1. Great Lakes Res. 21 (Supplement 1):348-363
Internat. Assoc. Great Lakes Res., 1995
Review of Genetics of Lake Trout in the Great Lakes: History, Molecular
Genetics, Physiology, Strain Comparisons, and Restoration Management
Charles C. Krueger! and Peter E. Ihssen2
I College
of Agriculture and Life Sciences, Department of Natural Resources
Fernow Hall, Cornell University, Ithaca, New York 14853
20ntario Ministry of Natural Resources
Fisheries Lab, Box 5000, Maple, Ontario L6A 1F9
ABSTRACT. This paper reviews historical differences among native lake trout (Salvelinus namaycush)
populations, genetic comparisons of populations, heritability of physiological traits, performance of
strains after stocking, and the role of genetics in management. Differences among lake trout were historically recognized by aborignal people, Jesuit missionaries, and French voyageurs, and later by naturalists
and biologists. Lean trout represented trout that typically spawned on shallow rocky shoals. Exceptions
included river spawning populations in Lake Superior and stocks reported to spawn over beds of algae in
Lakes Superior and Michigan. Sisco wets had high fat content, were caught in deep water, and likely
spawned year-round. Humpers resembled the siscowet but had thin ventral body walls, intermediate fat
content, and small size at maturity. The siscowet form and different stocks of lean trout were reported
from all the Great Lakes except Lake Ontario. Data from chromosomal banding, allozyme data, and
mitochondrial DNA analysis confirmed that genetic differences occur among the three forms. Genetic
data also provided evidence for distinctive populations within forms. Fat content, swimbladder gas retention, and developmental rates of eggs were different among some populations and appear to be heritable.
Differences among strains after stocking have occurred in survival, dispersal from stocking location,
depth distribution, and reproduction. Genetic considerations have been incorporated in species restoration plans but full use has not been made of available genetic information about lake trout. Reproductive
performance of different strains should be a central focus in the evaluation of stocking programs. In Lake
Superior, high priority should be given to the conservation of native stocks, the last remaining gene pools
of Great Lakes lake trout. Goals for management should embrace a vision that restoration is accomplished only when some level of diversity has been re-established. Achievement of restoration should
require the existence of naturally-reproducing, self-sustaining populations of different lake trout forms
that use a variety of habitats.
INDEX WORDS:
Lakes.
Siscowet, reproduction, stocking, mitochondrial DNA, genetics, lake trout, Great
INTRODUCTION
were absent from Lakes Ontario, Erie, Michigan, and most
of Lake Huron. Various inshore, shallow-water stocks of
lake trout in Lake Superior were greatly reduced in abundance or had also became extinct. Since then, fish management agencies have sought to rehabilitate lake trout in
the Great Lakes through sea lamprey control, regulation of
fishing, and stocking of different genetic strains of lake
trout. The rehabilitation effort has, as yet, only met with
limited success (e.g., Eshenroder et al. 1995).
Phenotypic characters such as body form and fin color
that helped distinguish the lake trout varieties reflected
variation from both genetic and environmental sources.
For some characters, genetics determines a high proportion of the phenotypic expression (e.g., the taxonomic
characters used to distinguish a species). For other charac-
Lake trout (Salvelinus namaycush) inhabited the Great
Lakes in a rich array of stocks that used a variety of habitats from rivers to the deepest waters, and varied in shape,
color, and fat content. The diversity of lake trout was recognized first by the aborignal people and the earliest European explorers, and later by naturalists who described it
as representing discrete, genetically different populations
and species (Brown et al. 1981, Goodier 1981). Heavy
exploitation of the stocks in the late 1800s and early
1900s caused noticeable declines in abundance that were
followed by mass extinctions of the stocks after the
predaceous, non-native sea lamprey (Petromyzon
marinus) invaded the four upper lakes between 1920 and
1950 (e.g., Holey et al. 1995). By 1960, native lake trout
348
Review of Lake Trout Genetics
ters like growth, the environmental variables of temperature and food abundance can be more important than genetics. The environment shapes the phenotypic expression
of the genetic character of an individual or population.
The historical reports of genetic diversity among lake
trout forms assumed a high reritability of the phenotypic
characters used to distinguish stocks. Unfortunately, direct
genetic comparisons of native lake trout populations to
confirm these early views were impossible because modern genetic techniques such as allozyme electrophoresis
(e.g., Bouck and Ball 1968, Wuntch and Goldberg 1970,
Clayton and Ihssen 1980) were not developed until well
after most stocks were extinct. Therefore, the original genetic diversity of lake trout in the Great Lakes can be inferred only from historical observations or from genetic
analysis of the native stocks that remain in Lake Superior.
Lake trout and the congeneric brook trout (S. fontinalis) and Arctic char (S. alpinus) are sympatric char
species that occur across northern North America. The
lake trout exhibits morphological and meristic characteristics that over time have led to its placement taxonomically in the genus Cristivorner separate from the other
chars in Salvelinus, in a subgenus Cristivorner within
Salvelinus, and as a species of Salvelinus (e.g., Morton
and Miller 1954, Vladykov 1954, Behnke 1980). Artificially produced hybrids between lake trout and either
brook trout or Arctic char are known to be fertile (Ayles
1974, Chevassus 1979, Berst et al. 1980). No natural hybrids have been reported for lake x brook trout (Behnke
1980); however, individuals identified as lake trout x
Arctic char hybrids were recently reported from northern
Labrador (Hammar et al. 1989) and Northwest Territories in Canada (Wilson and Hebert 1993). Lake trout
have 84 chromosomes (Wahl 1960) with the second
largest chromosome pair as the sex chromosome and
with an X-Y sex determining mechanism (Phillips and
Ihssen 1985a). The high fertility of lake trout hybrids is
probably due to their similarity in chromosome number
to brook trout (2N = 84, e.g., Wright 1955) and Arctic
char (2N = 80, e.g., Svardson 1945). The lake trout is endemic to North America where the southern edge of its
range approximates the southern extent of the most recent glaciation and the northern part of its range includes
Alaska, the Canadian Arctic coast, and Ungava and
Labrador to the east (Lindsey 1964). The range overlaps
in the south with the brook trout and in the north with
Arctic char (Scott and Crossman 1973). Lake trout and
brook trout originally coexisted in the Great Lakes. Remnant stocks of "coaster" brook trout are still found in
Lake Superior in some of the same waters as lake trout.
The purpose of this paper is to review historical evidence for differences among native Great Lakes populations, genetic studies that compare populations, the
heritability of physiological traits, the performance and
behavior of strains after stocking, and the role of genetics in recent lake trout management.
349
HISTORICAL EVIDENCE
FOR STOCK DIFFERENCES
Early recorded observations of lake trout in northeastern North America often ascribed species status to lake
trout of different regions, and sometimes to trout in individual lakes, based on differences in morphology and
coloration presumed to reflect large genetic differences.
For example, lake trout forms were described from different regions as follows: the togue (Salrno torna) occurred in the northeastern US and eastern Canada, the
black lunge (Salrno confinis) and silver lunge (Salrno narnaychus) were both noted from Lake Memphremagog of
Vermont and Quebec and the Brompton Lakes area of
southern Quebec, Salrno confinis and Salrno adirondakus
were reported to occur in lakes of New York, Pennsylvania, and adjoining Canadian waters, Salrno syrnrnetrica
occurred in Lakes Winnipissiogee and Monadnock in
New Hampshire, Salrno narnaycush was described as the
Mackinaw trout of the Great Lakes, and the fat trout
caught in the deep waters of the Great Lakes was noted
as Salrno siscowet (Hallock 1877, Goode 1884, Goode
1887, Scott 1875, Suckley 1874). As more biological information was gathered, observations focused on differences in spawning time that could reflect reproductive
isolation among groups; these differences were usually
denoted as racial distinctions rather than those of specific
or subspecific status. For example, Royce (1951) describes two "races" of lake trout in the Finger Lakes of
New York, one in Seneca Lake that spawns in late September and October and a second that was widespread
and spawns in shallow water later in the fall about when
lakes become homiothermal (fall turnover).
The Great Lakes, with a diversity of semi-isolated
spawning habitats from offshore shoals to rivers, yielded
a diversity of lake trout forms or varieties. Differences
among lake trout from various areas of the lakes were
not only recognized by naturalists (e.g., Jordan and Evermann 1911, Cook 1929, Koelz 1926) but much earlier by
aborignal people, Jesuit missionaries (Jesuit Relations
1670-71 by Goodier 1981), and French voyageurs (Roosevelt 1865). Two to four general forms of lake trout
were recognized from the Great Lakes based on fat content, morphology, location caught, and spawning condition and timing. Lean trout or Mackinaws, as they were
sometimes called, spawned in shallow water and had less
fat than other forms. In contrast, siscowets (also known
as fats) were the fattest and most oily of all forms and
were caught in deep offshore water, usually> 100 m.
Half-breeds, noted only from Lake Superior, appeared as
an intergrade between leans and sisco wets but resembled
siscowets morphologically and ecologically (Khan and
Qadri 1970). Humpers or paperbellies, also only noted
from Lake Superior, resembled the siscowet in appearance but had thin ventral body walls and small size at
maturity. Other forms have been described such as the
small salmon trout or bay trout that was found almost entirely in Green Bay of Lake Michigan but is now extinct
Krueger and Ihssen
350
(Brown et al. 1981). Different varieties of each form
were often recognized by commercial fishermen and naturalists. Comprehensive reviews by Goodier (1981) and
Brown et al. (1981) provide indirect descriptive evidence
from early naturalists and from interviews with former
fisherman that support the historical occurrence of separate stocks of lake trout in Lakes Superior and Michigan.
Below is a brief summary of the historical evidence for
stock diversity of lean, humper, and siscowet, and their
distribution in Lakes Huron, Erie, and Ontario. Halfbreed lake trout are not discussed because of a lack of
specific information about them and their lack of taxonomic distinctiveness (Khan and Qadri 1970). The purpose of this section is to describe the historical evidence
for genetic diversity in lake trout that existed in the
Great Lakes. The populations that contained this genetic
diversity are now extinct except in Lake Superior and at
two locations in eastern Lake Huron.
Lean Lake Trout
The occurrence of varieties of lean trout, especially in
the upper Great Lakes, was recognized by residents,
early naturalists, and later by biologists (e.g., Koelz
1926). French residents from the areas around Lakes
Huron and Superior identified three forms of lake trout
(in addition to siscowet) known as Truite des Battures trout of the rocky shallows, Truite des Greve - trout of
the muddy shoals, and Truite du Large - trout of the deep
open waters (Herbert 1851). Lean varieties in Canadian
waters later were referred to based on their most distinctive feature and included names such as blacks, redfins,
yellowfins, grays, salmon trout, moss trout, sand trout,
and racers (Goodier 1981). Two types of lean trout were
recognized by commercial fisherman along Wisconsin's
shoreline of Lake Superior, the Mackinaw (or red fin)
and the bank trout (Coberly and Horrall 1980). Lean varieties of lake trout in Lake Michigan were identified by
fishermen as Mackinaw, Beaver Island, redfin or reef,
yellowfin, moss, and shoal trout (Brown et al. 1981).
