Anthropogenic mortality of Asiatic black bears in two populations in northern Honshu, Japan

Toru Oi1

Kansai Research Center, Forestry and Forest Products Research Institute, Momoyama-cho, Fushimi-ku, Kyoto, 612-0855 Japan

Abstract: I examined the sex and age at death of Asiatic black bears (Ursus thibetanus) killed by sport hunters or during nuisance incidents in 2 neighboring mountain ranges (Kitakami Highland [KH] and Ohwu Mountains [OH]) in northern Honshu, Japan. Between 1993 and 2000, 1,005 bears were killed in these areas (361 nuisance kills, 644 sport-hunting kills). Nuisance bear removals were 1.3 times greater in KH than in OM. Males removed during nuisance incidents tended to be younger in OM than in KH; older males as well as females made up proportionately more of KH nuisance removals. The monthly nuisance removals varied widely by year in both areas, with the largest yearly variation in September in KH and August– September in OM. Female deaths accounted for much of the increase in nuisance kills in KH during September. Both sexes contributed to the increase in OM nuisance kills during August and September. The number of bears killed by sport hunting in KH was 4.7 times larger than in OM. OM terrain is steep and has deep snow during winter, which largely restricts human settlement and agriculture to the eastern edge of this area. Conversely, KH is gently sloping with less snow cover, allowing human settlement and agriculture to disperse more widely into mountainous bear habitat. Such differences in habitat conditions likely influence the degree of human–bear conflict and hunting pressure. Because the population was isolated and many females were removed in KH, I recommend more careful monitoring of the population by examining the sex and age structure of harvested animals relative to densities and real measures of hunting effort.

Key words: Asiatic black bear, northern Japan, nuisance kill, population, sex–age composition, sport hunting, Ursus thibetanus

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The Asiatic black bear (Ursus thibetanus) is listed when suspected of nuisance activities such as as vulnerable in the 2008 IUCN (International attacking humans and livestock or damaging crops, Union for Conservation of Nature and Natural orchards, fish farms, or other property. Resources) Red List of Threatened Species (IUCN The sex and age composition of bears killed has 2008). The Japanese Ministry of Environment (2002) been reported to vary with population structure, Red List indicates that some local Japanese popu- hunting pressure, capture method, capture season, lations are small, isolated, and in need of intensive and habitat conditions (Brannon et al. 1988, Rossell protection (Ministry of the Environment 2002). and Litvaitis 1994, Mano 1995, Noyce and Garshelis Nevertheless, 1,100–5,000 Asiatic black bears have 1997, Miller and Tutterrow 1999, Diefenbach et al. been killed annually over the past 20 years. 2004). These factors make reliable interpretation of Anthropogenic bear kills in Japan result primarily population trend from killed bear samples difficult from sport hunting and removal of nuisance (Paloheimo and Fraser 1981, Fraser et al. 1982, animals. The regulated sport-hunting season extends Harris and Metzgar 1987a,b), although the sex and from 15 November to 15 February annually, and age of killed bears can be useful in determining only firearms are permitted for hunting. Nuisance population trends (Caughley 1977). However, anal- animals are caught primarily in barrel or cage traps ysis of sex and age composition of harvested bears can be used to identify factors that can be controlled [email protected] to establish better management policies for sport

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Fig. 1. Study area and locations of hunting (#) and nuisance (n) kills of Asiatic black bears in Honshu, Japan, 1993–2000. Human settlements and agricultural areas are stippled. Eastern sections of the Kitakamik and Mabechi rivers pass through the Kitakami Highland (KH); western sections of the rivers pass through the Ohwu Mountain (OM) district. hunting and nuisance removals. Using this ap- spread along the riparian zones and appear to proach, I found contrasts between 2 populations prevent movement of bears between the 2 highlands. that may be related to differing habitat conditions Skull morphology differs between KH and OM and harvest periods. bear populations (Amano et al. 2004). Skulls from KH have shorter muzzles and wider faces than those from OM. In addition, the length of the molar row, Study areas which stops growing at an early stage of develop- Asiatic black bears inhabit 2 neighboring moun- ment, also differs; size of the molar row is not tain ranges in Iwate Prefecture of northern Honshu: influenced by environment. These skull differences the 9,800-km2 Kitakami Highland (KH) and the suggest genetic differentiation between populations, 4,300-m2 Ohwu Mountains (OM). Flood plains of and accordingly the 2 highland regions are treated as the Kitakami and Mabechi Rivers separate KH and separate management units by local governments. OM habitats (Fig. 1). The shortest distance between OM has steep terrain with deep snow during the 2 habitats is 2 or 3 kilometers. Human settle- winter (annual maximum snow depth of 180 cm at ments, highways, railroads, and cultivated fields Yuda meteorological station, altitude 250 m). As a

