博士 / 國立臺灣大學 / 海洋研究所 / 102 / Fishery stock assessment and management used to focus on single species method. FAO promoted the ecosystem-based fishery management (EBFM) for the sustainability of living aquatic resources. EBFM need to be taken into account with trophic structure and flows of biomass through species interactions. In present study, nitrogen and carbon stable isotopes analyses were applied to investigate the trophic structure of sailfish. A total of 263 sailfish muscle samples were examined. The δ15N values for sailfish ranged from 7.51 to 14.19 &;#8240; (mean=12.06&;#8240; ± 1.16) and the δ13C values ranged from -22.04 to -15.48 &;#8240; (mean=-17.62&;#8240; ± 1.10). The δ15N values were positively related to body length, while δ13C were negatively related to body length. The results revealed the different size class of sailfish occupied different trophic position of pelagic ecosystem. We postulate that the factors which influence on trophic position of sailfish between young and adult were food sources, habitats and migratory pattern.
Stable isotope ratios of a consumer are related to those of its prey. Stable isotope mixing model was used to estimate diet composition of consumer by mass balance equation. In this study, stable isotope mixing model was applied by carbon and nitrogen stable isotopes of sailfish to estimate the food sources of their prey. The sailfish were segregated by juveniles (<140cm, LJFL), maturing stage (141-180cm, LJFL) and adults (>181cm, LJFL) from previous research. The most important preys for juvenile sailfish were Bramidae (15.90%), Mene maculata (11.04%) and Clupeidae (9.62%). Therefore, adult sailfish feed on Trichiurus lepturus (32.63%), followed by Katsuwonus pelamis (15.82%) and Priacanthus macracanthus (11.30%). In spite of the apparent high prey diversity of diet composition for sailfish, they feed mainly on epipelagic species in the waters off eastern Taiwan.
Food web is an important element in pelagic ecosystem to transport nutrients and energy flow between consumers and prey. In order to investigate the role of sailfish and to explore the function and structure of pelagic ecosystem in eastern Taiwan waters, we applied Ecopath with Ecosim model inferred from stable isotope analysis, stomach content analysis and fisheries statistical data to perform pelagic trophic model of eastern Taiwan. The results reveal that the trophic level of the functional groups varied from 1.0 to 4.52. Marine mammals and shark are occupied top trophic level. Total ecosystem throughput is 3054.43 t/km2/yr. Sum of all production, sum of all consumption and sum of all respiratory flows are 1787.29, 824.89 and 528.62 t/km2/yr, respectively. Total primary production to total respiration ratio is 3.13. Connectance Index (CI) and System Omnivory Index (SOI) are 0.47 and 0.25, respectively. In this study, we preliminary established pelagic trophic model in eastern Taiwan and the results can provide scientific references for ecosystem-based fisheries management. Ecosim model was applied to predict biomass trajectories of each functional groups in next 50 years. The predicted biomass trends indicate that if we maintain current fishing efforts in eastern Taiwan will reduce most of biomass of top predators in the future (e.g. Marine mammals, tuna, billfish and shark). The results show current fishing efforts in eastern Taiwan is still high, we suggest the fish stock need to be monitored and fishing efforts should be further reduced.
| Identifer | oai:union.ndltd.org:TW/102NTU05279014 |
| Date | January 2014 |
| Creators | Chung-Nan Tsai, 蔡政南 |
| Contributors | 孫志陸 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 132 |
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