Fish Community Characteristics and River Health Assessment in Naejangsan National Park

This study examined the characteristics of fish communities and river health in the Naejangsan National Park, Korea, from June to September 2021. The survey identified 31 species across nine families from 23 survey stations in five districts. The dominant and subdominant species were Zacco temminckii (26.8%) and Z. platypus (18.3%), respectively. The second most abundant species were Rhinogobius brunneus (13.9%), Rhynchocypris oxycephalus (10.2%), Squalidus gracilis majimae (6.2%), Pungtungia herzi (4.3%), Z. koreanus (4.2%), Acheilognathus koreensis (4.1%), S. chankaensis tsuchigae (2.1%), Lepomis macrochirus (2.1%), and Micropterus salmoides (1.5%). Among the collected fish species, 16 (51.6%) were endemic to Korea: Rhodeus uyekii, Acheilognathus koreensis, S. gracilis majimae, S. chankaensis tsuchigae, Microphysogobio yaluensis, Z. koreanus, Iksookimia koreensis, I. long- icorpa, I. hugowolfeldi, Cobitis nalbanti, Pseudobagrus koreanus, Silurus microdorsalis, Liobagrus somjinensis, Coreoperca herzi, Odontobutis platycephala and O interrupta. In addition, three exotic species were recorded: M. salmoides and L. macrochirus, both classified as ecologically disturbed species, as well as C. cuvieri. A landlocked species, R. brunneus, was also identified. Community analysis revealed that dominance (0.493-1.000) was higher in the upstream areas, whereas diversity (0.169-1.889) and richness (0.446-2.124) were greater in the downstream areas. Evenness (0.154-0.952) showed no clear trend. The community structure was divided into four categories: uppermost stream (stations 1, 2, 7, 8, 9, 18, and 22), upper stream (stations 11, 14, 15, 16, 19, 20, and 23), near-lake + middle stream (stations 3, 4, 6, 10, 12, 13, 17, and 21), and lake (station 15). River health, assessed using the fish assessment index, was categorized as very good (14 stations), good (six stations), normal (two stations), or bad (one station). Although Naejang National Park is relatively well preserved, it faces ecological disturbances from species such as M. salmoides and L. macrochirus. Additionally, many weirs and debris barriers have been installed in streams, and river work has been observed in some areas. Therefore, conservation measures are needed to ensure stable fish habitats in the Naejangsan National Park. These measures include removing ecologically disturbed species (M. salmoides and L. macrochirus), installing fishways in weirs and debris barriers, and avoiding indiscriminate river work.