Volume 20, Number 1
SEASONAL OCCURRENCE OF SPERM WHALE (PHYSETER MACROCEPHALUS) SOUNDS IN THE
GULF OF ALASKA, 1999-2001. David K. Mellinger, Kathleen M. Stafford, and
Christopher G. Fox, pages 48-62.
An acoustic survey for sperm whales was conducted in the Gulf of Alaska.
Six autonomous hydrophones continuously recorded sound signals below 500
Hz from October 1999 to May 2001. After recovery, recordings were
processed using an automatic process to detect usual clicks of sperm
whales. The detection algorithm equalized background noise, summed the
data in a frequency band, and then used autocorrelation to detect the
whales' highly regular clicks. Detections were checked manually, revealing
that 98% of detections did contain clicks. Results indicate that sperm
whales are present in the Gulf of Alaska year-round; this result extends
what is known from whaling data, which were gathered principally in
summer. Sperm whales were more common in summer than winter by a factor of
roughly two, and occurred less often at the westernmost site surveyed
(52N, 157W) than elsewhere in the Gulf. This is the first study of sperm
whales based exclusively on remote acoustic sensing. This methodology is
feasible because sperm whale clicks extend to frequencies (100 Hz) low
enough to be recorded by low-sample-rate instruments that operate
continuously, and because the detection algorithm has a low
false-detection rate. The methodology may be replicated to facilitate
comparisons between different time periods and geographic regions.
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