The Faces of Lake Trout: Lake Superior’s Evolutionary Marvel
The crown jewel to the Great Lakes, Lake Superior, is the largest freshwater lake in the world by surface area. It is known for its lore, scenery, and vast amount of water. At its’ deepest point reaching 1336’, the contour and quality of water across Lake Superior make it an ideal habitat for cold water fish to thrive throughout the entirety of the water column. World-class fishing opportunities have drawn anglers from all over the world to take their chances at landing the fish of a lifetime.
“These are some of my favorite fish to target. The size, the fight, and the taste have my wife and I coming back for more!”-Mike Malone of Macomb, MI, showing off a magnificent lake trout.
Lake trout (Salvelinus namaycush) are a cornerstone species of the Great Lakes ecosystem, historically abundant across all five lakes. Native to cold, deep freshwater habitats, they thrived in these waters for thousands of years. Lake trout possess a genetic code that makes them highly adaptable. In a system as dynamic as Superior, this sets the scene for a unique phenomenon in freshwater fisheries. Lake Superior is the most natural among the Great Lakes and is home to multiple ectomorphs (i.e. forms or kinds) of lake trout.
So, you may be wonder what the most accurate word for different “kinds” within a species. The terms Morphotype and Ecotype are both used to describe phenotypic (genetic/physical traits) diversity, but there are specifics that differentiate the two. Morphotype focuses more on the distinct observable physical differences. Ecotype puts the emphasis of the ecological conditions and fits the definition best within this marvel of biodiversity within a single species on a large body of water. Scientists are now adopting the term Ecomorph, essentially a sub species description, to best describe the diversity of lake trout forms in Lake Superior.
A seasoned angler that has caught multiple fish of the same species across different water systems might notice that some fish simply look different in appearance from one another. The answer to why is due to phenotypic plasticity- the ability of an organism to change its phenotype in response to environmental conditions. This is a process of micro-evolution at its finest. Defining an ecotype is not cut and dry. The answer is fluid, considering a myriad of small differences based on environmental and life history factors, such as growth, diet, temperature, depth, reproduction, and habitat structure. These factors influence differences in the physical traits of the fish while not altering their genetic code. These variations enable fish to thrive within specific environments and areas of Lake Superior.
Shawn Sitar, DNR fisheries biologist, showing off a gargantuan 53” redfin lake trout that was captured and released from a survey completed in May 2019. To see that article, Click Here
Photo Courtesy of the Michigan Dept. of Natural Resources.
Shawn Sitar is a research biologist based out of Marquette, Michigan. His role with the Michigan DNR is to conduct scientific investigations to help fisheries managers serve the public by informing them on the status of populations and best ways to manage and protect fisheries resources for current and future generations. With an interest in serving his country and a great passion for biology, Shawn pursued both careers by enlisting in the United States Marine Corps Reserves, and completing an undergraduate degree in biology from Rochester Institute of Technology, and eventually earned a Masters of Science in Fisheries and Wildlife from Michigan State University. Since 1997, he has taken part in 81 publications and has been academically cited 1,154 times. When it comes to being a specialist in the field, he is the real deal with understanding the wealth of knowledge that includes deep water fisheries and lake trout as they relate to Lake Superior. In his career experience, he and his team have discovered lake trout at the deepest parts of the lake AND measured the oldest documented lake trout in the Great Lakes, a fish collected at Klondike reef (40 miles N. of Grand Marais) that was 62 years old.
Lake Superior covers an area of 31,700 sq. miles, roughly the size of South Carolina. The volume of water and characteristics of the lake provide a truly unique setting as a fishery for species to adapt.
Schmaltz, 2003
The distance between Isle Royal National Park and the mainland of the upper peninsula is 56 miles. To put that into perspective with another water wonder of the world- about the length of the Panama Canal. Within this area of the lake alone, the depths can easily range upwards to a thousand feet of water. The point is Lake Superior is VERY deep and made up of complex underwater contour structure. Isle Royal is similar to an isolated, large coral reef where there is a wide range of habitat differences that come with the variation of depths. Imagine having different neighborhoods best suited for individuals based on their life needs and functionality. The critical key to different ecotypes are found within depth. This factor enables the species to spread out so much that they have to and adapt to these specific environmental conditions to the point where they are noticeably different but still very much the same species.
The catch-all answer to how many ecomorphs of lake trout there are documented within the Great Lakes would be four- all of which can be found on Lake Superior. According to Shawn Sitar, there are more than four, but the others have not been formally designated and described yet.
