Is there enough food for Nessie?

It was a few months ago that my son came home from school with a triumphant look on his face. He proclaimed to me that his Biology class had proven that the Loch Ness Monster could not exist based on what he had learned about ecology and food chains. It was not him who deduced this but rather his science teacher that had debunked Nessie during an example study of a certain Highland loch. This just confirms to me that British education is going to the dogs!

So ask a sceptical person (for example, my son) why they don't believe in the Loch Ness Monster and you may get the following answer:

"There is not enough food in Loch Ness to sustain a breeding population of large predators, therefore they cannot exist."

Thus by the application of pure reason and critical thinking, the Loch Ness Monster disappears in a puff of logic. As a bonus, the modern thinker does not even need to consider the thousands of claimed sightings or the photographs, films and sonar contacts. They are irrelevant because logic has dictated that there are not enough fish swimming about the loch to sustain any such monster. Perhaps I should close down this blog and take up caber tossing because there is nothing more to say?

Well I do have something to say. I may not be a biologist with a PhD, but that does not preclude the ability to make some enquiries and challenges. In fact, the issue here is not so much the application of logic and deductive reasoning but rather the data that gets ground through the logic sausage maker. Because it is not just logic that matters here but data which has to be as raw and as refined from human prejudice as is possible. In other "Garbage in, Garbage out" is the watchword here. The logic may be perfect, but that is only half the story.

So for the sake of this article, we assume the exotic creature(s) known as the Loch Ness Monster are 100% dependent on the smaller animals that reside in the loch. We also assume there is a herd of them of varying sizes. So that means we exclude the following scenarios:

1. The Monster does not supplement its diet by making excursions to the sea (via river or underwater passage).

2. The Monster is not a paranormal phenomenon independent of the fish it swims past (or through?).

3. The Monster does not supplement its diet by going on to land to grab some deer or picking off the birds that float on the water. :)
4. The Monster is neither herbivorous or omnivorous.
5. The Monster does not cannibalise its dead.

THE QUANTITY

Now to establish food stock viability, at least two things have to be ascertained:

1. The biomass of the entire potential prey in the loch.
2. The amount of this prey consumed by Nessie predators.

As it turns out, nobody actually knows with precision what either of these numbers are, so like all the researchers before us, we take a journey into guesstimation land. An enquiry to the Ness and Beauly Fisheries Trust elicited the response that there were no reliable estimates for salmon, trout or char. Indeed, their 2008-2010 "Ness System and Fishery Action Plan" said this:

"It is recognised by the Ness & Beauly Fisheries Trust that the lack of data on lacustrine fish populations and in other locations such as the Caledonian Canal currently represents a major gap in knowledge. Similarly, little or no data is currently available with respect to the many small burns that flow into the Inverness and Beauly Firths."

In fact, as we come to this subject, all manner of questions crop up. For instance, what set of food stock figures does one use? Do we use the available data from 1933 when Nessie first hit the world news or as recent as possible or some combination? I say this because due to pollution and over-fishing, fish stocks are lower now than they were in 1933. If, for the sake of argument, we say that the Loch Ness Monster is no longer in the loch due to low food levels, that does not preclude asking whether it was once possible for the loch to sustain a certain number of such creatures. However, this blog does not accept the creature has vacated the premises or that there is too little food. In that light, we will use whatever numbers look reasonable given the murkiness of the subject matter.

ARCTIC CHAR

In terms of actual food supply, the types of aquatic livestock are well known. Swimming openly near the top part of the loch we have char and pike amongst others. At the bottom and at the sides we have eels and then there are the salmon and trout that visit Loch Ness on their seasonal runs. As it turns out, estimates of the varying species numbers is a pretty mixed bag. Using sonar, reasonable estimates can be made for the pelagic fish stock (i.e. those fish which swim in open water).

