Abstract
Sperm whales, Physeter macrocephalus, are deep-diving predators, and use echolocation to navigate and localize prey while diving. They regularly produce trains of echolocation clicks throughout their dives, as well as bursts of more rapid, lower intensity clicks known as buzzes while actively foraging. These foraging buzzes are used as a proxy for active foraging attempts, and are typically recorded using acoustic monitoring through animal borne tags. The aim of this study is to use a towed hydrophone array to detect foraging buzzes with depth and analyze foraging behavior throughout a dive, as a non-invasive method that allows sampling of a broader range of individuals. In 2016, acoustic recordings were collected off the east coast of the US and Canada using a towed hydrophone array, and sperm whale click trains and dive profiles were analyzed. The software PAMGuard was used to manually review 44 click trains for potential buzzes, and used to analyze foraging behavior. For 35 click trains, multiple whales were clicking simultaneously and individual buzzes could not be detected. For the nine click trains analyzed, audible buzzes, potential buzzes, and pauses were recorded manually using Raven Pro. The audible buzzes had an average duration of 2.14 seconds (range: 0.79-5.74 sec.) and average buzz depth of 700 meters (range: 300-1200 m). For five click trains, the time between the first and last buzz was used to assess the foraging phase (range: 2-12 min.). The large range of foraging depth found here using a towed array is consistent with numerous studies that record dive behavior using tags, however the number of buzzes recorded is lower on average than tagged whale data. Differences in foraging patterns throughout dives may indicate variations of whale feeding behaviors or prey availability, due to demographic, regional or temporal factors.