Lake Trout Ecosystems in a Changing Environment - Chapter 3 doc

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chapter three
Rehabilitation of lake trout
in the Great Lakes: past lessons
and future challenges
Charles C. Krueger
Great Lakes Fishery Commission
Mark Ebener
Great Lakes Fishery Commission
Contents
The lake trout fishery and its management: 1800–1950s
Rehabilitation management: 1950s to present
Causes for the slow recovery
Status of rehabilitation
Lake Superior
Lake Huron
Lake Michigan
Lake Erie
Lake Ontario
New management approaches
Pulse stocking
Creation of spawning areas
Transplantation of adults
Management lessons and future challenges
Conclusion
Acknowledgments
References
Lake trout Salvelinus namaycush, before colonization by European peoples, were native to
each of the five Great Lakes, occurring throughout Lake Superior, Lake Michigan, Lake
Huron, and Lake Ontario, and in the eastern basin of Lake Erie. Life history characteristics
of Great Lakes populations span the range for the species. For example, spawning typically

occurs in the fall, but some populations may spawn as early as August (Hansen et al.,
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1995) or even in the spring (Bronte, 1993). Age at first maturity is also highly variable
across the lakes. For some shallow-water populations in Lake Superior, age at first maturity
can be as late as age 9 or beyond, and some individuals may not spawn every year (e.g.,
Rahrer, 1967; Swanson and Swedburg, 1980). This maturity schedule is comparable to
those of some populations from Precambrian Shield lakes (Martin and Olver, 1980) or
northern Arctic lakes. On the other extreme, lake trout in lakes Erie and Ontario at the
southern edge of their native range mature at age 3, and all fish are mature at age 5 or 6
(Cornelius et al., 1995; Elrod et al., 1995). These life history differences can dramatically
affect the speed with which populations respond to management actions such as fishery
regulations and stocking.
The native lake trout of the Great Lakes used a diversity of semiisolated spawning
habitats from shallow near-shore reefs to deep offshore shoals to rivers, and this habitat
diversity yielded a variety of lake trout forms. Aboriginal peoples, Jesuit missionaries,
French voyageurs, commercial fishermen, and naturalists identified several types of lake
trout in the Great Lakes (e.g., Agassiz, 1850; Roosevelt, 1865; Goodier, 1981; Jordan and
Evermann, 1911). Three general forms or morphotypes — leans, siscowet, and humpers
(also known as bankers) — were recognized based on fat content, morphology, location
caught, and spawning condition and timing (Figure 3.1). Within these three forms, several
other types were often described (Krueger and Ihssen, 1995). For example, some of the
types of lean trout recognized by commercial fishermen were called Mackinaw, yellowfin,
redfin, moss, sand, and racer trout (Goodier, 1981; Brown et al., 1981). Whether these lean
types all represented significant genetic differentiation is unknown. The differences
between the deepwater (sicowet) and shallow-water (lean) forms are known to be heritable
phenotypic differences, and these differences probably represent important ecological
adaptations for the habitats they use. Deepwater forms appear to be adapted for rapid
vertical migration (Eshenroder et al., 1995a) because adults have high fat content and
therefore are nearly neutrally buoyant without gas in their swim bladders (Crawford,
1966; Henderson and Anderson, 2002). This level of differentiation and adaptation within

the Great Lakes stands in considerable contrast to the similarity of lake trout within and
among small Precambrian Shield lakes (Wilson and Mandrak, Chapter 2, this volume).
Unfortunately, the settlement of the Great Lakes basin by Europeans in the 1800s and
1900s threatened the rich diversity of life histories, forms, and adaptations expressed by
Great Lakes lake trout. This loss also jeopardized use of lake trout as a food and sport fish.
Lake trout populations declined catastrophically and, in some lakes, were lost because of
the stresses caused by commercial fisheries; the construction of canals for shipping; and
the timber industry. By the late 1950s, native lake trout were gone from Lake Ontario, Lake
Erie, and Lake Michigan; nearly gone in Lake Huron; and seriously depleted at most near-
shore locations in Lake Superior. Finally, when the remaining populations were threatened
by predation from the proliferating non-native sea lamprey Petromyzon marinus, manage-
ment programs began in earnest to protect and rehabilitate lake trout (Hansen, 1999).
This chapter reviews the history of the species in the Great Lakes during the past
century, describes the progress made toward lake trout rehabilitation, and identifies man-
agement lessons and challenges.
The lake trout fishery and its management: 1800–1950s
The history of Lake Superior and its lake trout provides a useful case history for the species
in the basin. Fishing for lake trout by native aboriginal people around Lake Superior was
ongoing when Louis Agassiz and his expedition made their journey to record the natural
history along the north shore (Agassiz, 1850). Lake trout were used as a subsistence food
fish and were bartered with the members of the expedition. The earliest records of
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commercial fisheries in Lake Superior are from the 1830s, when the Hudson’s Bay Com-
pany and the American Fur Company shipped salted fish in barrels from Lake Superior
(Bogue, 2000). Seines were used in the earliest days of the commercial fisheries. Later,
settlers to the region were quick to recognize the value of lake trout as a food fish. By
1875, 0.75 million kilograms of lake trout were caught from the lake. Efficiency of catching
fish increased with technological improvements. Pound nets were first used in the 1860s,
and steam tugs introduced in the early 1870s (Goodier, 1989). The efficiency of fishing
gear further expanded as gas- and diesel-powered fishing tugs were introduced after

