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Decompression Series Part Four: Finding Shelter in an Uncertain World

In the final of this four-part series on the history and development of tech decompression protocols, GUE founder and president, Jarrod Jablonski weaves together various forays into decompression science, including Brian Hill’s pioneering pearl diver study, the NEDU’s work on deep stops, evidence of individual susceptibility, and probabilistic decompression models in an attempt to define the state of our understanding. It may give you pause to stop. Feel free to add your comments.

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By Jarrod Jablonski

Header photo courtesy of the GUE archives

Did you miss Part III? Read it here.

The human quest to explore below the water’s surface began some 5,000 years ago . Since that time, our species has pursued deeper and longer immersions, charting a course through hundreds of years of diving activity and associated research. Many of the advances in procedure, technique, and equipment are a direct result of the compelling and valuable data and experience documented during underwater explorations. As with many novel activities, this process of advancement required pushing physical and intellectual barriers. 

During the 1980s and 90s, advances in technology supported an activity that became known as technical diving. This diving led to the development of ascent practices which were somewhat different from those of scientific, military, and commercial divers. A unique set of needs and limited relevant examples encouraged a great deal of experimentation among these early explorers, including adjustments to breathing gases and the distribution of decompression stops used during their ascent. Some technical divers began using a slower ascent from depth, in the hope this would control the formation of bubbles. These slow ascents became known as “deep stops” and were practiced in the hope they could reduce decompression stress and/or shorten decompression time. 

In fact, the idea of bubble control was not new. During the 1960s, physiologist Brian Hills sought to characterize the profiles of pearl divers who had been operating since the late 1800s. These divers were interesting because they were ascending in two-thirds of the time required by Navy tables, a time that would cut even more decompression from most modern-day ascent schedules. Hills believed the reduced decompression times were the result of a unique ascent profile, including stops deeper than those called for by the Navy tables. Years later, technical diving explorers started adopting similar techniques while reporting reductions in total decompression time. It is difficult to qualify if this perceived success was actually occurring since the groups were relatively small, not carefully monitored, and simultaneously adjusting numerous other factors during their ascent. Even absent these complications, the generally low risk of decompression sickness can greatly complicate evaluations between different strategies. 

The enthusiasm for deep stops likely reached its peak in the late 1990s and was dealt a serious blow by the previously discussed Navy Experimental Diving Unit (NEDU) study that was released in 2011. This study, and others, propose that deep stops are less efficient and may actually increase the risk of decompression sickness. The reader should refer to part three of this series for discussion and references. This series contends that opposition to deep stops is supported by prevailing research, but that a range of other variables need to be considered in order to effectively develop best practices. These aspects are particularly relevant to experienced divers, who report decompression sickness problems when eliminating slower ascents from depth.

Jarrod Jablonski with the Halcyon PVR-BASC semi-closed rebreather aka “The Fridge.” Photo courtesy of GUE archives

It is not my intent to re-litigate the previous three sections of this article, but an interesting, and I believe, underappreciated aspect of Brian Hills’ pearl diver study provides a nice segue. What I find most interesting are the roughly 3,000 deaths and injuries of an unknown quantity that helped shape those unique ascent profiles. In other words, how was this conclusion affected by the elimination of those who are more susceptible to injury, and how much was due to a lack of rigor in the study ? Hills concluded that the success of the profiles was “due to the much deeper initial decompression stops used” by the pearl divers. In a similar way, technical divers took note of the history, the encouragement from experts, and the perceived success by those in their community. 

Given new and mounting evidence against deep stops, can we now definitively conclude that Hills, the pearl divers, and the tech divers were wrong? Are we sure the perceived success was imagined? If some success occurred, was it more about the generally low levels of risk in decompression sickness? Or could something else worth considering be at play? Asked another way, we might inquire how the conclusions reached by Hills and those technical divers are different from the way modern-day decompression tables have come into being.

The history of pearl diving and deep stops is very different from that of most decompression research in at least two substantial ways. The first difference has to do with methodologies, and the second with objectives. In terms of methodology, most decompression research is conducted using the scientific method: developing a testable hypothesis and, hopefully, crafting well-devised experiments in order to interrogate the hypothesis. Open publication of methods and results, internal and external debate, and reproducibility of results are among the many ways in which a hypothesis will be tested over time, narrowing the results toward either a more or less trusted conclusion. The history of deep stops, and possibly to a lesser extent, that of pearl divers, share few, if any, of the rigors commonly associated with the scientific method.

Individual Susceptibility

Looking to the history of decompression research, the objective of a particular study is implicit, if not explicit, in the development and testing of a hypothesis. With decompression profiles, we seek to balance the safety of the majority while not unduly affecting the whole. For example, we seek ascent profiles that keep a high percentage of individuals from being injured while not greatly extending the decompression time of the group as a whole. What would the results look like if we instead sought the most efficient decompression for a select minority of individuals?

 Some researchers joke among themselves that they already know who will get bent among a group of test individuals. This is because research trials require a lot of volunteers among a relatively small population of willing participants, meaning that some of the same individuals are often involved in multiple experiments. This is not to say that a few individuals have skewed all research, but rather to say that a minority of subjects in all research projects can affect the outcome by being particularly susceptible to decompression stress. 

This individual susceptibility is likely no surprise to anyone and is relatively well established among researchers, as is the variability in one individual from one day to the next. We see such variability in almost every conceivable area of our lives, affecting the way we respond to everything from drugs and alcohol to food and criticism. How could it be otherwise? We are all a kind of genetic experiment, refined through time with an endless series of personal and species-wide successes and failures. If we are variably sensitive to decompression stress, as seems almost certain, then in what myriad of ways might that be playing out? 

It appears that some individuals bubble more and some less on the same profile. Might they also be more or less sensitive to whatever collection of bubbles are generated? Is it possible that we develop different collections of symptoms to various types of decompression stress? That we are individually more or less sensitive to similar symptoms? Some of these factors we believe to be true and some we might suspect to be true. Many others lurk in the background, and all impact our sense of what we might call decompression stress. 

