| A strange sound has oft' been heard in Haro Strait
by the fixed hydrophones of the OrcaSound array. During the summer months
(approximately July through September), the "heavy breather," puts a tremendous
amount of acoustic energy into the water. The sound occurs day and night, is
usually repeated 10-15 times in a particular sequence. Each sequence is
followed by 1-5+ minutes of silence. Within each sequence, the sounds are
separated by 30-90 seconds of silence. The sounds also get progressively
louder and longer until the middle of the sequence and then get softer and
shorter by the end.
Visual observations of a harbor seal that resides in a kelp bed just south of
the array correlate with the sound sequences. The seals head is consistently
above water during the inter-sequence silences. The seal is submerges 5-30
seconds before a sequence begins and emerges within 10-120 seconds after the
sequence ends.
Similar recordings and
observations in California confirm that the sound is a harbor seal, and
probably a male. Yet some questions remain unanswered, like: how is the sound
made and what is its purpose?
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