In search of Nessy

Views of the Loch Ness Monster

I discussed the application of “climate space envelope models” (also known as “species distribution models” or “ecological niche models”) to Sasquatch in an earlier post.  While I was writing that post I was racking my brain trying to remember a scientific paper on the Loch Ness Monster…  I distinctly remembered hearing about it in an undergraduate course but didn’t have any record of it in my notes.  The good news is I found the paper!  In fact, I found several!

The initial study

Sheldon and Kerr (1972) conducted a theoretical study into the possible existence of monsters in Loch Ness in their seminal paper “The population density of monsters in Loch Ness”. They open their discussion with the following statements:

It is well known that there are monsters in Loch Ness. Their most characteristic features are that they are rarely seen and never caught, but there are records of sightings extending back many centuries. The fact that they are rarely seen suggests that the population is small. It is known from direct observation that the animals themselves are large and it follows from this that the population must be small. It can be demonstrated quite easily from trophic-dynamic considerations that many large animals could not exist in Loch Ness; but a few could. It has been suggested from time to time that as the monsters are never caught it must therefore follow that they do not exist. This is both irresponsible and illogical.

Sheldon and Kerr apply standard ecological theory to the problem.  First, they calculate the productivity (the rate at which biomass is produced) of the fish communities in the Loch (around 0.55 kg.ha-1..yr-1).  From this they estimate the standing stock as between 0.55 and 2.75 kg.ha-1..yr-1.  They reason that, since ecologically-stable environments tend to have similar standing stocks of animals (in terms of biomass) irrespective of size, that by calculating the standing stock of fish they can infer the standing stock of monsters.  Assuming a minimum size of 100kg (anything less is “not suitably monstrous”) they estimate between 1 and 156 monsters in the loch.  To be more specific, they suggest that the absence of corpses suggests low mortality and long lifespans, which correspond to larger body size.  They conclude that a population of 10-20 1500kg monsters could survive in Loch Ness.  In a follow-up paper, Schneider and Wallis (1973) came to similar conclusions.  These authors used a different

The spoil-sport

Of course, someone had to come and rain on the parade, and that man was C. H. Mortimer (1973).  Mortimer (“a declared skeptic”) raises issues with the assumptions of the Sheldon and Kerr (1972) analysis.  Principally these are that no specimens, nor any part of one, have ever been found.  Mortimer acknowledges that cryptids are discovered from time to time and cites the discovery of the coelacanth as an example.  However, he points out that the coelacanth was discovered following the identification of a specimen as something unusual.  No such specimens have been found of Nessy. Mortimer also questions why we don’t have more sightings, given the extremely high boat traffic on the Loch, and questions some anomalies on sonar scans. However, as a good skeptic he finally concludes with this:

If the even less likely explanation – existence of Nessy – turns out to be the correct one, here is one skeptic who will be delighted to be confounded.

The response

Under Mortimer’s (fairly light-hearted) criticism, Sheldon and Kerr (1973) responded.  They point out that their methods, if nothing else, demonstrate that:

…if the food webs of oligotrophic lakes and oligotrophic oceans are similar and if the standing stock of fish is roughly what we assumed it to be then there exists in Loch Ness (and other large
bodies of freshwater) the potential for several thousand kilograms of living tissue to exist in relatively large lumps.

However, they also cite the fact that no carp larger than 24lb were caught in Britain prior to the 1950s.  However, a change in fishing styles brought about a substantial increase in the size of carp that were caught, up to and including “monstrous” 44lb specimens.  Therefore, large animals can reside, undetected, in well-watched water bodies for long periods of time.  They conclude with this:

Apparently, the trophic structure of tundra and alpine ecosystems is similar to that of the ocean. Now the tundra is an inhospitable place and it is best left to the musk-ox and other small animals, but the alpine system could be interesting. If we could find data for the standing stock of any trophic level in the Himalayan region we could estimate the population density of the Abominable Snowman.



Mortimer, C.H. (1973) The Loch Ness Monster-Limnology or Paralimnology? Limnology and Oceanography, 18 (2): 343-345.

Sheldon, R.W., & Kerr, S.R. (1972) The population density of monsters in Loch Ness, Limnology and Oceanography, 17 (5): 796-798.

Sheldon, R.W., & Kerr, S.R. (1973) The Loch Ness monster: Reply to comments of C. H. Mortimer, Limnology and Oceanography, 18 (2): 345-346.

Schneider, W. & Wallis, P. (1973) An alternate method of calculating the population density of monsters in Loch Ness, Limnology and Oceanography, 18 (2): 343.


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