Monster theories - food webs and energy flows
Is there enough food in Loch Ness to support a large creature?
There are about 2000 tonnes of algae in Loch Ness supporting 200 tonnes of plankton. This plankton supports about 20 tonnes of fish, which would support two tonnes of Loch Ness Monster.
The 3D Loch Ness Exhibition website has a range of educational resources looking at food and energy flow within the loch.
After the Food Chain and Food Pyramid games have been played, the activity can be extended by considering the number and type of animals involved. The games show that it is unlikely that there is enough food for a plesiosaur, but is it possible that some of the animals that have been suggested as possible candidates for the monster could live in Loch Ness with the known amount of food? (We’ll ignore the elephant as that was a visitor which did not actually feed there!)
Just a reminder - it is estimated that there are between 20 and 30 tonnes of fish in Loch Ness and each step in a food chain loses 90% of the energy, so if Nessie was eating the fish, the supplies would support a monster weighing two to three tonnes.
Giant eel
A one-metre-long eel has a mass of about 1.5 kg. As an eel doubles in length its mass roughly increases by a factor of eight, so a two-metre-long eel would be 12 kg and a four-metre-long eel would be 96 kg.
Some reports lead researchers to speculate that there is an eel of approximately eight metres or 1600 kg - is it possible that an eel of this size could exist in Loch Ness?
Is there enough food? If there isn’t, what size is the maximum-size eel that could exist with the levels of food available?
Sturgeon
Some Beluga sturgeons are claimed to weigh about 2000 kg each. But these are real monsters. A normal weight for a seven-foot-long white sturgeon would be 100 kg and a nine-foot-long beast would be about 250 kg.
There over 20 different species of sturgeon so these figures are simply rough estimates to work with.
Seal
If seals are just visiting Loch Ness and being misidentified then there are not necessarily any problems related to food. Just like many day visitors who feed before they arrive at the loch, the seals may do the same.
But what about the hypothetical long-necked seal? An adult grey seal is about two metres long and has an average weight of about 190 kg. Let’s add 10% to the size and weight for the extra length of neck. So that’s 2.2 metres and 210 kg.
Long-necked newt
Taking the largest species of newt known - the Japanese Giant Salamander (salamander and newt are just common names for animals of the same group) - and adding 10% to allow for an increased neck size, we would have a two-metre-long animal weighing in at a mere 70 kg.
Our lightest contender! Remember that newts are amphibians so they could get food from the land as well.
How many Nessies?
But there is one problem for all of these animals. Each of these situations is looking at only one animal. If there has been a Nessie since the Loch was formed some 10-12,000 years ago it must be very old.
The oldest reliably recorded age for an animal is 176 years; both a tortoise and a Koi carp died at this exact same age. Because of being kept in captivity all their lives, the age of each is reasonably well verified.
So if we assume that Nessie is like other animals then 12,000 years old is a bit off the mark. There is a way around this problem - there must be a breeding population.
At its lowest level a breeding population would have to be two animals and they in turn would have to have two offspring and so on. This is dangerous. What happens if one of the animals has an accident before it breeds? That’s the end of the monsters. And after the original parents, all the offspring are breeding between brother and sister; this is not good as it would lead to genetic weakness, which would make it more likely that they would die out.
What about if you don’t have a brother and sister - what if you have two brothers or two sisters? Again the animals will die out. To get around these problems and ensure you have the animals surviving into the future (even if it is just from the end of the last ice age to the modern day), you have to have a reasonably large population.
What about the young and the old Nessies? They won’t be breeding but they’ll still be present in the loch and their numbers will swell the population size, making it more likely that they will be seen. For a ballpark figure let's say we have a population of 10, six of whom are capable of breeding - because two are too old and two are too young. They will all still need food. Check your energy flows with these population figures. How large will your animal be now? Are there any candidates left? How would we search for this animal to prove its existence?
Text by Gordon Rutter, cryptozoologist and secondary science teacher.