The solar-powered Solaris slips away from the Hudson River Maritime Museum’s dock, glides through the Rondout Creek, and heads toward the Hudson River.

Wearing a flowing white gown, HariPrakaash sits on the boat’s floor before a large gong. She teaches Kundalini yoga, meditation, and gong sound healing, and during the summer she brings her practice onto the river. On this evening, the boat carries a dozen meditation participants, including me, along with sightseers and crew members.

Each strike of the mallet sends vibrations through our bodies and across the tidal river as the sun begins to set and a new moon rises. Somewhere beneath the Hudson’s surface, Atlantic sturgeon are producing a thunder of their own.

A team of researchers has made the first known recordings of sounds associated with Atlantic sturgeon spawning in the wild. The low-frequency pulses, recorded near Hyde Park and described as resembling distant thunder, could give scientists a noninvasive way to identify and protect spawning grounds without capturing the endangered fish.

The findings were published last year in Endangered Species Research. This spring, researchers placed additional underwater recorders in suspected spawning areas, including some that do not have federal habitat protections, according to Cornell University.

Atlantic sturgeon hatch in freshwater before migrating to the ocean and eventually returning to their natal rivers to spawn. Adults return to the Hudson in May and June. The slow-growing fish can live 60 years or longer, reach 14 feet, and weigh as much as 800 pounds.

Four whiskerlike appendages called barbels hang beneath the sturgeon’s long snout, just in front of its mouth. Instead of scales, the fish has five rows of bony plates, called scutes, running along its body. Its lineage reaches back before the age of the dinosaurs.

For thousands of years, Indigenous peoples along the Hudson harvested sturgeon for food and other materials. European settlement eventually transformed the fish into a commercial commodity. Its flesh became so common on  menus that it was known as “Albany beef,” while its eggs fed a lucrative caviar industry.

By the early 20th century, overfishing had devastated the population. Pollution, habitat degradation, vessel strikes, and accidental catches in other fisheries further contributed to its decline.

New York closed its Atlantic sturgeon fishery in 1998 as part of a coastwide moratorium. In 2012, the Hudson’s New York Bight population was listed as endangered under the federal Endangered Species Act.

The population remains severely depleted. An estimated 6,000 adult sturgeon once entered the Hudson to spawn each year, compared with fewer than 700 now, Rebecca Cohen, a postdoctoral researcher at the Cornell Lab of Ornithology and a lead researcher on the acoustic study, said.

The state Department of Environmental Conservation has monitored juvenile Atlantic sturgeon since 2004 and adults since 2006. Researchers catch, measure, tag, release, and monitor adults returning to spawn near Hyde Park.

On June 22, a department monitoring team caught a male weighing 116.8 pounds and measuring nearly 5 feet, 11 inches. Researchers tagged and released the fish. The catch did not by itself demonstrate that the population was recovering, but it gave scientists another opportunity to collect information about one of the Hudson’s remaining spawning adults.

The acoustic study brought together researchers from Cornell, the Department of Environmental Conservation, and six other academic and federal institutions. They used passive acoustic monitoring, a technique that employs hydrophones, or underwater microphones, to record sound over long periods.

Researchers deployed a recorder near the southern end of a known spawning area at Hyde Park. Positioned about 3 feet above the riverbed in roughly 26 feet of water, it captured a series of sounds that coincided with the presence of tagged adult sturgeon during spawning season.

Cohen described them as “thundering sounds, like there’s pulses in the thunder, like the roll of a timpani drum.”

Atlantic sturgeon spawn in deep, murky water, making their behavior difficult to observe in the wild. Scientists have instead drawn on observations of captive Atlantic sturgeon and wild Lake sturgeon, a related species that spawns in shallower water.

“A female will begin releasing her eggs over suitable habitat or substrate, and then one or more nearby males will come over and kind of thrash alongside her and release their milt in order to fertilize those eggs,” Cohen said.

Researchers suspect the thunder may be produced as males contract or thrash their bodies during fertilization, possibly causing their swim bladders to resonate. The evidence links the sounds to spawning activity, but scientists have not determined precisely how they are produced or whether the fish use them to communicate.

“It is a possibility that this thrashing sound is like an advertisement to other males to come and participate in fertilizing eggs,” Cohen said. “We can’t rule it out, but we don’t have anything definitive supporting that, either.”

The recordings could help researchers identify previously unknown spawning grounds, study the timing and behavior of the fish, and estimate their relative abundance. Unlike netting and tagging, passive acoustic monitoring can collect information continuously without handling the endangered animals.

On July 22, as the Hudson’s spawning season came to a close, researchers returned to the river to retrieve the listening devices. Back in their laboratories, they will analyze the recordings for additional evidence of sturgeon activity.

Back aboard the Solaris, HariPrakaash leads us through a rhythmic Circle of Light mantra meditation. In the tradition she teaches, this meditation is intended to foster a sense of protection and mental balance.

As the gong reverberates through the boat, I imagine myself moving through the river alongside the sturgeon. One thought returns again and again: Atlantic sturgeon have lived in these waters for millions of years, while we have been here for only a moment.

We still know remarkably little about this ancient fish. But now, in our moment together, we are finally listening.

Bennet Ratcliff is a contributing writer for The Overlook. Reach him at reporting@theoverlooknews.com.