A rehabilitated harbor seal moves on the beach during a release event. The seal is equipped with both a satellite tag on its back and an acoustic tag on its flipper. Photo by Mystic Aquarium.
To monitor growing seal populations in Rhode Island waters, researchers have turned to acoustic telemetry as a new source of information. Combined with satellite tag data and DNA barcoding, researchers are building a picture of seal behavior in Rhode Island and evaluating the success of rehabilitation efforts.
In Rhode Island, seals are becoming an increasingly familiar sight. Federal protections under the Marine Mammal Protection Act, signed into law in 1972, have helped the state’s seal population expand dramatically in recent years. On Block Island off the Rhode Island coast, aerial surveys in 2018 detected a few dozen seals. In 2025, this number reached almost 2,000. As the seal population grows in the state, researchers from Rhode Island Department of Environmental Management’s Division of Marine Fisheries (RIDMF), the Mystic Aquarium, and the Atlantic Marine Conservation Society (AMCS) want to understand these animals’ movement dynamics. To do this, they are equipping seals with satellite tags, and increasingly, using acoustic telemetry to track seal movement.
Four seal species can be found in the waters of Rhode Island. Harp seals and hooded seals are Arctic residents that occasionally visit New England during the winter. Harbor seals are a common winter migrant to Rhode Island, and gray seals now can be found on Block Island throughout the year. One of the goals of the project is to understand the residency patterns of gray seals. Although they stay in the state longer than their Arctic cousins, acoustic telemetry has shown that they also migrate long distances. Gray seals tagged in Rhode Island have been picked up by receivers as far north as Canada and as far south as Virginia.
RIDMF wants to know how long they stay in Rhode Island, how much they move around during that time, and when they come and go. Their increasing numbers come with shifting population dynamics, and managers want to better understand these dynamics.
RIDMF is also identifying what seals are eating during specific times of year and building a picture of their dietary patterns by DNA metabarcoding seal poop, or scat. DNA metabarcoding is a process in which researchers can extract and identify the DNA of prey species in scat, exposing what seals have eaten recently. By combining this data with data on fish and invertebrate communities captured in trawl surveys, researchers can identify overlap between seal and human use of fishery resources.
Seals can also become stranded when they get sick or are entangled in marine debris, such as lost fishing gear. In these cases, seals often require medical attention. In Rhode Island, where seal strandings are becoming more common with the increasing population, the Mystic Aquarium responds to reports of stranded seals. They take action to get them safely rehabilitated and returned to the water. In collaboration with Mystic Aquarium, Dr. Tara Plee, Principal Marine Biologist at RIDMF, manages a program tagging these rehabilitated seals. Before returning rehabilitated seals to the wild, RIDMF and AMCS fit them with an acoustic tag and occasionally a satellite tag. These tags will provide data on a seal’s location over time, allowing researchers to build a picture of movement patterns and track the success of their rehabilitation efforts.
Satellite and acoustic tags each have their own advantages and disadvantages for tracking seals. Satellite tags, unlike acoustic tags, can provide detailed, real-time data on a seal’s location and behavior. This data is only provided for short periods of time, however, as satellite tags fall off when a seal molts.
Researchers are finding that unlike satellite tags, acoustic tags are staying on even after the animal molts. With these tags, they can capture movement data over a longer period of time. Although the tags don’t provide real-time location data, the ACT Network, Ocean Tracking Network, and other affiliated networks enable researchers to track acoustically tagged seals over long distances, providing new information on migration routes.
As of 2025, RIDMF plans to tag 50 more seals over the next two years, expanding their database of tagged animals. They are also deploying more acoustic receivers to cover gaps in their study area. In the future, Dr. Plee hopes to expand the project to tagging wild-caught seals in addition to rehabilitated ones. This could shed light on behavioral effects of stranding and rehabilitation and build a better understanding of natural seal behavior in the area.
Data from this project will support the management of the growing seal population in Rhode Island. With acoustic telemetry, researchers are illuminating the movement patterns of resident seals and tracking Arctic species across their migrations. In addition, DNA metabarcoding and trawl data, combined with telemetry data, will answer critical questions about seals’ impact on fisheries in the state.
For more information, visit ACT Network Project RISME.
by Gabriel Stephenson