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result, human settlements and cultivated fields (902 km2) are restricted primarily to the eastern edge of this area. In contrast, KH is gently sloping with less snow cover (annual maximum snow depth of 25 cm at Tono meteorological station; altitude 273 m), allowing development of interspersed hu- man settlements and cultivated fields (1,710 km2) throughout the area.

Human A GIS vegetation analysis of digital map data settlements

or agricultural Other Total (Ministry of the Environment 1999) indicated that forest and human settlement or agricultural areas occupied 82% and 18% of the land area in KH and Tree 78% and 21% in OM (Table 1). This analysis also

plantations indicated that 35% and 19% of the forested portions of KH and OM, respectively, were vegetated by

for a study of Asiatic black bears in northern warm temperate plant communities (e.g., Camellia japonica, Machilus thunbergii, Ardisia japonica); 17% and 33% of the forest portions of KH and OM, Secondary vegetation: community respectively, were vegetated with cool temperate

warm temperate plant communities (e.g., Fagus crenata, Quercus mongolica, Aesculus turbinata). Secondary forests and conifer plantations (Cryptomeria japonica, Larix kaempferi, Pinus densiflora) occupied 93% and 69%, respectively, of the forested areas of KH and OM. ) with digital vegetation data supplied by the Japanese Ministry of the Primary

vegetation: community Hence, the forests in KH are more anthropogenically

warm temperate disturbed than those of OM. In recent years, over 100 bears have been killed annually in Iwate Prefecture. Between 1993 and 2000, 1,005 bears were killed. Of these, 361 were nuisance kills and the rest were sport-hunting kills.

Secondary Nuisance removals in Iwate Prefecture were permit- vegetation: community

cool temperate ted only around human settlements and agricultural areas. Hunters were required to report kill or capture site, sex, and estimated age of the bears they killed, but not hunting effort (e.g., actual trap nights and firearm-hunting days). Hunters estimated the age of Primary temperate community bears primarily by examining body size and tooth vegetation: cool wear.

Methods subalpine secondary community

Primary and I determined kill locations for 829 bears: 619 from KH and 210 from OM (Fig. 1). I estimated age by ) of vegetation types in Kitakami Highland (KH) and the Ohwu Mountain (OM),

2 counting cementum annuli of sectioned lower fourth premolar roots (Craighead et al. 1970). I determined

alpine age of all (n 5 258) samples (heads of bears) that Primary

vegetation: community hunters sent to our institute: 92 samples from nuisance kills in KH (66% of nuisance kills in KH), 79 samples from sport-hunting kills in KH (16% of sport-hunting kills in KH), 64 samples from Table 1. Areas (km Location KHOM 9.8 19.3 261.3 81.9 755.4 151.1 1204.7 383.8 311.6 76.4 2,478.8 576.2 3,821.3 1,443.2 1,713.9 901.9 10.0 9,763 28.5 4,309 Honshu, Japan, 1993–2000. AreasEnvironment were calculated (1999). using Arc View (ver. 3.02 nuisance kills in OM (59% of nuisance kills in OM),

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were examined using Fisher’s exact test (a 5 0.05, two-tailed); age differences between the populations were examined using Mann-Whitney U-tests (a 5 0.05, two-tailed). Cubs were excluded from the analysis because they depend on mothers.

