由 Lake Trout
Lake trout (Salvelinus namaycush) is a freshwater char living mainly in lakes in northern North America. Other names for it include laker, mackinaw, lake char (or charr), touladi, togue, and grey trout. In Lake Superior, it can also be variously known as siscowet, paperbelly and lean. The lake trout is prized both as a game fish and as a food fish. From a zoogeographical perspective, lake trout are quite rare. They are native only to the northern parts of North America, principally Canada, but also Alaska and, to some extent, the northeastern United States. Lake trout have been widely introduced into non-native waters in North America and into many other parts of the world, mainly Europe, but also into South America and certain parts of Asia. Although lake trout were introduced into Yellowstone National Park's Shoshone, Lewis and Heart lakes legally in the 1890s, they were illegally or accidentally introduced into Yellowstone lake in the 1980s where they are now considered invasive.
Lake trout are the largest of the chars; the record weighed almost 46.3 kilograms (102 lb) (netted) with a length of 50 inches (130 cm), and 15– to 40-pound fish are not uncommon. The average length is 24–36 inches (61–91 centimetres). The largest caught on a rod and reel according to the IGFA was 72 pounds (33 kg), caught in Great Bear Lake in 1995 with a length of 59 inches. When hooked, especially the big ones will make a short run and just thump and twist and turn.
Lake trout inhabit cold, oxygen-rich waters. They are pelagic during the period of summer stratification in dimictic lakes, often living at depths of 20–60 m (66–197 ft).
The lake trout is a slow-growing fish, typical of oligotrophic waters. It is also very late to mature. Populations are extremely susceptible to overfishing. Many native lake trout populations have been severely damaged through the combined effects of hatchery stocking (planting) and over harvest.
Three subspecies of Lake Trout are accepted. There is the Common Lake Trout (Salvelinus namaycush namaycush), the Siscowet Lake Trout (Salvelinus namaycush siscowet), and the less common Rush Lake Trout (Salvelinus namaycush huronicus). Some lakes do not have pelagic forage fish during the period of summer stratification. In these lakes, lake trout take on a life history known as planktivory. Lake trout in planktivorous populations are highly abundant, grow very slowly and mature at relatively small sizes. In those lakes that do contain deep-water forage, lake trout become piscivorous. Piscivorous lake trout grow much more quickly, mature at a larger size and are less abundant. Notwithstanding differences in abundance, the density of biomass of lake trout is fairly consistent in similar lakes, regardless of whether the lake trout populations they contain are planktivorous or piscivorous.
In Lake Superior,Common Lake Trout (S. n. namaycush) and Siscowet Lake Trout (S. n. siscowet) live together. Common Lake Trout tend to stay in shallower waters, while Siscowet Lake Trout stay in deeper water. Common Lake Trout (also called "lean" Lake Trout) are slimmer than the relatively fat Siscowet Lake Trout. Siscowet numbers have become greatly depressed over the years due to a combination of the extirpation of some of the fish's deep water coregonine prey and to overexploitation. Siscowet tend to grow extremely large and fat and attracted great commercial interest in the last century. Their populations have rebounded since 1970, with one estimate putting the number in Lake Superior at 100 million.