Just before their extinction in the 1950s, river spawning
populations were documented in six Lake Superior rivers
along the Canadian shoreline (Loftus 1957), although no
mention was made of river spawning populations in the
other Great Lakes. River spawning trout in Lake Superior were capable of ascending steep rapids such as in the
Dog River, Ontario and were observed to return to the
same river in successive spawning seasons. Areas of
rocky cobble without organic materials characterize most
descriptions of lake trout spawning substrate. Most unusual were the reports of some stocks of lake trout that
spawned over beds of filamentous algae in Lakes Superior and Michigan. In Lake Superior, certain stocks of
grays, and less frequently yellowfins, were reported to
spawn over algae beds at Prince Bay, north of Caribou
Island in Thunder Bay, and north of Pic Island (Goodier
1981). In Lake Michigan, moss trout were noted in
Grand Traverse Bay (Organ et al. 1978). Recently,
spawning by a naturalized population of Great Lakes origin on macrophyte beds (Chara delicatula) in deepwater
(40-60 m) was recorded in Lake Tahoe, Nevada
(Beauchamp et al. 1992).
Rumpers
No mention of different varieties or stocks of humper
trout in Lake Superior was found in the historical literature reviewed for this paper. This form of lake trout was
also referred to by fishermen as humpies, bankers, and
paperbellies. Isolated offshore reefs surrounded by water
deeper than 90 m served as the fishing grounds for this
lake trout (Rahrer 1965). Though apparently not exhibiting morphological differences among reefs, separate
stocks probably occurred due to their isolation by deep
water and distance from inshore stocks and from humper
stocks on other reefs. For example, humper trout from
different banks near Caribou Island in Michigan waters
exhibited significantly different growth rates (Patriarche
and Peck 1970). Humpers occurred on all the banks between Caribou and Michipicoten islands and were especially abundant on the northernmost bank of Superior
Shoal (Goodier 1981). They were also known from the
offshore waters around Isle Royale (Eschmeyer 1955). In
a study of morphometric and meristic variation, humpers
were clearly separated from leans and siscowets, but
Khan and Qadri (1970) were hesitant to assign this form
sub specific status until more was known of its biology
and distribution. Humpers mature at a smaller size than
is typical of the other lake trout forms (leans> 600 mm)
and begin spawning in August and September. In collections from Isle Royale, humper males as small as 323 mm
were mature and 100% of both sexes were mature at 485
mm (Rahrer 1965). The fat content of humpers has been
reported as intermediate between that of leans and siscowet, and also distinguishes humpers from other forms
(Eschmeyer and Phillips 1965).
Siscowet
The siscowet, fat lake trout most often caught in deep
water, was recognized by early inhabitants of the region as
being clearly different from the lean trout typically caught
in shallow water. Agassiz (1850) provided the original description in the literature of the siscowet; however, Roosevelt (1865) notes that aborignal people and French
Voyageurs had always distinguished the siscowet as separate from other lake trout. In addition, Nute (1926) reports
that correspondence from the American Fur Company in
1839 recognized differences between siscowet and lean
trout. "Siscowet" is derived from the Ojibway word that
means "cooks itself' (Goode 1887), in reference to this
fish's high fat content. The fat content of siscowet is a
characteristic mentioned in virtually every reference that
discusses siscowet. Siscowet trout were typically fished in
water from 90 m to 300 m deep (Eddy and Surber 1943,
Eschmeyer and Phillips 1965). The siscowet has been rec-
Review of Lake Trout Genetics
ognized taxonomically as a separate species (Agassiz
1850, Herbert 1851, Suckley 1874, Scott 1875, Hallock
1877, Garman 1884, Jordan and Evermann 1937), as a
subspecies of lake trout S. n. siscawet (Jordan and Gilbert
1882; Goode 1887; Evermann and Goldsborough 1907;
Nash 1908; Jordan and Evermann 1911; Greene 1935;
Hubbs and Lagler 1947, 1949), and sometimes simply as a
variety of lake trout (Jordan 1882, Wright 1892, Scott and
Crossman 1973). Khan and Qadri (1970) compared morphometric and meristic variation among lean, half breeds,
siscowet, and humper trout and concluded that only siscowet should be considered for subspecific status separate
from leans. Recently, two osteological characters, the dorsal opercular notch and radii on the anterodorsal part of
the supraethmoid, have been shown to be different between lean and siscowet trout (Burnham-Curtis and Smith
1994). As with the other forms of lake trout, different
stocks or varieties of siscowet seem possible. Sweeny
(1890) mentions that two varieties of siscowet occur but
possibly his second type was the humper or bank trout.
Around the waters of Isle Royale in Lake Superior, black
and white siscowet varieties were fished, with the black
much larger than the white (Rakestraw 1968). Spawning
time has been noted to be over a much broader time period
than the fall-spawning leans and humpers. During the
1800s, ripe females were reported to be encountered by
fishermen at all times of the year (Goode 1887, Sweeny
1890). Ripe or spent fish were noted from the Isle Royale
area for a six month period June to November (Eschmeyer
1955). Recently, a nearly-ripe male and a female with
eggs running from the vent were collected in late April
from the Apostle Islands area along the south shore of
Lake Superior (Bronte 1993).
Distribution of Forms in the Great Lakes
Different stocks of lake trout have been reported from
all the Great Lakes except Lake Ontario. The greatest variety was recorded from Lake Superior where different
lean and siscowet stocks plus the humper trout occurred.
The variety was probably due to the diversity of habitats
and Lake Superior's large size as compared to the other
lakes (see review by Goodier 1981). Similarly in Lake
Michigan, a wide variety of lake trout including stocks
of leans and a siscowet-like form was recognized (see review by Brown et al. 1981).
In Lake Huron, the occurrence of different stocks of
leans as well as the siscowet is well documented. For example, two stocks of lean trout, the buckskin and race,
were recognized from the waters in the vicinity of Thunder Bay (Goode 1884). Later, the occurrences of two
types were described again from the same general area,
the first being the common Mackinaw trout and the second the shoal trout (U.S. Commission of Fish and Fisheries 1900). The shoal trout was smaller and had different
markings than the Mackinaw, and spawned in September
over cobble, boulder, and gravel bottom in 1-3 m of
water. Another type of lean trout, the black trout, was
351
known from Yankee Reef (then called Big Reef) and was
reported to spawn as late as December (Koelz 1926, Eshenroder et al. 1995). Other varieties sought by fishermen
were redfins, summer trout, and winter trout (Goodier
1981). Siscowet trout were reported to occur in Lake
Huron including Georgian Bay by several authors (Herbert 1851, Strang 1855, Smith 1894, Nash 1908, Jordan
and Evermann 1937, Eshenroder et al. 1995).
In Lake Erie, different lake trout types were reported
to exist in the trout habitat of the deeper eastern basin.
Herbert (1851) describes his personal examination of
lake trout from Lake Erie that were similar to the rocky
shallows and muddy shoals trout which he described
from the upper Great Lakes (see above). In addition, siscowet trout were reported to have occurred in La~e Erie
(Nash 1908, Jordan and Evermann 1937). The occurrence of different forms of lake trout in Lake Erie seems
surprising due to the small amount of lake trout habitat
available relative to that in the other Great Lakes.
In Lake Ontario, no clear documentation could be
found for the occurrence of different types or forms of
lake trout. Only Dymond (1928) inferred that races of
trout may occur in Lake Ontario based on the variation
of ova counts from females of identical weights. If different forms of lake trout occurred, their lack of documentation could be due to two reasons. First, the
abundance of Atlantic salmon (Salrna salar) through the
early 1800s and its cultural importance may have focused the attention of natural history observations away
from lake trout (see Webster 1980). Second, the extinction of various forms and varieties of lake trout may
have occurred much earlier than in the upper lakes and
prior to naturalist observations and the more regular reporting by agencies such as the U.S. Fish Commission.
Inshore waters used by the seine fishery for lake trout
and whitefish were reported to be depleted by 1860
(Koelz 1926). Thus, possibly some near-shore stocks of
lake trout were already extinct by this time. By 1885, the
lake trout fishery in U.S. waters was insignificant (Koelz
1926) and most of the stocks would have been extinct.
For example, commercial catch of lake trout in the U.S.
declined 94% between 1880 and 1892 and was presumed
to reflect a collapse in the populations (Smith 1894). As
a result, remaining inshore varieties of lake trout could
have been lost during the 1880s. In contrast, the various
forms of lake trout in the upper lakes were fished well
into the 1900s, and commercial fishermen who fished
then were still available for interviews and could recall
the original stock diversity (Brown et al. 1981, Goodier
1981). We believe it is likely that varieties of lean trout
occurred with the siscowet in Lake Ontario in view of
their distribution throughout the rest of the Great Lakes.
CYTOGENETIC AND MOLECULAR GENETIC
DIFFERENCES AMONG STOCKS
The relative contribution of genetic differences and environmental variation to the existence of the lake trout
352
Krueger and Ihssen
morphotypes described above can not be determined
based on the historical reports. Qualitative characteristics
such as fin color and body shape as well as morphometric
measurements and meristic counts can have important
components of their expression determined by environmental variables such as water color, water temperature,
and food type and abundance (e.g., Barlow 1961). Thus,
such characteristics can be misleading as to the levels of
genetic differences that they reflect among the varieties of
lake trout. Genetic techniques such as allozyme electrophoresis yield data that reflect a more purely genetic
basis for comparisons of lean, siscowet, and humper trout.
Three methods, chromosomal banding, allozyme electrophoresis, and mitochondrial DNA analysis, have been
applied to compare lake trout populations in Lake Superior and the hatchery stocks used to restock the Great
Lakes. The data from these techniques have provided clear
evidence of popUlation differentiation among Lake Superior popUlations but not at the sub-specific or specific levels. Newer techniques such as ribosomal DNA (e.g.,
Phillips et al. 1992, Popodi et al. 1985) and microsatellite
nuclear DNA analysis (e.g., Phillips and Pleyte 1991, Estoup et at. 1993), which have not yet been used for such
comparisons, may provide further elucidation of the genetic relationships among various lake trout forms.
Some of the genetic techniques described below have
been used to compare different strains of lake trout that
have been propagated in hatcheries. However, no uniformity currently exists in the use of strain names in studies. The names, particularly for three strains, could be
confused and are described below. The Superior strain
refers to a widely distributed strain from a broodstock
originally propagated at the Marquette State Fish Hatchery with origins from lake trout collected near Marquette, Michigan on the south shore of Lake Superior
(Krueger et al. 1983). Other authors sometimes refer to
the Superior strain as the Marquette strain. The Jenny
strain refers to lake trout with origins from lake trout in
either Jenny or Lewis lakes, Wyoming. These fish were
naturalized from stockings before 1900 of trout from
northern Lake Michigan and are sometimes referred to as
the Wyoming or Lewis strain (Krueger et al. 1983). The
Seneca strain has its origins from an early autumn
spawning population in Seneca Lake, New York and is
sometimes referred to as the Finger Lakes strain.
