Boarfish (capros aper) target strength modelled from magnetic resonance imaging (mri) scans of its swimbladder

Boarfish (Capros aper) abundance has increased dramatically in the Northeast Atlantic from the early 1970s after successive years of good recruitment attributed to an increase in sea surface temperature. Due to increased commercial fishing over recent years, an acoustic boarfish survey funded by the...

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Bibliographic Details
Published in:ICES Journal of Marine Science
Main Authors: Fassler, S. M. M., O'Donnell, C., Jech, J. M.
Format: Article in Journal/Newspaper
Language:unknown
Published: Oxford University Press (OUP) 2013
Subjects:
acoustic survey
boarfish
kirchhoff-ray mode (krm)
stock assessment
target strength
relative frequency-response
pout trisopterus-esmarkii
herring clupea-harengus
cod gadus-morhua
species identification
atlantic mackerel
in-situ
kirchhoff-approximation
fisheries acoustics
walleye pollock
Gadus morhua
Northeast Atlantic
Online Access:http://hdl.handle.net/10379/11423
https://doi.org/10.1093/icesjms/fst095
Description
Summary:Boarfish (Capros aper) abundance has increased dramatically in the Northeast Atlantic from the early 1970s after successive years of good recruitment attributed to an increase in sea surface temperature. Due to increased commercial fishing over recent years, an acoustic boarfish survey funded by the Killybegs Fishermen's Organisation was initiated by the Marine Institute to establish a baseline for the future management of this stock. In the absence of any species-specific boarfish target strength (TS), acoustic backscatter was estimated by a Kirchhoff-ray mode model using reconstructed three-dimensional swimbladder shapes which were computed from magnetic resonance imaging scans of whole fish. The model predicted TS as a function of size, fish tilt angle, and operating frequency. Standardized directivity patterns revealed the increasing importance of changes in the inclination of the dorsal swimbladder surface at higher frequencies (120 and 200 kHz) and a less directive response at lower frequencies (18 and 38 kHz). The model predicted a TS-to-total fish length relationship of TS = 20 log(10)(L) - 66.2. The intercept is similar to 1 dB higher than in the general physoclist relationship, potentially reflecting the bulky nature of the boarfish swimbladder with its relatively large circumference.

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