The annual movement of salmon from the Great Lakes into their tributary streams is a significant ecological event that reshapes the state’s inland waterways each fall. This migration is the culmination of a life cycle that began when Pacific salmon species were first introduced decades ago to control an overpopulation of invasive alewives in the Great Lakes. The resultant sport fishery and nutrient cycling contribute substantially to the region’s environment and economy.
Understanding the Salmon Run
The term “salmon run” describes the upstream migration of adult salmon from the Great Lakes into tributary rivers and streams for reproduction. The Great Lakes act as the ocean phase for these fish, providing a vast area for them to feed and grow before maturity.
Environmental cues dictate the timing of the migration, with a drop in water temperature and an increase in stream flow acting as primary triggers. Salmon prefer water temperatures in the low to mid-60s Fahrenheit for their upstream journey. Significant rainfall events that increase the water level often initiate the largest surges of fish moving inland from the lakes.
Specific Spawning Timing by Species
The specific timing of the spawning process is staggered among the different salmon species, extending the run throughout the entire fall season.
Chinook Salmon
Chinook salmon are the first and largest of the Pacific salmon to enter the rivers. Their migration begins in late summer, with initial fish typically entering the rivers by mid-August. The run peaks throughout September and into early October.
Coho Salmon
Coho salmon generally follow a few weeks behind the Chinook run. Coho begin to enter the tributaries in September, but their most concentrated spawning activity occurs from late October through November. Some Coho runs can continue into December, depending on the river system and local conditions.
Atlantic Salmon
Atlantic salmon, which are also stocked in Michigan, have a run that overlaps significantly with both Pacific species. Their fall migration begins in late September and early October. The spawning run for Atlantic salmon can continue into December, often maintaining a steady trickle of fresh fish entering the river systems.
Where to Find Spawning Salmon
Spawning salmon primarily seek out tributary rivers and streams that flow into the Great Lakes, as these are the locations where they were either hatched or stocked. Several major river systems on the west side of Michigan’s Lower Peninsula, feeding into Lake Michigan, are known for significant salmon runs. These include the Manistee, Pere Marquette, Muskegon, and Platte Rivers.
The fish concentrate in areas where their upstream journey is slowed or halted, making these locations prime viewing spots. Man-made barriers like dams temporarily stop the migration, causing large numbers of salmon to gather below the structures. Fish ladders provide a chance to see the salmon actively working their way past these obstacles.
The actual spawning takes place in shallow, flowing sections of the river where the riverbed is composed of fine gravel. Female salmon select these locations to construct their nests, known as redds. Rivers like the Betsie and Little Manistee, as well as their smaller, gravel-bottomed tributaries, host both stocked and naturally reproducing salmon populations.
The Biology of Reproduction
The drive to return to freshwater streams to reproduce is a biological imperative for the mature salmon. This homing behavior is believed to be guided by a combination of magnetic fields and a memory of the unique chemical signature of their natal stream. Once the fish enter the rivers, they cease feeding and dedicate all remaining energy reserves to the reproductive process.
As they transition from the deep, cool waters of the Great Lakes to the shallower, warmer rivers, the salmon undergo physical transformations. Their silvery, open-water coloration darkens, and males develop a hooked jaw, called a kype, which is used for battling other males for access to females. These changes are fueled by hormones that prepare them for the rigors of the upstream journey and the subsequent spawning competition.
Once a female locates a suitable stretch of gravel, she uses her tail fin to vigorously clear a depression in the riverbed, creating the redd. She deposits her eggs into this nest, where a male immediately fertilizes them with milt. The female then covers the eggs with gravel to protect them from predators and ensure a flow of oxygenated water. Pacific salmon die shortly after the completion of the spawning process.