In the herring (Clupea harengus), the swim bladder is connected to both the alimentary canal and the anal opening. The anterior duct is used for filling the swim bladder with air. Gas release from the anal opening is often observed when the fish is scared or during ascent and descent. Here, the sounds produced by such a gas release are studied. The fish was kept in a low-pressure chamber. As the ambient pressure was reduced, the gas in the swim bladder expanded and was emitted through the anal opening. Herring sounds were also recorded in a fish trap and in the field. The characteristic sound made by herring during gas release is denoted as the pulsed chirp. This pulsed chirp is 32–133 ms long (N = 11) and consists of a series of 7–50 (N = 11) transient pulses with a continuous reduction of the frequency emphasis (centroid frequency of first pulse 4.1 kHz and of last pulse 3.0 kHz, N = 11). The source level of the chirp is 73 ± 8 dB re 1 μPa rms (root mean square) at 1 m (N = 19). The pulsed chirp is not known to be produced by any other marine animal and may be a good fingerprint for identifying schools of clupeid fish by natural predators, fishery scientists and fishermen. A model for the generation of the pulsed chirp is presented and tested on existing data.