These are mainly Arctic Char (Salvelinus alpinus) and sonar/trawl studies by Adrian Shine and Tony Martin for the Loch Ness Project estimated a stock of 17 tonnes in 1993 which can be viewed in their paper at this link. Another study by Kubecka, Duncan and Butterworth also in 1993 came up with 24 tonnes. Note these studies have less accurate accounting of fish swimming near the surface, bottom or sides of the loch which are less amenable to sonar.

So those two studies are in reasonable agreement given the uncertainty involved. However, a sonar survey done by D. G. George and I. J. Winfield in 1992 seems to put a fly in the ointment by coming up with an ultra-oligotrophic figure of 0.26 kg/ha for pelagic fish in Loch Ness. I say "ultra" because even Lake Superior which has been described as "the most oligotrophic lake in the world" recently hit 33 year lows of "only" 1.3 kg/ha - a figure five times greater than this study (link). A further search for other oligotrophic lakes failed to find such a low number, except one - the Dead Sea (though that does not preclude the existence of such lakes).

How can this number be more that 10 times smaller than the other two studies? Either all the studies are so speculative that they cannot be reliably used or there is a major difference in someone's methodology. Were the Shine/Kubecka studies less thorough? Reading the scope and depth of the survey in Adrian Shine's paper, I doubt this and even if it were true, I again doubt this would account for a ten fold discrepancy. So in this light I disregard the Winfield study for three reasons (in order of importance):

1. Two other studies produce higher and similar numbers (i.e. outvoted).
2. Adrian Shine's greater experience with sonar and ecology work at Loch Ness.
3. Lack of precedence for such a low number in other oligotrophic lakes.

Therefore, we start our estimate of fish stocks with 17-24 tonnes for char.

EELS

What about the other potential prey for a Loch Ness monster excluded from those studies? Moving onto the benthic (i.e. bottom) dwellers, we have the eels (Anguilla anguilla). It is not known how many eels inhabit the dark depths of Loch Ness. Tim Dinsdale thought there were "millions" of eels in Loch Ness and provided a ready source of nutrition to Nessie. An interesting quote from volume 5 of the Fishing News International in 1966 points to the abundance of eels in Loch Ness:

"HUNGARY is buying large quantities of eels from Scotland for settlement in her lakes and rivers. In 1965 she imported 2,500,000 fry and 800,000 young eels from Loch Ness in a drive to stock her waters to saturation point by 1970."

That adds up to 3,300,000 immature eels from Loch Ness not including adults. That single haul alone exceeded the estimated population of pelagic fish in the studies above (Adrian Shine estimated 2,434,000 in number). If we assume a glass eel weight of 0.3g and a juvenile weight of 4g that adds up to 4 tonnes but adults can grow from between 30g to 30kg. Now the population of pelagic fish would still be heavier but it begs the question as to how many adult eels inhabit Loch Ness. So we need some kind of number and it clearly has to be bigger than the 17-24 tonnes of pelagic fish.

If we speculatively say there are one million eels in Loch Ness with an average weight of 100g then they weigh in at 100 tonnes. This number does not include the fry and elver eels discussed above. But let us lowball it down to 50 tonnes in an attempt to steer a "via media" between Nessie sceptics and believers. If anyone objects that some are not always there due to migration then the 50 tonnes I hope offsets that but, in my opinion 50 tonnes is understating the total eel biomass of Loch Ness.

So the total is now 67-84 tonnes of food for the Loch Ness Monster.

SALMON

Moving onto the littoral (i.e. side) inhabitants, Adrian Shine says this of them in his previously mentioned paper:

"the littoral fish habitat, which is richer than the pelagic ..."

In other words, we can start on the assumption that this group of fish exceed the 17-24 tonnes biomass estimate. However, we run into an accounting problem here since this class of creature may include some of the aforementioned eels. So we have to be wary of double counting. There is also the issue of counting in migratory salmon (Salmo salar) and trout which tend to swim in the sonar blind spots near the surface or close to the shoreline. In that light, we will only concentrate on salmon and trout and ignore the other littoral fish such as char, pike and stickleback.

