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Lake trout [lake char(r)] (Salvelinus namaycush) lllustration Timothy Knepp, photographer unknown, published by U.S. Fish and Wildlife Service. Common names in English Lake trout. American lake trout. Great Lakes trout. Grey trout. Lake char(r). Great Lakes char(r). Landlocked salmon. Mountain trout. Salmon trout. Mackinaw trout. Siscowet. Laker. Forktail trout. Namaycush. Togue. Touladi. … and in other languages Danish: Amerikansk søørred. Canadarødding. Finnish: Harmaanieriä. French: Cristivomer. Omble d’Amérique. Omble du Canada. Touladi. Truite de lac d’Amérique. Truite grise. German: Amerikanischer Seesaibling. Amerikanische Seeforelle. Icelandic: Murta. Inuit: Akalukpik, Col-lic-puk, Iclook, Idlorak, Ihok, IIuuraq, Ikalukpik, Ikhiloktok, Ikhlorak, Ilortoq, Iqluq, Ishioraliktâq, Islorak, Isok, Isuuq, Isuuqiaq, Isuuqiq, Isuuraaryuk, Isuuraq, Ivitaruk, Keyteeleek, Milaqkkâyoq, Naaqtuuq, Näluarryuk, Nauktoq, Sigguayaq, Siuktuuk, Siyuktuuq. Italian: Salmerino di lago. Norwegian: Canadarøye. Polish: Palia Jeziorowa. Portuguese: Truta-do-lago. Salvelino-lacustre. Russian: Severoamerikanskiy kristivomer. Spanish: Trucha lacustre. Swedish: Kanadaröding. Scientific name Salvelinus namaycush Organism group Ray-finned fishes (Actinopterygii). Salmons (Salmoniformes). Salmonids (Salmonidae). Size and appearance Salvelinus namaycush has an elongate body that varies in colour between seasons and populations. Males and females are quite similar, although the male has a somewhat longer, more pointed snout. The head and jaw are strikingly large. Lake trout may be light green or grey, through dark yellowish brown or olive green, to nearly black, marbled with a pike-like pattern of small white or creamy spots on the body and a light-coloured belly. In some waters they may be silvery overall, with no light spots. Unlike brook trout (Salvelinus fontinalis), lake trout do not have pink or red spots. In addition, they have a more deeply forked tail fin. The fins have a white leading edge, and in some waters the fins and belly may be orange in colour. During the spawning season, the male develops dark lateral bands and its back becomes paler. Lake trout can live to a considerable age – getting on for 20–30 and even 50 years – and grow very large. The age of onset of sexual maturity is very high, varying according to environmental conditions. This is the largest of the North American Salvelinus species. There are reports of a maximum length of as much as 150 cm and a record weight of over 46 kg. Usually, though, lake trout reach just over half a metre in length and a weight of 3–5 kg. May be confused with – Geographical origin North America, where it occurs over most of Canada (apart from the islands of Newfoundland, Prince Edward Island and the High Arctic archipelago) and much of the eastern United States. The lake trout is also found in Alaska and on Banks and Victoria Islands in Arctic Canada. In the western United States, however, it is an introduced species. More than any other species, lake trout is regarded as a symbol of sport fishing in northern Canada (“Canada’s premier game fish”), as it is so perfectly adapted to the cold, deep lakes of that region. Namaycush is a North American Indian name meaning “dwellers of the deep”. First observed in Swedish waters The species was introduced to Sweden in 1958 as a gift from the Ontario Department of Lands and Forests, Fish and Wildlife, which donated 20,000 eggs to the Swedish Board of Fisheries’ Institute of Freshwater Research. Young lake trout were stocked in many parts of Sweden in the early 1960s, chiefly in waters in the north regulated for hydroelectric schemes, but also in Lake Vänern, Lake Mälaren (Lilla Ullevifjärden) and the Baltic Sea (Bråviken). By 1972 the species had been stocked in 111 lakes in Sweden, but it has only become established in a small number of waters. Occurrence in Swedish seas and coastal areas Lake trout can venture briefly into brackish or salt waters along the coasts of cold seas, but is in fact the least salt-tolerant Salvelinus species. In 1979–80 a few individuals were caught off the Uppland coast. According to the Baltic Sea Alien Species Database, the species has been observed in the Gulf of Bothnia. (Lake trout may not be stocked in Swedish waters without a special permit.) Occurrence in other sea areas Salvelinus namaycush has been introduced into a great many countries, but it is not mentioned in UNESCO’s Fishes of the Northeastern Atlantic and the Mediterranean, which suggests that it is not regarded as widespread in the marine