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DolphinWatch researchers confirm that bay dolphins travel from New Jersey and North Carolina

DolphinWatch researchers confirm that bay dolphins travel from New Jersey and North Carolina

You can learn a lot about dolphins by listening.

That’s what University of Maryland researchers have gathered over the past few years as studies spurred by proposed wind energy projects have led to a much broader understanding of the Atlantic bottlenose dolphins that frequent the Chesapeake Bay.

The hundreds of dolphins that come to the bay and its rivers each summer will likely encounter more and more offshore wind farms in coming years as they move up the Atlantic coast. Scientists have been using underwater recording devices called hydrophones to monitor the marine mammals’ comings and goings, so that offshore wind projects can schedule construction periods outside their peak travel seasons. The monitoring will also help them understand how the presence of turbines affects the animals over time.

But by having hydrophones in the water, continuously monitoring the species for months, scientists have made other discoveries.

Under a project called TailWinds, a team has been monitoring the presence of marine mammals off the coast of Ocean City, Maryland, for about a year. The project is funded by US Wind, Inc., which is developing a lease area for up to 22 wind turbines in these deep offshore waters.

Researchers have used hydrophones there and elsewhere to identify about 1,500 “signature whistles” belonging to individual dolphins. Scientists say these specific whistles develop during the first year of a dolphin’s life, when a mother calls to her nursing calf and the calf recognizes the call as a kind of name.

TailWinds researchers installed a Rockhopper acoustic recorder last spring. Photo: UMCES

“We were surprised by the number of fish we found in Ocean City that are also in the Chesapeake Bay,” said Helen Bailey, an assistant professor at the University of Maryland’s Center for Environmental Sciences.

Bailey is the founder of the Chesapeake DolphinWatch program, which was inspired in part by hydrophone work but also by a desire to better understand where and when dolphins travel in the bay. The citizen science project, which began in 2017, employs a smartphone app that the public can use to report dolphin sightings. The number of sightings has increased by hundreds each year, with more than 1,500 reported to the app by 2023.

“It’s interesting because I thought it would plateau at some point, but it’s still growing,” she said. “I think it reflects continued growth of the (citizen scientist) network and bottlenose dolphin use of the bay.”

Bailey has also been working with TailWinds, which has so far collected a year of baseline data, focusing on black sea bass as well as whales, porpoises and dolphins.

Prior to this, Bailey monitored marine mammals at the Chesapeake Biological Laboratory dock on Maryland’s Patuxent River in 2017. That’s when she started seeing how many dolphins were entering the bay.

Since then, Bailey and his team have used specialized software to examine hours of hydrophone recordings for patterns that identify particular individuals. Collectively, the work has confirmed that Atlantic bottlenose dolphins visiting the bay travel from as far south as North Carolina and as far north as Delaware and New Jersey.

Researchers working within the bay, such as the Potomac-Chesapeake Dolphin Project, have confirmed through their own observations and hydrophone recordings that dolphins use the bay to mate, give birth, and feed, and that they travel farther into the tributaries than previously believed.

Because dolphins travel so much, what happens on the coasts (including new energy projects) could affect their behavior.

Decades ago, Bailey began studying how loud noises, such as those produced by the construction of pilings used to anchor wind turbines to the seabed, affect the behavior and health of marine mammals. As a PhD student, she conducted research for a new wind farm off the coast of Scotland that focused on harbour porpoises.

“Overall, we found there was a period where animals might move further away from the turbines to avoid (the noise), but then they would come back,” Bailey said.

There is evidence that, after construction, underwater wind turbine structures actually attract dolphins and other marine mammals, because their underwater structures become artificial reefs that attract the fish they feed on.

But underwater pile driving is one of the loudest activities humans can perform in marine environments, second only to seismic surveys conducted during oil and gas exploration in some areas, Bailey said. In Scotland, they found that pile driving sounds could be heard about a kilometer away in the air, and even farther out in the water (about 70 kilometers, or 43 miles).

Because water molecules can carry sound over greater distances, one method of dampening underwater noise during wind turbine construction is the use of perforated air hoses that create a curtain of bubbles around the structures. The extra air helps reduce the amount of noise escaping from the immediate area.

Excessive underwater noise can also have a cumulative impact on animals. Last year, Bailey published a paper claiming that excessive noise makes it difficult for dolphins to communicate, causing them to increase the volume of their calls, much like humans might do in a noisy restaurant.

“These animals already have to deal with almost constant ship noise,” Bailey said. “Over the last 100 years, their soundscape has completely changed. They adapt their calls.”

This story first appeared on bayjournal.com on July 3, 2024.