A Long View of Seal Rescue

When Senior Rehabilitation Biologist Margot Madden combed through 32 years of data about the Aquarium's rescued seal patients, she noticed some interesting trends.

The National Oceanic and Atmospheric Administration (NOAA) and U.S. Fish and Wildlife Service first authorized the Aquarium to respond to sick and injured marine mammals and sea turtles on Maryland's coast in 1991. Today, the Aquarium is the only provider of long-term rehabilitation for seals in the mid-Atlantic. It also operates the National Aquarium Stranding Response Center in Ocean City, Maryland, which fills a critical need in the region by providing immediate care for sick and injured animals before they're transported to long-term care or returned to the ocean.

Thanks to the Marine Mammal Protection Act and other legislation, seal populations in our region are growing, so it makes sense that the number of rescued seals in need of care has also increased.

The Aquarium's Animal Rescue and Animal Health teams cared for an average of four individual seal patients during a typical rescue season from 2017 to 2023. The average was just one seal per season as recently as 2010 to 2016. Beyond this increase, Margot says there have been major changes in the species and ages of these seal patients.

Shifts in Species

Grey, harbor, harp and hooded seals are all found in the mid-Atlantic. Historically, harbor seals were the most abundant species in the region. Over the last decade, though, grey seals have become increasingly common here while the population of harbor seals has waned.

Data from National Aquarium Animal Rescue reflects this. Between 1991 and 2023, the number of rescued grey seals the Aquarium team cared for increased sharply—from three seals total during the program's first decade (1991 to 2001) to 20 seals during the most recent decade (2013 to 2023). At the same time, the number of harbor seal patients has dropped dramatically. The team cared for 35 harbor seals in the 10-year period from 1991 to 2001, then just 11 from 2013 to 2023.

Meanwhile, the numbers of rescued harp and hooded seals fell steadily from 1991 to the early 2000s. After that point, the number of rescued hooded seals continued to decline (from eight seals from 1991 to 2001 to zero from 2013 to 2023), while harps gradually began rising again (from 12 in 1991 to 2001, to a low of six in 2002 to 2012, and back up to 10 between 2013 and 2023).

Ages Skewing Younger

The increase in grey seals in our region can be attributed in part to a rookery (or breeding colony) developing on Cape Henlopen, Delaware, along a thin peninsula where the Delaware Bay meets the Atlantic Ocean. This area was once an established harbor seal colony that grey seals have taken over.

According to Margot, the fact that we're seeing a lot of grey seal juveniles and pups being rescued is a sign that the rookery is not yet fully established or successful. She explains that thriving rookeries share certain characteristics, like isolated, rugged terrain that's near a feeding ground and offers protection from humans and predators. The Cape Henlopen site seems to lack some of these features. It's relatively unprotected, far from a feeding ground, and close to people.

"Successful grey seal rookeries—like Sable Island National Park Reserve in Nova Scotia and Monomoy National Wildlife Refuge in Massachusetts—also allow mom to continuously stay with her pup during the entire nursing period of two to four weeks, and then pups can safely stay ashore for an additional two to four weeks," Margot says.

The Aquarium's Animal Rescue and Animal Health teams cared for their first maternally dependent grey seal pup in 2020 and have seen at least one per year ever since. In 2024, the team cared for their youngest patient to date—a one-week-old pup nicknamed Selkie. Baby seals that have been separated from their mother too early require much more intense care in rehab.

The seal rehab space at the Animal Care and Rescue Center has one triage area and two seal enclosures, which can accommodate a total of two to four animals at a time. The team has had to modify these rehab spaces to care for younger patients.

"Shallow, plastic kiddie pools are an essential tool for our maternally dependent pups and weaker patients," Margot says.

The alternate pools aren't the only extras these young patients need. Margot ticks through the resources they require. "They need more time in rehab, which matters because we have limited rehab spots for a large territory," she says. "Their cases are also more complex and require more hands-on care. We give them oral tube feedings three or four times a day, and eventually have to teach them how to catch and eat fish. We also frequently need to consult with specialty veterinarians as well as surgeons, dentists, radiologists and ophthalmologists."

Typical Timing

One data point that has remained consistent across the decades is the timing—when seals in the mid-Atlantic need to be rescued. Typically, the first seals are rescued at the end of December and sightings taper off in early May. The busiest weeks for seal rescue for the Aquarium team are consistently late February into early March.

During her research, Margot uncovered an interesting weather-related trend she'd like to study further. When she plotted weather patterns in rescue locations for a few days before and after rescues in 2020, 2021 and 2022, she noticed juvenile seals stranded following days with high winds.

"This needs a closer look before we can really draw conclusions, but it was interesting to see this weather-related pattern emerge across the Aquarium's cases," Margot said.

She adds that there are a few other things she's interested in tracking in the years ahead, too, such as whether the grey seals in Cape Henlopen will move on to a more suitable breeding ground, and if seal populations in the mid-Atlantic will continue to grow, necessitating more places where sick and injured seals can receive rehabilitation and care.

If you're in Maryland and see a seal or sea turtle, please report it to the National Aquarium's Animal Stranding Hotline at 410-576-3880. Outside Maryland, please report a stranded or injured marine animal to the appropriate U.S. organization, notify the appropriate Canadian organization of a marine mammal or sea turtle incident or sighting, or contact the Mexico Marine Wildlife Rescue Center.

All National Aquarium stranding response and seal rehabilitation activities are conducted under NOAA permit 18786-04.