Results Nuisance kills Nuisance kills accounted for 108 bears (51% of total mortalities) in OM and 137 bears (22% of total mortalities) in KH. The sex ratio (male:female) of nuisance-killed bears in OM (78:26, 4 sex unknown) was strongly weighted toward males (Fisher’s exact test, P 5 0.00031). Among nuisance-killed bears in KH, the sex ratio (81:50, 6 sex unknown) was slightly weighted toward males, but not significantly (P 5 0.061). The sex ratio in OM was more skewed toward males than that in KH (P 5 0.036). Males killed in OM (x¯ 5 5.9 yr, range 5 1–14, n 5 47) were younger than males killed in KH (x¯ 5 8.3 yr, range 5 1–19, n 5 57; U 5 1866, P 5 0.0010; Fig. 2). Age at death of females was not significantly different Fig. 2. Age-class frequency distribution of a sample of male (a) and female (b) nuisance-killed Asiatic between OM (x¯ 5 7.7 yr, range 5 3–11, n 5 17) and bears in Kitakami Highland (KH) and Ohwu Moun- KH (x¯ 5 7.0 yr, range 5 1–16, n 5 35; U 5 242, P 5 tains (OM), Honshu, Japan, 1993–2000. 0.28; Fig. 2). The number of animals killed per month in KH fluctuated the most during September, followed by and 23 samples from sport-hunting kills in OM (23% August (indicated by SD calculations, Table 2). I of sport-hunting kills in OM). I assumed that these segregated August and September data into 2 sets of were random samples because there was no reason years, the 4 years with the highest numbers of that hunters selected samples to send. I also made nuisance kills and the 4 years with the lowest use of 543 bear age estimates made by hunters for numbers of nuisance kills. Frequencies of the sex– calculations of age-class frequencies. Ages estimated age class (adult male, subadult male, adult female, by hunters correlated well with ages estimated from subadult female) in September differed significantly tooth-root cementum annuli counts (Kendall’s tau 5 between the 2 sets of years (1993, 1996, 1997, 2000 0.524, n 5 238, z 5 12, P , 0.001). Thus, I regarded versus 1994, 1995, 1998, 1999; 3 df, P 5 0.0053, hunter-assigned bear ages as rough but adequate Fig. 3). During September in the years with highest estimators for age-class calculations. The adult age number of nuisance kills, the proportion of adult class was assigned to bears .4 years old; these female deaths to the total number of deaths (0.51) animals were assumed to be reproductively mature was markedly higher than in years with the lowest (Komatsu et al. 1994, Katayama et al. 1996). Bears number of nuisance kills (0.076). In August, the KH 1–3 years old were assigned to the subadult category, sex and age–class frequencies in high-kill years and animals ,1 year old were assigned to the cub (1994, 1997, 1999, 2000) were not significantly category. different from low-kill years (1993, 1995, 1996, I tallied the sex and age composition of nuisance 1998; P 5 0.36; Fig. 3). and sport-hunting kills and the temporal change in In OM, the number of bear kills was also most monthly kill rates, and compared the sex and age variable in September (indicated by SD calculations, composition of kills between the 2 habitats. Depar- Table 2). The years with the highest numbers of tures from evenness in sex ratios, and pairwise sex nuisance kills in September (1993, 1996, 2000, and and age differences between times and populations 1997 in descending order) differed in KH from those

