Ju-Duk Yoon

Long-term changes in fish community and the impact of exotic fish, between the Nakdong River and Upo Wetlands

To evaluate fish community changes and the impact of exotic fish between the Nakdong River (lotic) and Upo Wetlands (lentic) using long-term ecological monitoring results, we conducted seasonal surveys of the fish community from 2005 to 2010. A fixed shore net (mesh 15 × 15 mm), cast net (7 × 7 mm), and scoop-net (5 × 5 mm) were used to collect fish specimens. Changes in the fish community were not significantly different in the Nakdong River and Upo Wetlands, respectively (R s > 0.322, N = 44, P < 0.05). Changes in the fish community between the Nakdong River and Upo Wet lands were identified as significant according to the results of cluster analysis. The relative abundance of exotic species increased steadily during the study period, and reached 34.2% and 89.7% in the Nakdong River and Upo Wetlands, respectively, in 2010. The bluegill (Lepomis macrochirus) was used to evaluate the level of health according to prevalence around all study sites. The length-weight relationship for bluegill in the Upo Wetlands was shown to have the highest values, via the formula (W = aL b ), with an average of 3.26 for the ‘b’ variable. According to the results of this study, lentic and lotic systems differed significantly; exotic species had an impact on both the lentic and lotic systems, but the impact of exotic species in lentic systems was greater than in the lotic systems. Additionally, the exotic species tested herein (bluegill) adapted well in the lentic system.

Evaluation of the Movement Pattern of Squaliobarbus curriculus Inhabiting in the Mid-lower Part of Geum River Using Acoustic Telemetry

Evaluation of the Movement Pattern of Squaliobarbus curriculus Inhabiting in the Mid-lower Part of Geum River Using Acoustic Telemetry. Yoon, Ju-Duk, Jeong-Hui Kim, Dong-Su In, Eun-Ji Hwang, Johee Yoon, Young-Joon Lee, Kwang-Hyeon Chang and Min-Ho Jang* (Biological Resource Center, Kongju National University, Gongju 314-701, Korea; Department of Biology Education, Kongju National University, Gongju 314-701, Korea; Geum-River Enviornment Research Center, National Institute of Environmental Research, Okcheon 373-804, Korea; Department of Environmental Science and Engineering, Kyung Hee University, Yongin 446-701, Korea)

Impact of estuary barrage construction on fish assemblages in the lower part of a river and the role of fishways as a passage

The construction of an estuary barrage, an instream structure in the lower reaches of a river, causes significant physical changes in water flow patterns and river morphology, and results in altered environmental conditions. Here, we examined the impact of the Geum River estuary barrage, completed in 1990, on fish assemblages by using a literature search and fresh surveys of fishways in the barrage. We found that fish assemblages upstream and downstream of the barrage were altered following its completion. After construction, more species were found in the freshwater area, with a particularly great increase in freshwater species. Conversely, estuarine and marine species were only consistently caught in the downstream salt-water area, although the number of species increased. In total, 15,829 fish from 47 species and 20 families were identified at the three types (pool and weir, rubble type, and boat passage) of fishways in the barrage. The dominant species were Chelon haematocheilus, an estuarine species, Coilia nasus, a diadromous species, and Erythroculter erythropterus, a freshwater species. The mean total length of fish (101.9 ± 76.0 mm) in the boat passage fishway was approximately 100 mm lesser than those in the pool and weir (207.2 ± 112.8 mm) and rubble type (205.8 ± 112.7 mm) fishways. The boat passage fishway was the most efficient for fish movements. The current fishway system is not sufficient for fish migration, and thus additional ways are required to improve the system such as the boat passage. Few estuarine or diadromous species were found in both freshwater and salt-water areas, but freshwater fishes that accidently moved to salt-water area actively used fishways. Therefore, fishway management in the Geum River estuary barrage has to focus on freshwater fish; however, this may need to change to a focus on migratory fishes depending on ecological life cycles of migratory fish.

Home range and habitat use of translocated endangered species, Cottus koreanus, in South Korea

ABSTRACT The home range and characteristics of Cottus koreanus were investigated using passive integrated transponder (PIT) telemetry in the Gulji Stream, Korea, where the target species was artificially translocated. After release, tagged individuals moved up to 78 m away from the release site in search of proper habitats. The average distance moved until settlement was 17.1 m. The observed home range of settled individuals had longitudinal sections of 9.9 ± 3.6 m and surface areas of 7.2 ± 2.7 m2. This is comparable to congeneric species that inhabit similar ecological habitats. Once individuals had settled, they rarely moved from that site except during the spring season. The typical microhabitat characteristics of the sites where the released individuals settled are: water depth of 5–10 cm, water velocity of 0.1–0.3 m s−1, and the size of boulders and cobbles of 10–20 cm in diameter. This study of translocated C. koreanus individuals provides detailed information about habitats that can be used for effective habitat restoration and successful translocations attempts of this species.

Fish Biodiversity Monitoring in Rivers of South Korea

During past three decades, high growth and industrialization have brought increasing development and utilization of stream catchments. As a result, the structure and functions of rivers and streams have been physically, chemically, and biologically changed in South Korea (Joo et al. 1997). Recently, rising interest in stream ecosystems has triggered an increasing amount of research, especially in defining the relations between biological organisms and water pollution. However, the overall understanding and evaluation of stream ecosystems using interdisciplinary fields (e.g., geology, physics, chemistry, biology) is relatively difficult because of structural and functional characteristics of the stream ecosystem.

Impact of Largemouth Bass (Micropterus salmoides) on the Population of Korean Native Fish, Crucian Carp (Carassius auratus)

Exotic species in aquatic ecosystem generate various problems domestically as well as globally. Largemouth bass (Micropterus salmoides) which is a well-known exotic species globally, acts as a substantial disturbance factor on the native fish communities in Korea due to the high predation pressure and hence designated as a ecologically harmful species by Ministry of Environ- ment. In this study, we investigated the impact of largemouth bass on Korean native fish population, crucian carp (Carassius auratus), to identify responses of the prey fish. Two fish species were col- lected at seven reservoirs distributed at the Nakdong River catchment area, and changes in length- frequency and length-weight relationship (LWR) were analysed depending on existence of large- mouth bass. At bass absent sites, ratio of under age 1 year individuals were small, and over age two years were dominant. Conversely, normal length-frequency distribution pattern was identi- fied at bass absent sites. The LWR of crucian carp (fish smaller than total length of 160 mm were only considered as it is frequently consumed by bass predation) was different depending upon bass existence. The value of parameter b at bass absent reservoirs was 2.909, which was smaller than that of bass present reservoirs, 3.100. Our results imply that crucian carp at bass present reser- voirs presented a different strategy to survive from predation by bass, through relatively rapid growth. We propose that other native species might have similar growth strategies like crucian carp.