Salmon, commonly recognized for their extensive ocean migrations, also inhabit freshwater lake environments. While many salmon species are anadromous, meaning they spend part of their lives in the ocean and return to freshwater to spawn, certain populations have adapted to complete their entire life cycle within lakes. This allows them to thrive without ever entering saltwater.
Salmon Species Found in Lakes
Several salmon species have established populations in lakes, some naturally landlocked and others through human introduction. Kokanee salmon, a freshwater form of the sockeye salmon (Oncorhynchus nerka), are found in many lakes across western North America, Japan, and Russia. These fish are typically smaller than their ocean-migrating relatives, averaging 10 to 18 inches in length.
Landlocked Atlantic salmon (Salmo salar) also spend their entire lives in freshwater, with no physical differences from their sea-run counterparts, though they tend to be smaller. These populations can be found in various lakes across eastern North America, such as Maine’s Sebago Lake, and in Northern Europe, including Sweden’s Lake Vänern and Finland’s Lake Saimaa.
Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) salmon, native to the Pacific Coast, have been successfully introduced into large freshwater systems like the Great Lakes. These introduced populations primarily rely on stocking programs due to limited natural reproduction in these new environments.
Life Cycle Adaptations in Lakes
Salmon living exclusively in lakes exhibit specific adaptations to their freshwater existence. Unlike ocean-migrating salmon that undergo smoltification—a physiological change preparing them for saltwater—landlocked populations do not require this transformation. Their entire life cycle, from egg to adult, is completed within the freshwater system.
Reproduction occurs in tributary streams or along gravelly lake shorelines, where females construct nests called redds. These redds are shallow depressions in the gravel, providing a protective environment for eggs, which remain buried for several months. After hatching, juvenile salmon, known as fry, feed on small aquatic insects, larvae, and zooplankton within the lake or its connected streams. As they mature, their diet shifts, with larger lake-dwelling salmon, such as Chinook and Coho, preying on smaller fish like alewives and smelt.
Factors Influencing Lake Salmon Presence
The presence of salmon in lakes is influenced by both natural historical processes and human activities. Natural landlocking occurred following glacial retreats approximately 10,000 years ago, as receding glaciers and shifting river courses isolated some salmon populations within newly formed lakes. This resulted in populations that adapted to a permanent freshwater existence, such as the indigenous landlocked Atlantic salmon.
Human interventions, primarily stocking programs, have also significantly contributed to salmon populations in lakes. For example, Chinook and Coho salmon were introduced to the Great Lakes in the 1960s to manage invasive alewife populations and establish recreational fisheries. Maintaining these stocked populations often requires continuous releases of hatchery-reared fish due to insufficient natural reproduction in these introduced environments. Lakes suitable for salmon possess specific environmental conditions, including clear, cold, and well-oxygenated waters, along with accessible tributary streams or shorelines offering suitable gravel for spawning.