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Table 2. Nuisance killed Asiatic black bears in Kitakami Highland (KH) and Ohwu Mountains (OM), Honshu, Japan, by month and year. Year Area Apr May Jun Jul Aug Sep Oct Nov Total 1993 KH 0 0 0 0 5 21 7 2 35 OM00006430 13 1994 KH 0 1 1 1 6 1 0 0 10 OM00045400 13 1995 KH 0 2 0 0 2 5 1 0 10 OM00000000 0 1996 KH 0 0 0 1 4 13 0 1 19 OM00007900 16 1997 KH 0 1 0 0 7 8 1 0 17 OM40102210 10 1998 KH 0 0 0 0 3 1 0 0 4 OM00007500 12 1999 KH 0 0 0 2 8 6 1 0 17 OM2202111030 30 2000 KH 0 4 0 2 11 8 0 0 25 OM04124300 14 Total KH 0 8 1 6 46 63 10 3 137 OM 6 6 2 8 42 37 7 0 108 x¯ KH 0 1.0 0.1 0.8 5.8 7.9 1.3 0.4 17.4 OM 0.8 0.8 0.3 1.0 5.3 4.6 0.9 0 13.5 SD KH 0 1.4 0.4 0.9 2.9 6.6 2.4 0.7 9.3 OM 1.5 1.5 0.5 1.5 3.4 3.4 1.4 0 8.3 in OM (1999, 1996, 1993, and 1998 in descending dead bears did not differ significantly between the order). August nuisance kills in OM also varied high- and low-kill year categories (Aug: 1993, 1996, widely among years. During August and September 1998, 1999 versus 1994, 1995, 1997, 2000; 3 df, P 5 in OM, the age–sex class frequency distributions of 0.68; Sep: 1996, 1998, 1999 versus 1993, 1994, 1995,

Fig. 3. Proportions of nuisance-killed Asiatic black bears by age–sex class in low-kill and high-kill years during (a) August in Kitakami Highland (KH), (b) September in KH, (c) August in Ohwu Mountains (OM), and (d) September in OM. Subadult: 1–3 yr old, adult: .4 yr old.

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Fig. 5. Monthly sport-hunting kills of Asiatic black bears in Ohwu Mountains (OM; bold line) and Kitakami Highland (KH; broken line), Honshu, Japan.

Discussion The bear kill in KH was about triple that in OM (1.3 times more nuisance kills and 4.7 times more sport-hunting kills in KH). The difference may be attributable in part to a larger habitat area in KH (2.3 times larger than in OM), although no precise estimates of bear density in the two highlands were available. The difference in the number of bears Fig. 4. Age-class composition of a sample of male harvested may also result from differences in hunting (a) and female (b) Asiatic black bears killed by sport hunters in Kitakami Highland (KH) and Ohwu effort. However, the number of hunters active in Mountains (OM), Honshu, Japan, 1993–2000. each of the mountain ranges was not known, although the total number of hunting licenses issued in Iwate Prefecture declined from 6,711 in 1993 to 1997, 2000; 3 df, P 5 1.0, Fig. 3). In short, male and 5,111 in 2000. Differences in climate and topography female nuisance deaths contributed equally to the likely influenced bear harvest. Deep snow and steep increase of OM totals in August and September in terrain in OM probably inhibit winter sport hunting. high-kill years. The more benign KH conditions allow ready access to hunters, even in winter, which is reflected in the Sport-hunting kills bear kills in each month of the hunting season. Sport hunting accounted for 102 (49% of total Younger males tended to be killed in nuisance mortalities) and 479 (77% of total mortalities) bear incidents in OM, whereas nuisance kills in KH, kills in OM and KH, respectively. The sex ratio of and sport-hunting kills both in OM and KH did bears killed by sport hunters in OM (64:35, 3 sex not show a marked pattern in sex or age. unknown) and KH (285:169, 6 sex unknown) were Inconsistency in sex and age patterns among OM skewed toward males (P 5 0.044 in OM, P 5 and KH sport-hunting kills, and OM and KH 0.00013 in KH). Sex ratios at OM and KH did not nuisance kills indicated that sex and age pattern of differ (P 5 0.82). Ages of bears killed by sport harvested bears was not a simple reflection of hunters at OM and KH did not differ for males (x¯ 5 populations (Paloheimo and Fraser 1981; Fraser 5.7 yr, range 5 1–16, n 5 17 in OM; x¯ 5 6.1, range et al. 1982; Harris and Metzgar 1987a,b; Brannon 5 1–16, n 5 44 in KH; U 5 410, P 5 0.57) or et al. 1988). females (x¯ 5 4.3, range 5 1–9, n 5 6 in OM; x¯ 5 6.1, Why did age and sex frequencies of the sport- range 5 1–13, n 5 35 in KH; U 5 137, P 5 0.24; hunting kills in OM differ so much from those of Fig. 4). other categories of mortalities? Differences in local No bears were killed in OM during January and conditions between the two highlands and differ- February during the study even though sport ence of capture sites between nuisance kills and hunting was permitted. In KH, bears were killed sport hunting may be the reason. Young male bears throughout the hunting season (Nov–Feb; Fig. 5). disperse actively into foothills both in OM and KH,