World War I. About 1930, cotton gill nets replaced those made of linen, and in the late
1940s multifilament nylon gill nets replaced cotton (Goodier, 1989; Hansen et al., 1995).
When gill net fisheries converted from cotton to multifilament nylon, their nets became
much better at catching fish (Pycha, 1962). Between 1913 and 1950, harvest of lake trout
averaged 2.0 million kilograms per year (Baldwin et al., 1979). During this same period,
sport fishing, though a minor contributor to the total catch, was culturally important at
locations such as Duluth, Minnesota, and Munising, Michigan. Anglers, while trolling for
lake trout, often used copper line to get lures deep. Overfishing was clearly evident when
fishing effort increased sharply after World War II and yield did not increase, even though
Figure 3.1 Siscowet (top), lean (middle), and humper (bottom) morphotypes are examples of the
phenotypic diversity of lake trout from the Great Lakes. (Photo courtesy of Gary Cholwek and Seth
Moore of the USGS Ashland Biological Station.)
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gear efficiency had increased further (Hile et al., 1951; Pycha and King, 1975). Populations
at this point had declined by 50%.
While overfishing of Lake Superior and other Great Lakes populations was occurring,
the sea lamprey invaded upstream from Lake Ontario. The sea lamprey gained access to
the upper lakes sometime in the late 1910s by passing around Niagara Falls via the Welland
Canal and associated feeder canal, built for the shipping industry (Eshenroder and Burn-
ham-Curtis, 1999). Sea lampreys were first recorded in Lake Erie in 1921, in Lake Michigan
in 1936, in Lake Huron in 1937, and in Lake Superior in 1938 (Smith and Tibbles, 1980).
By the 1950s, sea lampreys were very abundant in all the Great Lakes. Sea lamprey attached
to lake trout with their circular, suctorial mouth and fed on their blood and other body
fluids (Figure 3.2). Lake trout suffered serious mortality from these attacks. In Lake Supe-
rior, stocks of lake trout were already declining due to overfishing before the sea lamprey
invaded; however, the collapse of the stocks was undoubtedly accelerated by the added
mortality caused by sea lamprey (e.g., Hile et al., 1951; Coble et al., 1990). Although the
exact roles of overfishing and sea lamprey predation in the collapse of lake trout in the
other Great Lakes have been a source of debate (Coble et al., 1992; Eshenroder, 1992;
Eshenroder et al., 1995b), general agreement exists that both sources of mortality were

important in the ultimate demise of the species (Hansen, 1999).
Besides overfishing and sea lamprey predation, other environmental factors may have
also played a role in the decline of lake trout. Exotic species other than sea lamprey, such
as alewife Alosa pseudoharengus and smelt Osmerus mordax, invaded the Great Lakes, altered
food webs, and replaced native coregonines as a primary forage species for lake trout.
These species may also have directly controlled natural recruitment of lake trout through
competition with, and predation on, juvenile lake trout. In addition, a variety of toxic
Figure 3.2 Sea lamprey colonized the Great Lakes by using shipping canals to pass by barriers such
as Niagara Falls.
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substances, specifically organochlorine compounds, can become concentrated in lake trout
eggs, fry, and the environment. These compounds reduce the hatching success of lake
trout in the laboratory, but under natural conditions the relationship between toxic sub-
stances and lake trout mortality remains unclear (Zint et al., 1995). Quarrying operations
may have destroyed spawning habitat in some areas. During the late 1800s and early
1900s, a fleet of 45 schooners quarried cobble for more than 40 years from Lake Ontario
along 100 km of shoreline between Burlington and Whitby (Whillans, 1979). The timber
industry also may have affected some near-shore populations. Sawmills deposited large
amounts of woody debris and sawdust in the lakes (Lawrie and Rahrer, 1973; Bogue,
2000). This organic debris may have covered some near-shore spawning reefs. Logging
drives downriver may have affected river-spawning lake trout. Dams associated with
hydroelectric development such as on the Montreal River, a tributary to eastern Lake
Superior, must also have contributed to the decline in river-spawning lake trout.
What happened by 1960? Natural reproduction failed to sustain lake trout populations
in Lake Ontario, Lake Erie, and Lake Michigan. Wild lake trout were eliminated from
these systems. In Lake Huron only two small populations remained, one in Parry Sound
and the other in Iroquois Bay, both located on the eastern shore of the lake (Berst and
Spangler, 1973; Reid et al., 2001). Near-shore populations in Lake Superior were decimated,
although remnants of a few populations, such as the one adjacent to Gull Island Shoal,
persisted (Schram et al., 1995). Offshore lake trout in Lake Superior were comparatively

