捕殺個体を利用したニホンツキノワグマ (Ursus thibetanus japonicus) の 栄養状態および繁殖評価方法に関する研究

The Japanese black bear (Ursus thibetanus japonicus) is a subspecies of the Asiatic blackbear (Ursus thibetanus), which is classified as a vulnerable species in the IUCN red list. Inthe Japanese red list, six local populations of the Japanese black bear are designated asthreatened local populations, although the subspecies as a whole is not listed as threatened.The Japanese black bear is one of the largest mammals in forest ecosystems in Japan, andefforts in their conservation could contribute to the health of the forest ecosystems. On theother hand, as the distribution of the Japanese black bear has been expanding recently inmost regions of Japan, intrusions of bears into human residential areas have become asocial issue. Although solutions desirable for both humans and bears are being sought, aprimary countermeasure, at present, is killing bears under permission by local authorities.Biological information of the target species is basis for effective wildlife management.The necessary information varies depending on the goal of management, but nutritionaland reproductive statuses are of the most essential pieces of information. There are a fewapproaches to studying nutritional and reproductive conditions of Japanese black bears.One is the direct observation of wild bears. Another approach deals with captive bears. Thethird approach is research on killed bears. These approaches are not mutually exclusive,but complement each other. Bear carcasses are precious sources of biological information.72Exploring their effective uses should not be left behind in research of the Japanese blackbear. The purpose of this study is to establish evaluation methods for nutritional andreproductive conditions of the Japanese black bear using samples from carcasses. I alsokept in mind that the evaluation methods should fit the sample collection throughadministrative damage control kills, and contribute to population monitoring and betterunderstanding of intrusion mechanisms.I employed three body fat indices as indicators of nutritional conditions: femur marrowfat (FMF), modified kidney fat index (mKFI), and abdominal subcutaneous fat (ASF). Imeasured these indices on samples from bears killed in Gifu Prefecture, 2006, and revealedthe age dependency, sex dependency and seasonality of the indices. All the 3 body fatindices of cubs were significantly lower than those of the other age classes. mKFI and ASFin late fall (November and December) were significantly higher than those in summer(July-September). ASF of females was significantly lower than that of males. I examinedthe preferential order of catabolism among different fat depots, and found that low FMFsuggests a poor nutritional condition. Based on these results, I statistically analyzed theyearly change in the body fat indices of bears killed in Gifu and Fukushima prefecturesduring the summers (July-September) of 2005-2007, and investigated their relation to thenumber of control-killed bears. Since a negative correlation has been reported between foodabundance in bear habitat and the number of control-killed bears, I hypothesized that thenutritional condition of killed bears in years with more killed bears is poorer than in yearswith fewer killed bears. However, I found that the number of killed bears was higher in oneyear with better nutritional conditions of bears. This suggests that a poorer nutritionalcondition does not necessarily lead to more intrusions of bears into human residentialareas.To establish a method for reproductive evaluation, I observed corpora lutea, corporaalbicantia and placental scars in females killed in several prefectures on Honshu Islandfrom 2001 to 2009. I examined the postpartum durations of placental scars and corpora73albicantia, and found that placental scars remained at least until November, and that,under the present study’s method of histological examination, corpora albicantia were >95% detectable until August and became undetectable around February of the next year.From these results, I developed a method for determining the parturition history of femalesin the year of their capture, which constituted a foundation for new reproductive evaluationmethods. To assess the mating season and the age of first ovulation in the wild, I examinedthe monthly and age-specific changes in the proportion of females with corpora lutea. Ifound that most females had finished ovulation by August, and that the age at which mostfemales began to ovulate (standard age of first ovulation) was 4 years, with someprecocious ovulations at as early as 2 years of age. I introduced two parameters for newreproductive evaluation: the success rate of ovulation (SRO; the probability that solitaryfemales over the standard age of first ovulation actually succeed in ovulation) and earlylitter loss rate (ELLR; the probability that parenting females lose all of their cubs beforethe mating season). I established methods for estimating those parameters from thepresence or absence of placental scars, corpora albicantia and corpora lutea. The estimatesof those parameters were SRO = 0.93 and ELLR = 0.29. I also examined the agedependency of ovulation success (SRO 􀵈 ovulation rate), and found it almost constantamong females ≥ 4 years old. The ovulation success of females < 4 years old was found to belower than that of females ≥ 4 years old, but ovulation rates were similar.In the present study, I provided an essential guideline for the evaluation of nutritionalconditions of the Japanese black bear, and established new methods for reproductiveevaluation such as the determination of parturition history and new reproductiveparameters of SRO and ELLR. I believe that these achievements will bring a newdimension to research and management of the Japanese black bear.