Target strength and tilt-angle distribution of the lesser sandeel (Ammodytes marinus)

Kubilius, R., and Ona, E. 2012. Target strength and tilt-angle distribution of lesser sandeel (Ammodytes marinus) - ICES Journal of Marine Science, 69: 1099-1107.North Sea stocks of lesser sandeel have recently become depleted, and improved methods for abundance estimation are sought. This paper foc...

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Bibliographic Details
Published in:ICES journal of marine science 2012-07, Vol.69 (6), p.1099-1107
Main Authors: Kubilius, Rokas, Ona, Egil
Format: Article
Language:English
Subjects:
Acoustics
Ammodytes marinus
Cameras
Fish
Marine
Raw materials
Strength
Surveys
Uncertainty
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Summary:Kubilius, R., and Ona, E. 2012. Target strength and tilt-angle distribution of lesser sandeel (Ammodytes marinus) - ICES Journal of Marine Science, 69: 1099-1107.North Sea stocks of lesser sandeel have recently become depleted, and improved methods for abundance estimation are sought. This paper focuses on the acoustic target strength (TS) and orientation of sandeel, measured simultaneously in several field experiments. A specially designed cubic cage, fitted with an echosounder and a video camera, was lowered onto the sea bottom, trapping wild sandeel inside. Methods for manually selecting valid echotraces from individual sandeel are described. Scattered mean TS values from several experiments are reported. These are, in spite of the observed variability, summarized in a TS-fish length (cm) relationship as TS = 20logL - 93.1 (dB) at 200 kHz. We believe that the accuracy of the relationship may still be debated; incorporating larger uncertainty in the overall mean TS will increase the total uncertainty of the stock biomass estimate from sandeel acoustic surveys. This uncertainty is now, using standard narrow-beam echosounders, dominated by the fish patchiness relative to the survey coverage. Results from pilot investigations of the sandeel swimming orientation using video cameras are also presented, showing that sandeel usually has an anguilliform swimming pattern with substantial positive (head-up) tilt. The spread of the tilt-angle distribution is also larger than for more neutrally buoyant fishes.
ISSN:1054-3139
1095-9289
DOI:10.1093/icesjms/fss093