Patagonian lake monsters - the sustainability issue

 

Having looked into the environmental constraints to the potential cryptids in Patagonian lakes in our previous post, which are the following:

 

- Glacial origin of lakes means nothing lived in them before they were formed after the last glacial period about ten thousand years ago.

- Isolation in Patagonia by a wide “arid gap” makes it difficult for large mammals to reach the area (local ones are well adapted to the dry steppe conditions and are not too big –that is, big enough to be mistaken for a “monster”).

We should no look at other constraints. And a key issue is Food.

What do these “lake monsters” eat? The quantity of food pose a serious limitation on any animal, size-wise. A big animal (i.e. lake monster-sized) needs to eat a lot, and these lakes are not too abundant in food.

This takes us to the…

Sustainability issue

A key issue regarding “lake monsters” is that all Patagonian lakes are oligotrophic; that means they offer little to sustain life as they are very low in nutrient levels.
The Greek etymology of the word: oligo = small, few; and trophe = nutrients; give a concise idea of its meaning. These are lakes that cannot support a large sized water animal.

We have mentioned above that Patagonian lakes were carved by the glaciers in a process that began about one million years ago and ended about 13,000 years BP when the glaciers retired from the deep “U” shaped valleys, which then filled with water from the snow melting on the mountains that surround them.

These very deep lakes are exceptionally transparent, with extremely clean water, which is nearly distilled in purity and therefore lacks minerals because they do not leach from the hard insoluble rock of the lake beds.

This in turn leads to low algal production. Also, the steep shores, lack of nutrients in the soil and strong winds also limit the aquatic vegetation (such as reeds and bull rushes) on these lakes.
This limits the upstream food-chain, because these constrained algal and vegetable resources restrain the population size of crustaceans and mollusks that in turn are eaten by other animals (such as, until the 1900s, the local endemic fish population).

Tiny crab at Lake Nahuel Huapi. Do lake monsters eat this?
Copyright © 2008 by Austin Whittall

To make matters worse, exotic fish (trout and salmon) were introduced into the lakes altering the region’s natural food-chains.

The first salmonids were sown in 1904, at Nahuel Huapi, Espejo, Gutierrez and Traful lakes. Many Patagonian lakes are now home to the following species of trout and salmon: Salvelinus fontinalis, Salvelinus namaycush, Salmo salar sebago, Salmo trutta and Oncorhynchus mykiss. These exotic (European and North American) Salmonid fish disrupted the local fish community drastically; the bagre sapo (Otuno diplomistes viedmensis) and the puyén (Galaxias platei) did not compete amongst themselves for the use of the habitat, the salmonids do. They thus became vulnerable to the aggressive newcomers.

Even the Patagonian otter (huillín) was pressured by the salmonids because they compete for food in overlapping habitats; both eat crustaceans; furthermore, the exotic fish are too fast to be captured by the otters. This has greatly reduced the local otter population.

So… the sustainability issue means that there are no known carnivorous water creatures in Patagonia larger than the otter because the lakes cannot provide enough food for them, however, this may not impede the existence of large lake animals.

A local Bariloche writer, Ricardo Valmitjana, told the author while discussing the matter in February 2008, that he had recorded a television interview which addressed the oligotrophy issue.

In it a very old lady, a Bariloche resident who had seen a “water monster” in Lake Nahuel Huapi, was confronted by a reporter who said that such an animal could not survive due to lack of food in the lake. The old lady calmly replied that she had seen the animal come out of the lake and graze on the grass of a field by its shore.

Click Here to see a photograph of the fields that can be found by some Patagonian lakes.

Such a simple explanation, so evident yet often ignored. The food does not have to be inside the lake, it can be outside of it.

Large vegetarian beasts like African hippos or Arctic region’s moose do not care about the quantity of fish in their rivers or lakes; they simply munch the plants by the shore.

Our monster is a herbivore

So, if plant eating, the lake cryptids could graze the abundant vegetation that grow by the lakes. I am surprised that this was not mentioned before by those who criticize the possible existence of this animal based on the "lack of food" hypothesis.

I tend to favor the idea of a large mammal because it coincides with other "lake creatures" sighted in the region, especially the "plesiosaur" (which by the way was not a plesiosaur –extinct for over 65 million years- but some kind of mammal).

But that (the plesiosaur) is something we will look into in a future post.

Going back to the food constraint, another option is that the “cryptid” is a reptile.

Reptiles have lower energy requirements in comparison to mammals. So they need to eat less. A Reptile’s energy requirement is a tenth, a fifth or even less than those of a comparable sized endotherms (warm blooded animals such as birds and mammals).

Regarding "size", a paper[1] noted that:

an ectothermic [cold blooded] top herbivore was 16 times heavier than an endothermic [mammal] top herbivore. However, because ectotherms have lower mass-specific metabolic rates and hence food requirements than endotherms, the food requirements of ectothermic and endothermic top carnivores for a given land area proved to be the same.[1]

And regarding food availability:

Because the trophic pyramid implies 5–20 times more food available to herbivores than to carnivores, a given area can support a population of a herbivore species whose individuals consume 5–20 times more than does a carnivore; we actually found a ratio of 8 for the median food consumption of top herbivores to top carnivores.[1]

In other words, a herbivore reptile can be 16 times heavier than a herbivore mammal (i.e. bigger) eating the same ammount of food (vegetables), furthermore there is 5 to 20 (average = 8) time more "herbivore" food available than "carnivore" food. So the chances are that a "big" monster will be a herbivore reptile.

So the “snake-like” culebrón and lampalagua may be a reasonable explanation for Patagonian lake monsters.

Summing up. Lake monsters in Patagonia may be reptiles or herbivore mammals.

Bibliography.

[1] Burness, G. P., Diamond, J., Flannery, T., (2001). Dinosaurs, dragons, and dwarfs: The evolution of maximal body size. Proc Natl Acad Sci USA 98:14518–14523. Online.


Copyright 2009 by Austin Whittall ©

Patagonian Monsters