How many salmon swim through Loch Ness? As some readers may know, these majestic fish are involved in two voyages through Loch Ness. The first is when the adults return to their birth stream to spawn the next generation. The second run involves juvenile salmon who leave their nursery rivers to make the long trip to the Atlantic breeding grounds.

But how many salmon run through Loch Ness each year? One controversial study was done by Roy Mackal for his 1976 book "The Monsters of Loch Ness". In October 1971, Robert Rines' team had placed a camera 30 feet deep in Urquhart Bay near the mouth of the River Enrick as the salmon were heading upriver. It was a single photograph from that camera that Roy Mackal based his study on.

In that snap were visible three salmon from which Mackal extrapolated a total numer based on the cone of river entry, the speed of the salmon and a four day salmon run. This gave a total of 1,700,000 adult salmon entering the river. But that was not all for it did not include the other six main rivers feeding into Loch Ness (Coiltie, Moriston, Oich, Tarff, Foyers and Farigaig) not to mention the 30 other smaller streams which led Mackal to postulate upwards of 13 million adult salmon in Loch Ness. At an average weight of 4lbs for an adult salmon that added up to 66,000 tonnes. Note further that this does not even include the juveniles which subsequently hatched and made their way back downstream which could potentially add up to a further large number of tonnage.

Clearly such numbers are stupendous and were dismissed by A. V. Holden of the Freshwater Fisheries Laboratory in Perthshire (Ref: New Scientist 18-25 December 1975). Holden suggested the total salmon population in Scotland was less than one million based on the assumption that half of all running salmon are caught. Two assumptions, but which one is closer to the truth?

Roy Mackal in his book quotes a salmon run count of 13,000 up the River Beauly in 1967 which is far less than his 1,700,000 for the River Enrick (though it has to pointed out that the counter probably did not catch all the fish going up the river). We would suggest 13,000 is closer to the truth than a number more than 100 times greater than that. A total of 13,000 salmon weighs about 23.5 tonnes and if this is extrapolated to the other six Loch Ness rivers we get a total of about 164 tonnes. But since the Loch Ness rivers look inferior than the Beauly then we will halve that estimate to 82 tonnes which revises our total prey biomass to 149-166 tonnes.

Note this adds up to 39,000 salmon on average which is about 4.5% of the total number of salmon that Mr. Holden suggested enter Scotland's rivers each year. I would note here that Loch Ness is also a pathway for other salmon destined for rivers and streams not flowing into the loch but further down the Great Glen water system such as the River Garry which feeds into Loch Oich. Clearly, these too would be potential prey for a larger creature as they make their way down Loch Ness. It goes without saying that their numbers are unknown as well but clearly Loch Ness is a major conduit for migrating salmon in Scotland.

SEA TROUT

That leaves the final species which are the Sea Trout (Salmo trutta). A recent article dated 23rd September 2011 in the Daily Telegraph showed that a record 110,000 salmon and grisle had been caught in Scottish rivers in 2010 (how many went uncaught is of course an open question). The article also states that 27,704 trout were caught. Now I know the number of salmon anglers may not equal the number of trout anglers but in the absence of better data we'll assume these proportions apply to Loch Ness and that a trout is half the weight of a salmon. This gives a ballpark trout tonnage of about 20 tonnes (164 x 0.25 x 0.5).

PREY AND PREDATOR

Thus the final tonnage of Loch Ness fish is 169-186 tonnes. We'll use the average number which is 177 tonnes.

As you may guess, it is a numbers game but I don't think I have gone for extreme estimations. I would think that even twice this amount is perfectly defensible.

Now that we have an estimated tonnage of fishes, the second question concerns the eating requirements of one or more Loch Ness Monsters. To put it a better way, what is the prey to predator ratio? This ratio will help tell us what tonnage of monster could be expected to live off 177 tonnes of fish.

