Effects of Climate Change on the Fish Community, and Rhynchocypris kumgangensis (Cypriniformes: Cyprinidae) Distribution in Deogyusan National Park

Rhynchocypris kumgangensis, endemic to Korea, is limited to the upper Hangang River and Gucheondongcheon Stream. As a key and climate-sensitive biological indicator species in the Deogyusan National Park, it has a southern range limit in the Gucheondong Valley. Due to climate change, notable shifts in the activity, distribution, and population of R. kumgangensis on the Gucheondongcheon Stream are expected. This study examined trends between the 2020 field survey and previous surveys (2014–2018) for fish faunal changes at 13 sites in the Deogyusan National Park and for the population changes of R. kumgangensis at four sites in the Gucheondongcheon Stream. At 13 sites, we identified 996 individuals of 17 fish species in seven families, including 2 endangered (Pseudopungtungia nigra, Hemibarbus mylodon) and 11 Korea-endemic species. The Fish Assessment Index (FAI) of the 13 sites in the Deogyusan National Park was analyzed and found to be of A-grade in both the 2020 and past surveys, with high scores in all M1–M8 categories. Both the results of CCA and field surveys between the entire fish community and pH, DO, and water temperature revealed that the population of R. kumgangensis had a narrower distribution range and was more sensitive to water temperature than the same cold-water fish, R. oxycephalus. Climate change has been identified as causing the annual maximum temperature (°C) in the Deogyusan National Park to increase year on year and the R. kumgangensis population to decline, suggesting that the time for conservation efforts is “now”.