unaffected, especially the humper and deepwater siscowet forms, which continued to
support limited fisheries through the 1960s and 1970s (Peck et al., 1974). Distance offshore
and deep water may have provided some protection to these fish from commercial fisheries
and sea lamprey predation. The sequence of the collapse of lake trout stocks in the upper
lakes was Lake Huron first, Lake Michigan next, and Lake Superior last (see review in
Hansen, 1999). Another important commercial species in the upper Great Lakes, lake
whitefish Coregonus clupeaformis also declined to their lowest point in the late 1950 and
early 1960s because of the effects of sea lampreys, other non-native species, and overfish-
ing. By 1960, the lake trout and whitefish fisheries of the Great Lakes were devastated.
Rehabilitation management: 1950s to present
As lake trout populations declined precipitously through the 1950s in the Great Lakes,
the governments in Canada and the United States embarked on a program of fishery
rehabilitation focused on lake trout that has continued to the present. The two federal
governments undertook many of the early management actions used to restore the lake
trout and whitefish fisheries of the Great Lakes. For example, though the states have
authority for fishery management, essentially the U.S. Bureau of Commercial Fisheries
managed U.S. waters during the 1950s and early 1960s as a result of an absence of state
interest. Over time, however, the lake trout rehabilitation program shifted toward, and
has been sustained by, the eight Great Lakes states, the Province of Ontario, and the U.S.
aboriginal tribal authorities. In 1955, the two federal governments formed the international
Great Lakes Fishery Commission for the purpose of developing a program of sea lamprey
control, conducting fishery research, and promoting coordinated management (Figure 3.3).
The commission explicitly adopted lake trout population rehabilitation as one of its goals
and has always encouraged fishery management agencies to restore lake trout populations
(Great Lakes Fishery Commission, 2001)
.
A variety of management actions have been implemented since the late 1950s to
rehabilitate the fisheries and overcome the obstacles faced by lake trout in the Great Lakes.
Approximately 330 million yearling and fingerling lake trout were released into the Great
Lakes from 1950 to 2001, primarily into near-shore areas (Table 3.1). In Lake Superior,

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117 million lake trout were stocked, and of these 86% were yearlings. Lake trout fishing
was closed in 1962 in Lake Superior and restricted in the other lakes during the early
years of the rehabilitation program.
To reduce sea lamprey predation, selective lamprey toxicants (lampricides) were used
to kill sea lamprey larvae in streams. The first stream treatments began experimentally in
Lake Superior in 1958, and routine applications were extended to the upper Great Lakes
shortly thereafter (Smith and Tibbles, 1980). Sea lamprey control measures were imple-
mented later in Lake Ontario (1971) and in Lake Erie (1986). A suite of techniques is now
used to control the lamprey, including lampricides, adult trapping, the release of sterile
males, and the placement of barriers to block access to spawning streams. Beginning in
1966, management activities were coordinated through lake committees organized by the
Great Lakes Fishery Commission. These committees included a representative from each
fishery management authority on a lake. The lake committees developed lake trout man-
agement plans and helped to coordinate management actions such as stocking and fishery
regulations within each Great Lake.
During the 1960s, lake trout survived, and the abundance of subadults and adults
increased in the upper three Great Lakes (Superior, Huron, and Michigan) in response to
sea lamprey control, regulation of fishery harvests, and stocking. Most of these lake trout
were hatchery-origin fish, the survivors of past stockings. Similar increases in lake trout
abundance occurred in Lake Ontario in the late 1970s and in Lake Erie in the late 1980s
and early 1990s.
Unfortunately, rehabilitation management became increasingly complicated in the
mid-1960s because new sport fisheries began, particularly in Lake Huron, Lake Michigan,
and Lake Ontario, and were focused on catching non-native Pacific salmon (Oncorhynchus
sp.) (Bence and Smith, 1999; Kocik and Jones, 1999). Alewives had become enormously
abundant and were experiencing massive die-offs that fouled beaches and clogged the
water-intake pipes of cities. Salmon were stocked initially to control these fish and to create
new sport fisheries. Salmon stocking was successful, and the fisheries that resulted pro-
vided an economic stimulus for coastal communities after the loss of the commercial fishing

Figure 3.3 The convention between Canada and the United States that formed the Great Lakes
Fishery Commission was fully ratified in 1955.
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Table 3.1 Number of Fingerling and Yearling Lake Trout Stocked into the Great Lakes, 1950–2001
Year Superior Huron Michigan Erie Ontario Total
1950 50,000 0 0 0 0 50,000
1952 312,000 0 0 0 0 312,000
1953 472,000 0 0 0 0 472,000
1954 500,000 0 0 0 0 500,000
1955 164,000 0 0 0 0 164,000
1956 201,000 0 0 0 0 201,000
1958 1,020,000 0 0 0 0 1,020,000
1959 635,000 0 0 0 0 635,000
1960 1,050,000 0 113,000 0 0 1,163,000
1961 1,201,000 0 95,000 0 0 1,296,000
1962 1,852,000 0 73,000 0 0 1,925,000
1963 2,311,000 0 0 0 181,000 2,492,000
1964 2,651,000 0 0 0 111,000 2,763,000
1965 1,825,000 0 1,274,000 0 0 3,099,000
1966 3,279,000 0 1,766,000 0 0 5,046,000
1967 3,289,000 0 2,424,000 0 0 5,713,000
1968 3,375,000 0 1,876,000 0 0 5,251,000
1969 2,890,000 0 2,000,000 17,000 0 4,907,000
1970 2,785,000 0 1,960,000 0 0 4,745,000
1971 2,016,000 0 2,344,000 0 0 4,359,000
1972 2,103,000 0 2,926,000 0 0 5,029,000
1973 1,904,000 1,110,000 2,509,000 0 66,000 5,589,000
1974 2,527,000 793,000 2,397,000 26,000 1,163,000 6,907,000
1975 2,149,000 1,053,000 2,613,000 184,000 385,000 6,383,000
1976 2,453,000 1,024,000 2,548,000 202,000 531,000 6,757,000

