Making critical connections: Powering ice‑seal science in Alaska

Studying life beneath shifting Arctic sea ice is notoriously difficult, yet the changes unfolding there affect ecosystems, coastal communities and future climate resilience. Learn how UNH scientists, using our RT 6 acoustic releases, are able to deploy and recover hydrophones safely under moving ice—making it possible to capture the long‑term data needed to understand Alaska’s changing marine life and the people who depend on it.

The challenge

Coastal Indigenous communities in parts of Alaska rely on bearded seals for food security, cultural continuity and generational knowledge transfer. Blut changing sea‑ice patterns are disrupting when and where these seals appear – or whether they appear at all.

This shift raised urgent concerns about whether the seals’ breeding behaviour or distribution was changing. It’s a shift that scientists at the University of New Hampshire (UNH) are researching in support of – and with support from – the Ice Seal Committee (ISC) and the North Slope Borough Dept. of Wildlife Management.

As part of their work, UNH researchers are investigating two Alaskan regions. In Utqiaġvik, where sea ice is still reliably present in spring, they are studying the timing of the bearded seals’ unique breeding chorus in relation to when the ice breakup happens.

In Bristol Bay, where spring ice has become inconsistent or absent, their focus is on whether bearded seals are still breeding at all, following community reports of declines in sightings.

This required hydrophones to remain underwater for months beneath moving ice. Because any surface float or marker would be destroyed or dragged away, the entire system had to be fully subsurface, making a reliable acoustic release essential for recovering the instruments.

The solution

UNH selected Sonardyne RT 6‑1000 acoustic releases—the only way to safely moor long‑term acoustic instruments, without having any part of the system at the surface, in ice‑covered seas.

The RT 6‑1000 is our acoustic release transponder designed for seabed deployments, enabling users to deploy, track, locate and recover subsea equipment such as hydrophones, sensors and moorings.

It’s compact, but built for use in harsh environments. That includes being corrosion resistant and rated down to 1,000 m water depth.
It’s also able to support loads of up to 150 kg for periods of up to 13 months and, thanks to its inbuilt inclinometer, it’s easy to check loads have landed the right way up.
It’s also easy to use, either with a deck topside unit, NFC mobile phone app or any Sonardyne Ranger 2 USBL system, when you want full tracking and release control.
It can come with an optional rope canister, for raising tools, sensors or mooring lines as the device ascents, which can be useful in shallow or manual recovery environments.

The UNH set up

Rachel Lewis, a marine biology graduate student at UNH, has been working with our releases for this research. She works in UNH’s Marine Bioacoustics and Behavioral Ecology Lab—often called the “SeaBABEL” lab—led by Dr Michelle Fournet.

“UNH deploys a fully subsurface mooring system designed to withstand winter sea‑ice movement,” she explains. “Each mooring begins with a seabed anchor, topped with an RT 6‑1000 acoustic release, followed by a rope canister, the hydrophone, and a small subsurface float. The entire assembly is kept short—around 15–20 feet—to avoid interaction with drifting ice.”

In Utqiaġvik, the team uses arrays of five hydrophones to capture a wider soundscape.
In Bristol Bay, they deploy four hydrophones spaced well apart to detect any bearded‑seal calls across the coastal area. All systems are placed in autumn and record through the winter and the spring breeding season.

“Recovery is carried out in spring from small boats using a dunking transducer to command the RT 6 to release the anchor, allowing the float to bring the hydrophone line to the surface—even if ice has shifted the mooring,” explains Rachel.

One Bristol Bay unit was found around 2,000 m from where it was deployed but still responded to acoustic commands.

The results

Using the RT 6‑1000 acoustic releases allowed the UNH team to deploy and recover every hydrophone mooring, even in harsh under‑ice conditions where surface buoys are impossible.

“Without the RT 6‑1000 releases, the deployments wouldn’t happen because you can’t have a surface float in an area that gets sea ice,” says researcher Rachel Lewis. Across the project, the team completed 12 deployments and recovered all 12 instruments, which Lewis described as “kind of unheard of” in Arctic fieldwork.

The RT 6 also proved reliable even when equipment was moved significantly by ice. During one retrieval, a mooring had been dragged around 2,000 m, yet the release continued to respond, enabling the team to locate and recover it after several hours of searching. This performance gave the researchers confidence to run multi‑month, unattended winter deployments, knowing the systems would still be recoverable in spring.

Deployments

Recoveries

Success

What the data says

With full datasets from both Arctic and sub‑Arctic sites, the team have been able to document a consistent five‑day lag between sea‑ice breakup and the start of the bearded‑seal breeding chorus in Utqiaġvik. This indicates that the seals are following their preferred ice conditions northward as breakup occurs earlier each year.

In Bristol Bay, the same deployments confirmed no bearded‑seal breeding chorus during the 2025 season, suggesting a potential loss of breeding activity in this sub‑Arctic region, even though hunters still occasionally see seals locally.

“The ability to reliably deploy and retrieve these instruments means we can collect the continuous acoustic datasets needed to understand how bearded seals are responding to changing sea‑ice conditions in these regions,” says Rachel.

“This data is immediately useful to the people who live there: if breakup happens, we know seals start chorusing about five days later—which helps communities decide when to go out and look.

“Next, we’re taking these results back to the Ice Seal Committee, expanding our time series with historic and new recordings, and building an interactive site so hunters, students and managers can hear the chorus—or the lack of it—alongside the figures.”

Learn more:

Find out more about the Marine Bioacoustics and Behavior Lab (Sea BABEL) at the University of New Hampshire
Follow their work through their Instagram account.
Take a look at Rachel’s work