scholarly journals A method for evaluating the effects of biological factors on fish target strength

2003 ◽  
Vol 60 (3) ◽  
pp. 555-562 ◽  
Author(s):  
Elliott L Hazen ◽  
John K Horne
Keyword(s):  
Target Strength ◽  
Comparative Approach ◽  
Theragra Chalcogramma ◽  
Fish Length ◽  
Biological Factors ◽  
Backscatter Intensity ◽  
Relative Contribution ◽  
Walleye Pollock Theragra Chalcogramma ◽  
Improving Accuracy ◽  
The Relationship

Abstract Understanding the relationship between fish biology and target strength potentially improves the accuracy of acoustic assessments. The effects of individual biological factors (e.g., length, tilt, and depth) on backscatter amplitude have been examined, but the relative contribution of each factor has not been quantified. Dimensionless ratios, which facilitate comparison of disparate quantities, were used to evaluate the effects of individual biological factors on echo intensities. Ratios from 25 adult walleye pollock (Theragra chalcogramma) were calculated using a Kirchhoff-ray-mode, backscatter model parameterized for each fish. This comparative approach can be used to identify the influence of biological factors on backscatter intensity and is potentially a tool for improving accuracy when converting acoustic size to fish length.

scholarly journals The influence of ontogeny, physiology, and behaviour on the target strength of walleye pollock (Theragra chalcogramma)

2003 ◽  
Vol 60 (5) ◽  
pp. 1063-1074 ◽  
Author(s):  
John K Horne
Keyword(s):  
Adult Life ◽  
Dorsal Surface ◽  
Walleye Pollock ◽  
Target Strength ◽  
Theragra Chalcogramma ◽  
Physical Factors ◽  
Biological Factors ◽  
Factors Associated ◽  
Surface Areas ◽  
Walleye Pollock Theragra Chalcogramma

Abstract Variability in echo intensities from aquatic organisms is caused by physical factors associated with the transmission of sound through water, and by biological factors associated with the ontogeny, physiology, and behaviour of targets. Acoustic-based density estimates depend on accurately characterizing reflected or backscattered sound from any species of interest. Digitized lateral and dorsal radiographs of walleye pollock (Theragra chalcogramma) were used to characterize intra-specific variability among young-of-the-year, juvenile, and adult life-history stages. Kirchhoff-ray mode (KRM) models were used to quantify variability in backscatter intensities at 38 and 120 kHz. At these geometric scattering frequencies, swimbladder surface areas influence echo intensities. Dorsal swimbladder surface areas were proportionate to fish lengths and decreased after fish were fed. Corresponding changes in backscatter were not proportionate to the reduction in dorsal surface area. The ratio of dorsal to lateral swimbladder surface areas was consistent among gravid and non-gravid fish. Walleye pollock tilt angles were centred at 90° and did not differ among densities or between light and dark cycles. Target strength–length regressions and KRM-predicted backscatter models closely matched in situ target-strength measurements for walleye pollock in the Bering Sea. Backscatter variability can be minimized through judicious deployment of equipment and equipment-parameter settings, but the relative influence of biological factors on backscatter amplitude has not been determined.

scholarly journals Comparing the modelled and measured target-strength variability of walleye pollock, Theragra chalcogramma

2004 ◽  
Vol 61 (3) ◽  
pp. 363-377 ◽  
Author(s):  
Elliott L. Hazen ◽  
John K. Horne
Keyword(s):  
Ex Situ ◽  
Target Strength ◽  
Physical Factors ◽  
Fish Length ◽  
Acoustic Frequency ◽  
Backscatter Intensity ◽  
Model Predictions ◽  
Strength Variability ◽  
Boyle’S Law ◽  
Insight Into

Abstract Many biological and physical factors potentially affect target strength. While these sources have been identified, few studies have compared the relative effects of individual factors. Modelled and measured target strengths in non-dimensional metrics were used to compare and rank the effects of fish length, tilt, depth, and acoustic frequency on backscatter intensity. Ex situ measurements of target strength were used to examine the effects of tilt and depth and then compared to backscatter model predictions. Swimbladder volume reduction due to increasing pressure at depth was modelled using Boyle's law and by varying the ratio of dorsal to lateral compression. We found that length has the largest effect on the modelled and measured backscatter intensity, followed by tilt, frequency, and depth. Including tilt distributions in backscatter estimates improved the match between empirical target-strength measures and model predictions. Non-dimensional influence ratios provide insight into the sources and magnitudes of the backscatter variability.

scholarly journals Progress in determining southern blue whiting (Micromesistius australis) target strength: results of swimbladder modelling

2006 ◽  
Vol 63 (5) ◽  
pp. 952-955 ◽  
Author(s):  
Adam J. Dunford ◽  
Gavin J. Macaulay
Keyword(s):  
Gadus Morhua ◽  
Stock Assessment ◽  
Laser Scanner ◽  
Fork Length ◽  
Sensitivity Analyses ◽  
Target Strength ◽  
Fish Length ◽  
Angle Distribution ◽  
Blue Whiting ◽  
The Relationship

Abstract Southern blue whiting target strength (TS) results from Kirchhoff modelling of swimbladder casts scanned using a hand-held 3D laser scanner are presented. The data are compared with the relationship between TS and fish length used for New Zealand stock-assessment surveys; TS = 21.8 log10(fork length) − 72.8, at 38 kHz. This relationship has its origins in the relationship used for blue whiting (Micromesistius poutassou) in the northern hemisphere, and is based on measurements on juvenile cod (Gadus morhua). The results indicate that the blue whiting relationship is not appropriate for southern blue whiting, and suggest a much steeper slope, with TS = 38 log10(fork length) − 97, at 38 kHz. Sensitivity analyses indicate that further investigations of swimbladder tilt-angle distribution and swimbladder volume are unlikely to provide evidence to support the use of the blue whiting relationship for southern blue whiting.

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