| In recent years, marine farm is widely promoted as an innovative model in ourcountry to restore ecosystems and the growth of fisheries production. The demand formonitoring and effective assessment of the restoring fishery resources in artificialhabitats is increasing. In view of the development needs of the "green" fishing industry,the underwater acoustic measurement technique is becoming the important way ofresource survey and evaluation in artificial habitats, because not only does it have theadvantages of fast and effective features, wide survey area and no harm to livingresources but also it can provide the sustainable data.Research of fish Target Strength (TS) measurements is the foundation work offishery resource, and it is also an important parameter for the marine resource acousticalsurveys. The studies of target scattering strength of fish started late in domestic. Inrecent years, some domestic scholars used ‘wild fish observing’ method to measure thetarget scattering strength. But they can’t meet the needs of the acoustic surveys offisheries resources.Sebastiscus marmoratus is not only the major catch fishing operations andgill-netting operations in the waters around the island of Gouqi but also the majorityleisure fishing stock for the local and foreigners.A sudy of Sebastiscus marmoratusacoustic target strength is the basis for its scientific conservation and rationaldevelopment. It is also a need for its resources conservation, monitoring and evaluationof the seaweed bed.With the full-year advantage Sebastiscus marmoratus，in the waters around theisland of Gouqi, Zhoushan, being taken as the experimental samples in this study, wehave not only established a set of single fish target strength measurement system butalso conducted tentative measurements of Sebastiscus marmoratus by using theBioSonics DT-X Series echosounder. We have also verified the measurement results and established the empirical relationships of Sebastiscus marmoratus target strength usingcage experiments. In this article we aimed to explore methods and techniques of fishtarget strength measurement, which may lay a foundation for the research of fish targetstrength and the evaluation of the ecological resources recovery using the acousticmethod.This first chapter of this paper presents an overview about the basic concept of fishunderwater acoustic detection as well as the research and development at home andabroad. The second part emphasizes the target strength of Sebastiscus marmoratus inthe waters around the island of Gouqi, Zhoushan, and has brought up its target strength-length empirical formula. Chapter three takes advantage of the experimental results ofthe second chapter. Synchronization underwater acoustic surveys were conducted inmussel farming area and the waters around the north island of Gouqi, using BioSonicsDT-X Scientific Echosounder （430KHz）and Didson（the High Resolution in August2011.We make a preliminary evaluation of the major fish resources in the musselfarming waters. The main results are as follows:(1)The body length of Sebastiscus marmoratus ranged from7.4to14.8cm and thecorresponding range of average target strength was-45.6~-35.1dB. Relationshipbetween body length and the target strength of Sebastiscus marmoratus are as follows:TS=20lgL60.85. Changes in the tilt angle can cause the target strength of the sameexperimental fish values vary less than20dB at the same measurement depth.(2) This device can be seen as a kind of effective and feasible measurementexperimental device, which solved the controllable problem of different parameters inthe measurement of target strength of the single fish.(3) Different sizes of fish are of different percentage in the entire investigationwaters.The data investigated in August shows: The number of fish whose targetstrength values are-56dB～-54dB、-52dB、-44dB～-40dB is larger than3%.Andthe percentage of fish of-52dB to33.22%is significantly more than the other strengthof the fish. And the data investigated in September shows: The number of fish whosetarget strength values are-56dB、-54dB、-49dB～-46dB、-44dB～-41dB is largerthan3%.And the percentage of fish of-44dB to18.05%is also significantly more thanthe other strength of the fish. Fish density in the mussel farming area is obviouslyhigher than that in the peripheral waters, which shows that mussel farming has not only brought economic effects but also it is a conservation method for fishery resources.(4)A total amount of1715Sebastiscus marmoratus was detected on August22,2011,962on September7, and1065on September9. According to the experiment inChapter II,relationship between body length and the target strength of Sebastiscusmarmoratus is as follows: TS=20lgL-60.85. The body length of Sebastiscusmarmoratus whose target strength values are-43dB～-39dB, ranges from7.4to14.8cm, This result is basically the same as the resource surveys in the last two years.The innovation of this paper is that we have obtained the relationship betweenbody length and the target strength of Sebastiscus marmoratus using the improvedtethered control experiment and cage experiment. And at the same timesynchronization underwater acoustic surveys were conducted in the mussel farmingareas of Gouqi and the waters around using the experimental results. |
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