Salamanders, Buoyancy, and Loch Ness

My thanks to Christopher Hjelte, a reader of this blog who recently sent me a link to an interesting video about research into axolotls at Blackburn College in Carlinville, Illinois.  Midway though this 2 minute piece, we learn of a very odd and previously undocumented behavior first observed and later filmed by Blackburn students studying these aquatic salamanders.  A behavior that might possibly bear some implications for surface sightings of much larger cousins elsewhere!

https://www.youtube.com/watch?v=OLwQpU0Ga80&feature=youtube_gdata_player

Like most obligate-aquatic salamanders (that is, those salamanders with no terrestrial phase to their life cycles) axolotls (Ambystoma mexicanum) have retained their lungs, although as the video points out the utilization of these lungs hasn't seen much prior study.  While it's true lungs are the norm for aquatic salamanders, including the giant Cryptobranchidae, all these species primarily breathe through cutaneous respiration, absorbing oxygen from the water through their skins.  Furthermore,  the really neotenic forms such as axolotls normally retain their larval gills for life, thus giving them not one, not two, but three methods of respiration.  At first that seems like a bit of evolutionary over-kill, so I've trundled a bit down a line of research I'd been away from for awhile.

While they may never need their lungs for respiration while in water, the Blackburn research shows that axolotls sometimes inhale one gulp of air and hold onto it, apparently for the sole purpose of floating on the surface -- albeit they float upside down!  This orientation doesn't seem to bother them (perhaps no one has embarrassed them yet by telling them just how adorable it looks).  Their lungs must be located below their center of mass, not that this would matter under other circumstances.  But given that they have this ability to float, we can wonder why they choose to do so in the first place.

And to quote Mr. Hjelte, "Up turned boat, anyone?"


"FLOATERS" IN THE LOCH?

This leads back to one of the most important points I made in my previous article on surface sightings, and what they can tell us about the morphology of the Loch Ness Giant Salamander.  And this is equally applicable when observing any aquatic animal partially extruded on the water's surface:  animals that live in a three-dimensional, "weightless" environment, can and will float and swim in positions that are independent of our terrestrially biased, two-dimensional thinking.  Any aquatic animal can float head down and tail up, or at any angle, or list to either side, for any reason that suits it.  And in the case of at least one species of small, aquatic Mexican salamander, we now see that even upside-down surface floating is normal!

So it's behavior as well as morphology that determines what an eyewitness would see at Loch Ness, if any deep-living animal pays a rare visit to the surface.  Roy Mackal grappled with the problem of the Nessie's back contour, and the issue of multi-hump and variable hump sightings.  Eels at first seemed to be a problem candidate, as they have laterally flattened bodies and swim by sinusoidal flexure (side to side, not up and down).  Then he tells the story (in The Monsters Of Loch Ness, 1976, page 150) of having a revelation on this point while observing eels at Chicago's Shedd Aquarium:

"Eels occasionally swim on their sides, and when doing so at the surface, the series of undulations appear to the observer as vertical by virtue of the fact the animal is on its side.  This motion can easily produce a violent splashing of water at the surface and a series of humps above the waterline."

He received corroboration from Maurice Burton, who observed the same side-swimmng eel behavior at the London Zoo.  Alas, on my own visits to the Shedd, I've never stayed with the eels long enough to observe such delightful behavior, but then there's just so much to see there.

This is one example of how a seemingly incompatible morphology, in this case that of eels, can account for an observation, in this case vertical humps, once three-dimensional behavior is taken into account.  Or as I stressed in my previous article, the appearance of a long neck on a short-necked animal if it's floating with it's tail elevated above water.  Incidentally, on that trip to the Shedd, Mackal observed an eel floating vertically, head down, with it's tail sticking up straight out of the water as well!  (For the record, at that time Mackal still favored the variable dorsal contours of a giant amphibian as better accounting for the observational data from Loch Ness, even as he made these points about eels.  Salamanders will often float with their backs arched at a fairly acute angle, the degree of which would most readily account for both triangular humps on one hand, and the frequently observed upturned-boat effect on the other.)

So now, what can we say about this matter of belly-up "floaters" as it relates Nessie?  Yes, it's another way to explain the upturned-boat effect, but the dorsal profile the Loch Ness Giant Salamander has that accounted for already.  Personally I doubt it occurs, but to say it never occurs would make me guilty of two-dimensional thinking.  The animal will float as it pleases regardless of any human opinions.  The possibility does offer us a couple tidbits.

Criticism in the variation of reported details from sighting to sighting and from witness to witness have lead some to conclude there cannot be a real, unrecognized animal behind any of these observations.  I actually take exception with that, and would note the consistencies far outweigh inconsistencies.  Be that as it may, there has been noted variability in the reports regarding skin color, skin texture, and the lack or presence of a dorsal ridge.  The variability of the latter is already accounted for in my working morphology, depending on whether the hump is viewed from front or back.  However, if there are witnesses insisting there's a dorsal ridge running the whole length of the spine (I vaguely recall an instance or two where this might be mentioned), then smooth-back sightings would still be explainable by the belly-up floater.  I doubt we have to stretch anything that far though.  And Dinsdale solved the skin texture problem in terms of viewing conditions and distance long ago, without need to resort to flipping the beast over!

What is key here is that, as is typical of aquatic salamanders, we should expect Nessie to not only have lungs, but to occasionally use them.


