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Difference in the factors of effect on reproductive rate of feral raccoon (Procyon lotor) between high- (2008-2010) and low- (2015-2017) density terms in Kanagawa Prefecture, Japan

Takuya Kato1*, Kandai Doi1, Aki Tanaka1, Sachiko Moriguchi1 and Shin-ichi Hayama1
  • 1 Nippon Veterinary and Life Science University, Japan

The raccoon (Procyon lotor) is native to North America and is considered as an invasive alien species in Japan. Recently, the raccoon has feralized and expanded its distribution to include numerous prefectures in Japan. This expansion of feral raccoons was concerned to have negative impacts among native ecosystems and agriculture and was also known to damage houses by both invading and pollution of excreta (Ikeda et al. 2004). Furthermore, studies on feral raccoons had identified various harmful pathogens (e.g. Sato and Suzuki 2006; Lee et al. 2010; Horimoto et al. 2011). As these issues may become more serious with the expanding distribution and growing populations of feral raccoons, scientific and practical control programs are necessary to eradicate the feral raccoon population in Japan. In the Kanagawa Prefecture, the first incident of feral raccoon that was found invading a house was reported in 1988 (Nakamura 1991). Because the feral raccoons increased and expanded their distribution, the Kanagawa local government formulated the raccoon control program in 2006 based on the Invasive Alien Species Act in 2005. In this program, the raccoon capture data has been recorded to evaluate the relative population density of the feral raccoons using CPUE (Catch per Unit Effort) in each 1 km2 grid in the Kanagawa Prefecture. To date, approximately 20,000 raccoons have been captured in the Kanagawa Prefecture, where crop damage and house invading has declined over the past few years. Especially in two districts, Yokosuka city and Hayama town, the CPUEs of feral raccoons in recent years seemed to decline compared to those in a decade ago. However, the ecological background of this decreasing CPUE case has not been investigated yet. Although several studies of female raccoon reproduction in Japan had been published (Asano et al. 2003; Kato et al. 2009), little is known about spatio-temporal relationship between density change and reproductive status of the feral raccoons. The first objective of this study was thus to identify how factors affected the female reproductive rate. The second objective was to examine the presence of high productivity area in Yokosuka and Hayama area. The study area was Yokosuka city and Hayama town (118 km2), located on the southwest edge of the Kanto Plain, Japan. Based on the Kanagawa Raccoon Control Program, feral raccoons were captured using box traps (Havahart Live Animal Cage Trap Model 1079 or 1089; Woodstream, Lititz, PA, USA) and were euthanized by pentobarbital sodium injection or CO2 inhalation, according to the Guidelines for the Management of Invasive Alien Species (Japan Veterinary Medical Association 2007). CPUE was calculated the number of captured raccoons divided 100 TN (trap-night) in one km2 grid, was provided as relative population density of the feral raccoon. CPUE was modified into log CPUE for standardization in our study. Because it was considered that effect of population density was not one way, our study analyzed for two periods; first to assume relatively high density term (2008-2010) and second to assume comparatively low density term (2015-2017) depending on the CPUEs. From each raccoon carcasses were collected during these study periods, sex, body weight (BW) and body length (BL) were measured, and then the skinned head and female reproductive organ were collected for later examinations. After skinned heads were processed into skulls specimens, the raccoons were separated into three age classes, juvenile, yearling, and adult, according to age determination methods (Montgomery 1964; Grau et al. 1970; Junge and Hoffmeister 1980). Placental scars in the uterus were considered to indicate implantation in the most recent breeding season (Junge and Sanderson 1982). Reproductive status of female raccoons was identified whether the female was pregnant or with one or more placental scars in their uteri. Additionally, body mass index (BMI: BMI = BW (kg) / BL (m2)) was calculated for each raccoon as a relative index of body fat deposition (Kato et al. 2012). In order to characterize the difference of relative density between the first and second term, simple logistic regression was used to be term (first vs. second) as the outcome variable and log CPUE as the explanatory variable. Multivariable logistic regression (MLR) was performed to determine how ecological factor affected the reproductive rates of females in each term. The outcome variable was reproductive status (pregnant or parous vs. nulliparous). Explanatory variables included TN, log CPUE, age-class (score of 0-2), BL and BMI. Spearman’s rank correlation was used to confirm whether strongly collinear (rho > 0.8) was among all explanatory variables. Simple logistic regression was used to examine the relationships between the reproductive status and the explanatory variables. Variables that tended to be significantly associated with the reproductive status at an alpha level of ≤ 0.10 were included in the MLR model. The final MLR model was selected using Akaike’s Information