1977 2,509,000 1,658,000 2,418,000 125,000 586,000 7,295,000
1978 3,076,000 1,262,000 2,539,000 236,000 1,243,000 8,357,000
1979 2,740,000 2,171,000 2,497,000 709,000 887,000 9,004,000
1980 3,156,000 2,164,000 2,791,000 507,000 1,577,000 10,194,000
1981 3,643,000 2,117,000 2,642,000 41,000 1,531,000 9,973,000
1982 4,017,000 2,295,000 2,746,000 235,000 1,650,000 10,944,000
1983 4,102,000 2,808,000 2,241,000 222,000 1,469,000 10,842,000
1984 4,772,000 2,998,000 1,565,000 176,000 1,538,000 11,049,000
1985 5,073,000 4,075,000 3,782,000 154,000 1,911,000 14,995,000
1986 5,171,000 3,770,000 3,297,000 199,000 2,234,000 14,671,000
1987 4,818,000 3,236,000 1,998,000 205,000 2,313,000 12,570,000
1988 4,776,000 4,132,000 2,546,000 203,000 2,285,000 13,942,000
1989 2,516,000 3,147,000 5,377,000 273,000 982,000 12,295,000
1990 2,805,000 1,428,000 1,317,000 349,000 2,054,000 7,954,000
1991 3,445,000 2,496,000 2,779,000 326,000 2,083,000 11,129,000
1992 3,653,000 4,053,000 3,435,000 277,000 1,736,000 13,154,000
1993 1,936,000 3,163,000 2,697,000 258,000 1,066,000 9,120,000
1994 2,034,000 3,945,000 3,854,000 200,000 507,000 10,540,000
1995 1,971,000 3,280,000 2,265,000 160,000 500,000 8,175,000
1996 1,496,000 4,144,000 2,115,000 83,000 350,000 8,187,000
1997 1,291,000 3,288,000 2,235,000 120,000 500,000 7,435,000
1998 1,560,000 4,385,000 2,302,000 98,000 426,000 8,771,000
1999 1,371,000 3,401,000 2,348,000 199,000 476,000 7,794,000
2000 1,357,000 4,655,000 2,260,000 135,000 489,000 8,896,000
2001 234,000 1,217,000 2,382,000 120,000 500,000 4,452,000
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industry. Little contribution to the salmon fisheries came from natural recruitment, and
the fisheries were dependent on stocking.
In the decades that followed, mortality of adult hatchery-origin lake trout increased
to levels at which too few fish survived to either their first or second spawning. Angling

effort, in general, increased in the Great Lakes because of the salmon fisheries, and anglers
often caught lake trout. State and provincial agencies, in most cases, allowed anglers to
keep hatchery-origin lake trout even though these fish had been stocked for rehabilitation
purposes. Lake trout were harvested as by-catch in the salmon fisheries, but sometimes
lake trout were targeted by anglers. Gill-net fisheries grew as aboriginal peoples exercised
treaty rights in some U.S. waters. These fisheries harvested substantial numbers of lake
trout incidental to targeting lake whitefish (Brown et al., 1999; Hansen, 1999). Also, sea
lamprey in the 1960s and 1970s expanded into new spawning habitats because water
quality improved as a result of new environmental laws and policies such as the Great
Lakes Water Quality Agreement (e.g., Peshtigo River, Moore and Lychwick, 1980). In spite
of these new challenges, large, abundant stocks of hatchery-origin lake trout became
established in several localized areas of the Great Lakes. Surprisingly, little reproduction
and natural recruitment was observed in any of the lakes other than Lake Superior. The
lack of natural recruitment in the Great Lakes stands in sharp contrast to the frequent
establishment of naturally reproducing populations after stocking lake trout into the small
inland lakes of the Province of Ontario (Evans and Olver, 1995) and suitable western lakes
such as Yellowstone Lake (Kaeding et al., 1996). Why then was there so little successful
reproduction in the Great Lakes?
Causes of the slow recovery
Several hypotheses have been offered to explain why lake trout rehabilitation has been
slow in the Great Lakes (Eshenroder et al., 1984, 1999; Selgeby et al., 1995), and some of
these are described below. Among the explanations proposed, empirical data support
them all, but none accounts fully for the slow recovery. For example, one cause proposed
for the slow recovery is that too few fish survive to spawning age after stocking, and thus
natural reproduction is so low as not to be detectable or capable of sustaining a population.
Although lake trout at some locations have had difficulty attaining spawning age because
of excessive fishing and sea lamprey mortality, at many other locations catch rates of
spawning-age lake trout in gill nets have been comparable to, or exceeded, those observed
for wild populations in Lake Superior (Krueger et al., 1986; Elrod et al., 1995; Hansen,
1999).