Casey Mckinley, Jarrod Jablonski, and George Irvine before a dive with the Woodville Karst Plain Project (WKPP). Photo courtesy of the GUE archives.

Given a world filled with individuals, we must do our best to bridge the divide. The good news is that we do this relatively well seeing that some differences are important but most are not usually extreme. The tail of the distribution represented by a small number of resistant individuals may well be quite small. This means that building profiles for resistant individuals might not have much impact and/or might be unreasonably dangerous. Either way, this individual variability is highly relevant and holds promise for the future. The next big advancement in health care will likely involve personalized medicine. Most of us may not live to see the usefulness of these developments in medicine, much less in decompression research, but the process is nonetheless hopeful. For example, research on heart rate variability ( HRV ) might be one such development, allowing a theoretical computer to monitor your individual stress and adjust the ascent accordingly.

Managing individual susceptibility to a fluctuating range of variables is complicated, especially when many of these variables remain undiscovered, or at least poorly understood. Clearly, all is not lost, as we do a very good job managing the problem of decompression sickness. Depending upon our measure of success, we could say this problem is effectively solved. The fact that we are arguing about the nuances of decompression-stop arrangement and obsessing about relatively small adjustments to our total decompression time speaks to this success. We are likely refining along the margins beyond the point of diminishing returns. However, we should not fool ourselves into thinking that we have all the answers. 

It’s The Data, Stupid

Another way to look at the science of decompression is to say it has mostly been a data-gathering exercise around which we fit slowly evolving boundary conditions. The boundary conditions are prescribed by algorithms and work quite well as long as we stay roughly within their range. It is quite possible we are not capturing any kind of truth about the way things work but rather refining our boundaries as we gather more data. It is true that we briefly foray into the field for some bubble-dynamics or that we strive to define the boundaries with process-markers like immune response, but none of these aspects has yet to produce a credible change in current practices. 

By far the most useful part of decompression research has been the accumulation of data and the refinement of algorithms that capture these outcomes. Ideally, these algorithms would extend well beyond the data they describe, supporting “safe” diving profiles where sparse or even no data exists. Yet, evidence suggests that our models are especially bad in these outlier territories including very deep and/or very long dives. Most divers with meaningful experience in the 100+ meter range will admit they have little assurance of a clean ascent absent any symptoms of decompression sickness. These aspects further suggest that we are working in the proverbial dark, or at least just barely within the distant illumination of modern knowledge.  This appears true at least with respect to specific determinations of cause (mistakes made) and effect (DCS incidence). Attempts to manage this uncertainty are in process among researchers spanning the globe. 

Most experts are convinced that bubbles play a role in developing symptoms of decompression sickness, and most of these believe the effect is significant. In this regard, we have perhaps not come so far from Haldane or Buhlmann, who were both well aware of bubbles but lacked the tools to manage their development throughout a diver’s ascent. Likewise, the most recent deep stop studies do not propose that bubbles are irrelevant, only that deep stops appear inefficient and, in at least some cases, can increase risk. On the other side, we have evidence that slower ascents and/or deeper stops can reduce bubbling, but we remain unclear about the degree of importance the bubbling itself represents, especially over the long ascents conducted by technical divers. 

Even a perfect model of bubbles might fail to predict or appreciably reduce decompression sickness, given the many complications in asserting the specific effect of bubbles in a given individual or within a particular injury. We are probably far from a perfect bubble model and perhaps even farther from determining how the wide array of variables might impact different individuals over time. 

Perhaps we can find a way to manage our uncertainty while still progressing our understanding of the likelihood of a given outcome. For good reason, this process is reminiscent of mysteries coming to light in other fields. We seem to be discovering that more knowledge in a given area does not always result in a clearer understanding. Less than 50 years ago, most people were convinced we had “solved” the mystery of elementary particles, bundling the atom in nice packages of three constituents with simple-sounding names. Now the more we learn, the better we measure, the deeper we look, the more unsettling is the complexity. 

Probabilistic Models and Uncertainty

Despite the confusing world around us, we have managed to achieve a high degree of success, and this continues despite our uncertainty. Management of this uncertainty can be mitigated by the use of probabilistic models and is currently common in other disciplines. This is an interesting and promising field, though it seems unlikely probabilistic decompression models will greatly change our current decompression profiles. This assumption may be wrong but seems appropriate, partly because we already have very low levels of decompression sickness, and partly because we have many supporting dives validating current time/depth profiles. 

Jarrod Jablonski towing decompression bottles at the surface during a GUE project dive. Photo courtesy of the GUE archives.

Adjustments like deep stops temporarily promised to reduce decompression time, perhaps by as much as one-third, but failed to materialize when tested more rigorously. This seems likely to remain true, at least as long as we assert a primary objective in maintaining very low DCS risk for the overwhelming majority. There may be a variety of small improvements to be found, but our current approach seems broadly “correct,” at least within the bounds of most active diving profiles. 

In some ways, we already manage uncertainty but do so indirectly by assigning a very low level of acceptable risk to the profiles that we test. This ultimately impacts the resulting decompression schedule. Using probabilistic models might allow us to permit a high level of risk, which could conceivably shorten decompression time. However, it remains to be seen if these models will be released in a way that allows users to accept high levels of risk. Even if such options become available, I wonder how many divers would use them in an aggressive way. Regardless of these factors, probabilistic models might allow a rational selection of risk, especially for those with the requisite understanding. 

Current and foreseeable models may not be describing any sort of truth, but they do appear good at determining useful boundaries (time and depth limitations) around which a desired outcome (limited DCS risk) appears most likely. I do not mean to belittle that success in the least. We maintain a high degree of confidence we will not suffer decompression sickness on most dives, and that is no small achievement. Yet, it also brings us full circle and back to the idea that modern-day decompression tables are largely determined by those most susceptible to decompression sickness. 

The NEDU study was stopped when it reached a threshold relating to DCS outcome. In this case, 10 of 198 dives resulted in DCS symptoms. Most were mild, late onset, Type I, but with two cases of rapidly progressing CNS manifestations. Two of the DCS cases were experienced by one individual. Ethical considerations require that a manned diving trial with DCS as an end point be designed to limit unnecessary injury to divers by maintaining a low level of DCS risk. This is a sensible and inevitable outcome of human trials. 

