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Ref.: MsC Thesis, University of Algarve, November 2022
Abstract:
Ship strikes are one of the leading causes of premature mortality among whales, accounting for the deaths of
approximately 20,000 each year, with untold more being injured. Given the exponential increase in shipping
traffic, estimated at 2 - 3% year-over-year, the potential for collisions continues to grow. Due to their large
size, preferred habitats and sea surface behavior, the sperm whale is one of the species most vulnerable to
ship strikes. In some populations, collisions with maritime vessels are the leading cause of death, premature
or otherwise. This is particularly concerning considering that the sperm whale is listed on the IUCN Red List
of Threatened Species as “Vulnerable” globally and “Endangered” in the Mediterranean region.
Passive Acoustic Monitoring, or PAM, is an environmentally non-intrusive method by which naturally
generated underwater sounds, such as the clicks made by sperm whales, are picked up by hydrophones
(underwater recording devices) and analyzed to extract a variety of data, including the sound source’s
location. In the current research, we use a PAM methodology known as Time Difference of Arrival (TDOA)
analysis, whereby different acoustic paths taken by sound waves from their source to a hydrophone are
analyzed to extract the differences in time between their arrivals. Extracted TDOAs are compared to a
theoretical model (in our case, the Bellhop ray tracing model) to extrapolate the source’s localization, which
can then be fed into a live marine traffic system such as MarineTraffic (marinetraffic.com) to alert ships in
the area to the presence and locations of the whales, so that they may take preventative action. In this
dissertation, I present, inter alia, a working prototype, developed on the Matlab platform, for the detection
and localization of sperm whales based on their vocalizations (clicks).
Keywords: Sperm whales, Ship strikes, Passive Acoustic Monitoring, Acoustic
localization, Ray Tracing, Bellhop model.