The Currents Ocean Science Hub was created in summer 2015, when a team of researchers placed four hydrophones (underwater microphones) near Strawberry Island to eavesdrop on the sounds produced by humpback whales and harbor seals in Glacier Bay. If this is news to you, you may want to catch up on the blog posts at the beginning of this series.
The scientific results of this work are flowing in! Researcher Leanna Matthews recently completed her Ph.D. dissertation at Syracuse University and provided the following quick summary of one facet of her work on harbor seal calling behavior.
Many people think of harbor seals, one of Glacier Bay’s iconic creatures, as a quiet species, but listening underwater may change a few minds. During the summer, male harbor seals produce a vocalization, known as a roar, which is thought to function in male-male territory establishment and possibly as an attractant for female harbor seals. The males roar at all hours of the day and night in June and July. The summer is also peak tourist season in Glacier Bay, with hundreds of thousands of people visiting the park on cruise ships and smaller vessels. A key research question was whether male harbor seal calling behavior is affected by the noise from vessels.
Analyzing many hours of audio recordings from the hydrophones, we found that harbor seal males call louder and at a higher pitch when noise from vessels is evident. The seals also shorten the duration of their call during periods of vessel noise. These shifts in calling behavior are similar to other marine mammal species that have been studied, but this is the first information on how harbor seals adjust their vocalizations in vessel noise.
This work will be written up for scientific publication in the coming months. Earlier this year, our results on the loudness of harbor seal calls were published in the Journal of the Acoustical Society of America.