I am not advocating for a change to this strategy, but I am curious how this process affects our understanding of DCS, since we know little about the reactions occurring in more than 90 percent of test subjects. Would these individuals begin experiencing low-level symptoms after longer exposures? How much longer? Would we suddenly start seeing dangerous Type 2 symptoms in a rapidly escalating percentage of individuals? This rapidly escalating risk seems likely based upon experience with provocative profiles, but the details remain poorly defined. 

Team of divers descending into the cave. Photo courtesy of the GUE archives.

Maybe some individuals are more resistant to bubble formation while they or others are less sensitive to the bubbles that form. We can find many cases of prolific bubbling absent DCS symptoms. Meanwhile, DCS symptoms can be present with no detectable bubbles. This is to be expected, as symptoms are at least partly related to where bubbles are located. But these results might also hint at other differences in our response to bubbling. What if some divers form bubbles easily and/or experience high susceptibility to any formed bubbles? How would that knowledge affect any decompression recommendations? Is it conceivable that what works well for one diver or even the majority of divers is not optimal for all divers? 

All of this ambiguity should lead a thinking person to question the certainty of their pronouncements. We might be inclined to reduce our deep gradient and ascend more quickly from depth,  as the developing evidence indicates. But we should also respect the dive buddy that says they get bent when moving quicker in deep water. We can’t definitively say what works best, but we can say what seems to work well in the majority of cases for the majority of people. For most divers, these debates are largely academic, since the differences in profiles amount to minutes in one direction or another. 

Technical divers are progressively more affected by changes in recommended ascent profiles in relation to the length of their dives. Yet, even tech dives of relatively modest lengths show impacts of less than 10 minutes and are usually not worth nearly as much anxiety as one can find in the community. Having said this, it is easy to appreciate the desire to maximize efficiency. I am merely trying to suggest one should not be in a big hurry to change what seemed successful in the past. Those wishing to balance experience with evolving science might begin to raise their deeper gradients in a progressive fashion over time while paying attention to how they and their dive buddies respond. Or a person that perceives success with their current approach might choose to hold tight and make few, if any changes. I am arguing that we should recognize both opinions have merit and that we should take each perspective into account when working within our team to establish a given ascent schedule. 

The one definitive thing we can say about decompression is that it works well in the vast majority of cases, and when it doesn’t work, we probably will not know the exact reason. That reality is unlikely to change in the foreseeable future, although we certainly need to keep trying. A knowledgeable friend of mine once said that if we get bent, it is because we did not do enough decompression. Truer words have never been spoken. 

Personal Note:

I am very curious to hear about your experiences and opinions regarding evolving decompression science. Are most of you convinced that deep stops bring no value? How many think they are dangerous? Do you think I make too much of individual susceptibility, or do you see that in your own experiences? I welcome all points of view, critical and otherwise. Let the games begin :-).


Jarrod is an avid explorer, researcher, author, and instructor who teaches and dives in oceans and caves around the world. Trained as a geologist, Jarrod is the founder and president of GUE and CEO of Halcyon and Extreme Exposure while remaining active in conservation, exploration, and filming projects worldwide. His explorations regularly place him in the most remote locations in the world, including numerous world record cave dives with total immersions near 30 hours. Jarrod is also an author with dozens of publications, including three books.

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One Way The World Learns to Mermaid: The Mer-spective from PADI’s Karl Shreeves

InDepth’s editor-in-chief Michael Menduno reached out to PADI veteran Karl Shreeves to explore the trending global phenomena of mermaiding….

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by Michael Menduno

Header image and photos courtesy of PADI Inc. unless noted.

InDepth’s editor-in-chief Michael Menduno reached out to PADI veteran Karl Shreeves to explore the trending global phenomena of mermaiding, which may well surpass tech diving in terms of sheer numbers in the not so distant future! While you shouldn’t expect to see a Global Underwater Explorers  (GUE) “MER 1” class anytime soon, it’s fair to say that mermaiding is here to stay—and that’s arguably a good thing. Here’s why!

As a uniquely dominant force in the $2-3 billion worldwide sport diving market, with nearly 6600 affiliated dive centers and resorts and over 128,000 members, it’s not surprising that privately-held PADI Inc., the self-proclaimed, “Way The World Learns To Dive,” is one of the most closely watched and talked about companies in the business. 

Over the last thirty years, since the emergence of technical diving, PADI has arguably relied on others—“Brand X” in PADI parlance— to bring technological innovation to the diving market while keeping a careful eye on their progress. Once a sufficient market develops, PADI moves in to adopt, standardize, promote, and profit from the innovation, and help popularize and fuel its growth by virtue of PADI’s sheer scale, often to the dismay of competitors. It’s a tried and true model that the organization has applied to nitrox, open-circuit tech diving, recreational rebreathers, and recently even freediving.

So, it was perhaps inevitable, given the tremendous growth and interest in mermaiding over the last decade, along with the entry into the market by Scuba Schools International (SSI) and NAUI, that PADI would pick up the tail, err trail, and offer its own mermaid program aimed at aquatic consumers, and its own teeming instructor ranks. Τhe fifty-five year old training behemoth launched the program in December 2020 and kicked it into high gear last April, with a TikTok-savvy, mono-a-mono, Guinness World Record extravaganza —the largest mermaid show on Earth—held at the Atlantis Sanya hotel aquarium, in Sanya China. Cirque du Soleil move over! 

Accordingly, to get a perspective on the market, we reached out to PADI’s original tekkie, technical development executive Karl Shreeves, who helped field its mermaid program, and was instrumental in the development of PADI’s nitrox and tech diving courses. Here’s what the veteran educator had to say. 

InDepth: To start, let me ask you: How did PADI get involved in mermaiding? When did you start looking at it and thinking about creating a training program?

Karl Shreeves: PADI had actually gotten involved with mermaiding several years ago. We had several instructors who had become part of the existing mermaiding community that wanted to offer a distinctive specialty. So, they submitted the distinctive specialties outlines, and we approved them. And then it started to grow, and the interest started to grow, and we began to get calls for us to create a program like we have for freediving and scuba diving and other types of diving. 

