The Bizarre History of the Sea Mink

Researchers call them shell middens, and they once served as processing plants for coastal-dwelling Native Americans. Here, indigenous Americans shucked bivalves and disposed of scraps. In the process, they left behind all sorts of tools and butchered bones that date back thousands of years. Archeologists study the middens to understand their diets, movement patterns across the landscape, and the time at which they occupied the site.

The year was 1909, and shrouded by summer seaspray on the rocky shoreline of Flagg Island, Maine, Professor Frederic Loomis, a paleontologist at the University at Amerherst, combed through the remains of clams, whelk, fish, and oyster on an eroding shell midden. At that time, most of Maine’s shell middens were unmolested by development and mining, and the time was ripe for zoological discovery.

While flipping through the shells, Loomis discovered a skull fragment of unexplainable proportions. It looked like a mink—compressed, slender, sharp, with piercing canines and crushing molars, but much larger. Then, he found another and another and kept collecting them until he had 45. Loomis didn’t know it then, but his discovery sparked a century-long taxonomic debate that continues to this day.

Discovering The Sea Mink

Mink are the carnivorous slinkies that rule riparian ecosystems. Picture a fur-covered torpedo the length of a shin-high tube sock. With canines as sharp as a briar thorn and a tail like a rudder, mink swim at tremendous speeds and can cut with precision, allowing them to ambush trout, bass, minnows, and other fish. On land, they appear as miniature otters, bounding with hunched backs as they search every burrow, root overhang, and rock ledge for living prey.

Where they exist, muskrats are at the top of the list, but mink also enjoy crayfish, rabbits, mice, rats, and frogs. One clip even shows a particularly feisty mink taking down a full-grown swan. Fur trappers have long revered mink for their silky, dense, and insulative pelt, which typically fetches fair prices on the fur market. When Loomis discovered the mink skulls in the shell mound, they probably looked familiar, but as a paleontologist who had handled numerous specimens of common mink in his career, he couldn’t make sense of their extraordinary size.

Loomis estimated the skulls in his shell heap were anywhere between 200 to 400 years old. Since the depth of the shell heap indicated it was used for several centuries, he hypothesized that Native Americans continually harvested this extraordinarily large mink over that time period. He noted that every skull had a broken braincase, indicating that the Native Americans harvested the brain for food or other purposes.

He also identified abrasions on the lower mandibles that suggested the mink had been stripped of its hide and scraped of its flesh. Loomis took arduous notes and processed the specimens back at his office. Then, three years later, he published a research paper on his findings. In it, he declared he had found a new and extinct subspecies. He called it Lutreola vision antiquus, or “ancient mink.”

It’s not clear whether Loomis knew it or not, but several years before his discovery, another scientist, physician, and zoologist named Daniel Prentiss, collected a similar set of mysterious mink bones in a shell heap just 100 miles up the shore. Like Loomis’s bones, the specimens Prentiss collected looked just like mink, but substantially larger. They had robust jaws and massive teeth. Unlike Loomis, who interpreted the skulls as a subspecies of the common mink, Prentiss identified his specimen as an entirely new species. He named it Lutreola macradon, meaning “mink with big teeth.”

No records suggest that Prentiss and Loomis ever duked out their taxonomic disagreement, but they sparked a heated debate that continues to this day. Since their respective discoveries, dozens of large mink specimens have been collected in shell heaps from as far north as Canada and as far south as Connecticut. They’ve been found in association with bivalves and other food, often containing the butchered remains of moose, seal, and beaver. All researchers agree that the large mink specimens, now dubbed the sea mink, are undoubtedly large, but the scientific community is split. Is the sea mink simply a large variety of common mink, like those found in Alaska, or is it something else entirely?

Sea Mink in History

Travel back 200 years, and you’ll find a Maine coast much like the one that exists today. Waves crash upon its rocky shores, spouting briny sea spray that permeates the air. The thick air looms over the tidal pools and lays like a blanket over the bays. It infiltrates the townhomes and the people who have made a comfortable living off the sea since Maine was settled in 1607.

Nineteenth-century Mainers built ships and fished for cod. They created island communities and trapped lobster. But at a time when the American fur trade was in full swing, as fur trappers pushed into the uncharted territory of the Rocky Mountain west in search of beaver fur, Mainers found their own prospects. They trapped beaver and otter in the wetlands. They trapped fisher and pine marten in the forests. And on the rocky shores, they trapped sea mink.

