Sperm whale inter-pulse intervals and size: The anomaly called Yukusam

Yukusam is the name given to a male sperm whale who was first documented off northeastern Vancouver Island in February 2018. He spent several weeks in this area before traveling south to the inland waters of the Salish Sea in late March 2018. Sperm whale clicks have been used as a proxy to determine overall size by using the time difference of arrival between the initial noise pulse and its reflections within the spermaceti organ. Different equations have been derived in order to use this Inter-Pulse Interval (IPI) to estimate overall length. Here we use Yukusam’s usual clicks recorded from the Lime Kiln hydrophone on the west side of San Juan Island (WA State, USA) to compare IPI-based length estimates with visual observations. Photo and video documentation indicate that this whale is ~15 m in length. Our initial acoustic results indicate that equations in the literature underestimate his length by at least a few meters. The potential reasons behind these anomalies are explored in this presentation.