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Listening In

by Elizabeth Weinberg

What do a 100-ton blue whale and a three-centimeter snapping shrimp have in common? Sound.

Beneath the surface, the signals we take for granted above the water, like light and smell, are obscured by waves, darkness, and turbidity. But sound travels farther underwater than it does on land—even the smallest of sounds can travel for miles. From tiny snapping shrimp that can create a sound louder than a jet engine to enormous blue whales that vocalize in highly-structured rumbles, many marine animals rely on sound to gather and understand information about their marine environment.

But over the last century, the soundscape beneath the waves has changed considerably. As humans increasingly use the ocean for shipping, recreational boating, energy exploration, military defense operations, and more, the ocean has become a noisier place. Think of how hard it can be to concentrate or hear your friends in a bustling coffee shop or with the drone of an airplane engine nearby. For many marine creatures, that noisy coffee shop is an everyday reality that they cannot escape.

Scientific research has shown that anthropogenic, or human-sourced, noise is making it harder for animals to hear the sounds they depend on for navigation, locating food, finding mates, and avoiding predators—which in turn makes it harder for them to survive. Anthropogenic noise can also make it harder for groups of marine animals, like a pod of dolphins or a family of orcas, to communicate and build strong communities. And at its worst, noise from acute sound sources like airgun blasts can cause physical injury like hearing loss or tissue damage.

The good news is that the problem with ocean noise can stop if we simply turn down the volume. With that in mind, scientists in the National Marine Sanctuary System are working to understand how noise affects organisms that live within these protected areas so that noise can be better managed within their boundaries.

Recently, sanctuary scientists deployed deep and shallow water hydrophones at several national marine sanctuaries to compare soundscapes over time and at different sanctuary sites. Because each marine species makes specific, identifiable sounds, passive acoustic hydrophones can help scientists understand what species live in sanctuaries and how they use sound to communicate. Dr. Leila Hatch, a marine ecologist at Stellwagen Bank National Marine Sanctuary and co-lead of the NOAA Ocean Noise Strategy initiative, explains that "these comparisons are highlighting peak time periods for animal vocalization behavior, like lunar patterns in fish sound production and the seasonal presence of vocalizing baleen whales. They also highlight year-round calling within areas that support feeding by deep-diving toothed whales or resident fish and invertebrates."

In addition to sound generated by marine life, the hydrophones also record man-made noise. Hatch says that the "recorders are documenting contributions to sanctuary soundscapes by human activities, including both close and distant noise from large commercial ships, research vessels, geological and geophysical surveying, and other sources." Tracking noise sources will help sanctuary managers characterize the impacts of different human activities on sanctuary organisms. This in turn allows them to select the most useful tools, ranging from voluntary guidelines to new regulations, to prevent or minimize wildlife impacts.

"Noise doesn’t just affect individual marine animals, it affects the functioning of entire communities, and ultimately, ecosystems," explains Hatch. "Sanctuaries can serve as sentinel sites for the development of new scientific and policy tools that serve the need for place-based protection from ocean noise impacts. And those tools then can be applied throughout the world in places facing similar challenges."