Adrian Shine wrote another paper which explored the Sturgeon interpretation of some Loch Ness Monster reports. In it he states the following about the 17-24 tonnes of pelagic fish stock and predation upon it:

"... it should be borne in mind that predators upon this biomass should not amount to more than approximately a tenth of the gross weight."

It should be noted that Adrian Shine admits the stated biomass does not include benthic or littoral fish stocks which were not amenable to sonar surveys, but insists that this missing tonnage would not change his conclusion that there is not enough food to feed a herd of Loch Ness Monsters.

However, if we apply his ratio of 0.1 to the 177 tonnes then we get a Nessie tonnage of 17.7 tonnes which some would indeed deem not enough. But is it the case that this ratio should not exceed 0.1? Two studies I found show that this number is not a hard and fast rule. The first study on pike populations said this:

"The studies on the status of the ponds 'balanced or unbalanced' revealed that the predator ­ prey ratio, by weight of balanced ponds was between 1:1.4 to 1:10; 77% of the best 'balanced' populations had ratios of between 1:3 and 1:6. Conversely, 'unbalanced' populations had ratios of between 1:0.06 and 1:63; most unbalanced populations had a relatively small weight of predators in relation to the weight of prey."

Here we have a prey to predator ratio generally between 0.33 and 0.17 or 0.22 on average. Another study is however more telling. In 2009, Thomas Mehner published a paper entitled "A study of 66 European lakes" in which various ecological parameters, including the prey-predator ratios, were estimated. In this study he found quite a range of ratios between 0.061 and even 1.384 (i.e. more predator biomass than prey).

If this range was applied to our Loch Ness discussion, the potential Nessie tonnage could range from 11 tonnes to 245 tonnes. But if we use the author's median ratio of 0.321 then a fish tonnage of 177 tonnes could support about 57 tonnes of Loch Ness Monster.

Now critics may argue that Loch Ness Monsters are not pikes or other temperate lake fish and so these ratios should be used cautiously. I agree, any suggested ratio should be treated cautiously. Is my 0.321 ratio worse than the 0.1 value suggested? I doubt it. Is it better? I'll leave that for you readers to decide.

Incidentally, on the objection that the 0.321 ratio should not be so readily moved from smallish predators to huge ones like Nessie, one thing should be pointed out. Larger animals tend to have lower surface area to volume ratios than smaller animals. This means their rate of heat loss is less than smaller animals. The consequence is that for certain classes of animal, smaller ones have to eat more food per unit body weight than the larger animals. This certainly applies to mammals and possibly other animals too. The outcome of this, I suggest, is that a Loch Ness Monster may have to eat less than its equivalent weight in predatory fish such as pike, salmon and trout. In other words, a ratio of 0.321 may be too low.

THE OBJECTIONS

However, despite proposing these larger numbers, sceptics will still be unimpressed for other reasons. The objections go something like this:

1. The char are too diffuse and small to waste hunting energy on.
2. It is too dark to find the eels at the bottom and sides.
3. If the Monster ate salmon, we would see it break surface more often.

Are these objections sustainable? In the first case, it should be noted that the pelagic fish population are not evenly and diffusely distributed from the top to bottom of the loch's great depth. They in fact tend to be mainly found in the top 30m-40m of the water column. According to my calculations (allowing for areas not surveyed by sonar), for about 2.4 million fish that is one per cube of water measuring something like 7m in height.

Adrian Shine's netting survey yielded mainly char in open water but also some trout and stickleback. The char average weight was about 9g which looks not much of a morsel for the Loch Ness Monster. However, the range of size/weight went up as high as 30cm and over 300g.

But it has to be said that sonar contacts do not regularly show large sonar hits amongst these open water fish. So this is not a regular hunting ground for Nessies except in two speculative circumstances:

1. Sonar blind spots (e.g. within the top few metres and sides).
2. Juvenile Nessies of up to a few feet across which would be "lost" in the fish noise.

