Soundscapes in the Deep Pacific

The Pacific Islands Passive Acoustic Network (PIPAN) is a collection of 14 sites across the Central and Western Pacific Ocean initially selected for monitoring cetaceans. At each location, a bottom-mounted High-frequency Acoustic Recording Package (HARP) was deployed between 500 and 1000 m. The data were recorded at 200 kHz and downsampled to span 20–4000 Hz for soundscape analysis. Most of the recordings were duty cycled, with 5 min of recording separated by gaps of 1–35 min. At each site, recordings lasted between 3 months and 10 years, with intermittent gaps between deployments. These data span the years 2005–2020, although recording is ongoing at selected sites. The primary components of the soundscapes were biological, particularly the seasonal influx of baleen whales, and physical, such as the sounds from wind and waves. There were also “choruses,” or periodic, broadband energy at various frequencies. These choruses are strongly diel, peaking around sunset. There was very little anthropogenic sound at any site, with only a few locations having vessel or echosounder signals. Ongoing monitoring of these sites will be essential for effective management of human activities going forward, particularly at locations that are remote, but with the potential to be utilized for deep sea extraction.