Hunting the Gloucester Sea Serpent

by Brian Dunning
November 19, 2024

Just over 200 years ago, the fishing town of Gloucester, Massachusetts on the United States' east coast was plagued by a rash of sea monster sightings. They lasted two years. The monster never hurt anyone or damaged anything, but it remained inside Gloucester Harbor, putting itself on display for the people. Eventually the sightings ceased, and the mystery of what this creature was has remained unsolved ever since. Today, however, we have a few more tools at our disposal, and I believe that with a pretty good degree of certainty, we may finally be able to identify the Gloucester Sea Serpent.

Glossy, as I familiarly dub it (and as Gloucester Sea Serpent is quite a mouthful), was first spotted in 1817 by two women who saw a long line of humps moving along across Gloucester Harbor. Soon there were other reports. Once twenty or thirty people watched it from the shore, multiple times it was seen from boats. Nearly all the reports described it as a long line of humps; one witness described it as looking like "a rope lined with keg or cork buoys". Sometimes there were 10 humps, sometimes there were 32. As Glossy moved through the water, witnesses stated that it appeared to undulate vertically, like a dolphin, rather than laterally, like a fish. Glossy's length, judging by the humps, was variously reported as anywhere between 30 and 120 feet. But some also claimed to have seen its head, once described as like that of a giant snake, another time like that of a horse. Once the head was reported as eight feet out of the water. Several times Glossy was said to have what was written in the papers as a "sting," like a spear or stinger or pointed tusk sticking out the front of its head. There are at least two stories of men who went out in boats to try and kill it, one fired a pistol at it and others fired a cannon, both claiming to have hit it but with no effect.

By the end of 1817 there were eighteen published accounts. They continued but steadily declined, with the last known published sighting in 1819. Glossy remained uncaptured, unidentified, and soon was no longer even seen.

Investigator Joe Nickell tackled the mystery and published his identification for Glossy in a 2019 issue of Skeptical Inquirer magazine. Nickell keyed in on the four foot "sting," also described by another witness as twelve inches in length, and by another who saw the creature's open mouth with a "prong or spear" protruding two feet from its jaws. Considering all the reports that discussed the creature's behavior and appearance, Nickell concluded the best fit was a group of tusked narwhals who obligingly sometimes lined up to form the long row of humps. Although narwhals live only in the Arctic waters of Canada, Greenland, and Russia — waters that are nowhere near Massachusetts — Nickell cited a few rare cases of isolated narwhals spotted farther south.

If it were necessary to attribute Glossy to a known extant species of sea creature — and I don't think it is necessary — there are more plausible candidates than a single-file school of narwhals. If we decided the "sting" was the most distinctive characteristic, more so than up to 120 feet of humped body, we should probably look first to a swordfish, marlin, or other billfish. The east coast of the United States is in fact famous for sportfishing for swordfish; they are found along the entire coast, as are a number of other billfish species. All billfish feed on the surface (though many also feed in deeper waters), so seeing the bill poke above the water is not an unusual sight. I really don't see sufficient cause to introduce exceptionally rare errant narwhals as the most probable explanation.

However, if we decide that a very long line of barrel-sized, regularly spaced humps is the more distinctive feature, then we have one more highly probable candidate — one that has to do, in part, with Gloucester's geography.

Gloucester is located near the end of the Cape Ann Peninsula which juts out into the Gulf of Maine. Perhaps its most notable geographic feature is Gloucester Harbor, which provides very nice shelter for the Gloucester fishing fleet. Gloucester Harbor is about a mile wide and reaches about a mile and a half deep into the peninsula and faces away from the prevailing ocean swells. So while the seas off Cape Ann are frequently rough, inside Gloucester Harbor it's often calm, providing a smooth ride for the fishing boats to end their days coming back home for the night.

And with such a large fishing fleet there's hardly a moment when there are not at least a few boats chugging their way in or out, leaving wakes behind them. Boat wakes form a V-shaped pattern of parallel waves, one stretching out to port and the other to starboard, with an angle of about 39° between them in most conditions, as determined by Lord Kelvin's calculations giving us the Kelvin wake angle, and more recently refined by new calculations in 2019 at the Norwegian University of Science and Technology. Imagine two boats coming into the harbor together on parallel tracks, even if one is ahead of the other, the port wake of one will intersect with the starboard wake of the other. These two series of long parallel waves will intersect at an angle of 39° and produce a complex field where the waves constructively and destructively interfere at different points throughout the wavefield. Viewed from a low angle some distance away, such as the shore, this will manifest visually as the top half of a low-amplitude sine wave (the bottom half being below the visual line of sight) — homogenous humps separated by equidistant spaces. One might even describe it as looking like "a rope lined with keg or cork buoys".

