After the Deep Water Horizon oil spill concern arouse over the status of the sperm whale in the Gulf of Mexico. The status of sperm whale populations is usually determined by ship based surveys which are expensive. In this study the use of acoustic surveys using bottom moored buoys were used to provide information on the state of the whales1. An important measure of the state of a sperm whale population is the length of its individuals. The length of a sperm whale is a function of the whales’ age and sex. In this study sperm whale echolocation clicks were recorded by bottom moored buoys in the Gulf of Mexico during the summer of 2015. The multipulse nature of the echolocation clicks produced by sperm whales makes it possible to estimate the length of the whales by measuring the time intervals between component pulses (Figure1)2.Those intervals are known as the Inter Pulse Intervals (IPIs).This method only produces accurate measurements if the whale is pointing toward the hydrophone and not off axis from the hydrophone. Off-axis clicks produce p0, p1, and p2 pulses that are not suitable for use in whale length estimates (Figure 2)3. A method was developed to distinguish between on-axis and off-axis clicks which rejected clicks not suitable for length estimates. Other nearby whales clicking at the same time as the subject whale produce incorrect IPI measurements preventing accurate length estimates. A quality control test was developed that identified clicks containing clicks from more than one whale.
Subject: signal processing, marine biology, sperm whales
