Passive acoustic detection of schools of herring

Herring (Clupea pallasii and C. harengus) have been observed to release gas from their bladders during vertical migration likely to adjust buoyancy and also when under strong predation pressure. Based on recently measured and modeled sound for individual fish, spectral levels are estimated for entire herring schools in the ocean for both scenarios, and the feasibility of passive detection is explored. For a typical school of migrating herring near-surface spectral levels of about 50dB rel., 1μPa∕√Hz at 3–7kHz are predicted. If wind conditions are calm where migrating herring are found, such as for Pacific herring in Prince William Sound, Alaska, passive detection is very likely. For an exemplary 10 metric ton compact school, peak spectral source levels of about 80–90dB rel. 1μPa∕√Hz ref. 1m are predicted, yielding a range of detection against calm wind background of about 1000m. Field measurements of potential gas-release events agree with the predictions for the compact school scenario with regard to lev...