Scientists conducted passive acoustic monitoring (PAM) of whales in the northern Gulf of Mexico using two autonomous surface vehicles (ASVs) capable of recording marine mammal sounds. The researchers observed that ASVs required fewer personnel and created less noise compared to research vessels. ASVs provided a novel, cost-efficient, and quiet approach and expanded the range of frequencies and distances that a vessel-towed survey can monitor. Data from the ASVs and other acoustic surveys in the area will help scientists monitor the Deepwater Horizon oil spill’s long-term effects on marine mammals. The researchers published their findings in OCEANS 2016 MTS/IEEE Monterey: Using autonomous surface vehicles for passive acoustic monitoring (PAM).
The Deepwater Horizon oil spill occurred in an area of the Gulf of Mexico where marine mammals live and forage. Researchers tracked marine mammals near the spill site in 2007 and have continued to do so since then. The scientific community has steadily increased its use of PAM techniques to track marine mammals mainly because towed hydrophone arrays are easy to incorporate into research cruises for real-time data collection. However, large survey vessels that tow this equipment produce significant amounts of noise that can mask marine mammal sounds or disturb their populations.
This study’s researchers fitted two ASVs with towed hydrophone arrays configured to record marine mammal sounds, mounted them with a Seiche wireless communication system, and deployed them from the R/V Pelican for ten days. The two ASVs travelled at varying distances from the research vessel (500 – 1,000 m) to minimize noise from the support boat and optimize data collection.
The ASVs collected PAM data for phonations over a 20 Hz – 160 kHz range, which includes low-frequency whale calls and high-frequency echolocation pulses. The team used the Seiche system to monitor sounds in real time from the towed arrays and to detect, classify, and localize marine mammals. Automatic tonal detectors, mid- and high-frequency click detectors, and manual spectrograms helped the team search the recordings for sounds produced by Bryde’s whales, delphinid species, sperm whales, beaked whales, and Kogia (pygmy and dwarf sperm whales).
The team also deployed PAM systems on bottom-moored EARS (environmental acoustic recording system) buoys and a Kongsberg Seaglider AUV (automatic underwater vehicle), which remained in the study area for an extended time, continuously recording Gulf of Mexico soundscapes. Data collected from all three PAM platforms (ASV, bottom-moored buoy, and AUV) will help researchers determine geographic distributions and trends of the marine mammal population and help advance detection and classification algorithms.
Industry and governmental regulators are interested in autonomous, unmanned maritime systems as they offer greater efficiencies and cost savings than what has been available.
Data are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at 10.7266/N7222RSW.
This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to the Littoral Acoustic Demonstration Center – Gulf Ecological Monitoring and Modeling (LADC-GEMM) consortium.
The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit http://gulfresearchinitiative.org/.
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