Over the course of the summer I learned a great deal about hydroacoustic recording equipment, data collection, and acoustic analysis programs. I grew familiar with the vocal repertoire of these whales, the surrounding ecosystem, and the wonderful eccentricities of life at a remote field station. Photo Paul Sharpe.  

Over the course of the summer I learned a great deal about hydroacoustic recording equipment, data collection, and acoustic analysis programs. I grew familiar with the vocal repertoire of these whales, the surrounding ecosystem, and the wonderful eccentricities of life at a remote field station. Photo Paul Sharpe.  

It’s been some time now since my last post, and while my view has been my computer screen instead of spectacular Southeast Alaskan scenery, much has happened. At the end of last May, I arrived in at Five Finger Lighthouse full of excitement and with a vague idea of the acoustics project I would be part of and the questions I would undertake for my senior thesis. I left Alaska in the fall with a comprehensive dataset and a semester ahead of me to analyze the summer’s recordings and write my senior thesis. I am excited to share what I have found!

Humpback whales are remarkable vocalists, and the frequency range of their sounds aligns quite well with the hearing range of the human ear. Their calls are varied, ranging from high shrieks and screams to burping and laughing sounds to eerie, long tonal calls. While determining the function of these calls is very difficult, examining the context in which sounds are produced can provide valuable insight into what their function might be. Previous studies have looked at spatial and social contexts for calling behavior, e.g. certain classes of calls are heard when whales are in close proximity to one another, others are associated with very specific behaviors. I chose to focus on the environmental context for vocalizations, an area which has received less attention.

For the time that humpback whales are in Southeast Alaska, feeding is everything. Southeast Alaska is a rich and dynamic ecosystem. In the summertime, the difference between high and low tides regularly exceeds 20 feet vertical—while living in Alaska, I could feel our small island home grow at low tides, and during times of movement between high and low tide the water swirled around us, mixing, moving, whirling.  Photo Jodi Frediani. 

For the time that humpback whales are in Southeast Alaska, feeding is everything. Southeast Alaska is a rich and dynamic ecosystem. In the summertime, the difference between high and low tides regularly exceeds 20 feet vertical—while living in Alaska, I could feel our small island home grow at low tides, and during times of movement between high and low tide the water swirled around us, mixing, moving, whirling.  Photo Jodi Frediani. 

Because the tides have such a strong presence in the region and could be partially responsible for regulating the availability of the food supply, could they affect the humpbacks’ behavior? Could we possibly detect that sort of change through the sounds the whales produce? And so my thesis boils down to this question: What influence does the tidal cycle have on acoustic behavior of humpback whales in Southeast Alaska?

Feeding call spectrogram

Feeding call spectrogram

So, here’s what I found: Overall, the whales are not vocalizing more at any one period of the tidal cycle. However, when the vocalizations are classified by acoustic similarities, there is a significantly higher proportion of tonal calls on rising tides. Let me break down what that means a bit more—the tonal call class is the group which contains the highly stereotyped feeding call, which has been studied extensively by Fred Sharpe and others in Southeast Alaska, and evidently serves some function in the capture of schooling herring. These calls are very closely associated with foraging, and have not been recorded anywhere but on foraging grounds. Going back to the tides, it seems that foraging conditions may be enhanced on rising tides, and that this can be detected acoustically.

Presenting my thesis results.

Presenting my thesis results.

So what’s next? My thesis is complete. But my plan for this spring is to run a more detailed analysis and submit a paper to a journal for publication. It is a remarkable gift to experience this as an undergraduate—to see a project through from its conception to the point where many months of work can be represented in a several pages, some figures, and statistical results. I am grateful to know just what is behind those numbers: the waters and whales of Frederick Sound, the creatively designed hydrophone system and all of its character, and the many hours spent listening from a lighthouse in Southeast Alaska.

 


This project is the manifestation of a collaboration between the Alaska Whale Foundation, the Juneau Lighthouse Association, and the Keck Science Department of Claremont McKenna, Pitzer, and Scripps Colleges, and I am grateful to have had the chance to work with all of these entities. I’d like to say an especially big thank you to Dr. Fred Sharpe for offering me this unique opportunity, lighthouse keeper Paul Sharpe for all of his insight into the recording system and for being a fellow island resident and friend, Michelle Fournet for her friendship and remote guidance throughout the fieldwork and analysis processes, and Dr. Elise Ferree for her enthusiasm and support in the analysis and writing of my thesis. 


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