碩士 / 國立臺灣海洋大學 / 環境生物與漁業科學學系 / 106 / Taiwan government has been actively promoting construction of offshore wind powe. While the general public highly concerns the negative impacts that may brought from these massive anthropogenic objects, it is also believed that they would have positive fish aggregation effect. However, the effects need objectively be investigated by fisheries dependent and independent methods. Scientific echo sounder is one of the most important methods. In this study, we used joint survey of acoustic and scuba diving to evaluate fish aggregation effect among facilities in Miao-Li offshore wind farm areas. In order to evaluate such fish aggregation effect as well as to establish acoustic survey and post-processing method, three radial tracklines centered at present wind power facilities with radius of 500 meters were designed, by which acoustic surveys with vertical (90˚) and tilt (60˚) beam angles were conducted. The major results of the study are summarized below:
(1) Based on practical survey data, the single target fish detection parameters suitable for western offshore were determined, namely 6dB for the maximum beam compensation, 0.6 τ for the minimum normalized pulse and 1.5 τ for the maximum normalized pulse.
(2) In the artificial reef and wind turbine 2, the relationship between the TS values obtained by vertical survey and the scuba diving were basically consistent. However, in the wind tower and the wind turbine 1, a large amount of 5cm fish observed in the scuba diving were located outside the beam coverage, which leads to major discrepancy.
(3) In terms of the fish aggregation effect close to the wind turbine and the wind tower (<20m), detections by vertical beam angle showed that the single targets of each facility were concentrated between 15 m and 17 m in deep layer. In the case of tilt detection, the single targets were concentrated 6 m and 12 m in the middle and surface layer can only be detected.
(4) In comparisons of the fish aggregation effect among the four facilities in the two surveys, both wind turbines had higher value of Sv, NASC and estimated fish density no matter within 20 meter or 500 meter ranges, followed by the wind tower, and the lowest one was artificial reef.
There were some minor inconsistencies in TS and Sv values between acoustic and scuba diving surveys within 20 m range of the wind turbine. We speculated that such inconsistencies were mainly caused by dead zone of detection, which can be improved by tilting the detection beam angle. As for this the preliminary findings of relatively better fish aggregation effect in present wind power facilities, it was suggested that more follow-up joint surveys need to be done for further verification.
Keywords: Scientific echo sounder, Target strength, Offshore wind farm
| Identifer | oai:union.ndltd.org:TW/106NTOU5451023 |
| Date | January 2018 |
| Creators | Shih, Hsuan-Sun, 孫士軒 |
| Contributors | Lu, Hsueh-Jung, 呂學榮 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 71 |
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