So, we started developing that in 2018 into early 2019. At the time, for us, and by us, I mean what was then the mainstream diving community apart from mermaiding, it was pretty small potatoes. Mermaiding already existed. It popped up on its own track separately from diving. There were already mermaiding schools and people doing it who did not come from a diving background at all. They just got into mermaiding. 

Did things slow down with the pandemic?

On the contrary. The interesting thing was that the pandemic seemed to propel it. And the reason? What do water enthusiasts do when they can’t travel? They get into the local pool. The pandemic helped freediving as well, and in some areas, local diving did well. Scuba divers quickly figured out that, “Well, I can’t see as far in my local lake as I can in Grand Cayman, but it’s actually pretty cool.” They get a trained eye and a perspective. 

But as the pandemic forced us to stay closer to home, there was a growing interest among the traditional diving community in this form of diving because, unlike freediving and scuba diving, all of a sudden, there was an expressive form of diving. It’s underwater dance. The costumes are beautiful. Obviously, it borrows from other kinds of diving. They all borrow from each other, right? 

But you know, especially if you were going to be primarily in a pool, it gave water enthusiasts a new craft that is well suited to the swimming pool. While there is open water mermaiding, as you know, a lot of it is purely in a swimming pool or the various dedicated super pools, and it’s a really good fit there. So mermaiding is a new angle, if you will, for expressing yourself.

It’s a performance art in many ways, like synchronized swimming or water ballet.

Right. Of course, there are a lot of people who come from the diving side and they say, “Well, it’s a form of freediving.” But really, it’s not.” It shares a lot from freediving. It has borrowed a lot from free diving, but it’s really different. 

Freediving tends to be more about the performance of depth and duration. It’s an athletic accomplishment. And again, there’s overlap. I’m speaking a bit in absolutes, but don’t misunderstand me. Mermaiding is more about individual expression and fantasy made real—an ability to touch people in a way that goes as far as wearing make-up as well as some elaborate costumes. And yet, having to be able to swim. And not just swim, but to look elegant and interact with people. 

That’s where it’s got an appeal because that hasn’t previously existed much in diving. Probably the closest thing would be being an underwater model. Ironically, because of the pandemic, and lock-downs, I wasn’t able to be one of the shooters for our Mermaid eLearning course. If there was ever a shoot I wanted to do it was that one!

Ha! You were deprived! What about the language? You use ‘mermaid’ to refer to both genders, not mermaids and mermen, or merfolk?

Funny you ask about “mermaid” as a term, because we actually explain it at the beginning of the course. “Mermaid” denotes gender in English, but in many languages the translated term means “human fish” and doesn’t indicate gender unless you add words to do so. Some in mermaiding use the terms “merfolk” and “merman” etc., but broadly, “mermaid” is the term everyone knows. So, the PADI materials use “mermaid” in the sense of “human fish” as in languages like Chinese, Japanese, Korean, and Vietnamese. But obviously, it’s not a female-only sport by a long shot. Lots of men are mermaid divers and PADI Mermaid Instructors.

I’m sure some of our readers see mermaiding as a trend, something new, but the concept and fascination with mermaids goes back a long way.

It’s not new. It goes back over 1,000 years. There is something about this idea of a human fish that has endured. If you look at the movie Splash, right? 1984. The sixth largest grossing movie in China was The Mermaid. And they are talking about a sequel now. The Korean drama I keep talking about, Legend of the Blue Sea, is one of the most successful dramas they’ve had. Very popular, and people still watch it aftermarket and buy it on DVD. So, this is not a flash in the pan. It’s actually a cross-cultural mythology that we’ve enjoyed as humans. If it were just one culture you’d say, eh… But it’s not. 

Every culture independently created this myth. Now the modern mermaid tends to be the European mermaid, and we talk about this in the course too. Why? Because it’s practical. The European mermaid’s bottom half is fish and top half is human. Very easy to create a swimmable costume. But some, you can do it with computer graphics, it’s a fish with a human face. But my point is that when we look at this as the dive community and say, “Oh, that’s just a bunch of people playing around.” Yeah, it is, but that’s not new. This has been around. So this is going to stay. Now that we have the ability for people to go play mermaid in a serious, fun way, they are going to keep doing it because it’s cool.

In some ways, it enables us to reach back through time and connect with this myth that’s embedded deep in the human psyche.

Once humanity starts to picture something, we find ways of making it happen. And that’s what’s happened to the thousand-year-old dream of being a human who can live in water. We found a way to make it real.

Talk to me a little about the size of the market. Obviously if PADI is getting into it, you must think there is sizable potential. I was surprised when I attended the ADEX show in Singapore in 2019, and they had a huge mermaid section. In fact, it was bigger than the tech diving section! They had 30 or 40 famous mermaids there. I didn’t know who they were, but the people knew them and cheered for them. It was amazing.

Well, as I said, parts of the dive community had adopted mermaiding. It was already growing globally. In fact, it’s really big in Asia in terms of its visibility, but there’s actually a pretty strong community around the world. There are communities in Europe. Here in California, they have a small mermaid convention that’s been held for several years in the Bay Area. It’s not huge but it’s there, and quite separate from diving. It’s about mermaids and mermaiding. They get in the water; they talk about mermaid stories and myths. They role play, and there’s also a little bit of cosplay. Ι think that is part of the fun for some people.

But to give you an idea of scale, when we finally launched the full version of the program within, I want to say, it was a month or two months, we had 500 instructors.

Photo courtesy of Julie Ferrara.
Wow. That’s surprising! Evidently there’s a lot of pent up demand.

Right? When you pick up that many instructors that fast, it’s two things. One, it is popular. Two, it’s already widespread because you don’t learn to mermaid and then reach instructor qualification in two months. You actually have to already have the qualifications. And what we’re seeing is two prongs of appeal. 

First, it’s opened the eyes of divers who’ve never looked at it before and are most certainly going, “That’s cool.” A lot of them are free divers, but some of them are scuba divers. They’re like, “I want to give that a go.” But then we are also seeing that it’s pulling from the original market—people just interested in mermaids who want to live out the fantasy, as it were. That gives it a lot of youth appeal, especially among younger children. 

