Industrial development has caused biodiversity loss. To preserve biodiversity, studies about wildlife management has been fast developing. Wildlife management deals with invasive species eradication, endangered species protection, human-carnivore conflict, and crop damage, among others. In South Korea, there are two semi-aquatic mammals (Nutria, Myocastor coypus and Eurasian otter, Lutra lutra). Nutria is an invasive species and the Eurasian otter is an endangered species in South Korea. To manage the species, the first things to understand are their habitats, distribution, and status.
During the course of my Ph.D, my studies aimed to: (1) identify the distribution, spread, and habitat preferences of nutria invading the lower Nakdong River in South Korea, in order to facilitate current control and eradication endeavors, (2) determine the food habits of nutria using stable isotope analysis, (3) assess the impact of environmental policies on the re-establishment of the Eurasian otter through a literature review, (4) trace conservation activities for the otter in South Korea by reviewing newspapers from 1962–2010, (5) define distribution, habitats, and status of the otters in Nakdong River basin by applying ecological stream health assessment indices, (6) know advancement patterns in association with environmental factors, based on self-organizing map and diffusion kernel, and, finally, (7) identify prey items of the otters at the small swimmer fish dominant sites using DNA barcoding.
The studies highlights are: (1) Nutria populations were recorded in 45 of 236 sites investigated. The distribution patterns revealed that the spread of nutria from farming sites has mainly proceeded along rivers via tributaries. Important factors associated with the establishment of new populations were food availability, levees with suitable burrow materials, and slow water flow. The winter climate was also important, and the total number of days below -4℃ significantly affected nutria occurrence. To date, efforts to control or locally eradicate nutria populations have had little success due to insufficient budgets and the lack of coordinated management activities between local governments. To improve the efficiency of nutria eradication programs, local governments must establish an integrated and coordinated strategy that is overseen by a single, national agency.
(2) With regard to diet, isotope ratios suggested that coypu primarily fed on aquatic vegetation. Coypus appear to make more use of the heavier nitrogen isotope in hind-leg muscle during winter, presumably associated with muscle tissue metabolism contributing to weight loss. During winter, these higher metabolic requirements together with the decreased availability of aquatic vegetation suggest that baiting near waterways in winter could be an effective method to control invasive coypu populations.
(3) The Korean government implemented a policy in the 1980’s to promote the coexistence of nature conservation and development. We hypothesized that two distinct improvements (water quality improvement and forest development) in the environment enabled the distribution of otters to expand significantly. Overall, forest development in basins was the most important factor positively influencing the otter population.
(4) Since 2000, the number of newspaper articles about conflicts between otters and urban development, and the roles of otters in encouraging eco-tourism have increased significantly. About 12% of grid squares with otters were reported only in newspaper articles, mostly in urban areas. High citizen interest could be the basis for understanding the ecological importance of human-carnivore coexistence. Otters serve as a good example for establishing conservation strategies and citizen education for effective conservation.
(5) Habitat quality was investigated using the stream health assessment program (SHAP). We hypothesized that higher SHAP indices would indicate better habitat for otters. Benthic macro-invertebrate and otter population indices were highly related. Otter population indices provided better habitat information compared with presence-absence data. Stream health assessment indices had the highest correlation with otter distribution.
(6) Otter populations recovered rapidly in the southern peninsula of Korea. Two geographically separate populations (N and S) were identified by the diffusion kernel method. Otter population densities, environmental factors, and sample locations were effectively integrated according to the geo-SOM. Overall associations between otter populations and environmental factors were observed strongly for population establishment during the course of dispersal. Anthropogenic factors (e.g., distance to factory) were overall influential in the dispersal of otter populations while food sources (e.g., number of fish individuals) were preferred at the frontlines of advancement.
(7) Because the dominant Cyprinidae are small and fast swimmers at the study sites, otters fed more on frogs and benthic fishes. In a comparison between fish fauna and consumed items, in more than half of sites (62.5 %), all fishes of the fauna at the sites failed to match all fishes consumed, although the number of samples were limited. In addition, most food items coincidentally present in fish fauna were not the dominant fish species at the sites. Otter protection could be established on a large scale according to their large home range.
The results of my studies revealed the importance of governance and of highly improved public conservation awareness for wildlife management. Habitat condition is mainly based on food availability for both species. According to public efforts, nutria populations have decreased and otter populations have greatly recolonized in South Korea. Further studies will include fine scales of human and otter coexistence, genetic approaches for populations, and theoretical interactions between the environment and two species.