Near resonance acoustic scattering from organized schools of juvenile Atlantic bluefin tuna (Thunnus thynnus).
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Citations
Direct Assessment of Juvenile Atlantic Bluefin Tuna: Integrating Sonar and Aerial Results in Support of Fishery-Incident Surveys
Detecting, counting and sizing bluefin tuna schools using medium range sonars of baitboats in the Bay of Biscay.
Measurements of Juvenile Atlantic Bluefin Tuna ( Thunnus thynnus ) size using an Unmanned Aerial System
Bio- and Fishery Acoustics
Target strength distributions of Pacific sardine schools: Model results at 500 Hz to 10 kHz
References
The Multiple Scattering of Waves. I. General Theory of Isotropic Scattering by Randomly Distributed Scatterers
Multiple scattering of waves
Fisheries Acoustics: Theory and Practice
Related Papers (5)
Frequently Asked Questions (9)
Q2. How long did the distance between the vessel and the school decrease?
2. Between pings 8 and 135 (approximately 0.5 min), the distance between the vessel and the school (as imaged by MBES) decreased nearly linearly from 65 to 30 m.
Q3. How many beams did the MBES use?
This MBES uses a Mills cross array topology to form 256 beams between 664 with a nominal angular resolution of 1 0.5 (horizontal and vertical 3 dB beamwidths) and was oriented so that its center beam was pointed horizontally in the vertical plane and approximately 45 off the starboard bow.
Q4. What is the angular dependence in the modeled school target strength?
There is also a strong angular dependence in the modeled school target strength with increased backscatter when the school is ensonified along its short axis compared to the model outputs for ensonification along the long axis.
Q5. What is the depth dependence of the swimbladder?
This depth dependence is expected for fish that have adapted to depth, however, and if the tuna are rapidly changing depth within the school, the swimbladder resonance frequency is expected to vary more widely, following a (1þz/10)5/6 relationship with depth, z, or about a 75% variation for the ABFT observed here.
Q6. What is the acoustic response of the swimbladder of the tuna?
The resulting swimbladder resonance frequencies very between approximately 45 and 65 Hz with a standard deviation slightly greater than 3 Hz.
Q7. What is the acoustic amplitude of the swimbladder?
The complex scattering amplitude of the swimbladder is assumed to be the same for a gas bubble acting as a monopole radiator (Clay and Medwin, 1977)si ¼ a expð jkaÞx2o=x 2 1 jd ; (3)where a ¼ ð3vsb=4pÞ1=3 is assumed to be the effective swimbladder radius based on its volume vsb, xo is the resonance frequency of the fish in radians per second, and d is a3808 J. Acoust.
Q8. How many different school target strength models are considered?
For reference, the school target strength is also calculated assuming that the scattered contributions add incoherently at the receiverTSinc ¼ 10 log10X263 i¼1 jpj2A2 r4 : (7)In total, seven different school target strength models are considered.
Q9. What is the acoustic frequency of the swimbladder?
Both the resonance frequency and damping constant are calculated following the formulation given by Love (1978) assuming the swimbladder to be filled with air with a density of 1.3 kg/m3 and a sound speed of 340 m/s, sea water and fish flesh densities of 1000 kg/m3 and 1050 kg/ m3, respectively, a viscosity parameter of 50 Pa s, and a surface tension of 1000 N/m.