What we’re finding is that attraction is growing because some of these people realize that it also brings them a connection to diving. It’s like, “I’m not only going to become a mermaid, but, if I want, I can grow towards becoming a diver as well.” Some people find that out in the course. Because, as you might expect, a lot of the mermaid instructors also have their fins in the freediving camp. Those people tend to do a really good job of instructing because they know the difference. They know the difference between mermaiding and freediving. So, they don’t try to make mermaid divers freedivers, but they do train the mermaids in the techniques that apply from one to the other. 

In fact, somebody was asking me about this. “Oh, it’s just a form of freediving.” And I said, “No, not really.” However, when you are a buddy, that is the safety diver in mermaiding, that’s when you’re closest to being a freediver because basically you have the same job.



Makes sense. Freediving has developed safety techniques and protocols, which I would imagine apply to mermaiding too, so that mermaids don’t blackout underwater?

Yeah, in fact mermaiding basically borrowed that most directly. So, while mermaids don’t do static apnea, they swim dynamically as free divers call it. In other words, there’s lots of horizontal movement, but depth isn’t too great. Of course, the more experienced ones still get down there pretty well. But as soon as you shift—”Okay, it’s my turn to be the buddy.”—the mermaid tail comes off, the mask goes on (which is optional if you’re the mermaid), and you wear bi-fins because you need to be able to help and maneuver quickly in the event of a problem. So, that’s probably where you have the most and the strongest connection to conventional freediving.

Mermaids wear monofins but they use bi-fins when being a safety?

Right. They are required to use bi-fins for safety because they need to be fast and maneuverable as a safety. But by definition, if you’re a mermaid, what kind of fin are you going to have? I suppose somebody might come up with a bi-fin mermaid look, but basically, it’s all monofin. They’re going to learn both to be successful in the course.

In freediving, they have the one up, one down system, or one up, one prepping, one down in a team of three, in order to rescue the diver in case of hypoxia. So, mermaids also have somebody watching them who is ready to intervene when they’re holding their breath underwater?

Exactly! Freediving has done a lot for all breath-hold diving, just like tech contributed to all scuba diving. Tech taught us to be tighter with teams and also offered a mindset and approach that has been picked up. The alternate air source originally came from tech. Likewise, freediving has influenced breath-hold diving, even basic snorkeling. Divers are taught that they have to take the snorkel out of their mouth when you’re doing a breath-hold dive, so you don’t breathe a lung full of water in the event of unconsciousness.

Mermaid under Ice. Video courtesy of Teppo Lallukka
Nope! That applies to snorkelers as well! 

Of course, if you’re old school like me, and you came up the other way, as soon as you start freediving you’ve got a habit that you’ve got to change. The habit you learned first is the one that sticks. In instructional psychology we are still trying to figure out why this is. Of course, new divers are getting the right habits from the beginning, so they’re not going to have to relearn them.

Yeah, I had that problem too. My freediving instructor had to keep reminding me to spit out my snorkel when I dived! You mentioned open water mermaiding. I’m familiar with mermaid performances but do they also go out and conduct mermaid dives? Would a mermaid say, “Hey, let’s put on our tails and go dive the kelp forest?”

Because there is so much crossover between the communities, you have people who enjoy mermaid diving, and this is what we covered in the advanced mermaid course. They go out and they mermaid in the open water. There can be many motivations.

There are certainly venues, you know the classic going back decades is Weeki Wachee, of course, where you can watch. And that is more serious mermaiding. Just put brackets around it. It’s a little different from what a recreational mermaid learns. But it’s still the idea. 

Mermaids like to be in a natural environment and watch each other. If you are somewhere warm and nice—like Grand Cayman or Bonaire—and you are surrounded by beauty, it’s fun to go mermaiding. And if you’ve got underwater photographers who might want to take pictures of you, all the better. 

Are you aware of the Korean drama, “Legend of the Blue Sea?” It’s set in Korea but it begins somewhere in the mid-Pacific. The actress who plays the mermaid is swimming around coral and gorgeous stuff. The story is about how she swims all the way to Korea. So that was the performance. In recreational mermaiding, they have fun doing this. It’s something that can be done together in nature. In that case, they typically wear masks so they can see clearly, and they’ll swim down and see the fish. So, it’s a neat little aspect of mermaiding.

That’s right, you need a dive mask, not swim goggles, because you wouldn’t be able to equalize.

Right, and that’s another area where mermaiding differs from other forms of diving. The mask is optional. Some people prefer them, and or wear contact lenses that need to be kept dry. Conversely, in a place that’s not going to bother the eyes, where you see well enough to navigate, some will forgo the mask altogether. In the China video, you saw both.

Let’s talk a little about what has been in place prior to PADI’s and other training agencies’ entrance into mermaiding. How did people learn to be mermaids? I do know there are several schools out there like the LA Mermaid School, and I think Weeki Wachee has a program as well. That’s likely some of it.
Photo courtesy of Julie Ferrara.

Well, it’s kind of all over the map, like what you see in most swimming programs or water programs. There are numerous mermaid schools, as you call them, and there would be a ranking of typically a beginner and then an intermediate level and so on. I would say that—and I want to be sure I’m talking generally here because there are exceptions all over, things are starting to solidify, and community standards are evolving. However, generally compared to what diving offers many mermaid programs were comparatively unsophisticated but safe as far as I could tell. I saw nothing that looked unsafe. Some of them were pool-only and you always have grown-ups there, because there are children in the program, things like that. On the other hand there are some very sophisticated professional mermaid schools like LA Mermaid School and the Weeki Wachee program that offer top notch professional training.

I think what diving has brought to mermaiding is our experience in water safety and integrating it with breath-hold diving. If you take a PADI program, for example, and you are going to be a mermaid diver, you don’t need to be anything else. You just need to be okay on the medical (as any diver of any type), have basic swimming ability, and we’ll take it from there. You don’t have to be a “diver.” You’ll learn what you need to know to be a mermaid, which includes the stuff that’s come over from the other forms of diving.