Chromosomal Banding
Staining of lake trout chromosomes with quinacrine hydrochloride (Q-band) and chromomycin A3 yielded banding polymorphisms that distinguished lake trout from
various Great Lakes sources. Q-band and chromomycin
A3 polymorphisms were first reported in lake trout by
Phillips and Zajicek (1982) and Phillips and Ihssen
(1985b). Later these polymorphisms were shown to be
heritable in lake trout (Phillips and Ihssen 1986, Phillips et
al. 1989b). A combination of wild and hatchery populations from the Great Lakes region (probably all were lean
trout forms) was compared with both staining methods
(Phillips et al. 1989b). Based on the number of chromomycin A3 bands, three groups of trout were distinguished: first, a group from the northern shores of Lakes
Superior and Huron and inland lakes north of Lake Superior; second, a group from the southern shore of Lake Superior; and third, a group composed of two samples from
popUlations derived from stockings of Lake Michigan lake
trout. This study provided evidence that genetically different populations of lake trout existed in the Great Lakes.
Allozyme Variation
Allelic variation at loci that encode allozymes has been
used in several studies to compare wild populations in
Lake Superior and the hatchery sources of fish used to restock the Great Lakes. Banding patterns on starch gels
stained for specific proteins have been shown through inheritance studies of lake trout to be the expression of
genes that encode the proteins (May et al. 1979, 1980;
Hollister et al. 1984; Marsden et al. 1987). Based on data
from an analysis of 50 loci of which six were polymorphic, few significant differences were detected among
samples of lean trout from offshore areas spanning the
length of Lake Superior (Caribou Island, Stannard Rock,
Isle Royale, Dehring et al. 1981). Unfortunately, in this
study the collections were all made in the spring, many
months before spawning aggregations of lean trout develop and therefore the samples may have represented
mixtures of several populations. In the same study,
humpers at the three locations and siscowets at Caribou Island and Stannard Rock exhibited highly significant differences between the two forms and among humper
collections from different locations (P > 0.01 level). Fixation for alternate alleles did not occur among any forms
which could warrant taxonomic classifications at the
species level.
In another study, lean lake trout from Lake Superior
were sampled from five areas during the fall spawning
season and analyzed for variation at 28 allozyme loci, 17
of which were polymorphic (Ihssen et al. 1988). Four of
the five stocks had significantly different allelic frequencies at several loci. Two of the samples were not different and were of fish from spawning shoals in close
proximity (- 25 km apart). Additionally, this study compared allelic variation among collections of fish that
were from naturalized populations established from
stockings of trout from Lake Superior and Lake Michigan. In most cases, these transplanted populations were
similar to a general grouping of Lake Superior origin
samples and appeared to have retained their Great Lakes
genetic identity. Lake trout from other sources (Seneca,
Jenny, and Superior strains and Clearwater Lake Manitoba and Hill's Lake Ontario) also were analyzed and
typically showed high levels of differentiation from the
Lake Superior collections. Seven wild and two hatchery
samples in this study were from the same sources as
those used in the chromosomal banding study by Phillips
Review of Lake Trout Genetics
et al. (l989b). The genetic relationships exhibited among
these samples were similar between the two data sources.
Allozyme variation at 102 loci, 18 of which were
polymorphic, were analyzed in 14 collections from the
various hatchery sources of lake trout used for stocking
or proposed to be stocked in Lake Ontario and in one
sample each of lean and siscowet trout from the southshore Apostle Islands region of Lake Superior (Krueger
et al. 1989). Highly significant differences were observed between lean and siscowet trout from Lake Superior (P > 0.01); no fixed allelic differences were
observed between the two forms. This result supported
those of Dehring et al. (1981) that siscowet trout were
genetically distinct from lean trout as populations but not
as separate species. Allelic frequencies of the siscowet
trout from Lake Superior most resembled the hatcheryorigin Jenny strain fish also analyzed in this study. Historical reports about the origin of this strain suggest that
siscowet lake trout from northern Lake Michigan may
have been used to establish this strain in Jenny and
Lewis lakes in Wyoming (Krueger et al. 1983, Smith and
Snell 1891). Analysis of the other sources of lake trout
used for stocking or proposed to be stocked into Lake
Ontario indicated that the Seneca strain and lake trout
with origins from the Adirondacks region of New York
and Clearwater Lake Manitoba were considerably different from other Great Lakes lake trout-generally in
agreement with the results of Ihssen et al. (1988).
Mitochondrial DNA
Mitochondrial DNA (mtDNA) restriction site polymorphisms have provided another genetic character to
identify distinct populations of lake trout. Different from
allozyme characters that demonstrate biparental inheritance, mtDNA haplotypes are maternally inherited. The
resolution capability of mtDNA comparisons of populations appears to be enhanced by the rapid evolutionary
rate of mtDNA, estimated for some vertebrates to be six
to ten times the rate of the nuclear genome (Brown et al.
1979). A survey of mtDNA variation of one wild Lake
Superior popUlation and seven hatchery populations
based on 18 restriction enzymes resolved 13 mitochondrial clones which were organized into three haplotype
groups (Grewe and Herbert 1988). Sample sizes were
typically small « 15 trout per collection) but frequencies
of haplotypes revealed a geo,,",),raPhic distribution based
on the origins of the sample:: a western Great Lakes
group, a central Great Lakes group, and an eastern Great
Lakes group. This pattern roughly corresponded to the
grouping identified by chromosomal banding and allozymes (Phillips et al. 1989b, Ihssen et al. 1988). A
more intensive study of mtDNA variation was conducted
that compared collections of ~ 80 individuals per collection from each of the six lake trout strains stocked into
Lake Ontario (Grewe et al. 1993). Of the strains surveyed, five had origins in the Great Lakes basin: Killala
(Lake Superior drainage), Manitou (from Lake Manitou,
353
Manitoulin Island in Lake Huron), Jenny, Seneca, and
Superior. The other collection analyzed was the Clearwater strain from Clearwater Lake in northern Manitoba.
Four restriction enzymes Aval, BamHI, HinjI, and Taql
resolved seven mtDNA haplotypes. Frequencies of these
haplotypes were significantly different among the six
strains (P < 0.001); however, fixation for a unique haplotype did not occur in any strain. Differences between
haplotype frequencies of the Killala and Superior strains
permitted greater discrimination of these strains than allozyme data from Krueger et al. (1989).
Ribosomal DNA
Preliminary studies of ribosomal DNA (rDNA) variation in lake trout have not yielded genetic markers useful
for comparison of populations. Variation in the chromosomal location of the nuclear organizer regions (NORs)
has been observed in different populations of lake trout
(Phillips et al. 1989a). NORs are specific chromosomal
sites at which the rDNA is clustered in tandem arrays of
repeated units. Population specific rDNA variants have
been found in many organisms (e.g., Gerbi 1985).
Phillips (1990) used 24 restriction enzymes on 24 lake
trout from five stocks (Gull Island Shoal Lake Superior,
Lake Manitou, and the Seneca, Superior, and Jenny
strains) which exhibited variation in the intergenic
spacer (lGS) region of the rDNA. High levels of interindividual variation were observed and was later
shown to be due to variation in the number of repeating
units within the IGS (Zhuo 1991). This variation has potential for use in DNA fingerprinting of lake trout for
studies to determine the parental contribution of individuals to a year class such as in a hatchery. However, the
high level of variation, with almost every fish being
unique, makes it difficult to apply the methodology to
studies of popUlation differentiation. Variation in the sequence of the transcribed spacer region (ITS) of rDNA
was investigated recently to identify potential stock specific markers (Zhuo et al. 1994). Only minimal sequence
variation among individuals from five lake trout sources
(Seneca, Superior, Jenny, Gull Island Shoal, and Haliburton Lakes Ontario) was found. For 12 individuals
from four populations only one intraindividual polymorphism was found and it occurred in each population. No
interindividual sequence variation for the first internal
transcribed spacer region (ITS-I) was found among 10
individuals from five populations. The future challenge
is to find variation at a level between these highly conserved sequences and the hypervariable IGS length polymorphisms that can be used to distinguish populations.
HERITABILITY OF
PHYSIOLOGICAL CHARACTERISTICS
Several physiological characteristics of lake trout such
as fat content have been discovered to be heritable and
different among populations. Genetically different lake
Krueger and lhssen
354
trout populations must exhibit a level of reproductive isolation, and therefore may also serve as repositories for
specialized adaptive traits important to the survival of the
populations. Genetic differences observed among populations based on allozyme or mtDNA variation can rarely
be associated directly with physiological attributes essential to the survival and distribution of popUlations. Understanding the genetic basis for physiological
characteristics can help explain the functional significance of different lake trout populations in use of available niche space for the species. The sections below
review those studies that have examined the heritability
of various traits in lake trout and made comparisons
among populations.
Fat or Oil Content
Fat content differences between siscowet and lean lake
trout forms in several of the Great Lakes were obvious to
early explorers and naturalists and were thought to represent genetic differences; however, measurement of these
differences have only recently occurred. Siscowet lake
trout from Lake Superior have been shown to have oil
content as high as 64.2% (Karrick et al. 1956, Stansby
1962). In a comparison of fillets from 23 lean and 29 siscowet trout from Lake Superior, average oil content was
9.4% for leans and 48.5% for siscowet (Thurston 1962).
In a more detailed study, Eschmeyer and Phillips (1965)
demonstrated that % fat (dry weight) of flesh from the
mid-dorsal region in siscowets ranged from 32.5 to
88.8% and in leans from 6.6 to 52.3%. Fat content was
positively correlated to total length and explained much
of the individual variation in fat content. At a given
length, siscowets were always fatter than lean trout.
Twelve humper trout were also analyzed and were intermediate in fat content between leans and siscowets. Heritability of fat content was examined by rearing leans,
siscowets, and lean x siscowet hybrids under nearly identical hatchery conditions. Siscowets always had greater
fat content at a given length, lean trout were lowest, and
the hybrids were usually intermediate (three fish overlapped the fat content of leans). Given these results, fat
content appears to be a heritable trait distinctive for lean,
sisco wet, and humper lake trout in Lake Superior.
Swim bladder Gas Retention
Ability to retain gas in the swimbladder has been
shown to be heritable and associated with the ability to
live in deep water. As capability increases to retain gas,
the ability to maintain neutral buoyancy under the high
hydrostatic pressure of deep water improves. Tait (1959)
determined that for seven species of salmonids, relative
ability to keep the swimbladder filled was correlated
with depth distribution in their normal habitat. Lake trout
were found to have the best retention and brown trout
(Salrno trutta) the poorest. Heritability of swimbladder
gas retention was investigated by Ihssen and Tait (1974)
in lake trout propagated from gametes collected from
fish in Lakes Simcoe and Louisa in southern Ontario and
reared under identical hatchery conditions. Gas retention
was better in trout from Lake Simcoe than in those from
Lake Louisa and thus their abilities to maintain depths
should also be different. Crosses between the two populations were intermediate. Heritability (h 2 ) of this trait
was estimated as 0.58 ± 0.04. The two lakes were different in their limnology-the summer thermocline was
much deeper in Lake Simcoe than in Lake Louisa. The
lOOC isotherms in July were at 20 m in Simcoe and 8 m
in Louisa. Correspondingly, lake trout distribution in the
summer was reported to be much deeper in Simcoe (2535 m) than in Louisa (10-20 m) which corresponded to
their differences in gas retention abilities. Lake Simcoe
lake trout appeared better adapted for a deeper depth distribution than Lake Louisa fish.
