Why is MNR so concerned about Lake trout lakes?

MNR's concern about lake trout lakes is firmly tied to events that happened long before the first cottage was ever built in the wilds of the Canadian Shield.

I'd like you to imagine this area as it might have looked 10 or 15 million years ago. The great glaciers of the Wisconsin era covered the area of Parry Sound and points north under a layer of ice hundreds of metres thick. In their march southwards, the glaciers scraped whatever soil there might have been on these old rocks of the Precambrian Shield, and carried it south, leaving little but bare rock under the ice. Eventually the glaciers melted but their weight on the land left it depressed, ready to receive the waters which had been tied up in the ice of the glaciers. Huge lakes formed, covering this entire area. The shores of post-glacial lake Algonquin can still be followed today, more or less parallel to Highway 11, close to Algonquin Park. As the land rebounded from the crushing weight of the glaciers, the waters of the great glacial lakes flowed through a couple of major outlets to the sea , leaving behind a landscape dotted with large and small lakes set in the granite of the Canadian Shield.

The glaciers left little soil behind. The lakes which were created when the primordial lakes receded were virtually devoid of any nutrients. The pattern of invasion by fish species favoured strong swimmers that were long-lived and slow growing, and which could survive in these very low nutrient conditions. These early lakes were likely very cold, and not hospitable to fishes which prefer warmer conditions. As such they were ideal for the trouts and salmons to thrive. We don't know through which accident of nature the lake trout ended up colonizing many of these lakes, but we do know that the area from the Soo to Kingston boasts some 1200 of them. They range in size from the Great lakes Huron and Superior, to large inland lakes like Lake Simcoe, to a whole bunch of lakes which are less than 100 hectares (or 250 acres) in area, and yet contain. thriving lake trout populations.
The Ministry of Natural Resources is faced with a numbers game - there are only some 2200 lake trout lakes in the entire province, and it is estimated that these lakes constitute something like 20 to 25% of the total number of lake trout lakes in the world. To suggest that these lakes are rare in a global sense is to understate the obvious. The direction of this ministry is to maintain the sustainability of ecosystems. For fisheries staff, the lake trout lakes are the old growth forests of the aquatic realm. Once they are gone, there won't be any more.
So, why are these lakes so special that they need so much protection? Someone once called lake trout lakes “swimming pools cut out of granite". There are many of them that are still as clear as swimming pools, with an average visibility of 10 metres being quite common. Their purity makes them highly desirable as cottaging lakes. Many cottagers still drink the water from their lake - when there are relatively few of them on the lake. But, as more people carve out their own little slice of paradise, the water suddenly isn't so pure anymore. The loons which once sent their maniacal laughter up and down the lake become fewer and fewer, eventually disappearing altogether. The once excellent fishing gets worse and worse, and the waterskiers and jetskis start taking over the lake. One day we wake up and wonder, "What happened?".
Let's talk about how these aquatic ecosystems function, as best as we can. A coldwater lake has a life. As the seasons pass, the lake undergoes a cycle of changes. Winds blowing down the lake stir up the surface, mixing it with the deeper layers. The winds also bring oxygen into the surface
waters. Twice a year, the lake undergoes a major shakeup.
All water has an interesting property, which is crucial to the life of all lakes. At 4 degrees Celsius, the density or weight per unit volume of water is at its greatest. In other words, water at 4 degrees is heavier than water at 2 degrees or at 10 degrees. What does this all mean? Well, as the surface temperatures cool down to 4 degrees C in the fall, the cooler, well oxygenated surface water sinks to the bottom, replenishing the life giving oxygen of the lower layers. This process is repeated in the spring, as the cold surface waters warm up after ice out, become well oxygenated by the warm spring breezes, and sink to the bottom, starting the cycle once again. In between these times, the lake stratifies, or forms layers, in the winter because of a layer of ice, in the summer because of a phenomenon known as the thermocline, a layer of rapidly changing temperature which acts a barrier to water moving from the surface to the depths. It's a lot like locking all of us into a large room and sealing it so no air can get in. So what?
