A Review of Blue Whale Studies from HARUphones in the Pacific

Abstract

The earliest long-term monitoring of low-frequency signals of large whales was via cabled military arrays. These arrays provided valuable new data but were restricted in the locations that were monitored and there was no open access to the data collected. In order to monitor the low-frequency signals of large whales in different areas and over shorter time scales, Haruphones, single hydrophone, autonomous recording packages, were developed by the Pacific Marine Environmental Laboratory of the US National Oceanic and Atmospheric Administration and deployed in the Gulf of Alaska and the eastern tropical Pacific. By integrating the acoustic data from these broadly spaced deployments with other data streams, new discoveries about blue whales in the eastern Pacific Ocean were made. These included establishing the geographic range and migratory patterns of eastern north Pacific blue whales; establishing that the eastern tropical Pacific appears to be a blue whale “hot spot” where as many as four, but primarily three, acoustic populations of blue whales occur; determining that the Gulf of Alaska is a region where eastern and western North Pacific blue whales overlap in space and time; and showing that blue whale calling behavior has a diel pattern whereby animals produce more sounds at night than during the day. In aggregate, these data show that passive acoustic monitoring is a valuable tool for establishing blue whale population identity, determining habitat range, and studying behavioral ecology over long time periods and in remote regions of the ocean.