Blue-Sac Disease
Blue-sac disease, the abnormal accumulation of bluish
fluid in the yolksac of egg and sac fry stages of lake
trout, has been known by fish culturists since the late
1800s (Wolf 1956). This condition has been observed in
fry from the natural spawning of hatchery-origin lake
trout on Stony Island Reef in Lake Ontario during the
late 1980s and early 1990s (D. L. Perkins, Cornell University, personal communication 1993). The heritability
of the disease was investigated in 80 experimental families of lake trout. The variability in the occurrence of the
disease was partitioned as 55% due to environmental
sources, and 16% due to males, 27% due to females, and
2% due to male x female interactions (lhssen 1978). Heritability of the disease was further confirmed in the
splake hybrid (S. fontinalis x S. narnaycush) and was estimated as 0.74. Symula et al. (1990) found that mortality from the disease in lake trout propagated from
Seneca-strain hatchery-origin adults and captured in
Lake Ontario ranged from 7 to 48%.
Eye Lens Defects
Occlusions of the eye lens, known as cataracts, have
been regularly observed in hatchery lake trout and the
impaired vision presumed to affect growth and survival
after stocking. Causes of cataracts can be dietary deficiencies, mechanical trauma, gas supersaturation, ultraviolet light, and genotype. Four strains of yearling lake
trout, the Superior, Seneca, Jenny, and "Ontario" (reared
from gametes collected from hatchery-origin fish in Lake
Ontario) strains, were reared under identical conditions
and evaluated for the presence of cataracts before stocking (Kincaid and Elrod 1991). In two year classes examined, the Superior strain consistently had a lower
frequency of cataract (6.7-7.3%) when compared to the
Seneca (35-51%), Jenny (46%), and Ontario (32%).
These data indicated that strains have different genetic
predispositions to develop cataracts.
355
Review of Lake Trout Genetics
Early Developmental Rates
Developmental rates of fertilized eggs and fry of lake
trout populations may vary to control the timing of emergence so as to correspond with the spring thermal regime
for optimal survival of juveniles. Horns (1985) compared
the degree days required to hatch and emergence among
lake trout propagated from four populations: wild Apostle Islands Lake Superior, the Superior strain, Green
Lake (hatchery population of Lake Michigan origin), and
Trout Lake (wild population in a northern Wisconsin
lake). Trout Lake and Apostle Island fish were significantly different from each other in hatching and emergence (P > 0.005); Trout Lake fish hatched and emerged
first and Apostle Islands fish hatched and emerged last.
Hatching timing and emergence were not different between the two Lake Superior origin populations or between the Green Lake and Trout Lake fish. The most
likely explanation for the differences observed was that
developmental rates have a genetic basis.
Maturation
Timing differences in gamete ripening among hatchery
lake trout strains would reduce the potential for crosses
between strains stocked in the Great Lakes to occur naturally and could also affect the timing of egg deposition
with respect to optimal water and substrate quality for incubation. Adults of the Seneca, Superior, and Jenny
hatchery strains were held under similar light and temperature conditions for two years, and gamete ripening
times and concentrations of seven hormones in plasma
were compared (Foster et ai. 1993). No differences
among strains occurred in ovulation, spermiation onset
date, or in most hormonal levels. The lack of pronounced
interstrain differences in gamete ripening dates and reproductive endocrinology suggested nothing that would
provide temporal reproductive isolation of the strains. In
contrast, genetic differences among lake trout stocks
from the Great Lakes and Ontario inland lakes for age of
maturity have been deduced from full- and half-sib matings under controlled hatchery conditions (Ihssen, P. E.,
unpublished data). For example, 36% of male lake trout
with origins from Lake Louisa matured at age 3 whereas
only 4% of trout from Lake Opeongo matured. Crosses
between the two stocks were intermediate at 19%.
COMPARISON OF
STRAINS AFTER STOCKING
Evaluation of the performance and behavior of hatchery-raised lake trout strains after stocking can help to
identify those strains that will best achieve the goals of
management. For population re-establishment to occur in
the Great Lakes, stocked lake trout must first survive and
grow to maturity. At maturity, hatchery-origin lake trout
must locate spawning grounds, and spawn and deposit
eggs in substrates that will successfully incubate eggs
until they hatch and fry emerge. Effective use of available niche space for survival, growth, and reproduction
will be dependent on the dispersal of trout from stocking
locations and their depth distribution in the lake. Comparisons of strains in terms of performance and behavior
after stocking are reviewed below.
Survival
Few studies in the Great Lakes have been conducted
that compare survival and growth of lake trout strains
after stocking. Valid comparisons of survival have been
difficult to conduct because of confounding variables
such as suspected differential vulnerability of strains to
assessment gear used in the Great Lakes. In nine lakes of
the Adirondack region of northeastern New York, approximately 200,000 fish each of the Seneca (from
southcentral New York) and Upper Saranac Lake (from
the Adirondack region) strains were stocked from 1964
to 1968 (Plosila 1977). Relative survival for all lakes
combined was 15.9 to I in favor of the Upper Saranac
Lake strain of Adirondack origin. In this case, the local
native strain out performed the non-native strain. In a
similar comparison in four northern Minnesota lakes, a
local, native strain survived better after stocking than either a hatchery-propagated lean strain with origins in a
population near Isle Royale in Lake Superior or the Superior strain (Siesennop 1992).
Comparison of growth and survival of three lake trout
strains from a single stocking in a refuge in northern
Lake Michigan yielded no significant differences among
strains (Rybicki 1990). From 220,000 to 240,000 yearlings each of the Superior and Jenny strains, and an outcross between females of the Superior strain and males
from the Apostle Islands area of Lake Superior were
stocked in 1986 and later evaluated as 4-year-olds. No
significant differences were found in the relative survival
rate and growth.
An important source of mortality in the Great Lakes
has been sea lamprey (Petromyzon marinus) predation.
Coexistence of lake trout with sea lampreys in two of the
Finger Lakes of New York (Seneca and Cayuga lakes)
has led to the speculation that the Seneca strain may be
better adapted to a fish community that contains the sea
lamprey than lake trout elsewhere (Ihssen 1984). If so,
stocking of more Seneca strain could enhance survival of
lake trout in the Great Lakes. Under laboratory conditions this hypothesis has not proven to be true. In
aquaria, no significant difference was found in the survival of adult Superior and Seneca strains subjected to
single sea lamprey attacks (Swink and Hanson 1986).
However, survival of matched annual plants since 1985
of the Superior and Seneca strains in northern Lake
Huron waters and at the centrally located Six Fathom
Bank has been greatly different (Eshenroder et ai. 1995).
The Jenny strain, added later to stocking at Six Fathom
Bank, was also compared. In northern waters, the Seneca
strain was 43.4 times more abundant than the Superior
Krueger and Ihssen
356
strain. Better survival was associated with lower sea
lamprey attack rates on the Seneca strain than were observed on the Superior strain. Similarly, lake-wide recoveries of Seneca strain trout> 632 mm that had been
stocked earlier on Six Fathom Bank were 4.6 times
greater than the Superior strain and 3.0 times more than
the Jenny strain.
Dispersal and Depth Distribution
Behavior of lake trout as reflected by dispersal from
stocking locations and depth distribution after stocking
has been shown to vary due to strain. In Lake Ontario,
dispersal of the Superior, Seneca, and Clearwater strains
after stocking was investigated from 1980-1985 at 16 locations for up to 26 months after stocking (Elrod 1987).
Rates of dispersal for the Clearwater fish were similar to
those of the Superior strain at four south-shore stocking
sites; however, dispersal was less for Clearwater fish
stocked at sites in the eastern basin. Dispersal of the
Seneca strain (only stocked in the eastern basin) was
similar to that of the Superior strain. In another study,
Rybicki (1990) found that straying of the three stocked
strains out of the northern Lake Michigan refuge (described above) was not different among strains (1215%). Differences in seasonal bathythermal distribution
have been shown among the Superior, Seneca, and
Clearwater strains stocked in Lake Ontario (Elrod and
Schneider 1987). The mean depth of capture ranged from
3.9 to 10.2 m greater for age-2 Superior strain fish than
for age-2 Clearwater fish. The distribution of Seneca fish
was similar to that of the Superior strain. Bathythermal
distribution observed was probably related to the ability
of strains to retain swimbladder gas. The inheritance of
lake trout behavior has only been studied in terms of
comparisons to other char species such as brook trout
(e.g., Ferguson and Noakes 1982, Ferguson et al. 1983).
Reproduction
To estimate the reproductive success of hatchery
strains requires assessment by year class of the number
and proportion of young produced by each hatchery
strain or combination of hatchery strains. The comparison of reproductive success among strains requires identification of the parents of naturally produced young.
Young fish lack markers other than genes that can be
used to identify their strain origins. Genetic markers
(e.g., allozymes or mtDNA) can be used to identify the
parental origins of young lake trout when baseline data
on the genetic characteristics of the hatchery strains have
been obtained. Mixed stock analysis of such genetic data
can then provide the most probable composition of a
sample of fry in terms of pure-strain and inter-strain
crosses (MSA, Utter and Ryman 1993). Baseline data for
the lake trout strains stocked into Lake Ontario have
been developed for both allozymes (Krueger et al. 1989)
and mtDNA (Grewe et al. 1993).
The first estimate of the reproductive success of
hatchery strains in Lake Ontario came from a collection
of 75 fry from Stony Island Reef in 1986 (Marsden et al.
1989). Lake trout fry were estimated to have been produced predominately by Seneca x Seneca strain matings
(78%) and Seneca x Superior crosses (20%). Total contribution to the fry sample by the Seneca strain was estimated as 88%. These estimates were in marked contrast
to the proportions stocked in the lake which were mostly
Manitou, Clearwater, and Superior strains; the Seneca
strain comprised only 6% of the lake trout stocked in the
area of Stony Island.
In the late 1980s, two additional strains (Jenny and
Killala) matured and could have contributed to the origins of naturally-produced fry in Lake Ontario. As a result, mtDNA data were used in combination with
allozyme data to better distinguish the large number of
potential pure strain and inter-strain crosses possible in
fry collections (Grewe et al. 1994b). Parental strain origins of fry collections from Stony Island in 1988, 1989,
and 1990 were on average 75% Seneca (range 67.386.5%), 12.9% Killa1a (range 7.1 to 14.9 %), and 10.8%
Superior (range 3.6 to 15.9 %) based on MSA. The
parental contributions of the fry did not match the strain
proportions stocked in the lake. Based on stocking
records, the proportion of Seneca strain that should have
reproduced if all strains survived and spawned equally
varied between 6% and 35%. The Seneca strain consistently contributed more to the naturally produced fry at
Stony Island Reef than would have been predicted from
numbers stocked.
