As their name would suggest, Lake Trout are most common in deep, cold water lakes but are also occasionally found in streams and other shallow waters. They will generally keep to the deeper water, usually just over 30 m but sometimes as deep as 430 m, except in spring and fall when they move towards shallower waters in order to feed. Regardless of depth they will always stay close to the bottom and will sometimes congregate around deep reefs. They are heavily dependent on cold water temperatures, preferring water below 13°C and dying in waters above 23°C. Their salinity tolerance is usually close to 11-13 ppt. Lake Trout diet is dependent on size, with trout becoming more piscivorous as they get larger. In Lake Tahoe Lake Trout under 13 cm in length have traditionally fed on zooplankton but with the recent introduction of the opossum shrimp (Mysis relicta) the Daphnia zooplankton population in the lake has decreased, forcing small trout to prey on the Mysis instead. Individuals greater than 13 cm in length still feed heavily on zooplankton but begin to feed on small benthic fish species like the Paiute Sculpin. By the time Lake Trout reach 50 cm in length fish like the Tahoe Sucker have become the most common prey items.
Lake Trout will reach maturity sometime between their fifth and eleventh year and will spawn every year after. Mating occurs between mid-September and mid-November in areas with rubble and boulder bottoms deeper than 37 m. Males arrive first to clean rocks and macrophytes of silt and debris with their fins and body. Spawning takes place at night with a brief courtship ceremony where a single female will mate with multiple males. Unlike most trout species, the fertilized eggs of Lake Trout fall between cracks in the rocks rather than a constructed redd. An average of 3,400 eggs per female was measured in Lake Tahoe. Embryos hatch in the rocks 4-6 months later. The young will stay here for a month or so after hatching and are believed to stay on the bottom feeding on invertebrates and zooplankton for the next 1 to 2 years. During that first year they will grow to 12 cm and add 5-7 cm per year over the next 10 years. In Lake Tahoe they can live to be 17 years old and individuals as old as 41 have been found elsewhere. Individuals have been found in Lake Tahoe measuring longer than 1 m and weighing more than 9.1 kg.
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