Tag Archives: jellyfish

Limiting Factors in Marathon Swimming – Part 2 – Environmental Factors

In Part One I covered the physiological limiting factors in marathon swimming.

The various environmental aspects of a swim are not insignificant. They are especially important in that they all lay outside the swimmer’s control and often even outside the control of the support crew.

Water Temperature


This is generally a known factor prior to a swim. Swims are either cool or cold water like the English and North Channels or warm water swims like Maui, Rottnest, Manhattan or Chloe Maccardels’ upcoming Cuba to Florida attempt. A few fall into an intermediate category defined more by the swimmer’s experience, such as the Catalina and Gibraltar Channels. Sudden changes in temperature are rare in marathon swimming and where they are possible they are also understood; such as South Africa’s west coast which is prone to sudden wide water temperature changes, and the California coast where the sudden transition from very deep water to a shallower continental shelf very close to the  mainland can cause cold water upwelling at the end of a marathon swim. Air temperature is obviously much more variable and a condition of the weather but extremes of air temperature are not usual during a swim. A five degree Celsius differential can be significant for a swimmer if such a drop is also accompanied with a breeze or wind which can sap the swimmer of body heat.


Lion's Mane jellyfish
Lion’s Mane jellyfish

The recent and future attempts at a distance and time records by necessity are held in warmer waters such as Cuba to Florida.  These water are home to jellyfish with debilitating stings such as Box Jellyfish. While the cold waters  of the North and English Channels are home to Lion’s Mane and Portuguese Man O’War’s endurance records are less likely and jellyfish stings in the English Channel are rarely more than intermittent, though the North Channel (the Mouth of Hell) can have miles of Lion’s Mane blooms, part of what makes it the ultimate channel swim. Attempts to swim in these waters divide swimmers in two ways: whether attempts should be made in locations not considered possible without additional protection or exceptions to the usual rules, and if so are jellyfish protection suits acceptable or the thin edge of a wedge that will inevitably lead to more overt (or hidden) performance enhancing suits? (See Evan’s analysis of his survey of marathon swimmers for an excellent overview of the contradictions of divisions and unity in the community).


The Man In The Grey Suit is a subject of great concern (and discussion) for distance swimmers. Not of any real concern here in the north-eastern Atlantic, they are a greater hazard in the warmer waters elsewhere, particularly California, the Caribbean, Hawaii, South Africa and Australia. The Cook Strait Channel swim in New Zealand is unique in having a shark evacuation rule. Shark cages have been used for marathon swims in the Caribbean and South Africa at least. Shark cages are however considered swim assistance as they increase the swimmer’s speed through eddy current drag. Other possible control methods include electronic shark repellents (whose effectiveness is not entirely assured or quantified), armed boat crew or armed or otherwise scuba diver outriders.


These are amongst  the most variable of environmental factors and therefore potentially also the most limiting. Because swimmers move slowly relative to even a sailing boat, we are vulnerable to slight deviations, miscalculations or just insufficient data, the most likely cause. Even in such a well-travelled and mapped location as the English Channel, especially for swimming, pilots will occasionally speak of tides arriving early or late or with a difference force than expected. Tidal currents are understood at a larger scale, hundred of years of navigation have mapped the seas for craft, not for swimmers. Tides act in a similar chaotic way to a weather system, which means that small deviations will always creep in. The only way to improve accuracy of prediction is to improve the data, and this is not practically possible or even desired for small tidal variations. As swims occur in less well-known or new locations, the likelihood of discovering unknown local variations outside marine charts increases. Half a knot current, barely detectable to a boat, is enough to deviate a swim over hours from a projected or necessary course.

Global tides
Global tides

Crew and boat

Any English Channel pilot will confirm that one of the most likely causes of unsuccessful Channel swims is poor selection of support crew. The most likely cause is mal-du-mer, seasickness. For some people seasickness is a completely debilitating ailment that can sap all willpower and strength and there is no way to know whom it will strike. The solution of course is to have experienced crew. Even this can fail because people experienced on powered craft will be at the mercy of the choppy water amplified on an almost stationary craft. Other crew issues can also arise, whether accidents or other illness. Anyone who hasn’t been on a rocking boat looking down on a swimmer is unlikely to understand! And not unknown are mechanical problems on the pilot-boat. Most pilots are by necessity practical mechanics able to address problems as they arise, but not all problems can be fixed with a wrench and hammer while rocking about on the sea.

Channel boat The Viking Princess
Channel boat The Viking Princess out of the water


Weather changes are the bane of English and North Channel swimmers particularly. Other Channels like Tsugaru and Gibraltar and Cook are also subject to constantly variable and unpredictable weather patterns. If you are used to the predictable weather of the west US coast, with morning offshore and afternoon onshore breezes, knowing your swim will almost certainly take place with a 48 window, the difficulty of allocating two weeks or even long (like the North Channel) and still being completely unsure of getting in the water is shocking. Weather constraints obviously ran the full gamut. In the North, English and Gibraltar channels the main concern is wind (and its effect on the seas). Fog can also be a problem with 2012′s Channel season infamously seeing three solos on one day abandoned within a kilometre of France for the first time in 137 years. I’ve warned previously that fog may be the most dangerous weather condition for swimmers. In warmer humid climes like Round Manhattan, and the Caribbean, lightning storms are a serious cause for worry, a swimmer or boat caught exposed out on the water is in real danger. Having to wait for or even postpone a swim is something many marathon swimmers have undergone and the mental pressure this brings is often not inconsiderable, which I will discuss further in the next and final part.