Criterion (AIC) to balance model fit and parsimony. All statistical analyses were conducted using R (R Development Core Team, Vienna, Australia). The number of one km2 grid of raccoons captured were 25 in the first term and 53 in the second term, and these locations were mapped using QGIS (QGIS Development Team). This information was imported into SaTScan (Boston, USA) for cluster analysis using a space-time Poisson model and scanning for areas with high and low rates of the number of captured reproductive females using a circular window with a maximum spatial cluster size of 50 % of the population at risk. Two hundred ninety three and 298 raccoon carcasses were included in the capture data in detail as the first and second terms, respectively. From univariate analysis, the odds of being the first term had higher log CPUE (OR = 0.11, 95% CI = 0.07-0.18) compared to the second term. All juvenile females were neither pregnant nor having placental scars in both first (n = 47) and second (n = 58) terms. The pregnancy rates in the first term were 38.3% (18/47) in yearling and 84.6% (33/39) in adult, while those in the second term were 31.8 % (14/44) in yearling and 86.8 % (33/38) in adult. TN in both the first and second terms were not related to the reproductive status, and excluded from final MLR model in each term. Additionally, TN in the only first term negatively correlated to log CPUE (rho = -0.83, p < 0.001). In the final MLR model of the first term analysis, age-class (OR = 15.62, 95%CI = 6.47-37.7), log CPUE (OR = 3.54, 95%CI = 1.27-9.86), and BL (OR = 1.05, 95% CI = 1.03-1.07)) remained. These variables were positively related to reproductive status (pregnant or parous). On the other hand, age-class (OR = 22.29, 95%CI = 8.39-59.19) and log CPUE (OR = 0.48, 95%CI = 0.20-1.18) were also remained in the final MLR model of the second term. Although age-class was a positive variable for reproductive status, log CPUE was selected as a negative factor against reproductive status in the second term. Spatio-temporal analysis identified one cluster (radius 4.39 km, RR = 16.18) with high rate of productivity in the first term, while no cluster was identified in the second term. Pregnancy rate of female raccoon in adults was generally higher than that in yearlings (Gehrt 2003). Our results demonstrated that age-classes and BL of the females are considered to be important factors to determine reproductive rates. Moreover, the log CPUE was slightly positive relation to the reproductive rates in the first term. Mating system of the raccoon shifted from polygynous to promiscuous in high population area, which was suggested to increase the probability of mating success (Roy Nielsen and Nielsen 2007). In the first term, considering high population density, the mating system being promiscuous might be high reproductive rate in our study area. In conclusion, the relationships between relative density of feral raccoons and their reproductive rates differed from the first and second terms. Prange et al. (2003) suggested that raccoon inhabiting in urbanized area was high in population density and high in productivity. Our finding that derived the high productivity cluster in the first term supports that the high population density might have caused greater encounter rate with potential mates (Roy Nielsen and Nielsen 2007). In contrast, the reproductive rate in the second term did not decline despite of the low density, and BL was not found the relationship as the first term. Especially, TN in the second term might be insufficient to decline reproductive population of the feral raccoons, whereas increasing TN was related to declining CPUE in the first term. Hence, the Kanagawa local government should conduct an in-depth review of the management for the feral raccoons to maintain the appropriate TN. Finally, it is necessary for further study to examine in detail how the factors including food availability, immigration, and social network system, decline reproductive rate of feral raccoons.

Acknowledgements

We are grateful to the Kanagawa local government office for its cooperation in building the raccoon retrieval system, and the Yokosuka city and Hayama town offices for providing captured raccoons. We also thank the members of the Laboratory of Wildlife Medicine, Nippon Veterinary and Life Science University for their assistance with analyses.

References

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Keywords: Invasive Alien Species (IAS), Catch per unit effort (CPUE), Reproductive rate, Population density, Age class

Conference: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data, Davis, United States, 8 Oct - 10 Oct, 2019.

Presentation Type: Regular oral presentation

Topic: Real-time field data collection and visualization platforms

Citation: Kato T, Doi K, Tanaka A, Moriguchi S and Hayama S (2019). Difference in the factors of effect on reproductive rate of feral raccoon (Procyon lotor) between high- (2008-2010) and low- (2015-2017) density terms in Kanagawa Prefecture, Japan. Front. Vet. Sci. Conference Abstract: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data. doi: 10.3389/conf.fvets.2019.05.00024

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Received: 10 Jun 2019; Published Online: 27 Sep 2019.

* Correspondence: DVM, PhD. Takuya Kato, Nippon Veterinary and Life Science University, Musashino, Japan, tkato@nvlu.ac.jp