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Lake Trout Biology

Mack Days helps the ecological balance of Flathead Lake by thinning the mackinaw (also called lake trout) population. The  event succeeded in it's first event (2002 Fall) in stimulating the harvest of lake trout and in educating people about the Flathead Lake Fisheries Management Plan. Let’s keep a good thing going. Anglers help manage the lake by harvesting over abundant lake trout. Learn about the biology below by clicking on the buttons. You can also read an interesting blog spot about the history of lake trout in Flathead Lake by clicking here.

  • Basic Identification and Montana Distribution

    Also called the Mackinaw Trout, the lake trout is found mostly in the Fort Peck area with some occurrence in the western part of the state. The lake trout is a slate gray to bluish fish with numerous light colored spots. These spots can range in color from white to a pale yellow, but are never red or orange. However fins may have traces of orange, white leading edge is often present on fins as well. Lake trout may have pale wavy lines on their back.

    • Average Size: 14"-20"
    • Habitat: Deep, cold lakes and reservoirs.
    • Montana Record Catch: 42lbs 11.8 oz, 42.5" long & 31.5" around
    • Caught in Flathead Lake in 2004 by Ruth Barber.

    Tail: Deeply forked (center rays less than half length of longest rays).
    Dorsal Fin: Without spots or sometimes with light-colored oval markings.
    Body: With white or cream-colored spots (never pink or red) on darker background.
    Appearance: Overall gray or nearly black/white coloration, sometimes with yellow tinge on fins.

  • Physical Characteristics

    Lake trout are the largest trout native to North America. The largest lake trout on record weighed 46.3 kg (102 lb), which was caught by the commercial fishery at Lake Athabasca, Saskatchewan in 1961. The angling record contains a specimen weighing 32.8 kg (72.25 lb), caught in Great Bear Lake, Northwest Territories, in 1995. In Nova Scotia, the average lake trout caught is usually less than 2.0 kg (4.4 lb). A lake trout weighing 8.6 kg (19 lb) and measuring 81.3 cm (32 inches) was caught in Sherbrooke Lake, Nova Scotia in 1992.

    Typically, lake trout are long and slender, with a deeply forked caudal fin. This distinguishes them from other chars, such as speckled or brook trout.

    The overall coloration is light spots on a dark background, that varies from light green to almost black. Lake trout do not have the red spots found on speckled trout. Orange or red-orange may be present on the pelvic, pectoral, and, especially, anal fins, but this feature is usually more apparent in northern populations. A narrow white border is present on the lower fins, but it is never as immaculate or as wide as on the fins of a speckled trout. Dark bands may be noticeable on the sides of spawning males, but are not present in every population. Even during the mating season, the sexes can rarely be distinguished on the basis of color. Young lake trout or par have seven to twelve vertical bars on their sides. These are called par marks. The number of par marks varies, and the spaces between them are usually equal to or slightly greater than the width of an individual bar.

  • Lake Trout Facts

    • Lake trout are "negatively phototropic"; they avoid light.
    • Lake trout spawn at night.
    • In large bodies of water such as the Great Lakes, lake trout may migrate up to 300 km (186 mi) to their spawning grounds.
    • Lake trout scales are unreliable for aging purposes because the annuli cannot be distinguished. Researchers determine age by reading otoliths, which are calcified tissues of the inner ear used by fish for maintaining equilibrium and balance. The oldest fish on record, taken in the Northwest Territories, was aged at 65 years.
    • Female lake trout are crossed with male speckled trout to produce a fish known as splake, in a process called artificial hybridization. Hatcheries produce splake because this hybrid grows very quickly.

    Some Fishing Facts
    • Lake trout are easily caught because of their predatory nature.
    • Lake trout are caught with spinning gear, flies, spoons, jigs, and live bait, which are commonly used on down riggers. It is illegal however to use live bait in Montana's Flathead Lake.
    • Winter angling for lake trout through holes in the ice is a popular sport in some areas.