Another hypothesis is that lake trout do not reproduce successfully because they
cannot find spawning grounds or mates because of the absence of proper cues (olfactory
homing or pheromones). Hatchery-origin lake trout have spawned over inappropriate
substrates at some locations. Moreover, stocking often has occurred at locations where
little spawning habitat exists in the immediate vicinity. However, hatchery-origin lake
trout are also known to locate and readily spawn over clean natural substrate that has
been deposited along the shoreline, such as in Tawas Bay, Lake Huron (Foster and
Kennedy, 1995), as well as over natural reef substrate such as at Stony Island reef in Lake
Ontario (Perkins and Krueger, 1995).
A third proposed cause is that lake trout gametes are infertile because of toxic chemical
contamination and a thiamine nutritional deficiency. Toxic substances such as organochlo-
rines and their effects on gamete viability have been suspected of being one of the causes
of lake trout reproductive failure (Zint et al., 1995). A serious disease known as early
mortality syndrome (EMS) also occurs in adult lake trout from the Great Lakes, apparently
because of consumption of alewives, which are non-native (Fitzsimons et al., 1998). If lake
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trout feed heavily on alewives, adult females become thiamine deficient and their eggs
are not viable. However, Brown et al. (1998) reported that not all females captured from
Lake Ontario produced families that showed this syndrome. Also, lake trout gametes
collected from Lake Ontario in the 1980s from hatchery-origin adults were propagated
successfully in hatcheries. More than a million fish from this source were stocked back
into the lake (Elrod et al., 1995).
A fourth cause is that the wrong genetic types of lake trout were stocked, and these
fish were maladapted for survival and reproduction. The shallow-water, lean morphotype
has been the only form of lake trout stocked into the Great Lakes during the past 50 years,
and this form may be poorly adapted for colonizing the extensive offshore or deepwater
habitats (Krueger and Ihssen, 1995). Nevertheless, some sources such as the Superior strain
originating from the Apostle Islands region of Lake Superior and the Seneca strain from
the Finger Lakes region are known to successfully reproduce at some locations (e.g., Grewe
et al., 1994).

A fifth cause is that predation on lake trout eggs and fry by non-native and/or native
species inhibits natural recruitment. For example, predation by the non-native alewife on
lake trout fry has been implicated in preventing natural recruitment at some near-shore
locations (Figure 3.4; Johnson and VanAmberg, 1995; Krueger et al., 1995a). This source of
mortality, however, would be comparatively unimportant at offshore locations such as the
midlake reef in Lake Michigan or Six Fathom Bank in Lake Huron or in Lake Superior
and Lake Erie, where alewife abundance is apparently minimal.
Although evidence exists to support each of these hypotheses, no single one explains
the general lack of natural reproduction by lake trout. Probably, varying combinations of
each plus other causes account for the slow recovery of lake trout in the Great Lakes.
Status of rehabilitation
Lake Superior
Lake trout were declared rehabilitated along most of the Lake Superior shoreline in 1996
(Schreiner and Schram, 1997). Wild lake trout have continued to increase in abundance
since that time and may be more abundant now than at any time during the last century
in many areas of the lake (Wilberg et al., 2003). Substantial natural reproduction has been
Figure 3.4 Alewives invaded and colonized Lake Ontario around 1870.
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noted at most locations in the lake. Population recovery was first noted at areas where
remnant stocks were present, such as at Gull Island Shoal (Swanson and Swedburg, 1980),
Isle Royale, and Standard Rock, and recruitment, presumably from hatchery-origin lake
trout, was noted later in areas where wild lake trout were absent (Figure 3.5; Hansen et al.,
1995). Recovery at one location, Devils Island Shoal, was aided by the stocking of fertilized
eggs in artificial-turf incubators (Bronte et al., 2002). Rehabilitation has been slowest along
the Minnesota shoreline. Abundant and widely distributed spawning habitat, remnant
stocks, effective harvest regulation, and few non-native species such as the alewife prob-
ably all contributed to the success in Lake Superior. Supplemental stocking is no longer
required at most locations. Sea lampreys continue to cause lake trout mortality, and control
efforts must be maintained to protect the wild populations. Abundance of the siscowet or
deepwater form appears high and may be increasing (Bronte, C.R., U.S. Fish and Wildlife

Service, personal communication, 2003).
Lake Huron
Natural reproduction of lake trout has been detected at several sites in Lake Huron; but,
at only one site, Parry Sound in Ontario waters, has a self-sustaining population been
established (Reid et al., 2001). The success at Parry Sound appears to be caused by reduced
fishing mortality because of restrictive angling regulations, successful sea lamprey control,
and the establishment of a refuge. A remnant population of wild lake trout was also
present in Parry Sound and may have speeded the recovery. Naturally reproduced lake
trout have also been caught from an artificial reef in Tawas Bay (Foster and Kennedy,
1995) and from natural sites in South Bay (Anderson and Collins, 1995), Thunder Bay
Figure 3.5 Relative abundance of wild and hatchery lake trout caught in gill net surveys in U.S.
waters of Lake Superior and of all lake trout caught in waters <70 m deep in Canadian waters,
1950–1999. (Data from C.R. Bronte, U.S. Fish and Wildlife Service.)
Canadian Waters
0
10
20
30
40
50
60
70
80
1950 1960 1970 1980 1990
Year
Relative Abundance
U. S. Waters
0
10
20

