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Worldwide, seven species of porpoise are known. These have no overlap between their ranges, except for some between the harbour porpoise and Dall's porpoise in the North Pacific. Dall's porpoise is unusual among porpoises in that it is rather more dolphin-like than other porpoises, being more social and fast-moving.
Porpoises do not whistle, though the reason why is not clear. There is some evidence for a social communication role for clicks, as well as their known use for echo-location. Compared with dolphin clicks, porpoise clicks are relatively long and highly tonal. The chart below shows the waveform (red) and spectrum (black) with the scale units in kHz.
T-PODs have been used successfully to study the finless porpoise, Neophocaena phocaenoides and acoustic studies have shown that their clicks are very similar to those of the harbour porpoise.
It seems that porpoises are rarely silent in the wild. They normally produce clicks in trains that have click repetition rates varying from around 4/second to 600/second. The highest click rate logged with T-PODs is 1200/second. High rates - buzzes - are known to be used in the final stages of attempts to capture prey as the porpoise moves in rapidly to catch the fish in its mouth. The click beam has a 3dB width of 15 degrees horizontally by 10 vertically. The click spectrum does not change much at increasing angles from the centre of the beam. For more information on this species, please visit the Convention of Migratory Species web site.
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