Photo Courtesy of Shawn Sitar, 2024
Lean Lake Trout
Lean lake trout are the most widespread and historically common type found throughout the Great Lakes and in small lakes. These trout prefer deep, cold, oxygen-rich waters, where they primarily feed on smaller fish such as ciscoes and smelt. Lean lake trout are often targeted for their excellent taste and significant size, sometimes exceeding an imaginable size. They play a crucial role in the food web, acting as apex predators that help maintain the balance of the lake’s ecosystem. Despite their resilience, lean lake trout populations continue to require monitoring and support to ensure their long-term sustainability. Research data has indicated that lean lake trout occupy depths mostly shallower than 160 ft throughout the year.
“If you catch a lake trout in the lower Great Lakes, it is more than likely that it is a lean.”
Humper Lake Trout
Named for living on offshore humps or reefs, Humper lake trout inhabit deep offshore waters, especially around rocky reefs and submerged ridges. They are smaller than their lean counterparts, typically weighing less than 3 pounds. Humpers are less migratory, often remaining in the same area for their entire lives, and feed mostly on invertebrates. There is thought among scientists that this may be a dwarf form of lake trout. They are less frequently targeted by anglers due to their remote habitats and smaller size. Their presence, however, reflects the diversity and adaptability of lake trout within the Great Lakes.
Siscowet Lake Trout
Going deeper- Siscowet lake trout, also known as “fat lake trout,” are unique for their high-fat content, which allows them to thrive in the extremely cold and deep waters of Lake Superior. Their diet is diverse, incorporating fish, crustaceans, and other deep-water organisms. Siscowets can grow quite large, with some reaching over 40 pounds, but their oily flesh makes them less desirable for eating compared to lean lake trout. Siscowet have been measured to have over 85% fat content, compared to the 20-50% often seen in the other ecomorphs. Amongst other types of lake trout, they grow the slowest over time. Their adaptations highlight the remarkable ecological niches lake trout can occupy. What makes the siscowet even more fascinating is their ability to traverse throughout the water column between the surface and depths to 1,330 ft.
“This explains why we see rocks, sculpins (bottom fish), birds and flying ants in the same siscowet stomachs.” - Shawn Sitar
Redfin Lake Trout
The redfin demonstrates exactly that- orange and reddish fins that typically have white edges. Slender and muscular in their builds, they carry less than 10% body fat and swim around constantly following bait. Within dietary factors, consuming different organisms can enhance the color features. Carotenoids, a natural pigment found in crustaceans and other marine life, are the reason for this. Lake Superior has abundant populations of opossum shrimp, which is an essential food for most of the cold water fishes. Due to their cellular capabilities, these carotenoids enhance color in animals and plants. Similar to how flamingos can display varying levels of pink or the bright red witnessed in coho salmon- it all comes from diet. When you think of the redfin lake trout- think of them as someone who goes to the gym every day and eats healthily. They are often found deeper than leans but focus more on being close to the bottom. Their diet sometimes contains snails. Their lifestyle shows their body physically from what they eat and always being motion. These are the most popular photo-esque fish targeted by anglers for the enormous size, hard fighting potential, and defined beauty.
The different ecomorphs or “kinds” of lake trout—such as lean, humper, and siscowet—exist because of ecological adaptations to the diverse habitats found within their range, particularly in the Great Lakes. Over thousands of years, these fish have evolved to occupy specific niches within their environment, allowing them to reduce competition and thrive in varying conditions. This diversity is a result of environmental pressures such as food availability, temperature, water depth, and oxygen levels. Over time, natural selection favored traits that allowed lake trout to exploit specific habitats, leading to the emergence of these distinct forms. Their variation reflects the complexity and productivity of the Great Lakes ecosystem.
Conclusion: The Resilience of Lake Trout
Showing off a big catch and a bigger smile, Katie Malone appreciates all fish, especially those of the cold-water variety.
Lake trout are fascinating. There is no doubting that! They play a vital role within the Great Lakes ecosystem, showcasing impressive varieties- each well adapted to unique habitats and playing crucial roles in maintaining ecological balance. While the overall population of lake trout has faced historic challenges, ongoing efforts in conservation have allowed lake trout to recover in many areas. Being apex predators, they serve as indicators to the health of the Great Lakes while also sharing a reminder of the importance that comes with protecting and understanding fisheries and Lake Superior. Whether the respect comes from their biological determination to survive or from the angling appeal of sheer size and fight, lake trout are badass.
Foresight Fishing would like to extend a message of gratitude to Mr. Sitar from the Michigan Department of Natural Resources for sharing his years of expertise that went into this article. The Great Lakes stay GREAT because of so many hard-working, dedicated individuals, like Mr. Sitar, who put a tremendous amount of effort in the lab and field to enable an improved understanding of respected areas of ecology and conservation for a better future. For those interested in exploring his research further, be sure to visit this link: https://www.researchgate.net/profile/Shawn-Sitar