by various factors including climate, food availability and hunting pressure, which vary regionally. Therefore, fundamental information describing local populations, such as age structure and fecundity, is important for developing appropriate management plans. We assessed the age structure, reproduction and body growth of 301 deer killed in the Mt. Asama region of Nagano Prefecture, Japan, where deer populations and distributions have expanded since the 2000s. The proportion of young females (aged 0–1 year) tended to increase over time, suggesting that juvenile survival may not decrease as population density increases. The study population appeared to maintain high pregnancy rates, with that of yearlings (50.8%) slightly lower than those of other local populations, whereas adult females (aged>2 years) had a higher pregnancy rate (91.0%). Growth curves based on body weight attained a plateau in females and males at 5 and 12 years of age, respectively, whereas those based on the total skull length, a body size indicator, plateaued in females and males at 3–4 and 7–8 years, respectively. Therefore, compared to other local populations, the deer population in the Mt. Asama region is expected to grow more slowly and take longer to reach maximum body weight and size. Because juvenile survival is not decreasing and adult females are maintaining high pregnancy rates, this deer population may still be expanding. However, recent population density increases may have delayed the age at first pregnancy and slowed growth in terms of body weight and size. Greater hunting pressure is needed to suppress deer population growth in the study region, and continuous monitoring of captured deer is essential to evaluate population dynamics.
