Lake Michigan is one of the world’s largest freshwater systems and supports a major recreational fishery, primarily due to introduced salmonids. These species are a mix of true salmon and large trout, all belonging to the family Salmonidae, which thrive in the lake’s deep, cold waters. The success of this fishery is maintained through sustained stocking and the availability of abundant prey fish.
Identifying Salmon Species in Lake Michigan
The two primary species of true salmon present in Lake Michigan are the Chinook salmon, also known as King salmon, and the Coho salmon, often called Silver salmon. Chinook salmon are the larger species, with mature adults commonly weighing between 10 and 20 pounds. Anglers can identify a Chinook by its black mouth and gums, along with small dark spots that cover its entire tail fin.
Coho salmon are generally smaller, averaging between 6 and 9 pounds, and are distinguished by a silver body and a dark blue-green back. Coho have white or grayish gums, and their spots are usually confined to the upper lobe of the tail fin.
Other large, silvery fish are often grouped with salmon but are technically trout. Steelhead (migratory Rainbow Trout) and Brown Trout are also heavily stocked and actively fished. Steelhead have a light-colored mouth and a pinkish lateral line streak, while Brown Trout often have spots that sometimes show X-shaped markings.
A Stocked Fishery: Why Salmon are in Lake Michigan
The presence of these large fish resulted from a deliberate, large-scale ecological management program initiated in the 1960s. At that time, the Lake Michigan ecosystem suffered from the invasive Alewife, which entered the Great Lakes via shipping canals. These small forage fish reproduced rapidly, leading to massive die-offs that piled millions of rotting fish onto beaches, causing environmental and tourism problems.
Fishery managers recognized the need for a predator to control the Alewife population. Beginning in 1966, Pacific salmon species were introduced to serve as biological control agents, starting with Coho and shortly after with Chinook salmon. The introduction was successful, as the voracious salmon quickly began feeding on the abundant Alewife, helping to rebalance the ecosystem.
The salmon and trout populations are maintained almost entirely through continuous, state-sponsored stocking programs. While some natural reproduction occurs in tributary rivers, the success rate is not high enough to sustain the popular sport fishery. State hatcheries collect eggs from returning fish, rear the young, and then release millions of juvenile salmon into the lake each year.
Life in the Great Lakes: Diet, Size, and Spawning
The ability of Lake Michigan salmon to grow to impressive sizes is directly linked to their primary food source: the Alewife. Chinook and Coho salmon are highly predatory, and Alewife often constitutes over 90% of their diet. This abundant protein source allows the salmon to exhibit a growth rate similar to their native Pacific Ocean habitat.
These salmon also consume other small prey fish like Rainbow Smelt, which contributes to their rapid weight gain. Mature Chinook salmon typically have a lifespan of four to five years in the lake, while Coho salmon usually live for about three years. In the fall, adult salmon instinctively move toward tributary rivers in a spawning migration, an urge driven by their Pacific ancestry.
The salmon attempt to spawn in upstream gravel beds. However, environmental conditions and lack of suitable habitat in many Great Lakes tributaries often limit the success of natural reproduction. After the strenuous spawning run, the adult salmon die, completing their life cycle in the freshwater system.