Passive acoustic monitoring for mysticete whales using the multi-terabyte Ocean Bottom Seismic data archive: whale behavior during seismic airgun surveys



Since 1999, the NSF-funded National Ocean Bottom Seismograph Instrument Pool (OBSIP) has been used by U.S.  investigators to acquire seafloor seismic data from around the world.  By NSF mandate, all of these data sets are archived in a common format at the IRIS Data Management Center (DMC), and are openly accessible two years post data acquisition.  Given that these data come from well-located, well-timed, multi-station arrays that record continuously for durations of weeks to a year, they have the potential to allow monitoring and tracking of marine mammals that vocalize within the frequency band of these recordings.  We propose to investigate the utility of these seismic data sets for marine mammal studies by examining a large data set from an OBS array deployed in the Gulf of California in 2002.  The Gulf of California dataset is well suited for this exploratory project for several reasons; it is from the longest active-source experiment deployed by OBSIP, spanning 52 days.  These data contain numerous marine mammal vocalizations, and are complemented by visual data collected from concurrent shipboard and aerial surveys.  Finally, Lizarralde was the lead PI of the 2002 experiment, and thus has deep familiarity with this dataset.  We expect to reliably detect both fin (Balaenoptera physalus) and blue (Balaenoptera musculus) whales, which produce sounds in the frequency range recorded by the array, and which are known to occur in the Gulf of California, as well as possibly lower frequency sounds of several other whale species.  A variety of scientific avenues can be pursued, including characterization of the types (e.g., song vs.  social or feeding sounds) of whale calls, and examining the effects of both airgun shots and earthquakes on calling behavior.  Visual data from marine mammal observers can be used to verify species characterizations made from acoustic recordings, and these data can also provide valuable groundtruthing for studies aiming to document species occurrence based on either acoustic or visual data alone.  These data also may provide insights into parameters such as average dive times, which can be deduced from gaps in calling behavior when whales are at the surface or potentially determined directly from tracking.  Considering all available OBSIP data sets, the potential exists to study features such as seasonality in occurrence, movement patterns and vocal behavior of whales. 

The proposed work meets the goals of the WHOI Marine Mammal Center call for proposals, which requests “….collaborative research projects that are relevant to marine mammal research and conservation.  A major goal of WHOI MMC awards is to support collaborative research efforts that cross the boundaries of traditional disciplines and explore new collaborative approaches." The proposed work crosses the boundaries of biology, seismology, and physics, and has the potential to directly impact marine mammal conservation, in that it will utilize a large body of existing data to address both basic and applied questions regarding baleen whales and potential effects of seismic surveys on these whales.  However, given its exploratory nature, it is unlikely to be funded by conventional sources.  At the same time, a demonstration of the usefulness of OBS data for marine mammal studies will be a powerful argument for a larger-scale submission to NSF.  In addition to the expected outcomes relevant to cetacean biology and conservation, this innovative approach to studying cetaceans could lead to development of a larger scale research program that could reveal exciting and unexpected discoveries.