Download Salvelinus namaycush

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
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North European and Baltic Network on Invasive Alien Species: Salvelinus namaycush
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Baltic Sea Alien Species Database: Salvelinus namaycush
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ICES Working Group on Environmental Interactions of Mariculture
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FishBase: Salvelinus namaycush
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European Nature Information System Database (EUNIS): Salvelinus namaycush
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Ittiofauna.org: Il Salmonidi (webbplats om bl.a. laxfiskar i Europa)
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Alaska Department of Fish & Game: Lake trout
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Nova Scotia Fisheries and Aquaculture: Lake trout
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University of Toronto: Lake trout
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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
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Canadian Sportfishing: Lake trout
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U.S. Fish and Wildlife Service: Lake trout
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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
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Wisconsin Sea Grant: Lake trout
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US Geological Survey: NAS-Nonindigenous Aquatic Species: Salvelinus namaycush
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Cornell University: Fishes of New York: Lake trout
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NatureServe Explorer: Salvelinus namaycush
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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
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US Geological Survey: NAS-Nonindigenous Aquatic Species: Salvelinus fontinalis x namaycush
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Ontario Federation of Anglers and Hunters: Ontario's fish: Splake
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State of Maine: Splake Fact Sheet
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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
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This factsheet on Salvelinus namaycush was created on 30 November 2006
First update: 15 January 2007
Translated by Martin Naylor on 22 January 2007