“Some seventy-five years ago, and for many years thereafter, my father, who was a fur-buyer, used to have nearly all the furs taken on the islands of Penobscot Bay, from the the mouth of the Penobscot eastward to Frenchman's Bay,” Manly Hardy wrote in a 1903 issue of Forest and Stream. “Many of the mink, especially from Swan’s Island and Marshall's Island, were fully twice as large as the mink from inland, the smallest of them being as large as the largest inland mink and the largest fully twice the size of their inland relatives.”

Hardy is widely accredited as the first person to connect the discoveries of sea mink bones with historical accounts. In his article, Hardy explains that the sea mink furs were much redder and more coarse than common mink fur. He states that Maine trappers called inland mink “woods mink” to distinguish them from the large sea mink, and that sea mink were unusually fat and had a fishy stench.

Hardy also described how they were harvested. Instead of conventional traps, Mainers preferred to ambush sea mink at their rocky shoreline dens and hunt them with dogs. Hardy made a stout case for the differential characteristics between sea mink and their inland counterparts, but as for the conclusions of Prentiss, he couldn’t be more clear. He aligned himself staunchly with Loomis: “My opinion is that the so-called new mink is nothing more or less than the skull of one of these large mink.”

Thirty-two years later and 25 years after Hardy’s death, his daughter shared her opinions with Arthur Stupka, a naturalist at Acadia National Park. “My father laughed at inferences drawn from a single skull,” she said. “As to their being styled ‘species macradon,’ or ‘big toothed,’ of course an animal twice as large as another of the same sort would have bigger teeth and a bigger skull!”

In the over one-hundred years since Hardy’s article, many sea mink specimens have been found, and scholars have continually tried to justify their presence in some historical context. Over time, the pieces have started to come together. According to a 1966 report published by the United States Natural Museum, the Abenaki, Indigenous People of Maine, had a specific name for the sea mink. They called it mousebeysoo, meaning “wet thing.”

Sir Humphrey Gilbert, an English adventurer, is thought to have encountered a sea mink during his voyage to Newfoundland in 1853. In his notes, he writes about a seafaring creature that he describes as a “fish-like greyhound.”

Joseph Banks, a naturalist, and explorer who took part in the famous voyages of Captain Cook, is also thought to have encountered a sea mink. During a voyage along the Strait of Belle Isle in 1776, he described a fur-bearing water critter and also described it as something like a greyhound in the water.

By all accounts, scholars seem to agree that whatever the sea mink really was, it persisted until at least the 1860s, after which sightings dropped off precipitously. Scholars also agree that the last sea mink harvested was around 1880, near Jonesport, Maine. Despite some scant and dubious reports bleeding into the 20th century, the sea mink was declared extinct later that year.

The End of the Sea Mink Debate

Turner Farm, an organic livestock and vegetable farm in North Haven, Maine, lies on top of an archeological site inhabited for over 5,000 years. The site contains a shell midden, and its bones and shells pour out into Penobscot Bay as erosion tears away its shores. The Turner Farm shell midden is rife with artifacts, including one of the richest assortment of sea mink bones ever discovered.

In 2007, Dr. Rebecca Sealfon of Princeton University collected one hundred sea mink mandibles from the Turner Farm site. Then, she collected jaw bones from modern mink and fossilized, extinct species from the same family. She took 13 dental measurements on all of her specimens and applied statistical analysis to her data, quantifying the dental differences between the species. Her research aimed to put the one-hundred-year taxonomic debate to rest and finally answer the question as to whether or not the sea mink really was its own species.

Her results left no doubt. The sea mink specimens had statistically unique dentition. In particular, the sea mink specimens had broader carnassials, the cutting teeth specific to carnivores, than the other mink species. She attributes this to the sea mink’s unique diet, which likely involved crushing hard-shelled and hard-bodied ocean prey. In comparison, common mink have smaller teeth, better suited for inland and riparian quarry.

Dental divergence clearly indicates speciation, Dr. Sealfon explained in her paper, and the most significant result of her research is that it seals the taxonomic fate of the sea mink. Find any scientific paper that mentions the sea mink today, and it will use the nomenclature imbued by Daniel Prentiss over one hundred years ago, with the updated genus for mink, Neogale macradon, or “mink with big teeth.” A species of its own.

Some still maintain that the sea mink really was just a big ol’ mink and that legends of a seafaring “sea mink” are pure fantasy. Others claim that a few sea mink still slip around the oceanic islands surrounding Maine. Regardless, despite the hundreds of bones pried from eroding shell middens and the hundreds of researchers who have sought out after it, no one has ever procured a full, wholly preserved specimen of a sea mink. For now, its legacy lies in the bones in the shell middens, in scholarly speculation and debate, and in the forgotten memories of Maine’s early fur trappers.

Feature image is via the Smithsonian Institute’s Clark Collection.