| Summary: | 碩士 === 國立海洋大學 === 漁業科學研究所 === 86 === Wushykeng Creek is a 12-kilometer long mountain stream, a tributary to the Daan River, situated in the Taichung county in the central portion of Taiwan. In 1987-1989 the Taiwan Forestry Bureau constructed seven check-dams (sabo-dams) for the stream bed stabi ization, with nine fishways. From July 1995 to May 1997, the stream survey was conducted at eight stations to collect data on physical environment (stream flow, stream width, water depth, water velocity, bottom substrate, and shore line conditions), water quality (water temperature, dissolved oxygen content, pH, and conductivity and total dissolved solids) and fishes (species composition, and population structure and abundance) to assess the impacts of the check dams on stream ecosystem, and to evaluate the effectiveness of the fishways for fish passage. For the latter fish were also tagged and released immediately downstream from one of the fishways to assist the evalu tion.
The check dams had the heights of 7.5m to 13m, and undoubtedly became barricades for the upstream migration of fishes in the wushykeng Creek. In addition to their blocking fish migration, the check dams altered stream physicale nvironments and water quality, adversely affecting the stream ecosystem and fish life. In the immediately upstream areas of the dams, rocks and gravel were piled up, that rifted up the surface flowing stream, decreased its slope, water depth, water flow velocity, dissolved oxygen contents, and fluctuated its water temperature. The alternations of stream physical environments and water quality were particularly obvious in the dry season. In the downstream area, the water poured down the dams, deelpy excavated the downstream bed, and increased the shore erosion, water turbidity and dissolved solid contents. These downs tream alternations of the environment were most serious in Wusheykeng creek, of them Varicorhinus barbatulus (Family Cyprinidae) was most dominant. It was a resident species, spawning apparently throughout the year in the creek, but the mature fish showed seasonal migration: upstream migration at the end of the summer raining season (around October) and downstream migration at the beginning of the raining season (around March). Based on the monthly and longitudinal variations in the length frequency distribution of fish collected above and below the dams and on the results of the tagging experiment, there were strong evidences that V. barbatulus was able to pass the check dam(s) by utilizing the existing fishways (pool type) for its upstream migration.
Hemimyzon formosanum (Family Homaloperidae) apparently spawned outside the Wushykeng Creek, but some of the fish migrated to the creek at the end of the raining season for feeding during the dry season. Its body is equipped with an specific adherent apparatus formed by the ventral portion of body and laterally expanded pectoral and pelvic fins. This apparatus enables this species to attach itself on rocks in the rapid flowing creek. There were some evidences in this study that large fish (>5 cm) of this species may be able to climb directly over the check dams in its upstream migration.
The other six species included Rhinogobius bruneus, Rhinogobius rubromaculatus (Family Gobidae), Candidia barbata, Acrossocheilus parodoxus, Zacco pachycephalus (Family Cyprinidae), Leiobargus adiposaris (Family Bagridae). Of these species, R. bruneus like V. barbatulus was a resident species, occurring in the entire creek. The other species occurred in the downstream and were considered as occasional visitors for the Wushykeng Creek. Some fish of these species were also found in the Wushykeng Creek. Some fish of these species were also found in the upstream from the first check dam, indicating that these fish may also pass the fishway for the upstream migration, but lesser than those of V. barbatulus and H. formosanum.
Although there were evidences of successful passage of fishes through fishways mentioned above, the number of species and the abundance of fish in the creek showed decreases from downstream to upstream. Also, there was high mortality of fish in the section The results of this study suggested that the check dams in the ishykeng Creek adversely affected the physical environments, iter quality and fish life. In order to mitigate the adverse ffects, the following four approaches may be considered:
1.Repair existing fishways and develop a management program to maintain their proper function.
2.Replace existing fishways with portable fishways.
3.Remove existing check dams and fishways.
4.Replace each of the existing check dams and fishways with a series of low check dams, that are also functioned as a fishway.
For a long-term and cost-effective consideration, the fourth mitigation approach is recommended
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