In July 1989, a lone male harbour porpoise (Phocoena phocoena), estimated to be no more than a few days old, was found stranded on the coast near Newport, Oregon, USA. Six months later, following its arrival at the Point Defiance Zoo and Aquarium in Tacoma, Washington, sonar emissions were recorded from this animal. The orphaned porpoise calf had been raised separately under human care, isolated from the influence of any other dolphins.
During the recordings, the young Phocoena responded in a normal fashion to the presence of a hydrophone in the pool, emitting bursts of clicks while scanning the ‘foreign object’ in its environment. Analysis of its individual clicks revealed a dramatic similarity in wave shape to those of adult Phocoena sonar recorded previously with the same recording apparatus in Denmark in 1983. A slightly higher dominant frequency around 135 kHz was observed compared to a previously established high frequency component of 125 kHz in a subadult/ adult Phocoena. Within the constraint of a signal-to-noise ratio of 30dB and higher, an absence of whistling sounds was noted.