Knowing the reproductive characteristics of a species is essential for the appropriate conservation and management of wildlife. In this study, we investigated the demographic parameters, including age of primiparity, litter size, inter-birth interval, reproductive rate, and cub survival rate, of Hokkaido brown bears (Ursus arctos yesoensis) in the Rusha area on the Shiretoko Peninsula, Hokkaido, Japan, based on a long-term, individual-based monitoring survey. A total of 15 philopatric females were observed nearly every year from 2006 to 2016, and these observations were used to estimate reproductive parameters. The mean age of primiparity was 5.3 ± 0.2 (SE) years (n = 7, 95% CI = 5.0–5.6). We observed 81 cubs in 46 litters from 15 bears. Litter size ranged from one to three cubs, and averaged 1.76 ± 0.08 (SE) cubs/litter (95% CI = 1.61–1.91). Inter-birth intervals ranged from 1 to 4 years, and the mean value was estimated as 2.43 (95% CI = 2.16–2.76) and 2.53 (95% CI = 2.26–2.85) years in all litters and in litters that survived at least their first year, respectively. The reproductive rate was estimated from 0.70 to 0.76 young born/year/reproductive adult female, depending on the method of calculation. The cub survival rate between 0.5 and 1.5 years ranged from 60 to 73%. Most cub disappearances occurred in July and August, suggesting that cub mortality is mainly due to poor nutrition in the summer. All reproductive parameters observed in the Rusha area on the Shiretoko Peninsula fell within the range reported in Europe and North America, and were among the lowest or shortest age of primiparity, litter size, and inter-birth intervals, and ranked at a high level for reproductive rate.

Body condition is an important determinant of health, and its evaluation has practical applications for the conservation and management of mammals. We developed a noninvasive method that uses photographs to assess the body condition of free-ranging brown bears (Ursus arctos) in the Shiretoko Peninsula, Hokkaido, Japan. First, we weighed and measured 476 bears captured during 1998–2017 and calculated their body condition index (BCI) based on residuals from the regression of body mass against body length. BCI showed seasonal changes and was lower in spring and summer than in autumn. The torso height:body length ratio was strongly correlated with BCI, which suggests that it can be used as an indicator of body condition. Second, we examined the precision of photograph-based measurements using an identifiable bear in the Rusha area, a special wildlife protection area on the peninsula. A total of 220 lateral photographs of this bear were taken September 24–26, 2017, and classified according to bear posture. The torso height:body/torso length ratio was calculated with four measurement methods and compared among bear postures in the photographs. The results showed torso height:horizontal torso length (TH:HTL) to be the indicator that could be applied to photographs of the most diverse postures, and its coefficient of variation for measurements was <5%. In addition, when analyzing photographs of this bear taken from June to October during 2016–2018, TH:HTL was significantly higher in autumn than in spring/summer, which indicates that this ratio reflects seasonal changes in body condition in wild bears. Third, we calculated BCI from actual measurements of seven females captured in the Rusha area and TH:HTL from photographs of the same individuals. We found a significant positive relationship between TH:HTL and BCI, which suggests that the body condition of brown bears can be estimated with high accuracy based on photographs. Our simple and accurate method is useful for monitoring bear body condition repeatedly over the years and contributes to further investigation of the relationships among body condition, food habits, and reproductive success.

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ABSTRACT. To study the luteal and placental function of pinnipeds, we analyzed the localization of steroidogenic enzymes (P450scc, 3 β HSD and P450arom) in the corpus luteum and the placenta of ribbon seals (Phoca fasciata) and Steller sea lions (Eumetopias jubatus) immunohistochemically. P450scc and 3 β HSD were present in all luteal cells of both species. Almost all of the luteal cells were immunostained for P450arom, while P450scc and 3 β HSD were negatively immunostained in placentae and P450arom was present in the syncytiotrophoblast of placentae. These findings suggest that 1) corpora lutea of both species synthesize pregnenolone, progesterone and estrogen during the entire pregnancy period, and 2) like other terrestrial carnivores in the suborder Caniformia, placentae of both species do not have the capability for synthesizing progesterone in the latter half of active pregnancy period. KEY WORDS: corpus luteum, placenta, ribbon seal, Steller sea lion, steroidogenic enzyme.J. Vet. Med. Sci. 63(9): 955-959, 2001 Both the ribbon seal (Phoca fasciata) and the Steller sea lion (Eumetopias jubatus) are highly adapted for an aquatic lifestyle, and they are classified in the order Carnivora [13,20]. In the past, seals (family Phocidae), sea lions (family Otariidae) and walrus (family Odobenidae) were usually classified as a separate order, the Pinnipedia, or as a suborder of the order Carnivora. However, many morphological and molecular studies have recently revealed that affinities of the Pinnipedia lie within the suborder Caniformia of the order Carnivora, which includes Ursidae (bears) and Mustelidae (weasels, martens, etc.) [20].From the viewpoint of reproduction, delayed implantation occurs in most pinnipeds as it does in bears and martens [1,16,17]. Although the total pregnancy periods of ribbon seals and Steller sea lions last almost one year, their postimplantation periods (active pregnancy periods) are shorter due to delayed implantations [14]. Timing of implantation in ribbon seals is assumed to occur in August [2], although details are unknown. The attachment of blastocyst in Steller sea lions occurs in late September and October [19]. The peak of pupping of ribbon seals and Steller sea lions occurs early in April and early in June, respectively [3,19].In some terrestrial carnivorous animals, the corpus luteum is the most important source of progesterone during the entire gestation period [6,8,18,22,23]. In seals, however, it is not known whether the corpus luteum can synthesize progesterone in late pregnancy, or if the placenta replaces the corpus luteum as a principal source of progesterone, as occurs in sheep and humans [18]. The aim of this study is to clarify whether the corpus luteum and the placenta of ribbon seals and Steller sea lions in the latter half of an active pregnancy period are capable of steroidogenesis. MATERIALS AND METHODSOvaries and placentae were collected from 8 wild ribbon seals and 8 wild Steller sea lions. The animals were shot legally by hunters as part of nuisance contr...

Human habituation of large carnivores is becoming a serious problem that generates human–wildlife conflict, which often results in the removal of animals as nuisances. Although never tested, human habituation potentially reduces the fitness of adult females by reducing their offspring’s survival as well as their own, due to an increased likelihood of human-caused mortality. Here, we tested this hypothesis in brown bears inhabiting Shiretoko National Park, Japan. We estimated the frequency of human-caused mortality of independent young (aged 1–4 years) born to mothers living in areas with different maternal levels of human habituation and different proximities to areas of human activity. The overall mortality rate was higher in males than in females, and in females living near a town than those in a remote area of park. Surprisingly, more than 70% of males born to highly habituated mothers living around a remote wildlife protection area were killed by humans; this proportion is greater than that for males born to less-habituated mothers living in almost the same area. The current study clarified that interactions among maternal human habituation, birthplace (proximity to town), age, and sex determine the likelihood of human-caused mortality of brown bears at an early stage of life.