博士 / 國立臺灣海洋大學 / 水產養殖學系 / 100 / The dissertation has deeply involved in the investigation of the endangered landlocked Taiwan salmon (Oncorhynchus masou formosanus) on the fundamentals viewing from several aspects associated with its own life cycle including the biological studies of reproduction, growth and age, the ecological studies of the food composition and the autecological studies of the habitat and patterns of moving behavior of this species. Data, results and important conclusions are abbreviated which cover over one decade’s (2000 – 2011) cumulative efforts in order that these findings be contributed to the ever problems encountered in real actions pertaining to do with the conservation policies, in situ habitat managements and stock restorations.
The condition factor and fecundity of landlocked Taiwan salmon increased with increasing body length and with significant higher values exhibited by the hatchery reared female than those of wild ones. The major factor influencing the contemporary natural habitat carrying capacity and the size of wild females of all year classes was the frequency and landing numbers of typhoons. The gonado-somatic index (GSI) of early mature male 0+ was found greater than that of 1+. Significant difference between sex with mature male bearing higher values than those of mature female were examined through the ratios of the lengths of upper jaw / total body and lower jaw / total body. There were no significant differences in fertilization rates ranged between 93.6 ± 5.2and 96.6 ± 4.0 (%), hatching rates ranged between 76.4 ± 12.6 and 79.6 ± 11.3 (%) as well as swimming up rates ranged between56.8 ±10.8 and 69.6 ± 8.8 (%) among the four temperature treatments either at constant level of 11,13,15 ℃or at a spontaneous temperature condition using natural stream water source as control. The average size (range) of nest was 0.7± 0.5m2 (0.23~ 1.9m2). The range of nest water depth was 23.5 ~ 51.7cm. The average (range) speed of water current at the bottom of nests was 0.4 ± 0.1ms−1 (0.1~ 0.6 ms−1). The under gravel egg-laid depth range was 3.0 ~ 22.5cm, with an average depth of 8.3 ± 6.3cm.
The least maturation ages of Taiwan landlocked salmon were 0 + for male, 1 + for female, and the inevitable death after breeding might not happen in relative small proportion of fish. The maximum age limit updated was observed at age 3+. The size of the early male parr (0+) was significantly larger than that of the same age. The growth rate was reduced with increasing age, and significantly higher in male than in female.
The movement pattern of Taiwan landlocked salmon exhibited: 1) strongly diurnal behavior: daily movement behavior started near sunrise and ended at sunset and moved into flowing water during light time and moved back to a specific deep pool at night, and 2) habitat preference behavior: daily distance moved reduced with time after release and non-competitive individuals moved frequently upstream and downstream between pools staying in a state of instability situation looking for a suitable habitat, and 3) sedentary home range is 563m, and 4) home coming with the correct directional movement behaviors.
Terrestrial invertebrates contributed a greater proportion to the large sized fish, rather than to the small sized one of the con-specifics in terms of food preference, offering high availability among the food items of various trophic structural levels from stomach composition analyses. This high availability phenomenon was reflected by the higher proportion of terrestrial invertebrates in the stomach content of fish sampled at habitat sites with relatively larger canopy coverage area during wet season in comparisons to the other seasons of the year.
Re-habitation of fish to the historic streams in the water sheds of the extinct area still face threatens from the existed artificial dams and ever-lasting farm activities. The recommendations in the release strategy and in situ preparation as well as environmental management are listed as below: 1) Location selection: stream origins or tributaries, where the shelter area are large enough for fish to escape natural disaster from flood, with relative small flow rate during normal seasons. 2) Timing for release: release fish at period post of landing of typhoon, and one month before spawning season. 3) Release age (size): Release fish at age 1+ (around 1.5, 15 – 20cm) would yield high survival rate as well as high reproductive potential. 4) Multiple sites along release stream: Release fish to various sites may not only reduce natural risks but also create opportunities for population dispersion and expansion.
| Identifer | oai:union.ndltd.org:TW/100NTOU5086090 |
| Date | January 2012 |
| Creators | Lin-Yan Liao, 廖林彥 |
| Contributors | Yii-Shing Huang, 黃沂訓 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 168 |
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