A Noisy Ocean: A Q&A with Dr. Leila Hatch
If you're a marine animal, odds are good that you need sound. From whales to small invertebrates like shrimp, many marine organisms rely on sound and hearing for their survival. Sound is the most efficient means of communications over distance underwater, and is the primary way that many marine species gather and understand information about their environment.
Over the last century, human activity has increased along the coastlines and offshore, resulting in increased underwater noise. Dr. Leila Hatch, a marine ecologist at Stellwagen Bank National Marine Sanctuary, studies the effects of underwater noise on marine life and co-leads NOAA's Ocean Noise Strategy effort with Jason Gedamke and Jolie Harrison from NOAA Fisheries.
How do animals underwater use sound?
Sound travels much more efficiently than light underwater, so aquatic animals rely heavily on their ability to hear over a wide range of distances and in a variety of behavioral contexts. They listen for sounds made by their prey and their predators. They listen for cues that guide their navigation and directionality, ranging from larval stage settlement to adult and juvenile migration. And they listen to each other: aquatic animals from invertebrates to fish to mammals use sounds produced in all kinds of ways to communicate with one another, often during reproductive behavior but also antagonistically and to support group cohesion.
What kinds of problems does ocean noise produced by human activities present to animals?
Noise produced underwater by human activities can have different kinds of impacts on animals. Some types of loud noises produced at relatively close proximity to animals can cause injury, ranging from severe and permanent to temporary. In some contexts, some animals can respond behaviorally to noise sources, resulting in disturbance.
Also, due to the potential for noise energy from some source types to travel great distances, accumulated noise from many sources in an area can lead to higher levels of background noise and interfere with the ability of animals to hear important environmental cues.
Exactly how noisy has the ocean become over time? Hasn't there always been natural noise in the ocean?
Wind and waves, earthquakes, lightning strikes, and the movement and breaking of ice are some of the natural physical processes that contribute to noise levels underwater. Animals have evolved their hearing systems in the presence of these noise sources, in some cases taking advantage of the cues they provide.
We know that the amount of noise-producing human activities offshore and close to shore has been increasing steadily over the past 100 years, which is only a few generations of many long-lived marine species, such as large whales. There are only a few places where instrumentation has allowed us to measure that increase. Measurements off the U.S. West Coast reflect low frequency noise levels -- those that best reflect noise introduced by commercial shipping -- increasing by ~3 decibels every 10 years. That might not seem like a lot, but it represents a doubling of acoustic power at those frequencies every decade.
Do concerns about noise vary in different parts of the ocean, including sanctuaries?
While most of our national marine sanctuaries are inhabited, at one time or another, by animals that we know make or use sounds, not all these sites are equally impacted by noise produced by humans. We would expect, for example, that Gray's Reef National Marine Sanctuary off the coast of Georgia, which is relatively free of large commercial vessel traffic, has lower background noise levels at low frequencies than Stellwagen Bank National Marine Sanctuary, further up the coast off Massachusetts, since Stellwagen Bank is transited by a shipping lane. Right now, the sanctuary program is working with partners across NOAA to generate data to compare noise levels in a standardized way across sites, and to account for the many factors that will contribute to variability, both within sites over time and among sites.
How do national marine sanctuaries factor into the NOAA Ocean Noise Strategy?
The NOAA Ocean Noise Strategy showcases the importance of places like national marine sanctuaries in an agency-wide approach to reducing noise impacts to NOAA trust resources over the coming decade. Foremost, the strategy showcases the need to understand and manage noise impacts to the acoustic condition of animals' priority habitats, in addition to impacts to individual animals.
Further, it recognizes that acoustics mediate interactions among many species and play key roles in the health of biological communities. Where such communities exist within sanctuaries, NOAA is tasked, through the National Marine Sanctuaries Act, with maintaining, protecting, and when appropriate restoring the habitats, populations, and ecological processes that sustain them. The NOAA Ocean Noise Strategy highlights key roles for sanctuaries as sentinel sites for passive acoustic monitoring and characterization of trends in ocean noise.
Finally, sanctuaries are highlighted as key places to educate people about the wide-ranging problems with ocean noise, providing them with place-based environments to learn about the issue, the science NOAA is doing with partners to inform our approach to it, and how they can help.
What do you see as some possible solutions to the problem of noise? On the surface, this appears to be a complicated problem to solve.
NOAA's Ocean Noise Strategy outlines several approaches that NOAA is taking with other federal and non-federal partners to reduce noise impacts to the species and places we manage. Some are underway, including efforts to work internationally to support the development of quieter alternative technologies for noise sources like shipping and airguns used in oil and gas exploration. Others include better tools to identify high-risk places and species so that we can focus our mitigation efforts, including but not limited to time-area exclusions for noisy activities.
The strategy seeks to ensure that the agency is applying the tools we have to reduce impacts as effectively and efficiently as possible, looking over the wide range of science capacities and management techniques we have and ensuring that we are collectively pointed in the same direction.