Signals of the Sea
By Leila Hatch
March 2022
Two siblings come home from school. Amidst homework and dinner, they have a short time to practice their musical instruments. One plays the piano and the other plays the violin, and though they try to play in different rooms, the result is messy. To one, the sound of the violin makes it hard to hear the piano. To the other, the piano makes it hard to hear the violin. Which one is making noise, and which one is making music? It depends: it’s all in the ear of the listener.
Sound that has value versus unwanted interference is conditional for underwater listeners. In the ocean, vision is quickly compromised, but sound can travel long distances and efficiently carry important information. A wide range of marine animals have evolved to make use of sound, from the very smallest larval fish and crustaceans, to the largest animals on Earth—baleen whales. Humpback whales are among the most iconic of these critters, with a complex vocal repertoire that we call "whale song" when sung by males in places like Hawaiian Islands Humpback Whale National Marine Sanctuary. As part of the Sanctuary Soundscape Monitoring Project (SanctSound), NOAA and the Navy have been listening to the chorus of this wintertime humpback song throughout the Hawaiian archipelago, both in the sanctuary and in Papahānaumokuākea Marine National Monument.
But SanctSound has listened to more than just whales in Hawaiian waters. Although landlubbers, humans have long used the efficient underwater properties of sound, introducing signals and listening in order to send messages and decode responses. Some of the most sophisticated underwater signal transmission and listening systems that humans have built are used to support national security. For example, the U.S. Navy uses signals called “sonar” (sound navigation and ranging) that reflects off objects underwater and can identify potential threats to U.S. vessels or property. These capabilities are always evolving, so testing and training at sea are a big part of ensuring their readiness in a time of crisis. The waters off Hawai’i include important testing and training areas for the Navy. Although use of sonars for training and testing is limited in areas of the sanctuary during wintertime periods when humpbacks are singing, NOAA and Navy continue to seek the most effective and efficient ways to ensure that impacts to humpback whales are minimized in this important shared acoustic space.
To do this, the agencies need the best available information about the overlap in time and space between humpback whale signals (song) and Navy signals (sonar). SanctSound provided the opportunity to examine this in more detail, recording at five locations in sanctuary waters, and three in monument waters for the 2018 through 2021 humpback whale seasons.
The initial results suggest that at some locations in the monument and sanctuary, sonars contribute, albeit relatively rarely, to the soundscape, while at others they do not. Simply the presence of sonars and whales in the same soundscape does not mean that whales are at risk of disturbance at that location. However, refining the new tools used in this study will help the Navy and NOAA continue to identify patterns of overlap in acoustic use over much larger areas and much longer time periods. More efficient tools for examining patterns in sound data are critical to supporting our understanding and use of the signals of the sea (no matter whose signal you are talking about).
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