I looked at the requirements. You need to be able to swim of course.

Yeah. And if you get right down to it, almost all water sports have that. If you fall in the water, it would be good if you knew how to swim. Seems like a good basic safety concept.

Ha! I also thought it interesting that your mermaid programs were open to pre-teens.

Yeah, it’s breath-hold diving, we don’t have the concerns we have with scuba. There’s not a risk of lung overexpansion injuries. We’re not concerned with the kind of depths that limit the junior divers to about 21 m/70 ft. On top of that, this is where we are able to borrow from the community that was there before we got involved. Traditional mermaid courses brought in kids. Kids do this great. They love it. They’ve already been doing it. So it’s not like we had to craft something new to make it fun for kids. Kids already know it’s fun.

Photo courtesy of Julie Ferrara, PADI Mermaid Instructor Trainer and owner of Freedive Cozumel 
We talk a lot in our industry about getting more young people into diving, given the increasing average age of the scuba diving community. Looks to me like mermaiding has the potential to get more young people underwater which is what we want, right?

Absolutely, but also what you’re describing is Western-centric, and changing. We are seeing more young people getting certified. But when you go to the Eastern Hemisphere, it’s like our generation was when we were in our 20s and 30s. That’s who is going diving, the young people. And it’s huge, and I would say it’s much more social there as well. 

The ADEX shows are filled with young people. It’s a very different demographic than the US or Europe.

There is a senior crowd there as well. Interestingly, for a long time PADI Japan was top age heavy because of the demographic of their country, but now that is changing as more young people get involved.

Traditionally, Asian cultures have been better at revering the older generation than Western cultures, because they recognize that’s where wisdom lies. So, you bring the innovation and the enthusiasm of youth, and you pair it with the wisdom and lessons of the past. That’s where you get a really strong community. You can probably tell: I really admire that they bring that to our diving community.

PADI has a bazillion dive centres around the world. Are we going to start seeing mermaid programs and communities popping up everywhere?

I would say yes. It’s happening as we speak. I mean it has never happened before: a program was a fringe program, a specialty, that was going to be it. The market was that small. But like I said, the pandemic changed that like it changed so many things. We’ve never seen a program that went from essentially a fringe activity to something worthy of our full support with e-learning in a year and a half! I’ll tell you what, I’ve never had to type so fast in my life.

To me it’s exciting. It’s like, wow. Because diving could either have fallen on its face during what happened or it could do something new. And we’ve done something new. I mean it wasn’t “new new,” but it was new in the expansion and the attention it got and that caused it to grow. The community is even plugging into dedicated deep pools like K-26 in Korea, one of those purpose-built deep pools that goes down to 26 m/85 ft.

Ah yes, deep pools. We have a story about deep pools in this issue.

There are a number in Europe, and there are some being planned for the US. Mermaiding blends beautifully with these. Because it’s more than a pool but not quite open water, but you’ve got the controlled conditions, and you have depth. The freediving community has taken advantage of these, too. Most of these facilities have underwater windows as well. So now, in addition to performance art, you have the potential to make it a spectator sport, if you will, in diving.

Yeah, that’s really interesting. Talk to me about training. We will, of course, include links with the article about your courses etc., but tell me, what do you need to learn to be a mermaid? What is the main focus of the courses?

As I mentioned, a lot of it is stuff you’d learn as a freediver, but applied to mermaids. The first thing you learn is about the costumes because that’s a little different. What is or is not an appropriate mermaid tail? Because you can buy some out there that are purely costumes, they are not for swimming. You learn to swim in them, so there is a huge emphasis on dolphin kick. You learn breathing techniques. But again, as a mermaid, you may not have a snorkel or whatever so you learn how to float, you learn how to wade as a mermaid. At the same time, you are also learning to be a safety buddy. What do I have to watch? I’ve got to have these fins on, things like that.

Is mermaiding a team activity built around two or three people mermaiding together? 

Like other forms of diving, you can’t paint too tight a box around that. But what we teach is that you have somebody watching you. It wouldn’t be considered reasonable to have two mermaids on the bottom and one safety diver. But if you were diving in threes, say, one person would go down and then come back up and then another goes down and comes up, and then the third, so it’s a bit like free diving. In open water, the safety diver might escort you through the last 5 m/15 ft. But in pool-based mermaiding, just like in pool-based free diving, the safety diver just stays on the surface. 

They learn skills that were developed in freediving but have been mermaid adapted. Like doing a duck dive, which is a little bit different in a tail than in bi-fins. You learn some skills unique to mermaiding. There are more flourishes. Like C-shaped turns and back turns and the mermaid kiss. All these things that they love to do. Team handshakes. They get into the performance a little bit. 

The instructor also has the latitude to help the mermaids try the makeup. And again, it’s not your typical Mary Kay. It has to be two things. It has to be waterproof and then if you’re in open water, it has to be environmentally friendly. It can’t be something that would hurt the environment. In our program, the mermaids are taught about the environment and our role as stewards, and they are encouraged to join the community of torchbearers who are trying to speak for the oceans. 

You incorporate ocean and water conservation!

Yeah. All our programs have that tie. If you love the ocean, you can see what’s happening. You can also see that we can do something about it. And the most important thing right now is we all have a voice and a purpose when we come together on that. 

I’ll run slightly into the weeds here, but you may have heard a few years ago that Drew [PADI CEO Drew Richardson] committed the PADI family to one billion torchbearers by 2050. And that’s actually not that huge a number. Drew also didn’t just pull that number out of the air. When you look at social tipping points, the amount of the population that has to adopt a new view before society tips in that direction, one billion is about half that number. 

That’s a laudable goal!

So, obviously, when we start talking to mermaids, a lot of those folks are a crowd from outside our normal sphere. Of course, we want them to understand about the oceans and have a connection to it.

Photo courtesy of Julie Ferrara, PADI Mermaid Instructor Trainer and owner of Freedive Cozumel 
They are ambassadors. They are performing for people who may not be water people.

