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Autonomous Passive Acoustic Monitoring in the Northwestern Gulf of Mexico
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Bryde?s whales, Balaenoptera edeni, are the only year-round resident baleen whale
in the Gulf of Mexico, have an estimated abundance of 33 individuals (CV 1.07) in
the Gulf of Mexico population, and are found within a restricted range near the De
Soto Canyon in the northeastern Gulf. Based on their localized distribution, low
abundance, and recent evidence that this population represents a unique evolutionary
lineage and exhibits very low levels of genetic diversity, the Natural Resources Defense
Council (NRDC) has petitioned NMFS to list the Gulf of Mexico Bryde?s whale as an
endangered species and define critical habitat to enhance their protection. The NRDC
highlights the high levels of anthropogenic noise from shipping and seismic surveys
in the Gulf of Mexico as a major stressor. Historical whaling records found balaenopterids,
most likely Bryde?s whales, throughout a broader area than their currently known range,
including the western and central portions of the northern Gulf of Mexico, though
sightings are now rare in this region, despite substantial effort. Autonomous passive
acoustic methods are the most successful tool for finding rare whale species in areas
where they occur infrequently and areas where they were historically sighted by whalers.
The objectives of this study are to collect passive acoustic data for use in investigations
of 1) Bryde?s whale occurrence and distribution, and 2) ambient noise conditions in
the western Gulf of Mexico. We deployed 5 calibrated autonomous acoustic instruments
over a one year period from June 2016 ? June 2017 along the 200 m isobaths throughout
the western Gulf of Mexico predicted Bryde?s whale habitat. This will provide data
to investigate whether, where, and when Bryde?s whales occupy this habitat and will
be useful in designating critical habitat if this species is listed under the ESA.
By using calibrated instruments, an additional goal will be to obtain data to characterize
the ambient sound environment at these sites to determine whether acute or chronic
anthropogenic noise sources pose a risk to this species.
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