On the first warm Saturday in April, my eldest son and I were driving home to Freeport after a school fundraiser, absorbed in a book on tape, Susan Cooper’s “Over Sea, Under Stone.” With only a little way to go in the story, and the day so beautiful, we pulled down a side road to a town landing and parked next to a muddy, tidal estuary that stretches all the way back to our house. Here, the Haraseeket River “enters or retreats,” in the words of the poem “The Moose,” by Elizabeth Bishop, and “meets the bay coming in, the bay not at home.”

In summer, we often gather here with our neighbors to plunge into the high tide, warmed by the hot, silty mud below. Herons and ducks, osprey and cormorants are all common during those evening ablutions. Once, when my husband was underwater, a bald eagle swooped in and lowered its talons into the water just in front of him, a shock of yellow in the murky water, then rose through the bubbles with a shimmering fish.

But that April afternoon, all seemed calm. We watched the bay come home as we sat in our car, rapt as Cooper created an exciting yet perilous situation for her characters. The bay slowly filled the warm basin of mud and spartina grass. I noticed, but barely, an odd shape stuck in the mud. Bigger than the grail the children Barney, Jane and Simon were seeking in the story, it looked almost like a chunk of an old canoe. But focused as I was on the story, on the sun slanting over the brown grass and on the luxury of time alone with my 9-year-old, the odd shape didn’t hold my attention for long.

Some friends were making their way down to the dock, their children laughing and playing, when suddenly, with a flip of a tail, the shape moved. Still in storyland, for a moment I thought my mind was playing tricks, sending me a selkie through ancestral channels of gray matter. All at once I realized we were looking at an enormous seal.

NOT FROM AROUND HERE

It was a seal unlike any other I’d ever seen – silver, with a large black stain on its back that resembled the map of Greenland. The seal did a lap in the shallow warm water, poking its head up to watch the children, who were now rooted to the shore in awe. Then it flipped its tail and came to rest on the mud and grass.

A couple arrived to bird-watch – Freeport’s retired head librarian, Beth Edmonds and her husband, Dan Nickerson. Immediately, he spotted the unusual seal, and pulled out his camera. In voices excited, almost childish, we adults guessed aloud together.

“I’ve never seen a seal that big or that color,” I said, disbelieving my own eyes. Over his shoulder, Dan Nickerson suggested I look up “harp seal” on my phone. Wondering what a seal I associated with the Arctic could be doing in our estuary, I did. This one looked just like the pictures of those Northern creatures!

Was anything wrong? my son fretted. To him, the tail was flipping oddly, and he worried the seal was injured. Our small group huddled together discussing what to do. Eventually, we called Marine Mammals of Maine (MMoME), a Bath-based rescue organization.

When Lynda Doughty, a biologist and the organization’s executive director, arrived a few hours later, she identified the seal as a male harp, 5 to 7 years old, and most likely lost and tired. She instructed our group to continue to keep our distance. Already, some kayakers had come too close, despite warnings from the shore; they had scared the seal further into the muddy rivulets of the estuary. Keep dogs away, as well, Doughty added.

AN UPTICK IN STRANDINGS

Our native seals are harbor – like Andre – or gray seals. Ice seals, like harp, hooded and ringed seals, are rarer in Maine waters. (Some sub-species of ringed seals are listed as threatened by the National Oceanic and Atmospheric Administration Fisheries, or NOAA.) Female adult harps, or cows, it’s true, are known to come to our waters in the winter months to breed and pup on the sea ice around our coast. After the cow gives birth, she leaves her pup behind, and heads home to colder waters. The pups may stay here for two to three years before beginning their own instinctual northward migration back to the colder waters of the Arctic.

If they get sick or stranded, that’s when people like Doughty get calls. Typically, when a pup found in Maine is assessed to be sick, it is rescued by Marine Mammals of Maine, or Allied Whale, the latter based at the College of the Atlantic in Bar Harbor, and then transferred to the Mystic Aquarium’s Animal Rescue Clinic in Connecticut. The clinic rehabilitates and then releases these pups to head north on their own. A spokesperson for the clinic said they rehabilitate four to five harp seals a year, which usually arrive suffering from pneumonia or dehydration.

In the late 1990s, researchers noticed an uptick in juvenile harp seal strandings and sightings. At first, they attributed the high numbers to the curtailment of baby seal clubbing, a practice that had become highly controversial. More seals were surviving to adulthood, they reasoned, thus more were coming to Maine to give birth.