Coming in part three, Psychological Factors.


deepstar enigmatica

Here’s another weird underwater creature for swim nightmare fuel

What’s wrong with me that I like looking at all the scary things in the sea?

A few months ago, I collected some the related fears of open water, and suggested we use Megalohydrothalassophobia, as a name for the fear of underwater creatures. Here’s another one for the causal list.  The Cascade creature, aka deepstar enigmatica, or the Placental jellyfish, apparently though not rare, but only seen intact a few times. Checking around it seems like it’s about 50cm in diameter, and is usually a more common bell shape, but the turbulence from the submarine turns it inside out and give it that really creepy motion.

Anyone who’s ever had an unexpected encounter with a plastic bag while swimming will shudder at this one. Plastic bags are scarier than jellyfish.

More details/speculation on the creature here.

All the Megalohydrothalassophobia related articles:

List of open water fears (loneswimmer.com)

Anomalocaris. (loneswimmer.com)

Eel Shark. (loneswimmer.com) (My favourite)

Giant saltwater crocodile (loneswimmer.com)

Conger eels (loneswimmer.com)

Sea lice. (loneswimmer.com)

Now THAT’S a jellyfish. (loneswimmer.com)

Could jellyfish take over the world?

Aurelia aurita (Moon Jellyfish) - captive
Image by Arthur Chapman via Flickr

Ok, if you’re a regular here, you know by now I have an interest in these feckers, partly because we get a lot of them in Tramore Bay, I’ve been stung more times than I can remember (first two very minor stings of the year yesterday), AND they are fascinating. On one hand I like them more and more and find them increasingly interesting. On the other hand the various scientific mysteries associated with them can be worrying.

On the interesting side: For years there has been an apparent discrepancy in some figures associated with the sea. It seems when that the cumulative energy figures for winds and tides don’t account for sufficient energy to explain ocean mixing.

Ocean mixing is where the colder deeper water is mixed with warmer upper water. I mentioned recently that cold water carries the nutrients that are the basic of the ocean food chain. The thermohaline system and the tides and storms all mix the water, bringing up the rich cold water. But like the unaccounted-for missing mass and energy in the Universe as a whole, something similar seems to apply to the sea.

Various ideas have been proposed to account for the discrepancy. One theory was that it’s sea swimmers (fish & humans), who add the missing energy. Also considered is that mixing is now aided by krill, the microscopic crustaceans that Basking & Whale Sharks, and Baleen whales eat, because of Krill’s vast numbers. It also seems that large shoals of fish can cause as much turbulence as a storm.

The force that moves an aeroplane, a sail and a propellor, the Bernoulli Principle, causes a low pressure area behind swimming creatures with a high pressure system in front, dragging water behind, leading to mixing of the water, as really well illustrated in the 12-second jellyfish video.

Why is this important though? Well, ocean mixing is an important factor in Climate Change modelling. (Aside: Climate Change is real. Don’t agree? Read the 98% of science that confirms it.). The level of ocean mixing is known, but the contributory factors need to be understood better, since these can change.

Anyhoo. The worrisome side is the global increase of jellies. Some of you may have seen the National Geographic documentary on giant Nomura jellies in the Seas Of China and Korea, and the chaos they are causing to the fishing fleets. So there’s an impact on the human food chain. Of course there’s a theory that jellyfish are increasing BECAUSE of overfishing (since fish eat the young Medusae before maturity), which, given how we completely fail to protect fish stocks worldwide, certainly seems possible. there’s another possibility that the blooms are driven by climate change. So is there a Catch 22?

Overfishing and climate change causes jellyfish blooms, which is turn make fishing more difficult? Partly that could be seen a Gaian correction mechanism, if enough fish are left to consume the jellies, but what if there’s aren’t enough fish left to consume the blooms, as seems to be the case? Current economics dictate as fish get more rare, what actually happens is that prices increase ($396,00 for a single bluefin tuna), and the remaining fleets will work harder to the huge profits (Hardin’s Tragedy of the Commons, when something is owned by everyone, no-one is  responsible).

Jellyfish Shunt - effecting change in the marine food chain

And recently there’s been another disturbing discovery. Most animals in the oceanic food chain produce waste products that are used by other links in the chain. Not so with jellyfish which product a waste slime that is generally inedible. This is called shunting, where jellyfish remove resources from the food chain.

That’s extremely worrying because it obviously means less food available for the oceanic food web. That’s bad for all of us.

This is ongoing science. As many, or more, questions therefore as answers right now. But this is important stuff, more important than the few stings we pick up.

The jellies are important, very important.

There’s no such thing as a jellyfish

On my list I’d planned to write a post on the jellyfish life-cycle, since I’ve posted previously about how to identify them and how to deal with them.