The reproductive success of strains in Lake Ontario
was investigated at four spawning sites in eastern and at
four sites in western Lake Ontario. Fertilized eggs were
collected from six spawning locations around the lake in
the fall of 1992, reared to the fry stage, and then e1ectrophoretically analyzed (Perkins et al. 1995). Fry were
also captured from Stony Island Reef in 1991, 1992, and
1993 and similarly analyzed. These data were combined
with those from eggs collected from Yorkshire Bar reported by Grewe et al. (1994b). MSA of the collections
revealed that at three out of four eastern basin locations
the Seneca strain contributed from 73 to 95% to the fertilized eggs or fry. At the fourth location, the Manitou
(43%) and Superior/Killala (43%, baseline data for the
two strains were combined) contributed the most. In the
western basin at three out of four spawning areas, the
Seneca and Superior/Killala strains each contributed between 33-48% to the fertilized eggs. At a fourth area, the
Seneca strain was absent and most parental contributions
were from the Clearwater, Manitou, and Superior/Killala
strains. The prevalence of the Seneca strain at most
spawning areas and the departure of strain contributions
from predicted levels based on numbers stocked indicated
that, on a lake-wide basis, the Seneca strain was probably
better suited for reproduction in Lake Ontario than the
Review of Lake Trout Genetics
Superior/Killala strains, although all strains demonstrated
the ability to fertilize eggs at certain locations.
ROLE OF GENETICS IN RECENT
LAKE TROUT MANAGEMENT
Genetic considerations have been incorporated into
the lake trout rehabilitation strategies of fish management plans developed in the 1980s for the Great Lakes.
The use of genetics in these plans can be traced to the
recognition on the Pacific West Coast that discrete
spawning stocks of salmon occurred and that often they
possessed special traits important for their survival
(Ricker 1972). This idea became known as the stock
concept. Recognition of the importance of the stock concept and its application to lake trout management in the
Great Lakes was provided by Loftus (1976). He identified that the former lake trout stocks probably contained
genetically-encoded traits required for survival and reproduction in the Great Lakes. Their extinction therefore
was a potential obstacle to successful rehabilitation because the appropriate genetic diversity contained in these
fish could not be reintroduced. In 1980, the Stock Concept International Conference examined evidence for
separate stocks of Great Lakes fishes and identified potential applications of the stock concept to fish management (Billingsley 1981). The conference and its
proceedings, served as a catalyst during the 1980s for the
incorporation of the stock concept into Great Lakes fish
management.
In Lake Ontario, lake trout management strategies
were implemented to introduce a diversity of strains and
to develop a "Lake Ontario strain" through collections of
gametes from hatchery-origin adults that had survived to
maturity in the lake (Schneider et al. 1983). The Superior, Seneca, Clearwater, Jenny, Manitou, and Killala
strains were subsequently stocked and evaluated. The genetic stability of four year classes of the Seneca strain
used for stocking was compared through allozyme and
mtDNA analysis and found to generally show low variability (Grewe et al. 1994a). The purpose of developing
the "Lake Ontario strain" was to take advantage of the
forces of selection in Lake Ontario to establish a new
brood stock by the use of gametes from mature lake trout
that had survived for several years in the lake. The developers hoped that progeny from the brood stock would
show enhanced survival, and have a reproductive advantage over other strains. Three year classes of wild fry
from Stony Island Reef and six year classes of "Lake
Ontario strain" developed from adults captured adjacent
to the same reef were compared based on allelic frequencies of allozymes and MSA (Marsden et al. 1993). Wild
fry and the "Lake Ontario strain fish" were genetically
dissimilar. Survival and even aggregation adjacent to a
spawning reef by strains did not necessarily indicate that
they would successfully reproduce. Wild fry captured
from reef areas were recommended as a better source of
fish to develop the "Lake Ontario strain" than gametes of
357
hatchery-origin adults. The Lake Erie Lake Trout Rehabilitation Plan follows strategies similar to those for the
Lake Ontario plan (Lake Trout Task Group 1985).
In Lake Michigan, genetic considerations were incorporated into lake trout management plans developed for
a reef in Illinois (Coberly and Horrall 1982) and for lakewide management (Krueger et al. 1983, Lake Michigan
Lake Trout Technical Committee 1985). A variety of
lake trout strains was chosen for lake-wide introduction
into either deep or shallow water habitats. Two strains
were identified as desirable for stocking deep-water
habitats, the Seneca and Green Lake strains. The Seneca
strain was developed from a deep-water, early-fall
spawning population from Seneca Lake (Royce 1951).
The Green Lake hatchery strain, was originally derived
from a population in Green Lake, Wisconsin (Hacker
1956). The Green Lake population was maintained from
1886-1944 by stocking juveniles propagated from gametes of deep-water, southern Lake Michigan lake trout
(Krueger et al. 1983). Because of the extinction of lake
trout in Lake Michigan, the Green Lake strain represented one of the last genetic sources of Lake Michigan
origin trout. Unfortunately at the time of implementation
of the Lake Michigan plan, few fish of the Green Lake
strain remained as a hatchery strain. Brood-stock age
fish, however, were available in southern Lake Michigan
that were survivors from past plants made in middle
1970s and were identifiable by their fin-clip. Both the
remnant brood stock and Green Lake strain fish in southern Lake Michigan, therefore, were used when the reconstruction of the Green Lake stock was begun. Three
Green Lake strain year classes were developed in the
mid-1980s from feral fish captured from southern Lake
Michigan and their allozyme allelic frequencies were
compared to domestic progeny from the remnant brood
stock (Kincaid et al. 1993). The year classes from feral
parents were similar to each other but differed from the
domestic year class. A modified diallel mating design
was developed and implemented to produce a composite
brood stock from the remnant and feral sources.
Like that for Lake Michigan, the lake-wide management plan for the rehabilitation of lake trout in Lake
Huron established various zones in the lake that correspond to different habitats and rehabilitation priorities
(Argyle et al. 1991). To establish populations in these
zones, different strains with a variety of traits will be
necessary if historic spawning sites are to be re-populated. No explicit mention was made in the plan of which
strains will be used to stock different areas although,
upon implementation, the Superior, Jenny, and Seneca
strains were stocked (Eshenroder et al. 1995). The lakewide Lake Huron plan identifies that studies are needed
on the reproductive success. The mention of the evaluation of reproductive success, and not just the survival of
strains, was unique among the Great Lakes plans. Lake
Huron has two small remnant native populations, one in
McGregor Bay in the North Channel and another in
Krueger and lhssen
358
Parry Sound in Georgian Bay. Though no mention was
made in the lake-wide plan as to special management
considerations for these native populations (Argyle et al.
1991), their conservation, rehabilitation, and potential
use for reintroduction elsewhere in Lake Huron has been
described in the Ontario Ministry of Natural Resource's
(1995) plan for lake trout rehabilitation of Ontario's waters. The provincial plan also describes the proposed introduction of two Lake Superior stocks, Slate Island and
Michipicoten Island, into areas of Lake Huron where native stocks do not occur.
The management plan for lake trout in Lake Superior
identifies the stocking of hatchery fish propagated from
wild Lake Superior strains as an important strategy to
achieve rehabilitation (Busiahn et al. 1986). Lake Superior is unique in that many native off-shore stocks and a
few near-shore populations still exist. No management
considerations were given in the plan for the management of humper or siscowet lake trout or for the importance of special management of near-shore, remnant
native lean populations. Recently, management agencies
have agreed on fish community objectives for the lake
(Busiahn 1990). Unfortunately, considering the diversity
of stocks that remain, only brief mention was given to
the importance of the reestablishment and conservation
of native stocks.
CONCLUSIONS
Originally, the Great Lakes were the home to a wide
diversity of lake trout stocks, capable of using an extensive variety of habitats. Lake trout spawned on remote
offshore reefs and shoals, near-shore reefs, and tributary
streams, and at other times were capable of feeding and
growing in all depths of waters (> 300 m). Stock radiation of lake trout into these habitats was likely unrestrained after glaciation due to the scarcity of other
ecologically similar species. The diversity observed historically, and believed to have a genetic basis, was only
partly confirmed by modern genetic analysis because
stocks had become virtually extinct in the lower four
Great Lakes and reduced in number in Lake Superior by
the time these techniques were developed. Clear genetic
differences were observed among the lean, siscowet, and
humper forms from Lake Superior but these differences
reflected the levels of differentiation observed among
populations rather than among species as early naturalists thought. Distinguishing phenotypic traits of the
stocks such as fat content and depth distribution were
shown to have a heritable basis.
Closer attention to genetic considerations in lake trout
management will accelerate progress toward population
rehabilitation in the Great Lakes. Current management
has initiated an important first step of employing genetic
strategies in management actions, but full use of available genetic information about lake trout has not occurred. For example, the suspected poor performance of
the Clearwater strain in Lake Ontario was predictable
based on Ihssen and Tait's (1974) studies more than
twenty years ago on the retention of swimbladder gas
and its relationship to depth distribution. The Clearwater
strain originated from a shallow water population in
Clearwater Lake in northern Manitoba (approximately
54°N, 101 OW) where summer warming of waters does
not require a deep depth distribution (July-August summer thermocline from 9 to 24 m (personal communication, Doug Leroux, Department of Natural Resources,
Province of Manitoba). This strain was then introduced
into Lake Ontario at the southern edge of the species distribution of lake trout (43°30'N, 78°W). The summer
thermocline in the eastern basin of Lake Ontario regularly occurs at depths of 40 m. Not surprisingly, the bathythermal distribution of the Clearwater strain lake trout
was shallower than other strains stocked (Elrod and
Schneider 1987). Because of their shallower distribution,
they probably suffered greater angling mortality because
of the ease of fishing them in shallow waters. This strain
has shown little reproductive potential to produce fry
based on genetic analysis and MSA of naturally fertilized eggs and fry captured in Lake Ontario (Marsden et
al. 1989, Grewe et al. 1994b, Perkins et al. 1995).
Choice of lake trout strains for stocking should use
genetic sources from Great Lakes basin populations
combined with an environmental matching approach
where the original habitat of the strain to be stocked
should be similar to the waters to be rehabilitated
(Krueger et al. 1981, Ihssen 1984). Implementation of
this approach should make use of the native lean,
humper, and siscowet stocks of Lake Superior. For example, deep water habitats should be stocked with siscowet, the native deep water trout still abundant in Lake
Superior. Naturalized populations that have been established by stocking of lake trout of Great Lakes origin
provide other genetic sources for introduction to the
Great Lakes (e.g., Jenny strain from Wyoming). Typically these populations were established from Lakes
Michigan and Huron and may provide the opportunity to
reintroduce lake trout of a genetic character that has become extinct from these lakes. For example, the naturalized population in Lake Tahoe that spawns on vegetation
in deep water should be considered as a genetic source
for reintroduction into Lakes Michigan and Huron. This
population was established before 1900 through stocking
of fish reared from eggs of lake trout collected from the
Great Lakes. The first possible source of introduction to
Lake Tahoe was a shipment of eggs to Nevada in 1885
by the United States Fish Commission; however, their
distribution in Nevada was not reported (Smith 1896).
