Yukusam is the male sperm whale named after an island to the northeast of Vancouver Island where he was first sighted in February. Now he has moved south and was spotted in the San Juan Islands on March 31st, the first ever sighting of this animal in Washington Inland waters! Generally a deep ocean species, the last known occurrence of a sperm whale near these inland waters was further north in 1984 in the Johnstone Strait, but only acoustic detections were made with no sightings.
Sperm whales are the largest of the toothed whales. Within their distinctive head, which itself is about one third the body length, lies a large organ containing up to 500 gallons of spermaceti. A waxy oil once prized for manufacturing during the era of whaling, spermaceti is believed to focus sound created within the parabolic-shaped organ in order to magnify and direct their clicks. As a ‘pulse’ of sound is made by forcing air through a pair of tightly stretched lips within the head, it reverberates inside the spermaceti organ which creates ‘echoes’ of the pulse. The amount of time between reflections is known as the Interpulse Interval (IPI). Because the IPI is directly related to the size of the organ, which in turn is proportional to the overall size of the animal, decoding these clicks acts as a proxy to determine how big a sperm whale is.
Below are a spectrogram and waveform of Yukusam’s clicks while he travelled through Haro Strait, measured by our hydrophone at Lime Kiln State Park.
Zooming into one of the clicks in the waveform, we can identify the individual pulses which correspond to reverberations within the spermaceti organ.
Below is a recording of Yukusam as he passed through Haro Strait.
Based on preliminary analyses of a few clicks, the method using equations in Goold 1996 estimates that Yukusam should be around 10 m (33 ft) in length. This is relative to the accepted 40-45 ft estimate made by Jared Towers based on video comparison with his boat of known length. The lower estimate produced by the IPI method could be due to a distortion of clicks when received off axis. Additionally, more recent papers correlating IPI with sperm whale length (Growcott et al. 2011) have shown difficulty with young whales due to a lack of specimens. We will update the IPI estimate as we process more clicks.
Want to hear more underwater sounds? Check out the Limekiln live stream for the hydrophone that made the recordings in this article!
Goold, J. C. D. (1996). “Signal processing techniques for acoustic measurement of sperm whale body lengths,” J. Acoust. Soc. Am. 100, 3431–3441.
Growcott, A., Miller, B. S., Sirguey, P., Slooten, E. & Dawson, S. M (2011). “Measuring body length of male sperm whales from their clicks: the relationship between inter-pulse intervals and photogrammetrically measured lengths.” J. Acoust. Soc. Am. 130, 568–73.