In situ acoustic estimates of the swimbladder volume of Atlantic herring, Clupea harengus

Abstract

Most marine fish maintain swimbladder volumes equivalent to 4%–5% of their body weight in order to maintain neutral buoyancy. In many fish the addition or removal of gas from the swimbladder is accomplished with the gas gland, a blood invested portion of the swimbladder wall. However, several families, including the herring family, Clupeidae, lack a gas gland. Instead, these fish possess a pneumatic duct between the esophagus and the swimbladder by which they are believed to inflate their swimbladders by ‘‘gulping’’ atmospheric air at the sea surface. Acoustic measurements at 1.5–5 kHz on fish in the Gulf of Maine showed a swimbladder resonance peak near 2.3 kHz at 180 m depth. Midwater trawls confirmed that the fish were Atlantic herring (Clupea harengus) of 19–28 cm length. Calculations using a model of swimbladder resonance gives swimbladder volumes of 1.3% at 180 m. Extrapolation using Boyle’s law suggests that at the sea surface, these herring would need to inflate their swimbladders by up to four times the volume required for neutral buoyancy. In general, swimbladders of the Clupeidae may resonate at lower frequencies than previously expected. [Work supported by ONR and NMFS.]