Plan view of the acoustic optical system that was attached to the headline of the net. The main instruments are labeled. The distance in the along-track axis (upward direction in the figure) for the 120-kHz transducer and stereo cameras were 380 and −376 mm, respectively.
Echogram of volume backscatter (Sv) from transects over St Helens Hill; (a) acoustic data at 38 kHz from the vessel-mounted acoustics in moderate weather conditions; the 38 kHz (b) and 120 kHz (c) echograms from the trawl mounted acoustic optical system towed at a nominal depth of 450 m; (d) the corresponding composite color mixed 38 and 120 kHz echogram with orange roughy schools indicated.
(a) Distribution of volume backscatter, (dB m−1), for the region shown in Fig. 2 at 38 kHz (solid) and 120 kHz (dashed). (b) The distribution of the Sv difference, .
Mean Sv difference, , from the 17 schools; (a) mean against and (b) the standard deviation of against mean .
An example of stereo optical images of an orange roughy with its associated length, bearing, and tilt angle as obtained from the photo measuring software.
Orange roughy tilt angle shown against mean tracked TS at 38 kHz (a), mean tracked TS at 120 kHz (b), and mean TS difference (c). (d) The fish range against mean tracked at 38 kHz (see Table IV ).
Predictions of orange roughy TS at 38 kHz (asterisk) and 120 kHz (diamond) weighted by their frequency difference, , for a mean school Sv difference ( ) of −5.5 to−1 dB and standard deviation of 3.9 dB.
Orange roughy target strength at 38 kHz (asterisk) and 120 kHz (diamonds) based on the in situ visually verified tracked targets, assuming a Gaussian tilt distribution with mean of −30° to 0° and standard deviation of 15°.
Characteristic acoustic impedance of two orange roughy specimens relative to that of seawater, shown as a transverse average through the fish. Red and yellow areas are bone and the otoliths while the darker blue region below the spine is the swim bladder [(a) is fish OR2, a 33.4 cm female and (b) is a 35.8 cm male].
Model predictions of orange roughy target strength at 38 kHz (solid) and 120 kHz (dashed) for a 33.4 cm female fish OR2 (a) and a 35.8 cm male fish OR3 (b) for tilt angles from −40° to 40°. (c) Ensemble tilt-angle-averaged target strength with mean tilt angle of −15° to 15° and Gaussian distribution standard deviation of 15° for OR2 (asterisk) and OR3 (diamond) at 38 kHz (solid) and 120 kHz (dashed). (d) The predicted TS difference, , based on a Gaussian tilt distribution with modes of −15° to +15° and standard deviation of 15° for the OR2 (asterisk) and OR3 (diamond) orange roughy.
Echosounder parameters and settings and target strength analysis criteria.
Details on the two fish that were CT scanned. Lengths are standard length.
Summary of acoustic and optically measured fish that matched the search criteria within the acoustic and optical footprints, standard deviation in parentheses.
Correlations of variables with significant relationships in bold (p ≤ 0.05). The bearing distribution failed the normality test.
Summary of methods used to weight the optically verified in situ orange roughy targets (bold preferred), FEM model and recently published in situ and ex situ target strength results at 38 and 120 kHz.
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