environment. Probable means of introduction Aquaculture: cultivation, and both intentional stocking and unplanned releases. Habitat(s) in which species occurs The lake trout is very much a coldwater fish, most commonly found in the clear, cold, well-oxygenated waters of large, deep northern lakes, particularly in mountain areas. It prefers a water temperature of around 10°C. The species is found in warmer waters too, but will not survive at water temperatures exceeding around 23°C. It can also live in shallower lakes and in rivers, but usually only in the northern parts of its range. In spring, after ice-out, lake trout are found in the upper layers of lakes, but gradually they retreat to greater depths in search of colder water. During the summer they live below the thermocline (the boundary layer between warmer surface water and colder bottom water). Lake trout are bottom-dwelling fish (18–53 m, reportedly even down to depths of over 200 m). As adult fish feed on young of their own species, juveniles move down to greater depths than adults. The species is able to live in disturbed environments such as hydroelectric reservoirs. It is rarely found in waters with a pH of less than 5.2, however, and is highly susceptible to pollution, especially from insecticides. Lake trout primarily feed on other species of fish, such as smelt (Osmerus eperlanus), vendace (Coregonus albula), Arctic char (Salvelinus alpinus) and other salmonids, perch (Perca fluviatilis), and the young of other fish (e.g. smolts of rainbow trout Oncorhynchus mykiss). Their diet also includes zooplankton, mysids, benthic crustaceans, insect larvae, snails, leeches and small bivalves. The species is even known to catch and eat small mammals, such as mice, and small birds. Some populations of lake trout live exclusively on plankton, but they grow more slowly and attain a smaller size, mature more quickly, and die sooner than those that feed on fish. Ecological effects Non-native salmonids that are stocked in Swedish waters may form hybrids with native species. Often these hybrids are fertile, which means that they are able to reproduce in the wild. This is true, for example, of “larctic char” (a cross between lake trout and Arctic char) and “splake” (lake trout and brook trout). The name splake comes from speckled trout + lake trout. This hybrid is also known as wendigo. The fact that larctic char, splake, and the third hybrid combination, “sparctic char” (also known as “sparctic trout” or “spar”, a cross between brook trout and Arctic char), are able to reproduce naturally shows that Salvelinus species may be involved in the active formation of new species. In discussions about the genetic effects of non-native species finding their way into Swedish waters, the focus has been very much on salmonids, since such fish are farmed and stocked on a large scale and, what is more, hatchery-reared fish quite often escape into the wild. In this context, “genetic effects” means changes in the genetic makeup of native species that can result from the incorporation of genes from the new organisms. The risks associated with introducing nonnative populations or genes into the natural environment come under three main headings: extinction, hybridization, and loss of genetic variation. When closely related species or distinct populations of a single species interbreed, hybridization can result. This can happen if individuals of a non-native species mate with individuals of a native one. The offspring exhibit characteristics differing, to a greater or lesser degree, from those of the native parent. In the long term, this may result in wild populations of a species losing some of their ability to adapt to their environment. Stocked fish, for example, are less well adapted to their new environment than the wild fish with which they mix. At worst, the introduction and spread of non-native populations or genes may drive native species to extinction. This may happen either because the native species is outcompeted and displaced, or because of genetic changes in the offspring (hybrid) of the alien and native species which mean that the offspring is unable to survive. If the hybrid is fertile, however, the next step may be an exchange of genes with the parent population. Non-native genetic material will then be incorporated into the native species, and in the long run the effect of this could be to eliminate local variants. Mixing of non-native species or genetic variants with local populations may have implications for Sweden’s populations of Arctic char, Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). Over