Acoustic backscattering by deepwater fish measured in situ from a manned submersible |
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| Institution: | 1. Department of Zoology, Hawaii Institute of Marine Biology, P.O. Box 1106, Kailua, HI 96734, USA;2. Hawaii Institute of Marine Biology, P.O. Box 1106, Kailua, HI 96734, USA;3. Hawaii Undersea Research Laboratory, University of Hawaii at Manoa, Honolulu, HI 96822, USA;1. Institute of Marine Research, PO Box 1870, 5817 Bergen, Norway;2. Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;3. Department of Biosciences, University of Bergen, Bergen, Norway;4. Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, Blindern, N-0316 Oslo, Norway;1. Thünen Institute of Baltic Sea Fisheries, Alter Hafen Süd 2, 18069 Rostock, Germany;2. F³: Forschung. Fakten. Fantasie, Am Reff 1, 24226 Heikendorf, Germany;3. DTU Aqua, Technical University of Denmark, Kemi Torvet, 2800 Kgs. Lyngby, Denmark;1. Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan;2. Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato, Hakodate, Hokkaido 041-8611, Japan;3. National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan;1. NOAA Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543, USA;2. Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive MC 0205, La Jolla, CA 92037, USA;1. Irstea, UR EPBX, 50 avenue de Verdun, 33612 Cestas Cedex, France;2. IRD, UMR EME/IMARPE, Esquina Gamarra y General Valle S/N Chucuito, Callao, Peru;3. IRD, UMR LEMAR, BP 70, 29280 Plouzané, France |
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| Abstract: | An outstanding problem in fisheries acoustics is the depth dependence of scattering characteristics of swimbladder-bearing fish, and the effects of pressure on the target strength of physoclistous fish remain unresolved. In situ echoes from deepwater snappers were obtained with a sonar transducer mounted on a manned submersible next to a low-light video camera, permitting simultaneous echo recording and identification of species, fish size and orientation. The sonar system, consisting of a transducer, single board computer, hard disk, and analog-to-digital converter, used a 80 μs, broadband signal (bandwidth 35 kHz, center frequency 120 kHz). The observed relationship between fish length and in situ target strength shows no difference from the relationship measured at the surface. No differences in the species-specific temporal echo characteristics were observed between surface and in situ measures. This indicates that the size and shape of the snappers’ swimbladders are maintained both at the surface and at depths of up to 250 m. Information obtained through controlled backscatter measurements of tethered, anesthetized fish at the surface can be applied to free-swimming fish at depth. This is the first published account of the use of a manned submersible to measure in situ scattering from identified, individual animals with known orientations. The distinct advantage of this technique compared with other in situ techniques is the ability to observe the target fish, obtaining accurate species, size, and orientation information. |
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