ONCE IN A VERY GREAT WHILE

One obvious but secondary use for those lungs would be respiration when out of the water.  One must assume this is a secondary function, because land sightings of the Loch Ness Giant Salamander are so rare as to be almost non-existent.  But then, for all known species of aquatic salamanders, leaving the water is also extremely rare, even though we've long known (through dissection) that they certainly have functional lungs.  (In fact among all extant amphibians in all four orders, lungs are only absent in one clade of salamanders, the plethodontids, which are minute and terrestrial, and in two species of caecilians.  Lungs are of course present in frogs, but even the primitive and aquatic sirens have retained functional lungs.)

To avoid hypoxia, aquatic salamanders do indeed stick their heads out of the water and use their lungs for respiration, a life-saving backup plan should the oxygen content of the water become too low.  This however would not be a factor in the cold and highly oxygenated waters of Loch Ness.  Although perhaps even in Loch Ness, an amphibian might need to gulp auxiliary oxygen following some unusually aerobic activity -- courtship behavior among salamanders can be extremely demanding.


NOW TAKE A DEEP BREATH...AND HOLD IT

But the primary use of lungs observed in aquatic salamanders is buoyancy control.  Inflated lungs serve as hydrostatic organs and allow for continuous floating at either the surface, or a desired depth, with little or no expenditure of energy.  This could not otherwise be achieved because, unlike ray-finned fish, amphibians have no swim bladder.

What they do have though is a specific gravity greater than one (1), which means they sink to the bottom.  (Objects with a specific gravity of 1 are neutrally buoyant in water, those with a specific gravity greater than 1 are denser than water, and so will sink in it, and those with a specific gravity of less than 1 are less dense than water, and so will float.  The number is calculated by dividing mass by volume.)

So in many cases, the lack of hydrostatic control would prove lethal.  Axolotls might not need it as much as other species, as the video above seems to imply they are amateurs at it.  Their relatives, the tiger salamanders, depend on it, at least in their larval stage. Tadpoles of the tiger salamander need to float overnight at a specific depth, rather high in the water column, in order to feed on Daphnia, which is all they can eat at that stage.  But they have a specific gravity greater than 1, which would leave them either trapped on the bottom or paddling to maintain "altitude" all night, expending more energy than they might take in from feeding.  The solution is to swim to the surface, inhale just enough air to lower their specific gravity to exactly 1, then swim to the desired depth where they can float all night, and gorge themselves without burning more calories.  Come morning they release the air, and sink to the bottom to hide in safety.  Once they become much larger, terrestrial adults, capable of larger prey, they still continue this behavior anyway because they seem to just plain like the Daphnia.

So it seems the regulation of buoyancy may be the primary reason aquatic salamanders retain their lungs for life, although that ability to breathe surface air does occasionally come in handy under extreme or unusual circumstances.  But while in well oxygenated water, they don't need to exhale because they are still getting their oxygen via cutaneous gas exchange.  They hold only the air they want to maintain the buoyancy they want, and for as long as they want.  Hydrostatic regulation of this sort has been observed in many salamanders, including the Cryptobranchids, and is no doubt utilized by all salamanders.  This alone was reason enough for evolution to retain lungs in aquatic salamanders no matter how little else they might use them.

All of which of course has profound implications for strange things seen in Loch Ness, if the cause were a giant salamander.

Smooth vertical submersions without a noticeable disturbance of the water would be expected, as that's the normal exit for floating salamanders.  And that is the most oft reported exit Nessie has been reported to make.  That would most likely be a planned return to the very bottom of the Loch, where these animals spend the majority of their time.  One wishing to keep it's air to maintain a specific gravity of 1 (to cruise at a certain depth) would of course have to swim down, which would occasionally result in some splashing.

Also riding too high in the water,  frequently a critique of some reports, and especially of the Hugh Gray photograph, should be less of an issue knowing that a specific level of buoyancy is actually under control of the animal itself.  A hump two feet above water may not require as gargantuan an animal as one would think.

Juveniles, surfacing for the first time might even experience some trouble getting used to their lungs, as they will be taking their first breaths.  And they could already be of substantial size at an early age.  The axolotls may only have trouble floating right-side up,  but other salamanders have been observed rolling on taking in air on their first tries, because only one lung inflates on the first go, listing them over to float sideways, and when they try to compensate with paddling they send themselves into a little spin.  (In Nessie's case, "little" might be the wrong word.)  Eventually they learn they need to exhale, relax, and try again.  The belly-up axolotls at Blackburn College may be forgetting to exhale, stranded on the surface like a kitten stuck up the first tree it's ever climbed and wondering how to get down.  Apparently hydrostatic regulation in salamanders takes a little practice to get right!  Would that a Loch Ness Giant Salamander were to get stuck on the surface for a nice long sighting, although you might not want to be in a small boat close by while it was rolling, thrashing, and trying to figure things out.

Of course hydrostatic regulation is a very useful skill.  The main supply of fish in Loch Ness are not at the bottom, they are found in the shallower waters, the littoral regions.  Incessant swimming to maintain the right depth would be extremely costly to a predator, and salamanders are extremely stingy about spending energy to hunt -- they don't chase, they lurk.  This gives Nessie its reason to climb to the surface, taking in just enough air to establish specific gravity 1, so it can swim down and maintain station effortlessly when it wants to feed at the depth of the prey, if that is indeed its preferred method of feeding.

Notably, inflated lungs would show up on sonar, but unless the animals regularly held onto extra air during a forced dive they would return a much weaker echo.  Which means you might get a strong contact one day, but not again for a very long time.

Much of this will sound very, very familiar to those who have looked at data and sighting reports from Loch Ness.  There may be a very good reason for that.