30
40
50
60
70
80
1970 1975 1980 1985 1990 1995
Year
Relative Abundance
Wild
Hatchery
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(Johnson and VanAmberg, 1995), Gravelly Bay, Six Fathom Bank, and Iroquois Bay (Woldt
et al., in press). Assessment data from these sites indicate that natural reproduction is not
sufficient to sustain populations. Although these successes are encouraging, rehabilitation
has not occurred lake-wide. Excessive fishery harvests, sea lamprey-caused mortality, and
low lake-wide stocking rates are the major obstacles to lake trout rehabilitation in Lake
Huron (Eshenroder et al., 1995b). Recent efforts to apply lampricides in the St. Mary’s
River may help to reduce sea lamprey abundance in Lake Huron, especially in northern
waters. Increased stocking of lake trout could also help reestablish northern populations.
Lake Michigan
Mature hatchery-origin lake trout have been abundant for many years at several spawning
locations but have failed to produce detectable natural recruitment. Naturally produced
fry were collected from rock rubble deposited at two locations in Grand Traverse Bay
(Wagner, 1981), from rock covering a power-plant water-intake pipe in southeastern Lake
Michigan (Jude et al., 1981), and from rock deposited at Burns Waterway Harbor in Indiana
(Marsden, 1994). Viable fertilized eggs have been recovered from several locations on the
east and west shorelines as well as in Traverse Bay (Holey et al., 1995). Wild yearling and
older lake trout of the 1976, 1981, and 1983 year classes were caught from Grand Traverse
Bay and nearby Platte Bay (Rybicki, 1991). Excessive fishing mortality at these two loca-

tions during the mid- to late 1980s may have eliminated the wild year classes and the
hatchery-origin adults responsible for the natural reproduction (Hansen, 1999). No wild
fry or yearling lake trout have been recovered recently, but few studies are under way to
catch these life stages. Predation by round gobies Neogobius melanostomous on lake trout
eggs and by alewives on fry is believed to be an important block to successful recruitment.
Zebra mussel Dreissena polymorpha and quagga mussel D. bugensi colonization of some
reefs may increase damage to and mortality of lake trout eggs after deposition (Marsden
and Chotkowski, 2001).
Lake Erie
No detectable natural recruitment of lake trout has occurred in Lake Erie. This lake has
the least lake trout habitat of any of the Great Lakes, and suitable waters are restricted to
the eastern basin of the lake. Lake Erie was the last Great Lake to be managed for lake
trout rehabilitation, so the lack of success may not be surprising because of the short time
since the program began. Lake trout stocking has exceeded 150,000 yearlings each year
since 1982, and sea lamprey control began in 1986 (Cornelius et al., 1995). Since control
began, hatchery trout have survived better, and maximum age now exceeds 14. Fitzsimons
and Williston (2000) sampled three natural spawning reefs in late autumn of 1994 and
1995 for lake trout eggs. Eggs were found at two reefs along the New York shoreline but
not at one reef on the north shore near Port Dover, Ontario. Egg densities at the two sites
ranged from 4.8 to 62.5 eggs/m
2
. Concentrations of mature lake trout in the fall have not
been detected at Brocton Shoal, located on the south shore. This reef has the requisite
characteristics for lake trout spawning (Edsall et al., 1992) and may be one of the best reefs
in the area. The New York State Department of Environmental Conservation plans, in
cooperation with U.S. Fish and Wildlife Service, to stock 30,000 yearlings of the humper
morphotype at this location in 2004. These deepwater fish will be propagated from a
broodstock that originated from Klondike Reef in eastern Lake Superior. This planting
will be the first time that a morphotype other than the lean shallow-water form has been
stocked in the Great Lakes.

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Lake Ontario
Limited natural recruitment has been detected on a lake-wide basis since 1993. Fertilized
eggs have been caught at both the eastern and western ends of the lake (Perkins et al.,
1995). Evidence of successful reproduction by stocked lake trout was documented in 1982
with the capture of a single lake trout fry by the New York State Department of Environ-
mental Conservation and by a collection of 75 fry off the north end of Stony Island in 1986
(Marsden et al., 1988). Lake trout fry were captured from Stony Island reef every year that
surveys were conducted, 1986–1993 (Marsden and Krueger, 1991; Krueger et al., 1995a).
Nevertheless, no detectable naturally produced year classes of age-1 and older lake trout
occurred until the early 1990s. Since then, a few age-1 or older wild lake trout have been
caught (approximately 175 fish). The lake trout population in Lake Ontario continues to
depend on hatchery stocking as its primary source of recruitment.
New management approaches
The slow recovery of lake trout populations prompts the consideration of different man-
agement approaches than have been used in the past. For decades, the typical management
practice was to stock near-shore areas with yearling lake trout, conduct sea lamprey
control, and provide a modest level of protection from fisheries. The widespread lack of
success (except in Lake Superior) supports the notion of experimentally trying some
different approaches. One alternative approach that appeared to show some success was
the stocking of fertilized eggs instead of lake trout yearlings at Devils Island Shoal in Lake
Superior. Fertilized eggs were placed in bundles of artificial turf and anchored over Devils
Island Shoal in Lake Superior from 1981 to 1995 (Bronte et al., 2002). Approximately
17 million eggs were stocked in this way. Stocking this life stage was based on the concept
that the hatched fry would leave the turf incubators, reside in the rock rubble of the shoal,
imprint to the site, and increase the number of adults homing to the site. Beginning in
1992, the presence of mature adult lake trout without evidence of being of hatchery origin
(no fin clips) rose sharply in the samples obtained by assessment gill netting (Bronte et al.,
2002). The recruitment of unclipped spawners from 1985 to 1997 showed a closer relation-
ship to the number of eggs planted in previous years than to the number of adult lake