These eggs were collected by the Commission from
northern Lake Michigan (probably the Beaver Island
area) through the port of Thompson, Michigan and from
the island shoals of Thunder Bay, Lake Huron through
the port of Alpena, Michigan (U.S. Commission of Fish
and Fisheries 1887). The first confirmed stocking of lake
trout young in Lake Tahoe occurred in 1889. Collections
Review of Lake Trout Genetics
of eggs in the fall of 1888 that served as the source for
these fish were primarily from lake trout in northern
Lake Michigan through the port of Thompson (U.S.
Commission of Fish and Fisheries 1892). From these introductions in the 1880s, lake trout in Lake Tahoe were
reported to be "multiplying" and weighing up to 5 kg by
1895 (Smith 1896). In 1895 and 1896, additional plants
of lake trout with origins from Lakes Michigan and
Huron occurred (U.S. Commission of Fish and Fisheries
1896, Smith 1896, Miller and Alcorn 1943). Since that
time, the lake trout population in Lake Tahoe may have
preserved some of the genetics of the original native lake
trout from northern Lake Michigan and Lake Huron.
The reproductive performance of lake trout strains
after stocking should be a central focus of the evaluation
of stocking programs when the goal of management is
population rehabilitation. Survival to maturity is an important characteristic required for reproduction but
should not be viewed as equivalent to reproductive potential. A strain having modest survival after stocking
relative to other strains could well contribute the most to
year-class recruitment through natural reproduction. In
rehabilitation programs, the foremost attribute for evaluation of strains after stocking is their contributions as
parents to the next generation. Only the Lake Huron plan
identified the reproduction of strains as an important aspect for evaluation (Argyleet al. 1991). The genetic
analysis of naturally produced trout from the spawning
of hatchery-origin adults combined with MSA (such as
has occurred in Lake Ontario) provides a methodology
for the reproductive evaluation of lake trout strains in the
Great Lakes.
Different genetic strategies of management will need
to be employed in Lake Superior than in the other Great
Lakes. Though reduced in number, many native stocks
remain in Lake Superior including the original lean,
humper, and siscowet forms. High priority should be
given to the conservation of these stocks, the largest remaining gene pools of Great Lakes lake trout. Unfortunately only brief mention of the importance of the
genetic diversity of lake trout (or other native species)
occurs in the Fish Community Objectives for Lake Superior recently established by the management agencies
(Busiahn 1990). Depressed stocks should be protected
from sea lamprey predation and overfishing and allowed
sufficient time for recovery. Population recovery can be
achieved, and has been documented for the south shore
stocks of Gull Island Reef (Swanson and Swedberg
1980) and Stannard Rock (Curtis 1990). Stocking of lake
trout flo supplement or increase the number of fish in a
nati4'e population can pose extinction risks to the native
stock and risks corruption of the native gene pool if nonnati ve sources are stocked (Evans and Wilcox 1991).
Such management actions must be avoided if native
stocks are to persist.
Goals and objectives for lake trout management of the
Great Lakes should explicitly embrace a vision that pop-
359
ulation rehabilitation is accomplished only when a level
of phenotypic diversity has been re-established. "Successful" rehabilitation should require the existence of
naturally-reproducing, self-sustaining populations of different lake trout forms that use a variety of habitats. Historically, a diversity of lake trout stocks occurred in the
Great Lakes; however, most attention in fish management has been given to the establishment of near-shore,
shallow-water-spawning lean trout (the one exception is
use in the deep waters of Lake Michigan of the Green
Lake and Seneca strains as described above). Emphasis
on phenotypic diversity as a strategy for management
could be as simple as giving consideration to rehabilitation of both shallow-water and deep-water habitats and
introducing the appropriate forms of lake trout. Establishment of near-shore lean trout stocks may be the most
difficult to accomplish due to their vulnerability to fishing, sea lamprey predation, effects of exotic species, and
habitat degradation. A diversified approach to lake trout
management provides the opportunity for achievement of
population rehabilitation in more than one habitat.
ACKNOWLEDGMENTS
Special thanks are given to Lisa Bishop-Oltz, Heidi
Kretser, and William Shepherd for assistance in assembling the literature reviewed. Edward H. Brown, Jf. and
David P. Philipp provided several helpful comments on
an earlier draft. This work was sponsored by the Great
Lakes Fishery Commission and by the New York State
College of Agriculture and Life Sciences, Cornell University, Hatch Projects 1476402 and 1477402.
REFERENCES
Agassiz, L. 1850. Fishes of Lake Superior. In Lake Superior:
Physical Character, Vegetation, and Animals, Compared
with those of Other and Similar Regions, pp. 332-336.
Boston, Mass.: Gould, Kendall and Lincoln.
Argyle, R., Bowen, c., Ebener, M., Johnson, J., Morse, T.,
Munroe, S., Payne, R., Weise, J., and Wright, G. 1991.
Lakewide management plan for lake trout rebabilitation in
Lake Huron. Lake Huron Committee, Great Lakes Fish.
Comm.
Ayles, G. B. 1974. Relative importance of additive genetic and
maternal sources of variation in early survival of young
splake hybrids (Salvelinus fontinalis x S. namaycush). J.
Fish. Res. Board Can. 31:1499-1502.
Barlow, G. W. 1961. Causes and significance of morphological
variation in fishes. Syst. Zool. 10: 105-117.
Beauchamp, D. A., Allen, B. C., Richards, R. c., Wurtsbaugh,
W. A., and Goldman, C. R. 1992. Lake trout spawning in
Lake Tahoe: egg incubation in deepwater macrophyte beds.
N. Am. J. Fish. Manage. 12:442-449.
Behnke, R. R. 1980. A systematic review of the genus Salvelinus. In Charrs: salmonid fishes of the genus Salvelinus, ed.
E. K. Balon, pp. 441-480. The Hague, Netherlands: Dr. W.
Junk bv Pub.
360
Krueger and Ihssen
Berst, A. H., Ihssen, P. E., Spangler, G. R., Ayles, G. B., and
Martin, G. W. 1980. The splake, a hybrid charr Salvelinus
namaycush x S. fontinalis. In Charrs: salmonid fishes of the
genus Salvelinus, ed. E. K. Balon, pp. 841-887. The Hague,
Netherlands: Dr. W. Junk bv Pub.
Billingsley, L. W., ed. 1981. Proceedings of the stock concept
international symposium. Can. J. Fish. Aquat. Sci.
38:1457-1921.
Bouck, G. R., and Ball, R. C. 1968. Comparative electrophoretic patterns of lactate dehydrogenase in three
species of trout. J. Fish. Res. Board Can. 25:1323-1331.
Bronte, C. R. 1993. Evidence of spring spawning lake trout in
Lake Superior. J. Great Lakes Res. 19:625-629.
Brown, E. H., Jr., Eck, G. W., Foster, N. R., Horrall, R. M.,
and Coberly, C. E. 1981. Historical evidence for discrete
stocks of lake trout (Salvelinus namaycush) in Lake Michigan. Can. J. Fish. Aquat. Sci. 38:1747-1758.
Brown, W. M., George, J. R., and Wilson, A. C. 1979. Rapid
evolution of animal _mitochondrial DNA. Proc. Nat. A cad.
Sci. USA 76:1967-1971.
Burnham-Curtis, M. K., and Smith, G. R. 1994. Osteological
evidence of genetic divergence of lake trout (Salvelinus
namaycush) in Lake Superior. Copeia 1994:843-850.
Busiahn, T. R., ed. 1990. Fish community objectives for Lake
Superior. Great Lakes Fish. Comm., Spec. Publ. 90-1.
_ _ _" Eger, W., Eshenroder, R., Hansen, M., MacCallum,
W., Pycha, R., Schorfhaar, R., Selgeby, J., Spurrier, J., and
Swanson, B. 1986. A lake trout rehabilitation plan for Lake
Superior. The Lake Superior Committee, Great Lakes Fish.
Comm.
Chevassus, B. 1979. Hybridization in salmonids: results and
perspectives. Aquaculture 17: 113-128.
Clayton, J. W., and Ihssen, P. E. 1980. Dehydrogenase
isozymes in Salvelinus: genetic and inter species phenotypic
comparisons. In Charrs: salmonid fishes of the genus
Salvelinus, ed. E. K. Balon, pp. 339-356. The Hague,
Netherlands: Dr. W. Junk bv Pub.
Coberly, C. E., and Horrall, R. M. 1980. Fish \pawning
grounds in Wisconsin waters of the Great Lakes. Marine
Studies Center, University of Wisconsin, Madison.
_ _ _ , and Horrall, R. M. 1982. A strategy for re-establishing self-sustaining lake trout stocks in Illinois waters of
Lake Michigan. Marine Studies Center, Univ. Wisc., Madison. Rep. No. 42.
Cook, W. A. 1929. A brief summary of work of the Bureau of
Fisheries in the Lake Superior region. Trans. Am. Fish. Soc.
59:56-62.
Curtis, G. L. 1990. Recovery of an offshore lake trout (Salvelinus namaycush) populations in eastern Lake Superior. J.
Great Lakes Res. 16:279-287.
Dehring, T. R., Brown, A. F., Daugherty, C. H., and Phelps, S.
R. 1981. Survey of the genetic variation among eastern
Lake Superior lake trout (Salvelinus namaycush). Can. J.
Fish. Aquat. Sci. 38: 1738-1746.
Dymond, J. R. 1928. Some factors affecting the production of
lake trout (Cristivomer namycush) in Lake Ontario. University of Toronto Studies, Biological Studies No. 31, Pub. Onto
Fish. Res. Lab. XXXlll.
Eddy, S., and Surber, T. 1943. Northern fishes. Minneapolis,
Minn.: University of Minnesota Press.
Elrod, J. H. 1987. Dispersal of three strains of hatchery-reared
lake trout in Lake Ontario. J. Great Lakes Res. 13:157-167.
_ _ _ , and Schneider, C. P. 1987. Seasonal bathythermal
distribution of juvenile lake trout in Lake Ontario. J. Great
Lakes Res. 13:121-134.
Eschmeyer, P. H. 1955. The reproduction of lake trout in
southern Lake Superior. Trans. Am. Fish. Soc. 84:47-74.
_ _ _, and Phillips, Jr., A. M. 1965. Fat content of the flesh
of siscowets and lake trout from Lake Superior. Trans. Am.
Fish. Soc. 94:62-74.
Eshenroder, R. L., Payne, N. R., Johnson, J. E., Bowen, C., II,
and Ebner, M. P. 1995. Lake trout rehabilitation in Lake
Huron. J. Great Lakes Res. 21(Supplement 1):108-127.