time, native salmonid stocks have adapted to conditions in their particular lakes and rivers, gradually becoming genetically distinct from every other stock of the same species. The loss of such local adaptations may leave a population less well equipped to survive. Stocking of hatchery-reared fish can also lead to inbreeding depression. This occurs when closely related individuals mate with one another, and may result in offspring that are unviable or have difficulty surviving. Lake trout have been stocked in several regulated mountain lakes in Sweden, with the aim of replacing the brown trout eliminated by such interventions with a new species that preys on small whitefish (Coregonus spp.) or Arctic char populations. In Lake Ånnsjön in Jämtland, lake trout were introduced by accident, and now the wellestablished population of the species poses a major threat to the local stocks of Arctic char and brown trout. What is more, the lake has for a long time had an established population of brook trout. Other effects Lake trout are of very significant economic value as a food and game fish in North America. In Sweden, the economic value of introduced lake trout is probably limited to the species’ role as a substitute for brown trout as a predator on small whitefish in regulated mountain lakes. FIND OUT MORE • North European and Baltic Network on Invasive Alien Species: Salvelinus namaycush • Baltic Sea Alien Species Database: Salvelinus namaycush • ICES Working Group on Environmental Interactions of Mariculture • FishBase: Salvelinus namaycush • European Nature Information System Database (EUNIS): Salvelinus namaycush • Ittiofauna.org: Il Salmonidi (webbplats om bl.a. laxfiskar i Europa) • Alaska Department of Fish & Game: Lake trout • Nova Scotia Fisheries and Aquaculture: Lake trout • University of Toronto: Lake trout • Ontario Federation of Anglers and Hunters: Ontario's fish: Lake trout http://www.nobanis.org/speciesInfo.asp?taxaID=701 http://www.ku.lt/nemo/directory_details.php?sp_name=Salvelinus+namaycush http://www.ices.dk/iceswork/wgdetail.asp?wg=WGEIM http://www.fishbase.org/Summary/SpeciesSummary.php?id=248 http://eunis.eea.europa.eu/species-factsheet.jsp?idSpecies=9978&idSpeciesLink=9978 http://www.ittiofauna.org/webmuseum/pesciossei/salmoniformes/salmonidae/salmonidae.htm http://www.adfg.state.ak.us/pubs/notebook/fish/ltrout.php http://www.gov.ns.ca/nsaf/sportfishing/species/lktrout.shtml http://www.zoo.utoronto.ca/manuesteve/UTlaketrout.html http://www.ofah.org/fishing/description.cfm?Species=Cold_Water&FishID=22 • Canadian Sportfishing: Lake trout • U.S. Fish and Wildlife Service: Lake trout • • National Wildlife Foundation: Salvelinus namaycush http://www.enature.com/fieldguides/detail.asp?shapeID=994&curGroupID=3&lgfromWhere=&curPageNum=16 Mt. Baker-Snoqualmie National Forest Pacific Northwest Fisheries Program: Lake Trout • Wisconsin Sea Grant: Lake trout • US Geological Survey: NAS-Nonindigenous Aquatic Species: Salvelinus namaycush • Cornell University: Fishes of New York: Lake trout • NatureServe Explorer: Salvelinus namaycush • Trouts and Seasons of The Mountain Village: Salvelinus namaycush http://www.canadiansportfishing.com/Tips&Techniques/Species_Info/Default1.asp?Species_Name=LAKE%20TROUT http://www.fws.gov/midwest/Fisheries/topic-laketrout.htm http://www.fs.fed.us/r6/fishing/forests/fishresources/mtbsno_coldwater.html#lake http://www.seagrant.wisc.edu/greatlakesfish/laketrout.html http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=942 http://fish.dnr.cornell.edu/nyfish/Salmonidae/lake_trout.html http://www.natureserve.org/explorer/servlet/NatureServe?searchName=Salvelinus namaycush http://www.amago.jp.lv/trout/trout32.html Spake • US Geological Survey: NAS-Nonindigenous Aquatic Species: Salvelinus fontinalis x namaycush • Ontario Federation of Anglers and Hunters: Ontario's fish: Splake • State of Maine: Splake Fact Sheet • Wisconsin Department of Natural Resources: Lake Trout--Splake-"Coaster" Brook Trout comparison http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=940 http://www.ofah.org/fishing/description.cfm?Species=Cold_Water&FishID=24 http://www.state.me.us/ifw/fishing/fishidentification/splake.htm http://www.dnr.state.wi.us/org/gmu/superior/Fish/Fish ID.htm IMAGES CREDIT Illustration: Timothy Knepp Photographer: unknown Images are published under public domain by U.S. Fish and Wildlife Service, Digital Library Service: Lake trout http://images.fws.gov • • • This factsheet on Salvelinus namaycush was created on 30 November 2006 First update: 15 January 2007 Translated by Martin Naylor on 22 January 2007