All biological processes need oxygen. All animals breathe it and need it to live. So do the bacteria and other organisms which help to dispose of dead material. Lakes are no different. In the summer growing season, microscopic plants called algae, thrive in the sunny surface waters of our lakes. If these plants get lots of nutrients, they bloom, just like your lawn does when you fertilize it. If they don't get many nutrients, they don't grow nearly as well, and don't produce as thick a crop. Most of our lake trout lakes are like this - they have few nutrients, or fertilizers, if you will, and algae don't grow very well. These algae have a short life - they grow, they bloom and they die. When they die, they sink to the bottom, and form a fuzzy layer of rotting algae. This layer of algae uses up valuable oxygen - the more algae, the more oxygen is used up as the summer progresses. The important thing to remember is that the amount of algae is directly linked to the amount of nutrients making it into the water, and that the amount of nutrients is directly linked to human activities on the shoreline.
Where does all this leave the lake trout? Lake trout start their life as eggs spawned in the fall, and scattered over shallow, rocky rubble bottom shoals, exposed to the prevailing winds. Surprisingly, most lakes which contain lake trout have very few spawning areas which are suitable, often only two or three per lake. It doesn't take a lot of disturbance before the fish are scared off these sites, never to return. Docks, boathouses and removal of the actual· rock rubble can lead to the destruction of these relatively few critical habitat features. That's why MNR will not issue a work permit for construction which might have an adverse effect on them. But, this is only one of the lake trout's worries.
Adult lake trout lay relatively few eggs, as fish go. The eggs are relatively large, 3-4 nun in diameter, but there is no parental care. The spawning act just scatters the eggs over the shoals, and the fertilized eggs float down into the cracks between the rocks. During the six months or so it takes for them to develop, they need oxygen. If they are covered by silt or algae, they die. Even under the best conditions, survival is poor. Small fish eat the eggs, some are infertile, and others just die. The result is that very few of the eggs survive to grow into young fish.
The young fish, or fry, hatch in late winter, but stay in the nooks and crannies among the rocks for a month or so. When they emerge, shortly after ice-out, they head for deep water, hugging the bottom, and seeking cover from predation. It's a fish-eat-fish world out in the lake. For most
fish species, if the prey fits into the jaws, it's fair game. lake trout are no different, and don't distinguish between the young of their own species and other small prey fish. Lake trout is the only major, homegrown sport fish species adapted to the deep cold waters of infertile lakes. Especially in the summer, they inhabit the deep zones of the lake, as most who have fished for them know. Guess what one of their favourite foods is? What else but young lake trout.
Under normal conditions, these young lake trout literally live on the bottom, and are able to escape predation from above. But when the oxygen conditions at the bottom become. limiting, they have to move, and the only · way is up - right into the waiting jaws of their older mates. Researchers have found that the oxygen concentration of· the bottom waters is not all the same - as summer ends, the conditions, due to the decay of dead algae and other material, are much worse near the bottom than higher up in the water column. But the higher up a fish goes, the warmer it gets. lake trout can't handle warmer temperatures for any length of time, and avoid the surface layers (where. the oxygen is better) So they are squeezed between the warm temperatures near the surface, and the low oxygen concentrations near the bottom: On large lakes, where the deep layers make up a significant fraction of the total lake volume, this is not usually much of a problem, but on many of the smaller, less than 500 hectare (1200 acre) lakes, this is a major problem. So both young and adult lake trout end up inhabiting the same part of the lake, the one providing food for the other, but in the worst case scenario resulting in the genetic death of the population, since too few young fish survive to reproduce.
Recent reworking of some early fish physiology studies suggest a safe limit for oxygen depletion in the hypolimnion or deep layer, of lake trout lakes. This work recommends that the mean oxygen concentration of this layer should not fall below 7 ppm. Thanks to our friends at MOEE, we now
have the science to model the effects of increased nutrient input from shoreline activities on the hypolimnetic oxygen concentration. We also are bound by a piece of federal legislation known as the Fisheries Act. The Act clearly states that we cannot stand idly by and allow the "destruction or harmful alteration" of fish habitat. That is why MNR has set "decision criteria" for use in the models developed by MOEE to serve as a limit to the amount of nutrients which can be allowed to enter a lake trout lake as a result of shoreline activities.
By policy, MNR has a stewardship role over the natural resources of the province. By the laws of Canada, we have the responsibility to protect fish habitat from harm and destruction. Lake trout lakes are perhaps our most sensitive aquatic resource. That's why MNR is concerned about the pressures of development on lake trout lakes in this area.
As a wise man once said, "We don't inherit our resources from our parents, we borrow them from our children."
Thank you.