Ursus 20(1):22–29 (2009) 28 ANTHROPOGENIC JAPANESE BEAR MORTALITY N Oi causing problems in the fields and villages, resulting bear harvest has been documented between New in potentially more mortalities than among mem- Hampshire and Minnesota during poor fruit bers of other populations. This behavioral tendency years, although the reason for the contrast was has been reported in American black bears (U. unclear (Noyce and Garshelis 1997). In New americanus; Schwartz and Franzmann 1992, Noyce Hampshire, a lower proportion of females was and Garshelis 1997), but I know of no similar observed in the harvest, while a high proportion behavioral studies on Japanese black bears. How- of females was observed in Minnesota kills. This ever, the influence of young male dispersion on sex contrast may be due to differing sex and age and age composition of killed bears was masked by compositions among populations or, in the case of high-kill rates in females and older males in KH, the OM and KH populations, the contrast may be because the KH landscape allows more extensive due to differing human development patterns human settlement in former wilderness, leading to whereby the accessibility and vulnerability of exposures of female and older males to conflict with females was more pronounced in KH during poor humans. food years. The sex ratios skewed toward males in both OM and KH sport hunts may be due to the behavioral tendencies of males (Bunnell and Tait 1980). In Management implications American black bears, males appear more vulnerable The harvest of American black bears is strongly to hunters because they travel widely and seem less influenced by alteration of their habitat condition by inhibited about feeding near humans, so they are humans (Rossell and Litvaitis 1994). My data more likely than females to encounter sport hunters strongly suggest that the habitat conditions of the with firearms (Noyce and Garshelis 1997, Koehler Asiatic black bear in Japan also influence the degree and Pierce 2005). The less skewed sex ratio in OM of human–bear conflicts and hunting pressure. and KH sport-hunting kills than in OM nuisance Because human–bear conflicts are more numerous kills is because sport hunters intruded into forest and many female bears tend to be killed in KH, and areas to hunt bears and could encounter more because KH is more isolated (whereas OM is females than in nuisance incidences, where only continuous with other bear habitats in neighboring dispersed bears were killed around agricultural area prefectures; Amano et al. 2004), more careful popu- and human settlements. lation monitoring are warranted for KH. Future There have been marked yearly differences in the monitoring should evaluate the impact of bear kills on number of nuisance kills in OM and KH, with the the local bear population more carefully by examining highest kill rates typically observed during autumn. the sex and age structure of harvested animals relative This may be related to the fall food supply, especially to densities and real measures of hunting effort, such beechnuts (Fagus crenata) and acorns (Oka et al. as hours of active quarry pursuit and numbers of trap 2004). In both areas, apples, paddy rice, and cattle nights (unavailable in the present study). forage such as corn appear to be major attractants for bears when forest plants fail to fruit. However, the high-kill years in OM and KH were not Acknowledgments synchronized (Oka et al. 2004); vegetation types This study was supported partly by the Pollution differ between the regions (Table 1), and forage Control Research Fund of the Ministry of the availability probably also differs between the two, Environment, Japan. I thank the Hunters’ Associa- resulting in the asynchronous variation in nuisance tion of Iwate Prefecture and the Nature Conserva- activities. tion Division of the Iwate Prefectural Government. Such fluctuations in food supply appeared to Comments by D.C. Anderson, R.B. Harris, R. have a strong effect on females, as was observed Shideler, and an anonymous referee greatly im- in American black bears in Minnesota (Noyce and proved this manuscript. Garshelis 1997). The number of females killed in September increased markedly in KH during higher kill years; in OM the numbers of both Literature cited male and female deaths increased during higher AMANO, M., T. OI, AND A. HAYANO. 2004. Morphological kill years. A similar contrasting tendency in the differentiation between adjacent populations of Asiatic

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