The potential for a mermaid to get in front of non-divers is in some ways better and at least different. And so they are reaching a new audience. Look at Mermaid Linden . How many kids does she talk to? You start talking with her about the ocean, and you won’t leave without knowing that it’s in trouble, it’s worth saving, and we can do it. She’s reminding six-year olds that they can help.

That’s powerful. I don’t know that the scuba community even talks to six-year olds. Get them while they are young, right? Karl, you and your colleagues have been involved in the development of many, many training programs. Was there anything unique or challenging about creating a mermaid program?

I’d say, fortunately, we’ve done this enough that we have learned where to look. In the past, I would’ve said that the challenge might have been finding the experts that we needed to go over what you’ve done and help us look for gaps and things like that. I would say, if there was any challenge, it would be this, and that was when we got to the e-learning part. 

Because of the lockdowns and everything we were very limited in what we could do in terms of finding talent and locations and photographers. We always try our best to show as much multicultural diversity as possible in our products, but this one had to be shot entirely by our China team. We were able to get some stock photos and so on to show more than Asian faces, but you can tell, if you look at the program, that they handled the imaging for us. 

Photo courtesy of Julie Ferrara,

But I’ll have to say, if we had to have a challenge, I’ll take that one any day of the week. They did a great job with what they did. They found some really, really talented mermaids to act in the stills and videos. We found enough stock shots of other faces that we could show our diversity. Plus, anybody who knows us, knows that we are probably the most culturally diverse group in diving.

PADI is not the only agency to see an opportunity. SSI launched their mermaid program in 2018. NAUI launched theirs in 2020. As far as Global Underwater Explorers (GUE) is concerned, I don’t expect to see “MER 1” anytime soon. But who knows? Do you anticipate more agencies jumping in on the tail wagon, as it were?

Yes, I believe we are going to see others pick this up as well as it grows. Success breeds competition. It’s happening, but that’s cool. 

I remember once asking undersea pioneer Phil Nuytten, who invented the modern one-atmosphere suit, if he expected to have any competitors. He told me, “I hope we have competition. In fact, I hope we have a lot of competitors. Because if we don’t, it means that it wasn’t a very good idea.” I’m guessing that the people at SSI and NAUI are at least feeling validated!

Competition also keeps everyone sharp! 

All the better for the mermaids, right? You launched your program in December 2020, and then last April PADI held this huge extravaganza in China. It was what, the largest underwater mermaid show ever?

The event was held at Atlantis Sanya in China and it set a Guinness World Record in their giant aquarium. It involved more than 100 PADI Mermaid divers, plus support divers and topside personnel. The divers spent three days rehearsing a synchronized dive—you can imagine what it takes to get 100+ divers to descend at the same time and then swim in a coordinated manner. It was spectacular though—and had a lot of international coverage.

Are you ready to get your mer on? Push play!
I heard that the event got 170 million views on TikTok—OMG!—and PADI now has something like 600 mermaid instructors and 50 dive centers in China offering your mermaid program.

I don’t know the numbers off the top of my head, but yes, the PADI Mermaid Program has gotten a lot of attention around the world. More than 600 instructors in China alone sounds right – it’s been eye-opening.

Talk to me a little about technology. Do your courses deal with working with surface supplied gas, or scuba, or the use of nitrox as a pre-breathe? Would that be technical mermaiding? Ha!

It’s not within our program nor any of the programs you’ve mentioned, to my knowledge. It wouldn’t surprise me if we get there. Now I do know that the Weeki Wachee program, which has been around for years, is training professionals. There you have to be a scuba diver because you are going to breathe compressed air, if I am not mistaken. Of course, you have to know how important it is to be exhaling as you ascend. Exactly the opposite of what you would normally do as a free diver or mermaid diver. Right now, that kind of thing is outside of what recreational mermaiding, for lack of a better term, is about. But come ask me again in a few years. I’m serious. We saw freediving do it, right? You just said it—technical free diving. Whoever thought, oh, I can breathe up using a gas with a high oxygen fraction and stay down longer on my one breath. That’s helpful. Who knows? One of the cool things about diving is that divers tend to get what they want instead of what someone thinks they ought to want.

I was speaking to Virginia Hankins at the LA Mermaid School and SHEROES Entertainment that provide professional mermaids for film and photoshoots and professional engagements. They are trained to use underwater breathing equipment. She’s one of your instructor trainers.

Yes, absolutely. We were talking about “Legend of the Blue Sea” earlier, and I’m sure it was true in “Splash”—when you start talking about Hollywood productions, they are going to use scuba. Again, that’s beyond what we are teaching in our recreational program. It requires additional education.

Let’s talk about equipment. I attended Eric Albinsson’s webinar on PADI mermaiding. He said that the global mermaid tail market was valued at $80 million in 2020—that’s annual revenue, and was expected to grow to $150 million by 2026, a compound average growth rate (CAGR) of 9.5%. That blew me away!

I don’t know what number he’s quoting, but it’s definitely there. And again, it’s not new, if you think about it. In our courses, the minimum is a monofin. But look at the variety of tales in that China mermaid video. 

They’re exotic and amazing. Some of them look like a real biological tail!

Yeah, so there’s absolutely a market that’s growing. And it’s been there, but it’s accelerating. And again, the pandemic probably helped it.

Obviously, PADI sees this as a business opportunity, not just for itself, but for its dive centers, instructors, and professionals.

Absolutely. For one thing, it’s reaching a new market, and some of these people will likely get exposed to freediving and scuba. So, you get this neat cross-pollination of the three markets, or rather the three communities. The second thing is, it’s a great resource to use. If you have a pool, or if you go to a pool a lot, you can do a lot there. People can go all the way through mermaid without going to open water. So, the center can offer two full certifications, plus the experience. If I ran a dive center, I would definitely at least be dabbling in it right now. I don’t think I’d want to ignore it.

It seems to me it’s a lot like adding freediving to a scuba center.

It’s similar. Your upfront investment isn’t that high. If you’ve got an instructor who wants to get into it, that person trains up and they learn to teach. You don’t need to buy another compressor or a mixed gas blending system. If you’re already catering to freedivers, you’ve already got all that covered. So basically, you’re talking about adding mermaid tails.

