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<p>Sound is a key sensory modality for Hawaiian spinner dolphins. Like many other
marine animals, these dolphins rely on sound and their acoustic environment for many
aspects of their daily lives, making it is essential to understand soundscape in areas
that are critical to their survival. Hawaiian spinner dolphins rest during the day
in shallow coastal areas and forage offshore at night. In my dissertation I focus
on the soundscape of the bays where Hawaiian spinner dolphins rest taking a soundscape
ecology approach. I primarily relied on passive acoustic monitoring using four DSG-Ocean
acoustic loggers in four Hawaiian spinner dolphin resting bays on the Kona Coast of
Hawai‛i Island. 30-second recordings were made every four minutes in each of the bays
for 20 to 27 months between January 8, 2011 and March 30, 2013. I also utilized concomitant
vessel-based visual surveys in the four bays to provide context for these recordings.
In my first chapter I used the contributions of the dolphins to the soundscape to
monitor presence in the bays and found the degree of presence varied greatly from
less than 40% to nearly 90% of days monitored with dolphins present. Having established
these bays as important to the animals, in my second chapter I explored the many components
of their resting bay soundscape and evaluated the influence of natural and human events
on the soundscape. I characterized the overall soundscape in each of the four bays,
used the tsunami event of March 2011 to approximate a natural soundscape and identified
all loud daytime outliers. Overall, sound levels were consistently louder at night
and quieter during the daytime due to the sounds from snapping shrimp. In fact, peak
Hawaiian spinner dolphin resting time co-occurs with the quietest part of the day.
However, I also found that humans drastically alter this daytime soundscape with sound
from offshore aquaculture, vessel sound and military mid-frequency active sonar. During
one recorded mid-frequency active sonar event in August 2011, sound pressure levels
in the 3.15 kHz 1/3rd-octave band were as high as 45.8 dB above median ambient noise
levels. Human activity both inside (vessels) and outside (sonar and aquaculture) the
bays significantly altered the resting bay soundscape. Inside the bays there are high
levels of human activity including vessel-based tourism directly targeting the dolphins.
The interactions between humans and dolphins in their resting bays are of concern;
therefore, my third chapter aimed to assess the acoustic response of the dolphins
to human activity. Using days where acoustic recordings overlapped with visual surveys
I found the greatest response in a bay with dolphin-centric activities, not in the
bay with the most vessel activity, indicating that it is not the magnitude that elicits
a response but the focus of the activity. In my fourth chapter I summarize the key
results from my first three chapters to illustrate the power of multiple site design
to prioritize action to protect Hawaiian spinner dolphins in their resting bays, a
chapter I hope will be useful for managers should they take further action to protect
the dolphins.</p>
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