Estoup, A., Presa, P., Krieg, F., Vaiman, D., and Guyomard, R.
1993. (CT)n and (GT)n microsatellites a new class of genetic
markers for Salmo trutta L. (brown trout). Heredity
71 :488-496.
Evans, D.O., and Willox, C. C. 1991. Loss of exploited,
indigenous populations of lake trout, Salve linus namaycush,
by stocking of non-native stocks. Can. J. Fish. Aquat. Sci.
48(Suppl. 1):134-147.
Evermann, B. W., and Goldsborough, E. L. 1907. A checklist
of the freshwater fishes of Canada. Proc. BioI. Soc. Wash.
20:89-120.
Ferguson, M. M., and Noakes, D. L. G. 1982. Genetics of
social behaviour in charrs (Salvelinus species). Anim.
Behav. 30: 128-134.
_ _ _ , Noakes, D. L. G., and Romani, D. 1983. Restricted
behavioural plasticity of juvenile lake charr, Salvelinus
namaycush. Env. BioI. Fish. 8:151-156.
Foster, N. R., O'Connor, D. V., and Schreck, C. B. 1993.
Gamete ripening and hormonal correlates in three strains of
lake trout. Trans. Am. Fish. Soc. 122:252-267.
Garman, S. 1884. The American salmon and trout, including
introduced species. In Tenth Annual Report of the Commissioners on Inland fisheries, for the year ending January 1,
1876, pp. 61-81. Public Document No. 25. Boston,
Mass.:Wright & Potter State Printers.
Gerbi, S. A. 1985. Evolution of ribosomal DNA. In Molecular
evolutinary genetics, R. J. Macintyre (ed.). N.Y.: Plenum
Press.
Goode, G. B. 1884. The fisheries and fishery industries of the
U.S. Section 1. Natural history of useful aquatic animals.
U.S. Comm. Fish Fisheries. Washington, D.C.:Gov. Printing
Offc.
_ _ _ . 1887. The lake trouts. In American Fishes A Popular
Treatise Upon the Game and Food Fishes of North
America, pp. 462-468. Boston, Mass.:L. C. Page & Co.
Pub.
Goodier, J. L. 1981. Native lake trout (Salvelinus namaycush)
stocks in the Canadian water of Lake Superior prior to 1955.
Can. J. Fish. Aquat. Sci. 38:1724-l737.
Greene, C. W. 1935. The distribution of Wisconsin fishes.
Madison: State of Wisconsin Conserv. Comm.
Grewe, P. M., and Hebert, P. D. N. 1988. Mitochondrial DNA
Review of Lake Trout Genetics
diversity among broodstocks of the lake trout, Salvelinus
namaycush. Can. J. Fish. Aquat. Sci. 45:2114-2122.
_ _ _ , Krueger, C. C., Aquadro, C. F., Bermingham, E.,
Kincaid, H. L., and May, B. 1993. Mitochondrial DNA variation among lake trout (Salvelinus namaycush) strains
stocked into Lake Ontario. Can. J. Fish. Aquat. Sci.
50:2397-2403
_ _ _ , Krueger, C. C., Aquadro, C. F., and May, B. 1994a.
Stability of allozyme and mitochondrial DNA markers
among three year classes of lake trout propagated from
Seneca Lake, New York. N. Am. J. Fish. Manage. 14:
467--474.
_ _ _ , Krueger, C. C., Marsden, J. E., Aquadro, C. F., and
May, B. 1994b. Hatchery origins of naturally produced lake
trout fry captured in Lake Ontario: temporal and spatial
variability based on allozyme and mitochondrial DNA data.
Trans. Am. Fish. Soc. 123:309-320.
Hacker, V. A. 1956. Biology and management of lake trout in
Green Lake, Wisconsin. Trans. Am. Fish. Soc. 86:71-81.
Hallock, C. 1877. The sportsman's gazetteer and general
guide. New York: Forest and Stream Pub!. Co.
Hammar, J., Dempson, J. B., and Skold, E. 1989. Natural
hybridization between arctic char (Salvelinus alpinus) and
lake char (S. namaycush): evidence from northern Labrador.
Nordic J. Freshw. Res. 65:54-70.
Herbert, H. W. 1851. Frank Forester's fish and fishing of the
United States and British provinces of North America. New
York: Stringer & Townsend.
Holey, M. E., Rybicki, R. W., Eck, G. W., Brown Jr., E. H.,
Marsden, J. E., Lavis, D. S., Toneys, M. L., Trudeau, T. N.,
and Horrall, R. M. 1995. Progress toward lake trout restoration in Lake Michigan. J. Great Lakes Res. 21(Supplement
1): 128-151.
Hollister, A., Johnson, K. R., and Wright, J. E., Jr. 1984. Linkage associations in hybridized Salvelinus genomes. J.
Hered. 75:253-259.
Horns, W. H. 1985. Differences in early development among
lake trout (Salvelinus namaycush) populations. Can. J. Fish.
Aquat. Sci. 42:737-743
Hubbs, C. L., and Lagler, K. F. 1947. Fishes of the Great Lakes
region. Bloomfield Hills, Mich.: The Cranbrook Press.
_ _ _, and Lagler, K. F. 1949. Fishes of Isle Royale, Lake
Superior, Michigan. Pap. Mich. Acad. Sci. Arts Lettrs.
(1947) 33:73-133.
Ihssen, P. E. 1978. Inheritance of bluesac disease for hatchery
charr of the genus Salvelinus. Env. Bioi. Fish. 3:317-320.
_ _ _ . 1984. Genetics. In Strategies for Rehabilitation of
Lake Trout in the Great Lakes: Proceedings of a Conference on Lake Trout Research, August 1983, eds., R. L. Eshenroder, T. P. Poe, and C. H. Olver, pp. 15-21. Great Lakes
Fish. Comm. Tech. Rep. No. 40.
_ _ _ , and Tait, J. S. 1974. Genetic differences in retention
of swimbladder gas between two populations of lake trout
(Salve linus namaycush). J. Fish. Res. Board Can.
31: 1351-1354
_ _ _, Casselman, J. M., Martin, G. W., and Phillips, R. B.
1988. Biochemical genetic differentiation of lake trout
361
(Salvelinus namaycush) stocks of the Great Lakes region.
Can. J. Fish. Aquat. Sci. 45:1018-1029.
Jesuit Relations. 1670-71. Relation of the mission at Saint
Ignace at Missilimakinac v. 55. In Jesuit relations and
allied documents, R. G. Thwaites (ed.).
Jordan, D. L. 1882. Report on the fishes of Ohio. In Report of
the Geological Survey of Ohio, Volume IV, Zoology and
Botany, Part I., pp. 735-1002. Columbus, Ohio: Nevins &
Meyers, State Printers.
Jordan, D. S., and Evermann, B. W. 1911. A review of the
sal monoid fishes of the Great Lakes, with notes on the
whitefishes of other regions. Bull. U. S. Bur. Fish. 29:41p.
____, and Evermann, B. W. 1937. American Food and
Game Fishes. A Popular Account of all the Species Found
in America North of the Equator, with Keys or Ready Identification, Life Histories and Methods of Capture. Garden
City, NY: Doubleday, Doran & Company, Inc.
_ _ _ , and Gilbert, C. H. 1882. Synopsis of the fishes of
North America. U.S. National Museum Bull. 16. Washington: Government Printing Office.
Karrick, N., Clegg, W., and Stansby, M. E. 1956. Composition
of fresh-water fish - No. 1. Comm. Fish. Rev. 18: 13-16.
Khan, N. Y., and Qadri, S. U. 1970. Morphological differences
in Lake Superior lake char. J. Fish. Res. Board Can.
27:161-167.
Kincaid, H. L., and Elrod, J. H. 1991. Growth and survival of
stocked lake trout with nuclear cataracts in Lake Ontario. N.
Am. J. Fish. Manage. 11 :429--434.
_ _ _ , Krueger, C. c., and May, B. 1993. Preservation of
genetic variation in the Green Lake strain lake trout derived
from remnant domestic and feral populations. N. Am. J.
Fish. Manage. 13:318-325.
Koelz, W. 1926. Fishing industry of the Great Lakes. In Report
of the U.S. Commissioner of fisheries for 1925, pp.
554-616. Bureau of Fisheries Doc. No. 1001. Washington,
D.C.: Gov. Printing Offc.
Krueger, C. C., Gharrett, A. J., Dehring, T. R., and Allendor, F.
W. 1981. Genetic aspects of fisheries rehabilitation programs. Can. J. Fish. Aquat. Sci. 38:1877-1881.
_ _ _, HorraH, R. M., and Gruenthal, H. 1983. Strategy for
the use of lake trout strains in Lake Michigan. Wisc. Dept.
Nat. Res. Admin. Rep. 17.
_ _ _ , Marsden, J. E., Kincaid, H. L., and May, B. 1989.
Genetic differentiation among lake trout strains stocked in
Lake Ontario. Trans. Am. Fish. Soc. 118:317-330.
Lake Michigan Lake Trout Technical Committee. 1985. A
lakewide management plan for lake trout rehabilitation in
Lake Michigan. Lake Michigan Committee, Great Lakes
Fish. Comm.
Lake Trout Task Group of the Lake Erie Committee. 1985. A
strategic plan for the rehabilitation of lake trout in eastern
Lake Erie. Lake Erie Committee, Great Lakes Fish. 90mm.
Lindsey, C. C. 1964. Problems in zoogeography of the lake
trout, Salve linus namaycush. J. Fish. Res. Board Can.
21:977-994.
Loftus, K. H. 1957. Studies on river-spawning populations of
lake trout in eastern Lake Superior. Trans. Am. Fish. Soc.
87:259-277
362
Krueger and Ihssen
1976. Science for Canada's fisheries rehabilitation
needs. 1. Fish. Res. Board Can. 33:1822-1857.
Marsden, J. E., Krueger, C. C., Kincaid, H. L., and May, B.
1987. Inheritance of duplicated fumarase and phosphoglucomutase loci in lake trout (Salvelinus namaycush). Heredity 58:365-372.
_ _ _ , Krueger, C. C., and May, B. 1989. Identification of
parental origins of naturally produced lake trout in Lake
Ontario: application of mixed-stock analysis to a second
generation. N. Am. 1. Fish. Manage. 9:257-268.
_ _ _ , Krueger, C. C., Grewe, P. M., Kincaid, H. L., and
May, B. 1993. Genetic comparison of naturally spawned
and artificially propagated Lake Ontario lake trout fry: evaluation of a stocking strategy for species rehabilitation.
N. Am. 1. Fish. Manage. 13:304-317.
May, B., Wright, J. E., Jr., and Stoneking, M. 1979. Joint segregation of biochemical loci in Salmonidae: results from
experiments with Salve linus and review of the literature on
other species. 1. Fish. Res. Board Can. 36:1114-1128.
