Swimbladders under pressure: anatomical and acoustic responses by walleye pollock

• Published in: ICES Journal of Marine Science
• Main Authors: Horne, John K., Sawada, Kouichi, Abe, Koki, Kreisberg, Richard B., Barbee, David H., Sadayasu, Kazuhiro
• Format: Text
• Language: English
• Published: Oxford University Press 2009
• Subjects: SEAFACTS; Theragra chalcogramma
• Online Access: http://icesjms.oxfordjournals.org/cgi/content/short/fsp101v1; https://doi.org/10.1093/icesjms/fsp101

<qd> Horne, J. K., Sawada, K., Abe, K., Kreisberg, R. B., Barbee, D. H., and Sadayasu, K. 2009. Swimbladders under pressure: anatomical and acoustic responses by walleye pollock. – ICES Journal of Marine Science, 66: 000–000. </qd>Pressure influences echo intensities from fish through changes in swimbladder volumes and surface areas. Volume reduction is expected to correspond to Boyle’s law (volume α pressure−1), but the effects of deforming the dorsal-aspect surface area of the swimbladder on the target strength ( TS ) of a physoclist have not been quantified at geometric scattering frequencies. Dorsal and lateral radiographs of three juvenile walleye pollock ( Theragra chalcogramma ) in a pressure chamber were used to image swimbladders from ambient to a maximum of 4.9 × 105 Pa (i.e. 5 atm). Radiographs from an additional 16 0-group, 21 juvenile, and 28 adult fish were used to compare swimbladder sizes and shapes across life-history stages. The directional elliptical eccentricity, which describes the relative compression in dorsal and lateral planes, was formulated to define swimbladder shapes and their variation. As pressure increased, dorsal-aspect surface areas of the swimbladder decreased at a constant rate. Swimbladder-volume reductions were similar among individuals, but less than those predicted by Boyle’s law. Compression was greatest in the dorsal–ventral plane and asymmetric anterior to posterior. The Kirchhoff-ray mode backscatter model predicted that TS at 38 and 120 kHz decreased by ∼4 dB as pressure increased from ambient to 4.9 × 105 Pa.