While this phenomenon might be much less likely to be apparent on rougher open ocean waters, inside Gloucester Harbor (or anyplace there are boats in calm conditions) it's likely to happen every day. They're not always distinctive enough to stand out, but sometimes they can be markedly well defined, and have been found to be the explanation for various lake monster photos and videos on many occasions. Bolstering this explanation is that all of the sightings for which the specific location was given were located inside Gloucester Harbor.

Taken altogether, this might sound like we have pretty adequate everyday explanations for Glossy: the wave phenomenon fits very nicely for all the reports of a long line of regularly spaced humps, and the swordfish — or even the rogue narwhal — spotted elsewhere by someone else, perhaps a young fisherman or someone unfamiliar with billfish, can explain the reports of a "sting". But in suggesting an everyday explanation for Glossy, we create a new problem for ourselves. If it was really something that can be seen any time, why were the only reports from 1817 through 1819?

One possibility is that something appeared in the Gloucester waters from 1817 to 1819 that was extraordinary enough that it became a famous story, much more extraordinary than wave phenomena or swordfish. But there's also another possibility.

In the early 19th century, Gloucester was already well established as a fishing city; indeed, it was one of the biggest and most productive. But Cape Ann also had another resource: granite. By 1817-1819, its granite industry — though secondary to its fishing industry — was exploding, mainly in the town of Rockport but also in Gloucester. Miners and quarry workers immigrated at unprecedented rates. And to support them, people of every other profession moved in as well. Bankers, merchants, suppliers; they all converged on Cape Ann. And not one of them had any experience with the ocean or waves or swordfish. I did not find any documented evidence that this is what happened, but I have general common sense as well as the experience of two decades of researching such legends: Imagine these newcomers to ocean waters seeing the long string of humps out in Gloucester Harbor. Imagine someone seeing the bill of a swordfish poking up out of the sea. Suddenly we'd have all sorts of sensationalized news articles about a sea monster, the best explanation the recent granite immigrants could come up with. And then, in the somewhat slower-than-Internet-speed grapevine of information that existed in the early 19th century, experienced seamen and fishermen laughed and jeered and pointed out what had always been obvious to them, that these were merely waves and/or swordfish, things they knew very well.

Since mundane explanations don't generate newspaper-selling headlines, explanations debunking Glossy's existence do not appear to have made it into the contemporary newspaper articles of the day. We're left with two years of panicked reports to the papers, which were probably followed up (back in the day) with jeering and local knowledge that set everyone straight but wasn't newsworthy; and then 200 years of nothing being unexplained and extraordinary to the experienced local reporters. Thus there was nothing of any special interest to the editors of the day, and so we find nothing of note in the online newspaper archives from the 1820s through to today.

Dismissing Glossy as a wave pattern does not, by itself, explain why all these different people over two years or more reported seeing a sea serpent. While most saw the regular pattern of undulating humps, others saw a head with a "sting" and yet others saw what looked like the head of a great snake or horse. The wide diversity of sightings is further evidence that an actual animal was not responsible for the Glossy phenomenon. What probably is responsible for the larger phenomenon of diverse reports over two years are a set of sociological phenomena familiar to anyone who researches these cases with lots of witnesses, whether it's a UFO coming down, a miraculous appearance of some religious figure, or Bigfoot or Nessie.

These include social contagion and social conformity, whereby beliefs can quickly spread throughout a community, even among those who have not witnessed anything. People who have heard about Glossy are impacted by the availability heuristic, where the idea that's forefront in their minds is quickly adopted as the explanation when they see anything weird in the water like a log or a splashing bird or fish. And those eyewitness events are always going to have been prompted by the prior knowledge of what other people are reporting, then pareidolia and confirmation bias combine to make them see what they expect to see rather than what's actually there. These effects are well proven, and they're exactly what we expect to happen in a case like this. The surprise would be if there were only one or two reports, and then no others coming from the community.

And so we leave the mystery of the Gloucester Sea Serpent perhaps somewhat less mysterious. Even today, these wave interference patterns fool smart people every day into thinking they're seeing a multi-humped creature out in the water; so we should be unsurprised that Cape Ann's early 19th century immigrants from inland — most of whom had probably never seen the ocean before — might have seen the same thing, and have been amazed by an incredible creature that defied all explanation.

By Brian Dunning
Follow @BrianDunning