trout that had been observed on the reef during the spawning season.
Three other “new” ideas are described below that are also somewhat different from
the typical approach used in the past.
Pulse stocking
First, we propose stocking all available hatchery-reared lake trout allocated to a lake in a
given year into one selected locality that has an abundance of spawning habitat, leaving
other areas of the lake unstocked. In the next year all lake trout would be stocked in a
different area of abundant spawning habitat. This process would continue each year until
all comparable areas have received a pulse of hatchery lake trout, and then repeat the
cycle. This approach is proposed for two reasons. First, the best survival of stocked fish
always occurs early in a rehabilitation program (e.g., Elrod et al., 1995; Hansen et al., 1994).
Survival of stocked lake trout consistently declines 8 to 10 years after stocking is initiated,
when adults become abundant. Poor survival of hatchery yearlings may result from
cannibalism of newly stocked fish by adult hatchery-origin lake trout. Our approach
should minimize this problem. Second, if reproduction should occur, wild recruits should
have a better chance for survival without competition from stocked hatchery yearlings.
Pulse stocking should minimize competition.
© 2004 by CRC Press LLC
Creation of spawning areas
Second, we propose that large areas of rock rubble be deposited in near-shore locations
to create spawning areas where mature hatchery lake trout congregate in the fall. This
approach was developed from the universal observation in the Great Lakes that rock
structures, if placed in suitable near-shore lake trout habitat, are quickly discovered by
adult hatchery-origin fish and used for spawning (e.g., Wagner, 1981; Marsden, 1994;
Marsden et al., 1995). In some cases, lake trout spawning over such areas have successfully
produced measurable recruitment of age-1+ lake trout (Peck, 1986; Rybicki, 1991). Spawn-
ing shoals would be most appropriately placed in areas where severe loss of near-shore
habitat has occurred. These reefs are to create areas for spawning, not fishing. Shoal
placement should be combined with refuge or no-fishing regulations that protect fish from
all forms of fishing mortality within a sizable area around the reef. The primary rationale

for this approach is simply that past experience shows it will work. Artificial spawning
reefs could be the key catalyst for establishment of new near-shore populations. New
populations established through the use of this approach could serve as surrogates for
remnant populations. Rehabilitation success most often has been observed where remnant
populations survived (Lake Superior and Parry Sound). New wild populations could,
through straying of individual fish, help to colonize other areas of the lake. Careful design
and placement of man-made spawning shoals, when combined with assessment, will
reveal much about spawning-site selection and demonstrate its potential as a rehabilitation
strategy. Artificial spawning shoals could be designed and created as sets of experiments
to improve understanding of lake trout spawning-site selection, reproductive success, and
adult homing.
Reefs would need to be placed in waters deep enough to avoid processes that could
cause mortality of eggs, such as ice scour and high wave energy. Sites should also be
selected to avoid areas subject to severe long-shore transport and deposition of sediment.
Employment of this approach presumes that survival from egg deposition to the yearling
life stage is possible and not precluded by egg and fry predators and that sea lamprey
control, stocking, and harvest regulation continue. The creation of new spawning reefs
must be on a spatial scale that produces enough juveniles to sustain populations. Based
on past observations of egg deposition and survival by hatchery trout on a natural reef
in Lake Ontario (Perkins and Krueger, 1995), a 2-ha spawning area could generate from
64,000 to 131,000 yearlings and, assuming 60% survival thereafter, could in the first gen-
eration establish a population of 3,000 to 6,000 age-7 spawners.
Transplantation of adults
Third, we suggest experimentally transplanting wild adult lake trout from Lake Superior
into isolated offshore areas possessing suitable spawning habitats such as the midlake reef
complex in Lake Michigan or the Six Fathom Bank in Lake Huron. This approach addresses
three problems observed in lake trout rehabilitation. First, hatchery-origin lake trout have
difficulty finding and using off-shore areas of suitable spawning habitat (e.g., Krueger
et al., 1986). This approach attempts to circumvent this problem by placing spawning-
condition adults directly on a suitable reef. Because of the impending urgency of spawning,

mature lake trout placed directly on offshore spawning areas in late September or October
may spawn on these reefs. After the first spawning, they may remain in the area or return
in subsequent spawning seasons. Second, lake trout rehabilitation takes a long time
because lake trout require 5 to 7 years or more to attain maturity. Stocking eggs, fry, or
yearlings requires managers to wait until fish mature before they can assess the success
or failure of their actions. The proposed approach will accelerate this process by as much
© 2004 by CRC Press LLC
as 5 to 7 years because the lake trout are already mature. Natural seeding of the reef with
eggs would immediately occur, and these eggs would have the rearing advantages asso-
ciated with natural substrates (e.g., fry imprinting). If these events took place, populations
could become established rapidly.
Third, nearly all lake trout currently stocked may suffer from domestication effects
(Reisenbichler et al., 2003) because they have been raised in a hatchery for more than 1
year and are the products of hatchery brood stocks. Because of the small numbers of adults
transplanted, areas stocked should have complete protection from fishing. Transplantation
of wild adults avoids the problem of reduced fitness in the wild caused by domestication
because this approach does not use hatcheries. Adult transfers have proven amazingly
successful in the management and restoration of fish (Kerr et al., 1996; Lasenby and Kerr,
2000) and wildlife populations. For example, the stocking of domestic and domestic-wild
turkeys failed to reestablish populations within their native range during the 1920s to
1940s. With the development and use of live-capture and transfer techniques in the 1950s,
successful reestablishment of turkey populations was widespread across North America
(Hewitt, 1967). Similarly, reestablishment of self-sustaining populations of other birds and
mammals was based on trapping and transfer of adults (Wolf et al., 1996).
The slow recovery of lake trout in the Great Lakes indicates that new management
approaches should be tried and tested. In the situation where fertilized eggs were stocked
in artificial turf in Lake Superior (described above), stocking and its assessment was
undertaken for 20 years, and this persistence was a critical element that fostered learning.
Implementation of new strategies must have a long-term commitment and must incorpo-
rate carefully designed assessment studies.

