Ex situ and in situ measurements of juvenile yellowfin tuna Thunnus albacares target strength |
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| Authors: | Hsueh-Jung Lu Myounghee Kang Hsing-Han Huang Chi-Chang Lai Long-Jin Wu |
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| Affiliation: | (1) Department of Environmental Biology and Fisheries Science, National Taiwan Ocean University, 2 Pei-Ning Rd, Keelung, 202, Taiwan, ROC;(2) Center of Excellence for Marine Bioenvironment and Biotechnology, National Taiwan Ocean University, 2 Pei-Ning Rd, Keelung, 202, Taiwan, ROC;(3) Myriax Software Pty Ltd, 110 Murray Street, Hobart, TAS, 7000, Australia;(4) Coastal and Offshore Resource Research Center, Taiwan Fishery Research Institute, No.1-1, Yugang N. 1st Rd., Cianjhen District, Kaohsiung, 80672, Taiwan, ROC; |
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| Abstract: | To provide target strength (TS) information for estimating the body length of yellowfin tuna Thunnus albacares and its abundance around fish aggregating devices, TS was measured ex situ and in situ. In the ex situ TS measurements, two cameras synchronized with a 200 kHz echosounder were used to obtain the precise orientation of the yellowfin tuna under free swimming conditions. The ex situ TS (dB re 1 m2)–fork length (FL, cm) regression was: TS = 27.06 log (FL) − 85.04. Ex situ TS was found to reach its maximum in the tilt angle range of −15° to −20° after excluding TS samples with insignificant correlation to the tilt angle. The angle between the vertebra and the swim bladder was approximately 25° according to X-ray images, supporting the above tilt range. The relationship between the swim bladder volume (V SB, ml) and the fork length was: V SB = 0.000213 FL3. The results from the in situ TS measurements indicated that the tilt angle was highly concentrated between −10° and 15°. The results from a calculation using the ex situ TS–FL equation with the fork length from biological sampling agreed strongly with the average in situ TS. |
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