But a huge spike in sightings and strandings in 2001 compelled researchers to pay more attention. Through the next several years, the entire region of New England tallied record numbers of juvenile harps, from “150 to 300 a year,” said Mendy Garron, regional marine mammal strandings coordinator for NOAA Fisheries. The trend continued, she said, until the mid 2000s, when, suddenly, it precipitously fell away.

“In 2012, there were eight in our region,” she said, adding, “Our changing environment is having some kind of impact.”

What kind of impact, scientists don’t yet fully understand. NOAA Fisheries has been working with Fisheries and Oceans Canada, its Canadian counterpart, to monitor the interplay of a decrease in the juvenile seal population with the loss of sea ice, due to climate change.

“If all the ice disappears, we don’t know if (the harp seals) will find other haul-out areas to breed and pup,” Garron said. “That’s where a lot of the research is now focused.”

A 2012 article in National Geographic said that harp seal babies are drowning or are crushed by broken chunks of melting ice, adding “…as climate change continues to degrade the amount of good ice, the average pup survival rate is likely to drop over the years, experts say.”

Nor do scientists know why some seals stray so far from their usual territory. Perhaps, they are following their food. Allied Whale’s Dan DenDanto fingered the dramatically decreased codfish population, which, he said, is affecting the distribution patterns of harp seals.

“Everything is changing,” he said.

REST AND REGULATION

What made our sighting more unusual than most is that we were looking at an adult male, or bull seal. The last time Doughty remembered responding to a call about a bull seal in southern Maine was in 2011. Strangely enough, it was in the very same estuary.

“Typically we see juveniles, not adults,” Garron concurred.

Despite the rarity of his presence in our marsh, “our” harp seal, as we now thought of him, was perfectly healthy, according to Doughty’s assessment. His body weight was good, and he was “perfectly aware of his surroundings.” He needed rest, she said. She assumed he had gotten lost and, given the sudden warm spring temperatures, he needed to thermo regulate, too. The way he was arching and spreading out his hind flippers is how he cools himself down, she explained. So this is what my son’s keen eyes had seen! Although harp seals typically hydrate by chomping on ice, she wasn’t worried about dehydration. “He’ll get fresh water from eating fish and crustaceans,” she reassured us.

The bigger issue was that semiaquatic harp seals aren’t accustomed to mud and grass, so after they “haul out,” they don’t understand that they should stay close to water, not head deeper into, say, a muddy estuary. “We will find the species in roads or on back lawns,” she said.

Seals of all sorts end up in even odder places, said Jennifer Goebel, spokeswoman for the Greater Atlantic region of NOAA: “Sometimes we find seals in strange places.” In 2016, a gray seal, the sort that normally makes its home on Maine’s rocky coastline, swam up New York’s Hudson River. “It was perfectly happy eating the fish,” she said, “but it wasn’t a safe place for it to be.” Eventually, marine researchers found it in a lock north of Albany that connects the Hudson to Lake Champlain. “We had to drain the locks to capture the seal and bring it back to the ocean.”

THE BITTER WITH THE SWEET

As darkness approached on that lovely, warm April day, Doughty said she felt comfortable leaving our harp in the estuary. No need for a rescue, she said. As long as he could get some rest that night and perhaps into the next day, she predicted he would be fine.

The next morning, my husband and sons and I packed up our binoculars, water bottles and a bag of clementines and headed down to the landing to check on the seal. On the way, we bumped into the friend who’d been there with us the day before.

“It’s gone,” she told us. “A neighbor’s dog went down and scared it last night.” Sure enough, when we reached the little dock and muddy flats, our seal was nowhere to be seen.

“I just wish it had been able to get the rest it needed,” Doughty said when I told her what had happened. “But I feel comfortable saying that in all likelihood it will survive.”

At the end of her poem “The Moose,” Bishop writes of the transcendence a bus full of people feel after witnessing the huge creature standing in the road:

“Why, why do we feel (we all feel) this sweet sensation of joy?”

Ah. That’s the thing: When we have a chance to witness these vulnerable, distinctive creatures up close and personal, our hearts open just long enough to give us a sensation of such pure and innocent joy. That feeling, though, is followed these days by the inevitable stab of worry that this may all vanish before our own children are grandparents.

Caitlin Shetterly is the author of “Modified: GMOs and the Threat to Our Food, Our Land, Our Future” (Putnam, 2016), a winner of the Maine Writers & Publishers Alliance 2017 Maine Literary Award for Nonfiction.

CORRECTION: This story was updated at 12:20 pm. Monday May 7, 2018, to correct the name of Freeport’s retired head librarian.