  • Natural History

    Namaycush is a North American Indian name that means "dwellers of the deep". Lake trout inhabit deep, clear, rocky lakes with preferred temperatures of about 10°C (50°F) and oxygen levels of six to twelve milligrams per liter. Lake trout have an upper lethal temperature of about 23.5°C (74.3°F). They also inhabit shallow lakes and rivers, but this is usually in the northern parts of their range. The lake trout is a bottom oriented species regardless of depth. Juveniles are usually found in deeper water than adults. This may be a mechanism for survival, because adults are cannibalistic.

    Lake trout also feed on aquatic insects, crustaceans, and smaller fish such as minnows, lake whitefish, yellow perch, alewives (gaspereau), and rainbow smelt. In large lakes with many fish species, lake trout are typically piscivorous, meaning they eat other fish. In smaller lakes, with fewer forage species, lake trout tend to be planktivorous for much of the year. In these lakes, they tend to prey upon small crustaceans and several species of aquatic insects.

    Lake trout are fall spawners and normally reproduce every second year from September to November in most parts of their range. Temperature, light, and wind are factors which contribute to the onset and duration of spawning activities. Spawning begins when water temperatures fall to 10°C (50°F) and lower. Lake trout spawn on offshore shoals, near shorelines and points near islands exposed to the prevailing winds. The substrate is a combination of broken rubble and edged rocks 3-15 cm (1-6 in.) in diameter.

    Lake trout do not construct reds like most other salmonids, nor do they form single mating pairs. Spawning may involve several females laying their eggs into crevices in the rocks or spaces between the rocks. Several males may fertilize the eggs. The fish do not cover or care for the eggs. Females typically release 800-1800 eggs per kilogram of body weight. Egg incubation lasts for four to five months depending on temperature and oxygen levels. The eggs hatch between February and April, but the fry do not emerge from the rubble until their yolk sacs are absorbed a month later. The fry ascend to the surface to fill their swim bladders and then descend into cooler, deeper water where they remain for two to three years.

    Lake trout have few predators with the exception of man and the sea lamprey, which almost wiped out some Great Lakes stocks following the opening of the Welland Canal between Lake Ontario and Lake Erie in 1829. Lake trout eggs are eaten by other fish species, and often by lake trout themselves.

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Lake Trout Biology

Mack Days helps the ecological balance of Flathead Lake by thinning the mackinaw (also called lake trout) population. Anglers help manage the lake by harvesting over abundant lake trout. Learn about the biology below by clicking on the buttons.

  • Basic ID & Distribution

    Also called the Mackinaw Trout, the lake trout is found mostly in the Fort Peck area with some occurrence in the western part of the state.

    • Average Size: 14"-20"
    • Habitat: Deep, cold lakes and reservoirs.
    • Montana Record Catch: 42lbs 11.8 oz, 42.5" long & 31.5" around. Caught in Flathead Lake in 2004.
    Tail: Deeply forked (center rays less than half length of longest rays).
    Dorsal Fin: Without spots or sometimes with light-colored oval markings.
    Body: With white or cream-colored spots (never pink or red) on darker background.
    Appearance: Overall gray or nearly black/white coloration, sometimes with yellow tinge on fins.

  • Lake Trout Facts

    • Lake trout are "negatively phototropic"; they avoid light.
    • Lake trout may not spawn every year, and northerly stocks tend to have fewer spawning fish in any one year. They spawn at night.
    • Lake trout scales are unreliable for aging purposes. Researchers determine age by reading otoliths. The oldest fish on record, taken in the Northwest Territories, was aged at 65 years.

  • Natural History

    Lake trout inhabit deep, clear, rocky lakes with preferred temperatures of about 10°C (50°F) and oxygen levels of six to twelve milligrams per liter. Lake trout have an upper lethal temperature of about 23.5°C (74.3°F). Lake trout also feed on aquatic insects, crustaceans, and smaller fish such as minnows, lake whitefish, yellow perch, alewives (gaspereau), and rainbow smelt. In large lakes with many fish species, lake trout are typically piscivorous. Lake trout are fall spawners and normally reproduce every second year from September to November in most parts of their range. Lake trout do not construct reds like most other salmonids, nor do they form single mating pairs. Spawning may involve several females laying their eggs into crevices in the rocks or spaces between the rocks. Several males may fertilize the eggs. Lake trout have few predators with the exception of man.

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