Abstract
Herring (Clupea pallasii and C. harengus) are known to release gas from their swim bladder to assist a number of complex behaviors, such as buoyancy adjustments and predator avoidance. The noise associated with the release has recently been reported in the literature and related to oscillating bubbles. Average source levels (SLs) of 73 dB with regard to microPa rms reference 1 m have been reported for bubbles produced by herring in the laboratory. A model is provided for predicting the SL in terms of the gas flow rate from the swim bladder into the bubbles. Based on these laboratory conditions, an inversion yields a rate of 0.9 (0.3-3.2) ml/min. Furthermore, the model predicts an acoustic SL of 89 (79-99) dB with regard to microPa rms reference 1 m for pulses emitted by herring in a natural shallow water environment at unknown distance corresponding to a flow rate of 2.5 ml/min. An analysis of published acoustic data suggests that herring is capable of controlling the gas flow and the corresponding acoustic levels over a wide range according to different behavioral needs. The proposed model allows an extrapolation of the laboratory results to situations that are relevant for bubble release of herring schools in the ocean.
