Life History
Lake trout inhabit cold, oxygen-rich waters. They are pelagic during the period of summer stratification in dimictic lakes, often living at depths of 20–60 m (60–200 ft).
The lake trout is a slow-growing fish, typical of oligotrophic waters. It is also very late to mature. Populations are extremely susceptible to overfishing. Many native lake trout populations have been severely damaged through the combined effects of hatchery stocking (planting) and overharvest.
Two basic types of lake trout populations are generally accepted. Some lakes do not have pelagic forage fish during the period of summer stratification. In these lakes, lake trout take on a life history known as planktivory. Lake trout in planktivorous populations are highly abundant, grow very slowly and mature at relatively small sizes. In those lakes that do contain deep-water forage, lake trout become piscivorous. Piscivorous lake trout grow much more quickly, mature at a larger size and are less abundant. Notwithstanding differences in abundance, the density of biomass of lake trout is fairly consistent in similar lakes, regardless of whether the lake trout populations they contain are planktivorous or piscivorous.
In Lake Superior, three distinct phenotypes of lake trout persist, commonly known as "siscowet", "paperbelly" and "lean". The distinct groups operate, to some level at least, under genetic control and are not mere environmental adaptations. Siscowet numbers, especially, have become greatly depressed over the years due to a combination of the extirpation of some of the fish's deep water coregonine prey and to overexploitation. Siscowet tend to grow extremely large and fat and attracted great commercial interest in the last century. Their populations have rebounded since 1970, with one estimate putting the number in Lake Superior at 100 million.
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