Sparse targets in hydroacoustic surveys: Balancing quantity and quality of in situ target strength data

Sparse targets in hydroacoustic surveys: Balancing quantity and quality of in situ target strength data

[Display omitted] •A transducer calibration indicated stability in mean TS estimates up to 18 dB maximum beam compensation.•Maximum beam compensation contributed proportionally small amounts of uncertainty to in situ mean TS estimates from fish track data.•Increasing maximum beam compensation up to...

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Bibliographic Details
Published in:Fisheries research Vol. 188; pp. 173 - 182
Main Authors: DuFour, Mark R., Mayer, Christine M., Kocovsky, Patrick M., Qian, Song S., Warner, Dave M., Kraus, Richard T., Vandergoot, Christopher S.
Format: Journal Article
Language:English
Published: Elsevier B.V 01-04-2017
Subjects:
Beam compensation
Fisheries
Great Lakes
Low-density
Shallow-water
Walleye
Beam compensation
Low-density
Fisheries
Shallow-water
Great Lakes
Walleye
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Summary:[Display omitted] •A transducer calibration indicated stability in mean TS estimates up to 18 dB maximum beam compensation.•Maximum beam compensation contributed proportionally small amounts of uncertainty to in situ mean TS estimates from fish track data.•Increasing maximum beam compensation up to 18dB provided greater TS quantity with minimal reduction in TS quality, leading to improved hydroacoustic size-structure and density estimates. Hydroacoustic sampling of low-density fish in shallow water can lead to low sample sizes of naturally variable target strength (TS) estimates, resulting in both sparse and variable data. Increasing maximum beam compensation (BC) beyond conventional values (i.e., 3dB beam width) can recover more targets during data analysis; however, data quality decreases near the acoustic beam edges. We identified the optimal balance between data quantity and quality with increasing BC using a standard sphere calibration, and we quantified the effect of BC on fish track variability, size structure, and density estimates of Lake Erie walleye (Sander vitreus). Standard sphere mean TS estimates were consistent with theoretical values (−39.6dB) up to 18-dB BC, while estimates decreased at greater BC values. Natural sources (i.e., residual and mean TS) dominated total fish track variation, while contributions from measurement related error (i.e., number of single echo detections (SEDs) and BC) were proportionally low. Increasing BC led to more fish encounters and SEDs per fish, while stability in size structure and density were observed at intermediate values (e.g., 18dB). Detection of medium to large fish (i.e., age-2+ walleye) benefited most from increasing BC, as proportional changes in size structure and density were greatest in these size categories. Therefore, when TS data are sparse and variable, increasing BC to an optimal value (here 18dB) will maximize the TS data quantity while limiting lower-quality data near the beam edges.
ISSN:0165-7836
1872-6763
DOI:10.1016/j.fishres.2016.12.020