Scientists Examine Shifts In Marine Life Behaviour In Midst Of Slowdown

Travel and economic slowdown due to the Covid-19 pandemic have combined to put the brakes on shipping, seafloor exploration, and many other human activities in the ocean, creating a unique moment to begin a time-series study of the impacts of sound on marine life.

A community of scientists has identified more than 200 non-military ocean hydrophones worldwide and hopes to make the most of the unprecedented opportunity to pool their recorded data into the 2020 quiet ocean assessment and to help monitor the ocean soundscape long into the future.

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They aim for a total of 500 hydrophones capturing the signals of whales and other marine life while assessing the racket levels of human activity.

Combined with other sea life monitoring tools and methods such as animal tagging, the work will help reveal the extent to which noise in "the Anthropocene seas" impacts ocean species.

Sound travels far in the ocean, and a hydrophone can pick up low-frequency signals from hundreds, even thousands of kilometers away. The highest concentrations of non-military hydrophones are along the North American coasts — Atlantic, Pacific, and the Arctic — Hawaii, Europe, and Antarctica, with some scattered through the Asia-Pacific region.

For over a century, navies have used sound to reveal submarines and underwater mines and for other national security purposes. Marine animals likewise use sound and natural sonar to navigate and communicate across the ocean.

But the effects of human-generated ocean sounds on marine life remain poorly understood.

"Measuring variability and change in ambient, or background, ocean sound over time forms the basis for characterizing marine soundscapes," says collaborator Peter L. Tyack, Professor of Marine Mammal Biology at the University of St Andrews, Scotland.

"Assessing the risks of underwater sound for marine life requires understanding what sound levels cause harmful effects and wherein the ocean vulnerable animals may be exposed to sound exceeding these levels. Sparse, sporadic deployment of hydrophones and obstacles to integrating the measurements that are made have narrowly limited what we confidently know."

In 2011, concerned experts began developing the International Quiet Ocean Experiment (IQOE), launched in 2015 with the International Quiet Ocean Experiment Science Plan. Among their goals: create a time series of measurements of ambient sound in many ocean locations to reveal variability and changes in intensity and other properties of sound at a range of frequencies.

The plan also included designating 2022 "the Year of the Quiet Ocean".

Due to Covid-19, however, "the oceans are unlikely to be as quiet as during April 2020 for many decades to come," says project originator Jesse Ausubel, Director of the Program for the Human Environment at The Rockefeller University.

"The Covid-19 pandemic provided an unanticipated event that reduced sound levels more than we dreamed possible based on voluntary sound reductions. IQOE will consider 2020 the Year of the Quiet Ocean and is focusing project resources to encourage the study of changes in sound levels and effects on organisms that occurred in 2020, based on observations from hundreds of hydrophones deployed by the worldwide ocean acoustics community in 2019-2021."

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With IQOE encouragement, the number of civilian hydrophones operating in North America, Europe, and elsewhere for research and operational purposes has increased dramatically. With these, IQOE and the ocean sound research community can shed needed light on humans' influences on marine life and ecosystems.

The existing hydrophone network covers shallow coastal and shelf areas most influenced by local changes in human activity. It also includes deep stations that can measure the effects of low-frequency sound sources over large open ocean areas. (IANS/KB)