臺灣博碩士論文加值系統

為能藉由黃鰭鮪幼魚標物反射強度 (TS) 之特性，評估聚集於人工集魚器 (Fish aggregating devices, FAD) 之黃鰭鮪幼魚體長及減少幼魚之混獲，本研究在水槽中設置同步之雙攝影機系統，搭配頻率200 kHz之魚探機，擷取黃鰭鮪自然游動之TS、俯仰角及尾叉長 (FL)，依據黃鰭鮪之俯仰角及TS，探討俯仰角對於TS之影響。另外，量測黃鰭鮪之泳鰾體積，建立其與FL之成長關係，且透過黃鰭鮪魚體X光照片，了解泳鰾於黃鰭鮪魚體內之位置。最後，在FAD現場計測水下魚群之TS，並使用曳繩釣進行生物採樣，以水槽實驗所獲之TS特性篩選單體回訊，分析FAD聚集魚種之資訊。本研究主要之成果摘述如下：

(一) 尾叉長25 ~ 69 cm之黃鰭鮪幼魚，其依200 kHz魚探機所測得之TS，與尾叉長對數具有明顯之線性關係，25 cm與69 cm之黃鰭鮪，正背部TS約相差達13 dB。

(二) 黃鰭鮪之TS明顯受到俯仰角變化影響，當俯仰角為負時 (向下洄游)，易產生較大之TS，由俯仰角分組比較實測TS得知，TS與Log (FL) 迴歸線之截距在 [−15° to −20°] 為最大，故最大之TS出現在此俯仰角範圍。

(三) 泳鰾於魚體內位置並非與脊椎平行，而有一約25°之夾角，造成黃鰭鮪本研究實測TS最大值表現於俯仰角-15°~ -20°間，未成熟黃鰭鮪之泳鰾開始發育後，TS明顯增大，且俯仰角影響更趨明顯。

(四) 本研究嘗試從FAD現場之單體魚軌跡中篩選黃鰭鮪之回訊，以向下游動且TS呈現遞增者為對象篩選，篩選之TS經水槽實驗之TS-體長關係式轉換，其平均體長 (47.53 cm) 與現場曳繩釣捕獲之黃鰭鮪體長範圍 (39 ~ 46 cm)相近，顯示篩選規則有利黃鰭鮪幼魚之判別。

To provide target strength (TS) information for estimating the body length of yellowfin tuna (Thunnus albacores, YFT) and its abundance around fish aggregating devices, ex situ TS and in situ TS were measured for reducing the by-catch of juvenile YFT. In ex situ TS measurement, two cameras synchronized with a 200 kHz echosounder were used to obtain precise TS, orientation and fork length (FL; cm) of YFT under free swimming conditions. The orientation and TS of YFT were combined for finding out how the orientation affected to the TS. On the other hand, the swim bladder volume (VSB; ml) of YFT were measured to establish the relationship between the VSB and FL. The X-ray images were taken for examining the position of swim bladder in YFT’s body. In in situ TS measurement, one hour of stationary FAD survey was conducted for analyzing the fish around FAD. After TS measurement, the troll line was used to biological sample the fish around FAD for examining the species of aggregated fish around FAD. From ex situ and in situ TS measurement, the sound scattering characteristic of living juvenile YFT were summarized as the followings:

1. The TS of juvenile yellowfin tunas with length around 25 ~ 69 cm were positive significantly related to logarithmic fork length when the 200 kHz frequency transducer was used. Furthermore, the TS of yellowfin tuna with fork length in 69 cm was 13 dB more than in 25 cm.

2. The TS of yellowfin tuna changed significantly with the orientation of yellowfin tuna, and the larger TS always expressed with the negative orientation. From the interception of TS-Log(FL) regression for the grouped orientation analysis, the largest TS of yellowfin tuna was found in the group of [−15° to −20°].

3. It’s a significant trend that the swim bladder of yellowfin tuna grew synchronized with the fork length. The development of swim bladder volume in the stage of juvenile yellowfin tuna was faster than in the stage of adult. The largest TS expressed with the orientation around -15° to -20° because the interior angle between the swim bladder and vertebra was 25° approximately in the yellowfin tuna’s body.

4. We segregated single target echoes collected in the FAD waters with condition of increasing TS while conducting downward swimming. The echoes were transformed into FL by the TS-FL equation established from the tank experiment. The mean FL (47.53 cm) was very close to those measured from yellowfin tuna sampled by troll lines (39 ~ 46 cm). The segregating method developed in this study may be useful for discrimination of young yellowfin echoes.

摘要 I
Abstract III
目錄 V
表目錄 VII
圖目錄 VIII
壹、前言 1
貳、材料與方法 8
一、 非現場活體黃鰭鮪之單體標物反射強度計測 8
(一) 活體黃鰭鮪幼魚樣本取得 8
(二) 聲探系統 9
(三) 水槽實驗設計 9
(四) 黃鰭鮪之TS擷取 10
(五) 攝影影像讀取及解析 11
(六) 魚體尾叉長計算 12
(七) 資料分析 13
二、 黃鰭鮪泳鰾體積量測 14
三、 FAD之現場TS計測調查 15
参、結果 16
一、 黃鰭鮪TS水槽實驗 16
(一) TS與FL之關係 16
(二) 俯仰角與TS之關係 17
二、 黃鰭鮪泳鰾體積 18
三、 FAD現場TS調查 20
肆、討論與結論 22
一、 活魚水槽實驗設計之限制與改良 23
二、 影響TS之因素及FAD現場黃鰭鮪體長推定 24
三、 現場黃鰭鮪幼魚之辨別與減少混獲運用 28
四、 結論與展望 32
伍、參考文獻 34

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