제주도산 (濟州島産) 실뱀장어의 소상동태에 (溯上動態) 관한 연구 - 특히 환경요인과의 관계를 중심으로 - = Studies on the Upstream Status and Environmental Factors of Glass - Eel Collected in the Cheju Island , Korea -

다국어 초록 (Multilingual Abstract)

In order to know the upstream mechanism and the related environmental factors of Glass-Eel in Cheju island, samples and environmental data were collected and analyzed during the period from March 5, 1973 to April 19, 1974 in 5 stations, including Cheonji stream. The results are summarized as follows: 1. The upstream duration of the Glass-Eels lasts about 140 days from Jan. 20 to June 15. The upstream period can be divided by their frequency as following: 1) Beginning Jan. 20-mid. Feb. 2) Beginning of peak late Feb.-late Mar. 3) Last of peak early Apr.-late Apr. 4) Last early May-mid. May 5) Stopping period late May-mid. June 2. The yearly total upstream fries in Cheju island as a whole amount about 60kg of which Cheonji stream takes the share of 45.30% ; Kangjeong stream, 32.29%; Shinyangri, Sungsan-myun, 18.68% ; Oedo, 2.55% ; and Ongpo stream, 1.18%. It suggests that southbound streams take the outstanding majority of the total upstream fries, i.e. 96.27%. 3. The mean body length of fries was 56.37mm in 1973, 56.23mm in 1974 : comparing to the Japanese data the fry of Cheju island was 1.048-1.411mm smaller than the Japanese. Generally the early upstream fries tend to be larger than the late ones. 4. In Cheju Island, temperature was suspected not to be a limiting factor which controlled the upstream amount; but when the water temperature downs sharply, the number of fries tended to be reduced. 5. The numbers of upstream fries seemed to be large during both 1st to 5th and 13th to 15th of the moon age. However, the correlation coefficient r=-0.0597 suggested that the relation of the moon age to the number of upstream fries was negligible. 6. The relation between cloud degree and upstream number of fries was negligible as r=0.1239. In other word, upstream amounts tended to be relatively large at cloud degree 6, but there were still some amounts of upstream at degree 0. These facts suggest that cloud degree cannot be a limiting factor to control the upstreams. 7. Tide is the most important limiting factor. During two hours from 90 minutes before high water to 30 minutes after the high water, about 80% of total samples were collected. It suggests that high water provides better condition to upstream fries. 8. As r=5.5287, the correlation between the tidal range and upstream numbers is relatively high. The greatest upstream numbers appeared at high water period when 1.5 to 2.5m tidal interval was recorded. 9. Diurnal change of upstream numbers tends to show high value at the time 3 hours after sunset. Particularly when the time matches with high water the number reaches greatest. 10. Phototaxis of fry appeared to be negligible as r=-0.1154. The light which was used during collecting samples seemed to promote catch efficiency rather than concentrating school. 11. The Glass-Eels which submerged beneath the bottom were observed during ebb-tide period of day time. The result showed that early-stage fries with under-developed body pigment took negative stereotaxis; However elver took positive stereotaxis. 12. Marking and recapturing experiment proved that the younger Glass-Eels showed more positive rheotaxis. On the other hand, the upstream speed was calculated 2.5 m/minute, which was far slower than 36 m/minute reported by foreign scientist. But the speed seemed to be affected by condition of streams and ebb-tide.