But then I found this fantastic and fairly short clip. It has fantastic HD video definition and you see the beauty of these creatures that some of us know so well, along with basic descriptions of life cycle and kingdoms. Enjoy.

They’re BA-aack!

Compass Jellyfish
Image via Wikipedia

Yes, our friends the jellyfish have returned. The other day I saw Common (aka Moon ), Compass (pictured) and Blue Stingers.

The Common (Moon, below) is completely harmless, but all jellies cause most people to have a small freakout. So knowing when not to be afraid is useful.

I mentioned previously about the late spring/early summer arrival, one of the defining events of the coming summer swim season. The worst case (for me) is the arrival to be caused by a south-east wind when swimming in Tramore Bay, where the jellies will be blown into the swimming area. Luckily it’s been a few years since this happened to me. Instead it is the normal population increase, not noticing anything for weeks, then one day seeing 10 or 12.

I’ve linked the ID charts before but it’s never wasted doing it again. Here’s the first chart, and the second.

As I asked Maura to tell the local swim list yesterday, it’s time to start carrying a bottle of vinegar in  your swim box again.

One small word of advice: transfer the vinegar to a plastic bottle. I had a glass bottle in the car two years ago and it broke at the inaugural Beginish Swim, so the inside of the car smelled like a chip-shop for the remainder of the week!

April and Jellyfish …

Yes folks, time to warn you all. Spring has been well and truly under-way in the ocean for some time now. The dead give-away is the deepening green of the water indicating the first and largest plankton blooms. (Note the banner colour of my blog again!).

Early “action” isn’t particularly visible but the next most visible sign for us in the South and South East is the April jellyfish explosion. One day none, next day everywhere (if you are unlucky).

The last few years it’s been the third or fourth week of April that they become obvious when we get the big blooms.

So, in Tramore Bay, we have the cold water current coming in on the west (swimming) side of the bay. Jellies generally drift and only adjust height/depth in water. So many will come in on the current. And the bay is deep enough to hold jellies at all tides.

  • So, before it happens, watch out for days with South Easterlies or Easterly winds. These will cause large masses of jellies to accumulate around our side of the bay. The jellies will last a day or two AFTER these conditions also.

The area that seems worst is between the Guillamemes and Colomene rock, and about halfway from the Colomene to the Pier.

(Funnily enough the same conditions pertain to Baile Na Gaul to Helvick Head, but the water is shallower so it’s not as bad. Between Helvick Pier and Helvick Head, behind the small island, is the worst.)

The Open Water Swimming Association did a poll of things OW swimmers most disliked/feared and jellies/stingray were 2nd on the list after sharks. (Obviously mostly warm water swimmers!).

So the good news:

MOST JELLIES ARE HARMLESS (from an Irish South Coast point of view anyway).

A swimmers adage is, ‘it’s the jellyfish you don’t see that will get you”.

The Moon/Common jellyfish is just that, most common, and doesn’t sting (thought the guide says it has apparently a mild sting). “Moon” because it’s a translucent white. Jack-by-the-wind (Jack-the-Sailor) are also harmless.

So…jellyfish and jellyfish stings.

  • Don’t panic.
  • Reactions vary by person. But most people will find jelly stings cause no more than mild brief discomfort.
  • The initial sting will be sharp, like a nettle sting. For myself, Purple and Blue Stinger strikes taper off very quickly and last only about 10 minutes of a tingling sensation. Portugese Man O’War is much worse and lasts for up to 4 to 5 hours.
  • Sea-water, luckily, dulls stings, so you might as well stay in the water anyway.
  • If you do get stung a lot, and have a greater reaction, it’s good to know what to do.
  • Don’t touch the sting. No rubbing with a towel or scratching.
  • Always carry vinegar with your swim gear. Douse the area with vinegar. Don’t have a fresh water shower until well after the sting has abated. (You can get stung in the winter but it’s unlikely as the jellies will be lower down)
  • Scraping a stung area with something straight like the edge of a bank card will also remove some of the barbules.

(Save yourself learning the hard way, like I did and transfer the vinegar immediately to a plastic bottle, rather than leaving it in the glass bottle, which WILL break and you will smell like a chip shop).

A jellyfish sting is actually a collection of barbules which have venom in them. Vinegar will stop those barbs firing which are in your skin but haven’t yet fired. Those barbs which have already fired will not be affected by the vinegar. As I said above delay having a shower. Fresh water will cause the stings to feel worse.

There are jellyfish sting creams available, (though not widely in Ireland). Danny says he tried one (Safe Sea) which he got in work and it was good. Anti-histamines should work as well if you have a particularly bad reaction.

But let me stress again, there’s not that much to worry about. I was stung about 40 times in a 3k Helvick swim a few years ago, and I could only tell because I could count the visible stings afterwards. I only actually felt a few of them, and they weren’t bad.

We get occasional Lion’s Mane jellies in the South-east later in the summer which have a worse sting , but they are very noticeable because they get quite large, are infrequent, so easy to avoid, and I’ve only seen them out around the Metalman and further.

Purple and Compass jellies are the two I dislike most but are not a problem at this time of the year.