_ _ _ , Wright, J. E., Jr., and Stoneking, M. 1980. Joint segregation of biochemical loci in Salmonidae. II. Linkage
associations from a hybridized Salve linus genome (S.
namaycush x S.fontinalis). Genetics 95:707-726.
Miller, R. R., and Alcorn, J. R. 1943. The introduced fishes of
Nevada, with a history of their introduction. Trans. Am.
Fish. Soc. 73: 173-193.
Morton, W. M., and Miller, R. R. 1954. Systematic position of
the lake trout, Salvelinus namaycush. Copeia
1954:116-124.
Nash, C. W. 1908. Vertebrates of Ontario. The Legislative
Assembly of Ontario, Toronto, Canada.
Nute, G. L. 1926. The American fur company's fishing enterprises on Lake Superior. Miss. Valley Hist. Rev.
12:483-503.
Ontario Ministry of Natural Resources. 1995. Lake trout rehabilitation plan for the Ontario waters of Lake Huron. Lake
Huron Fisheries Management Unit 1994 Annual Report.
Organ, W. L., Towns, G. L., Walter, M. 0., Pelletier, R. B.,
and Riege, D. A. 1978. Past and presently known spawning
grounds of fishes in the Michigan coastal waters of the
Great Lakes. Unpublished manuscript, Aquatic Systems,
Inc., Ludington, MI.
Patriarche, M. H., and Peck, J. W. 1970. Lake trout fishery on
the Caribou Island grounds. Mich. Dept. Nat. Res., Res.
Dev. Rep. No. 207.
Perkins, D. L., Fitzsimons, J. D., Marsden, J. E., Krueger, C.
C., and May, B. 1995. Differences in reproduction among
hatchery strains of lake trout in eight spawning areas in
Lake Ontario: genetic evidence from mixed-stock analysis.
1. Great Lakes Res. 21(Supplement 1):364-374.
Phillips, R. B. 1990. Identification of lake trout stocks using
nuclear ribosomal DNA. Research Completion Report. Ann
Arbor: Great Lakes Fishery Commission
_ _ _, and Ihssen, P. E. 1985a. Identification of sex chromosomes in lake trout (Salvelinus namaycush). Cytogenet.
Cell Genet. 39: 14-18.
_ _ _ , and Ihssen, P. E. 1985b. Chromosome banding in
salmonid fishes: nucleolar organizer regions in Salmo and
Salvelinus. Can. 1. Genet. Cytol. 27:433-440.
_ _ _, and Ihssen, P. E. 1986. Inheritance of Q band chromosomal polymorphisms in lake trout. 1. Hered. 77:93-97.
_ _ _ , and Pleyte, K. A. 1991. Nuclear DNA and salmonid
phylogenetics. 1. Fish Bioi. 39 (Supple. A):259-275.
_ _ _" and Zajicek, K. D. 1982. Q band chromosomal banding polymorphisms in lake trout (Salvelinus namaycush).
Genetics 101 :222-234.
_ _ _, Van Ert, L. E., Pleyte, K. A., and Hartley, S. E.
1989a. Evolution of nucleolar organizer regions (NORs)
and ribosomal RNA genes in fishes of the genus Salvelinus.
In Biology of charrs and masu salmon, pp. 429--447. Physiology and Ecology Japan. Special Vol. 1.
_ _ _ , Zajicek, K. D., and Ihssen, P. E. 1989b. Population
differences in chromosome-banding polymorphisms in lake
trout. Trans. Am. Fish. Soc. 118:64-73.
_ _ _ , Pleyte, K. A., and Brown, M. R. 1992. Salmonid
phylogeny inferred from ribosomal DNA restriction maps.
Can. 1. Fish. Aquat. Sci. 49:2345-2353.
Plosila, D. S. 1977. Relationship of strain and size at stocking
to survival of lake trout in Adirondack Lakes. New York
Fish Game 1. 24: 1-24.
Popodi, E. M., Greve, D., Phillips, R. B., and Wejksnora, P. J.
1985. The ribosomal RNA genes of three salmonid species.
Biochemical Genetics 23:997-1010.
Rahrer, J. F. 1965. Age, growth, maturity, and fecundity of
"humper" lake trout, Isle Royale, Lake Superior. Trans. Am.
Fish. Soc. 94:75-83.
Rakestraw, L. 1968. Commercial fishing on Isle Royale. Isle
Royal Nat. Hist. Assoc., Michigan.
Ricker, W. E. 1972. Hereditary and environmental factors
affecting certain salmonid populations. In The stock concept
in Pacific salmon, pp. 19-160. H. R. MacMillan Lectures in
Fisheries. Vancouver, B.C.: Univ. Brit. Columbia.
Roosevelt, R. B. 1865. Superior Fishing; Or, The Striped Bass,
Trout, and Black Bass of the Northern States. New York,
New York: Carleton Pub.
Royce, W. F. 1951. Breeding habits of lake trout in New York.
Fish Bull 59, 52:59-76
Rybicki, R. W. 1990. Growth, survival, and straying of three
lake trout strains in the refuge of Northern Lake Michigan.
Mich. Dept. Nat. Res. Fish. Res. Rep. No. 1977.
Schneider, C. P., Kolenosky, D. P., and Goldthwaite, D. B.
1983. A joint plan for the rehabilitation of lake trout in
Lake Ontario. Lake Ontario Committee, Great Lakes Fish.
Comm.
Scott, G. C. 1875. Fishing in American Waters. New York,
New York: Harper & Brothers, Pub.
Scott, W. B., and Crossman, E. J. 1973. Freshwater fishes of
Canada. Bull. Fish. Res. Board Can. 184.
Siesennop, G. D. 1992. Survival, growth, sexual maturation, and
angler harvest of three lake trout strains in four northeastern
Minnesota lakes. Minn. Dept. Nat. Res. Invest. Rep. 419.
Smith, H. M. 1894. The fisheries of the Great Lakes. In Report
Review of Lake Trout Genetics
of the Commissioner for 1892, pp. 361-462. U.S. Comm.
Fish Fisheries, Part XVIII. Washington, D.C.: Gov. Printing
Offc.
_ _ _ _ . 1896. A review of the history and results of
the attempts to acclimatize fish and other water animals in
the Pacific states. Bull. U.S. Fish Comm. (for 1895)
15:379-472
_ _ _ , and Snell, M. -M. 1891. The fisheries of Lake Michigan. In Report of the Commissioner for 1887, eds. H. M.
Smith, M. -M. Snell, and J. W. Collins, pp. 71-204. U.S.
Comm. Fish Fisheries, Part XV. Washington, D.C.: Gov.
Printing Offc.
Stansby, M. E. 1962. Proximate composition of fish. In Fish in
Nutrition, eds. E. Heen and R. Kreuzer, pp. 55-60. London,
England: Fishing News (Books).
Strang, J. J. 1855. Some remarks on the natural history of
Beaver Islands, Michigan. In 9th Ann. Rep. Board Regents
Smithsonian Inst., pp. 282-288. Washington, D.C.: A. O. P.
Nicholson.
Suckley, G. 1874. On the North American species of salmon
and trout. In Rep. U. S. Comm. Fish. (1872-1873), pp.
151-152. Washington, D.C.: Gov. Printing Off.
Svardson, G. 1945. Chromosome studies of Salmonidae. Inst.
Fresh Water Res. Drottningholm (Sweden) 23: 1-151.
Swanson, B. L., and Swedberg, D. V. 1980. Decline and recovery of the Lake Superior Gull Island Reef lake trout
(Salvelinus namaycush) population and the role of sea lamprey (Petromyzon marinus) predation. Can. J. Fish. Aquat.
Sci. 37:2074-2080.
Sweeny, R. 0., Sr. 1890. The Siskiwit. Trans. Am. Fish. Soc.
19:84-86.
Swink, W. D., and Hanson, L. H. 1986. Survival from sea lamprey (Petromyzon marinus) predation by two strains of lake
trout (Salvelinus namaycush). Can. J. Fish. Aquat. Sci.
43:2528-2531.
Symula, J., Meade, J., Skea, J. C., Cummings, L., Colquhoun,
J. R., Dean, H. J., and Miccoli, J. 1990. Blue-sac disease in
Lake Ontario lake trout. J. Great Lakes Res. 16:41-52.
Tait, J. S. 1959. Swimbladder studies in salmonoids relating to
problems of depth. Ph. D. thesis. Univ. Toronto, Ontario.
Thurston, C. E. 1962. Physical characteristics and chemical
composition of two subspecies of lake trout. J. Fish. Res.
Board Can. 19:39-44.
363
U.S. Commission of Fish and Fisheries. 1887. Report of the
commissioner for 1885. Part XIII. Washington, D.C.: Gov.
Printing Offc.
____ . 1892. Report of the commissioner for 1888. Part
XVI. Washington, D.C.: Gov. Printing Offc.
_ _ _ . 1896. Report of the commissioner for the year ending
June 30, 1895. Part XXI. Washington, D.C.: Gov. Printing
Offc.
_ _ _ . 1900. A manual of fish-culture based on the methods
of the United States Commission of Fish and Fisheries, with
chapters on the cultivation of oysters and frogs. Revised
edition. Washington, D.C.: Gov. Printing Offc.
Utter, F., and Ryman, N. 1993. Genetic markers and mixed
stock fisheries. Fisheries (Bethesda) 18(8): 11-21.
Vladykov, V. D. 1954. Taxonomic characters of the eastern
North America chars (Salvelinus and Cristivomer). J. Fish.
Res. Board Can. 11 :904-932.
Wahl, R. W. 1960. Chromosome morphology in lake trout
Salvelinus namaycush. Copeia 1960:16-19.
Webster, D. A. 1980. Early history of the Atlantic salmon in
New York. N. Y. Fish Game J. 29:26-44.
Wilson, C. c., and Hebert, P. D. N. 1993. Natural hybridization
between Arctic char (Salvelinus alpinus) and lake trout (S.
namaycush) in the Canadian Arctic. Can. J. Fish. Aquat.
Sci. 50:2652-2658
Wolf, K. 1956. Experimental induction of blue-sac disease.
Trans. Am. Fish. Soc. 86:61-70.
Wright, J. E. 1955. Chromosome numbers in trout. The Prog.
Fish-Cult. 17:172-175.
Wright, R. 1892. Preliminary report on the fish and fisheries of
Ontario. In Commissioners' Rep. 1892, pp. 419-476.
Toronto: Ontario Game and Fish Comm.
Wuntch, T., and Goldberg, E. 1970. A comparative physicochemical characterization of lactate dehydrogenase:
Isozymes in brook trout, lake trout, and their hybrid splake
trout. J. Exp. Zool. 174:233-252.
Zhuo, L. 1991. Molecular cytogenetic analysis of ribosomal
DNA variants in lake trout (Salvelinus namaycush). Ph.D.
dissertation, Univ. Wisconsin - Milwaukee.
_ _ _ , L., Sajdak, S. L., and Phillips, R. B. 1994. Minimal
intraspecific variation in the sequence of the transcribed
spacer regions of the ribosomal DNA of lake trout (Salvelinus namaycush). Genome 37:664-671.