That does not preclude such fish being off the menu, however. Fish move around and as the char circulate closer to shore, the benthic dwelling Nessie could pick them off.

The other objection about being unable to see eels in the dark is a straw man argument (or should I say a "straw plesiosaur" as in the populist image of Nessie portrayed above by William Owen?) since it assumes a very simplistic view of a Loch Ness Monster which swims around guided only by its eyes. But Nature has shown us how wonderfully diverse is the sensor array of aquatic creatures. Indeed, how could any nocturnal animal survive otherwise?

But to name a few strategies. We have sharks with snouts which can pick up changes in local electric fields. They also have skin which can detect varying salinity levels. We have the sturgeon with vibration sensitive pits on its head. And of course there is the good old fashioned sense of smell.

As to hunting strategy, why the requirement for the Loch Ness Monster to be continuously moving? Why can't it employ a strategy similar to that of the Angel Shark which lies dormant for potentially days under silt in darkness before its keen senses detect its prey and it rises to seize them (see video below)? Let's get away from two dimensional thinking about the Loch Ness Monster and look beyond the stereoypes.

Finally, there is the objection that if Nessie hunted salmon, it would be seen surfacing more often. This argument is again based on the presumption that Nessie must hunt in a certain way. It is true that salmon swim in the top 10ft-20ft (though spent salmon (kelts) have been detected at up to 200ft depth - Dinsdale) but a Loch Ness Monster with a six foot maximum diameter at a depth of only four feet as measured at the midpoint of its maximum girth is unlikely to be visible above.

In my opinion, the Loch Ness Monster is a secretive predator in the manner of the Angel Shark which remains hidden from its prey until it is time to strike. How it exactly achieves this is an open question and depends on your view of Loch Ness Monster behaviour and morphology. This could be achieved by lying on rock outcrops underwater and striking out with its long neck (certainly in the Duncan MacDonald case, the creature was observed sitting on an underwater ledge - see link). Furthermore, this covert predation may also explain why it generally stays secretive to observers. The trade-off between high and low mobility in the matter of predation in a generally dark environment seems to have swung towards a mainly inert creature (though at times the creature can move rapidly if driven to do so).

THE HERD

And so we have about 57 tonnes of Loch Ness Monster. If there are indeed multiple creatures (as sightings data indicates) then how many are there?

Estimates varying according to opinions on how to maintain a diverse and healthy group. But again without an ID on Nessie, it is guesswork. However, a number I have heard sometimes suggested is 10 to 20 creatures (Adrian Shine in his sturgeon paper suggests an absolute minimum of ten).

Twenty animals gives an average of 2.85 tonnes per creature. Given the 30ft to 40ft estimates of witnesses and assuming 1/3 is tail, 1/3 is spheroidal body and the final 1/3 is long neck, we get something around four tonnes. But then again, not all Loch Ness Monsters are equal in size and weight. Using the analogy of other herd animals, we could have a trio of maximum sized bulls, some smaller females and a number of juveniles going down to sub-tonne levels. So, speculating here, we could have three bulls of four tonnes each, six females of two tonnes each and ten juveniles of a tonne and under which gives us 19 animals adding up to only 34 tonnes out of the maximum 57 tonnes we have postulated. You can plug in your own numbers here and come to your own conclusions.

CONCLUSIONS

Estimating food stock viability for the Loch Ness Monster is a numbers game. In this brief study we have used some assumptions, used what hard numbers we found and lowballed in a few circumstances. As a result we have come up with viable numbers for sustaining a number of large multi-tonne creatures.

Others may use different assumptions, different numbers and lowball/highball their calculations. You may say there are errors in my assumptions. My reply is that the whole process is about assumptions and the media hype about science proving there is not enough food for Nessie is itself "not enough".

On the contrary and in my opinion, there is enough food in Loch Ness to viably sustain a number of large and unknown creatures.