Management lessons and future challenges
Much has been learned during five decades of lake trout rehabilitation efforts in the Great
Lakes. Certainly, one can conclude that this effort has been much more difficult and
complicated than anyone dreamed back in the late 1950s when it began. The successful
rehabilitation of Lake Superior and of Parry Sound in Lake Huron and the capture of
naturally produced juveniles from Lake Michigan and Lake Ontario clearly indicate the
feasibility of the rehabilitation goal. Described below are lessons that future managers
need to consider if the mistakes of the past are not to be repeated (see Krueger et al., 1995b).
1. Fishing mortality must be controlled to rehabilitate populations. Populations cannot be
reestablished if excessive mortality of subadults and adults is permitted. A refuge
(no harvest) and severe angling restrictions were believed to be key management
practices that led to the successful restoration of the Parry Sound population (Reid
et al., 2001). If population rehabilitation is the management goal, it does not make
sense to have directed fisheries on the species before establishment of self-sustain-
ing populations. Lenient harvest regulations are inconsistent with the goal of
rehabilitation. Control of all forms of mortality, such as from sea lampreys, is
important, but fishery harvest is typically the portion of mortality that managers
have the most ability to control.
2. Non-native species can seriously impede rehabilitation. New invasions from non-native
species pose an unpredictable, serious threat to the success of lake trout rehabili-
tation in the Great Lakes. Further invasion of non-native aquatic organisms must
be prevented. Non-native organisms can be serious predators on lake trout eggs
and fry (Krueger et al., 1995a; Marsden, 1997; Chotkowski and Marsden, 1999),
can alter habitat (Marsden and Chotkowski, 2001), and have community level
© 2004 by CRC Press LLC
effects (O’Gorman et al., 2000). Fishery and environmental agencies must imme-
diately take action to prevent any further colonization by exotic aquatic organisms.
3. Survival and reproduction of stocked fish is related to their genetic origins. Some strains
of lake trout survive and reproduce better than others. Yet, little consideration has
been given to matching lake trout types or strains to particular habitats (e.g.,

Krueger et al., 1981). The predominant and formerly most productive lake trout
habitats in the Great Lakes are deepwater areas and offshore shoals (Eshenroder
et al., 1995c). These areas, with few exceptions, have been virtually ignored when
considering the sources of lake trout to stock. The lake trout reintroduced to these
areas should be those that have the genetic adaptations required for survival and
reproduction in these habitats. Siscowet lake trout should be ideal for deep-water
areas, and humpers are suited for offshore shoals. More consideration needs to be
given to restoring the full complement of phenotypic diversity of lake trout to the
Great Lakes (Krueger et al., 1995b).
4. Long-lived species take a long time to restore. Though this lesson may seem obvious,
the problem of time has both ecological and social implications. Wild, self-sustain-
ing, naturally reproducing populations of lake trout in the Great Lakes typically
had 13 or more adult age classes (age 7 to 20 or more). Thus, the buildup of age
classes typical of wild populations takes decades, but they are fragile and vulner-
able and can be disrupted by a few short years of over harvest (see lesson 1!). One
brief lapse of protection can set back for decades the possibility of success for
rehabilitation. Fish management agencies and the public must be vigilant to protect
fish and be patient for success. Unfortunately, the time frame required for lake trout
rehabilitation spans well beyond the careers of managers, biologists, and politicians.
Even more serious is sustaining public support for such long-term programs. An
extraordinary level of commitment is required from members of the public who
may not experience any benefits in their lifetimes from a rehabilitation effort.
5. Coordinated management is essential to management success in multijurisdictional waters.
Jurisdictions share authority for management on every Great Lake. Coordinated
management actions consistent with agreed-on goals are critical for success in lake
trout rehabilitation. The annual meetings of the Great Lakes Fishery Commission’s
lake committees have provided the forum where fish management agencies discuss
and decide on common strategies and actions to accomplish their goals. Without
this approach, the successes experienced so far in lake trout rehabilitation would
not have occurred.

Conclusion
What does the future hold for lake trout rehabilitation? We don’t know! If it was the mid-
1980s, we could make a confident prediction that rehabilitation successes are likely if
mortality (fishing and sea lamprey) is controlled and intensive stocking included a variety
of lake trout strains. Unfortunately, in the 2000s major ecological disruptions to the food
web are occurring rapidly as a result of new invasions of aquatic species from Eurasia.
High levels of ecological instability currently characterize the Great Lakes food web. The
possibility exists that critical native components of the food web such as the amphipod
Diporeia or the opossum shrimp Mysis relicta may be lost through interactions with non-
native species. Yet-to-come invading species could be even more effective predators of
lake trout eggs and fry than the presently established alewife and round goby. Stemming
the biological pollution caused by the flow of invading species to the Great Lakes is critical
if progress in lake trout rehabilitation is not to be lost and new successes are to be gained.
© 2004 by CRC Press LLC
Acknowledgments
Shawn Riley, Heather Kirshman, and William Alguire assisted with the review of literature
used in this chapter. C. I. Goddard and R. L. Eshenroder provided many helpful sugges-
tions on earlier drafts of this chapter.
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