Gulf of Mexico Stones deep water ocean soundscape project: the first passive acoustic deployment of the Gulf Research Program of the National Academies of Sciences, Engineering and Medicine.

The Gulf Research Program of the National Academies of Sciences, Engineering and Medicine (GRP) collaborated with Shell to convert an existing mooring into the first long-term deep ocean observatory in the Gulf of Mexico (GoM). Known as the Stones Metocean Observatory Project, the goal of the collaboration is to gather marine data to improve understanding of the GoM large marine ecosystem. In 2018, GRP funded the deployment of an Autonomous Multichannel Acoustic Recorder (AMAR, JASCO Applied Sciences) unit to collect the first deep water (~3000 m) recordings of the GoM soundscape. The AMAR recorded for 126 days before it was swapped with a second unit. The recorded signal had a broadband sound pressure level ranging from 103.7 to 127.5 dB re 1 µPa with anthropogenic sounds dominating the soundscape, including sounds associated with vessels, distant seismic impulses, the Shell Turritella floating production, storage and offloading facility, and oceanographic data collection sensors. Acoustic signals from three marine mammal species, or species group, were present in the data. Sperm whale (Physeter macrocephalus) vocalizations occurred daily. There were instances of beaked whale clicks, identified as potentially Gervais’ beaked whales (Mesoplodon europaeus). Dolphin clicks and whistles occurred regularly in the data set. Given the recording location, possible sources of the vocalizations include Fraser’s dolphins (Lagenodelphis hosei), which are capable of deep dives but uncommon in the GoM, striped dolphins (Stenella coeruleoalba), which may dive to approximately 700 m and are known to occur in the deep ocean of the GoM (NOAA Fisheries 2019), or Clymene dolphins (Stenella clymene), which occur in large numbers in deep water (Würsig 2017) but whose diving limits are unknown. Seasonal vocalization patterns were not observed in the first deployment. Impacts of oceanographic conditions, recorded on the Stones Metocean Observatory, on seasonal patterns and acoustic propagation of anthropogenic sound will be investigated once the second deployment data is available.