Tails! There we go again. I’ve often thought our job as an industry is just to get people into the water. Create water enthusiasts and then they’ll find whatever pathways work for them. Mermaiding is another fun thing to do in the water. 
Last question: Where do you see this going? Where will mermaiding be ten or fifteen years from now?

Boy, that’s such a hard one to call because if you had asked me that question a year and a half ago, I would’ve said, “Well, maybe we’ll have a supplemental program someday.” And here we have a full e-Learning program we’re about to debut.

I don’t want to call this one. It’s going to grow. I can say that with confidence because it’s got the inertia now, it’s already happening, it’s already popular, and it’s global. There’s attention to it. It’s beautiful, it gets people in the water. There isn’t a whole lot to say against it. So, it’s going to be bigger. How much bigger? I don’t know. It could really take off in some communities that have not been connected to diving, where that visual appeal is important, and there are a lot of young people involved.  

Thanks Karl. Call me crazy, but I find all of this really interesting.

Additional Resources:

The Darker Side of Mermaids

Wired: Fantastically Wrong: The Murderous, Sometimes Sexy History of the Mermaid

The Filthy Mermaid: Got-To-Have-Goods for For Mermaids Gone Bad

Events:

MerFest International 2021 (South Haven, MI 20-22 August, 2021)

Mermaids In Paradise (Ramrod Key, Fl 15-22 September, 2021) 

Training:

Photo by Lila Jones

NAUI: Fantasy Becoming Reality – When Divers Become Mermaids

PADI: How To Become a Mermaid

Photo by Casey McNutt

SSI: Join An SSI Mermaid Program


Michael Menduno/M2 is InDepth’s editor-in-chief and an award-winning journalist and technologist who has written about diving and diving technology for more than 30 years. He coined the term “technical diving.” His magazine “aquaCORPS: The Journal for Technical Diving” (1990-1996), helped usher tech diving into mainstream sports diving and he produced the first tek.Conferences and Rebreather Forums 1.0 & 2.0. In addition to InDepth, Menduno serves as an editor/reporter for DAN Europe’s Alert Diver magazine, a contributing editor for X-Ray mag, and writes for DeeperBlue.com. He is on the board of the Historical Diving Society (USA), and a member of the Rebreather Training Council.

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Historical records reveal the Greek philosopher Aristotle describing the use of a snorkel, relating the occurrence of ruptured eardrums, and outlining the use of the first diving bell by Alexander the Great.

Summary by Mitchell SJ, Doolette DJ. Extreme scuba diving medicine.

“The few studies available at the time of adoption of deep stops by technical divers [53,55] have been interpreted to support this notion. The earliest of these papers, an observational study of the practices of pearl divers in the Torres Strait of Australia [53], often cited as unqualified support for deep stops, is difficult to obtain and worth summarizing here. These pearl divers performed air dives to depths up to 80 msw followed by empirically-derived decompression schedules that had deeper stops and were somewhat shorter than accepted navy decompression schedules. Thirteen depth/time recordings were made of such dives, and these dives resulted in 6 cases of DCS (46% incidence). The remaining data was a count of dives performed from four fishing vessels over a two month period and these 468 man-dives resulted in 31 reported cases of DCS (7% incidence). It takes a certain cognitive dissonance to interpret these high incidences of DCS as supporting a deep stops approach.”

In: Feletti F, editor. Extreme sports medicine. Basel: Springer International Publishing; 2016. p. 313-33.

Note: Data regarding the 468 man dives was collected by interviewing Japanese surface tenders and looking at their (Japanese) logs, relying mainly on their memories for what the decompression profiles were, and how many DCS cases occurred.

LeMessurier DH, Hills BA.
Decompression sickness: a thermodynamic approach arising from a study of Torres Strait diving techniques.
Hvalradet Skrifter 1965;48:84.

Heart rate variability is the physiological phenomenon of variation in the time interval between heartbeats. It is measured by the variation in the beat-to-beat interval. Other terms used include: "cycle length variability," "RR variability," and "heart period variability".

https://www.health.harvard.edu/blog/heart-rate-variability-new-way-track-well-2017112212789

Statistics includes the process of finding out about patterns in the real-world using data such as the incidence of injury for a given time at a given depth.

When solving statistical problems, it is often helpful to make models of real world situations based on observations of data, on assumptions about the context, and on theoretical probability. The model can then be used to make predictions, test assumptions, and solve problems.

A deterministic model does not include elements of randomness. Every time you run the model with the same initial conditions you will get the same results. Most simple mathematical models of everyday situations are deterministic. For example, calculating the return on a loan with a given interest rate over x number of years. Simple statistical statements, which do not mention or consider variation, could be viewed as deterministic models.

A probabilistic model includes elements of randomness. Every time you run the model, you are likely to get different results, even with the same initial conditions. A probabilistic model is one which incorporates some aspect of random variation. Deterministic models and probabilistic models for the same situation can give very different results.

Probabilistic decompression models are designed to calculate the risk (or probability) of decompression sickness (DCS) occurring on a given decompression profile. These models can vary the decompression stop depths and times to arrive at a final decompression schedule that assumes a specified probability of DCS occurring. The model does this while minimizing the total decompression time.

Probabilistic models allow selection of risk in ways that support rational choices. As with most tools, this power can also be used irrationally though the tool should not to be blamed for such abuse. For example, one might do three dives a day for five days, each with an established one percent risk. The risk of at least one DCS in that series is 1-(1-0.01)^15=0.14.

Alternatively, a diver might select one big dive with all the risk captured in that one dive, i.e. 14%, benefiting from the associated faster decompression. The extent to which modelers might allow users to make those choices remains an open question. Meanwhile, the consequences of accepting higher or even very high risk remain largely unknown. For example, to what extent would a 20% risk of DCS make me vulnerable to serious forms of DCS sickness? Should I be allowed to take those chances if I choose. If so, what sort of disclaimer is needed and/or what should be required of me to ensure I understand the risk I am taking?

More on Probabilistic Models:
https://en.wikipedia.org/wiki/Decompression_theory#Probabilistic_models