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Lake Trout in the Great Lakes


by
Michael J. Hansen
National Biological Service
James W. Peck
Michigan Department of Natural Resources
Lake trout (Salvelinus namaycush) populations in the Great Lakes collapsed catastrophically during the 1940's and 1950's because of excessive predation by the sea lamprey (Petromyzon marinus) and exploitation by fisheries. The lake trout was the top-level predator in most of the Great Lakes as well as an important species harvested by commercial fisheries. Interagency efforts to restore lake trout into the Great Lakes included comprehensive control of sea lamprey populations (Smith 1971), regulation of commercial and recreational fisheries, and stocking (Eschmeyer 1968). It was hoped that without sea lamprey predation and fishery exploitation, stocked lake trout could reproduce and eventually restore wild lake trout populations in each of the Great Lakes. Lake trout restoration began during the 1950's in Lake Superior (Hansen et al. 1995), the 1960's in Lake Michigan (Holey et al. 1995), the 1970's in Lake Huron (Eshenroder et al. 1995) and Lake Ontario (Elrod et al. 1995), and the 1980's in Lake Erie (Cornelius et al. 1995).
Long-term monitoring of lake trout populations relied on catch records of commercial fisheries before the populations collapsed. Later monitoring of lake trout populations relied on assessment fisheries to measure the increase in abundance of stocked fish and, subsequently, of naturally produced fish. At present, natural reproduction by lake trout has been widespread only in Lake Superior. In contrast, lake trout reproduced in only limited areas of Lakes Huron, Michigan, and Ontario, and only in Lake Huron have progeny survived to adulthood. We describe the historical collapse and subsequent restoration of lake trout populations in U.S. waters of Lake Superior. We also describe the limited natural reproduction that has occurred in the other Great Lakes.
We compiled data describing abundance trends of lake trout in Lake Superior during 1929-93, expressed as the number of fish caught in a specified length of gill net. Data sources were for Michigan during 1929-49 (Hile et al. 1951), Michigan and Wisconsin during 1950-70 (Pycha and King 1975), and Michigan and Wisconsin during 1970-93 (Hansen et al. 1995).
Fishing was by commercial fishers during 1929-58 and by commercial-fisher contractors or state agencies during 1959-93. Lake trout populations in Lake Superior during 1929-43 sustained stable yields in commercial fisheries, providing a benchmark for judging restoration status. Therefore, lake trout abundance, expressed as a percentage of the 1929-43 average, directly compares lake trout abundance during the various phases of population collapse and recovery. Hatchery lake trout were all marked by removal of one or more fins before stocking. Thus, we show the abundance of stocked lake trout (one or more fins missing) separately from that of wild-origin lake trout (no fins missing). Comparable data are not available for Canadian waters of Lake Superior.

Status and Trends
Lake Superior
Figure. Abundance of stocked and wild lake trout (Salvelinus namaycush) in Michigan and Wisconsin waters of Lake Superior in 1929-93, expressed as a percentage of the 1929-43 mean (from Hansen et al. 1995).
Abundance of wild lake trout in Michigan declined from stable levels in the 1930's to nearly zero in the late 1960's (Figure; Hansen et al. 1995). In the 1970's and 1980's, abundance of wild lake trout increased steadily, but in the late 1980's and early 1990's decreased slowly because of increased commercial fishing and sea lamprey predation. The abundance of stocked fish increased in the late 1960's well beyond the 1929-43 average and remained there during most of the 1970's.
Abundance of stocked lake trout declined rapidly in the late 1970's and 1980's and has remained less than 10% of the 1929-43 average since 1988. Stocked lake trout reproduced in the late 1960's and produced an increased abundance of wild fish in the 1970's and 1980's.
The key to this successful natural reproduction was the presence of abundant inshore spawning grounds that inexperienced stocked lake trout easily located. Also, the decline in abundance of wild lake trout in the late 1970's and 1980's was evidently due to the earlier decline in stocked lake trout. The decline was less severe, however, because of reproduction by wild fish, the progeny of the first stocked spawners.
By 1993, 80%-90% of the lake trout in Michigan were wild, but abundance of wild lake trout was only 61% of the 1929-43 average. Fishery management agencies deferred lake trout restoration in eastern Michigan (Whitefish Bay) so that court-affirmed Native American fisheries could maximize their harvest in that area.
In Wisconsin, abundance of wild lake trout declined irregularly through 1968 and increased after that (Figure; Hansen et al. 1995). The abundance of wild lake trout in Wisconsin, even at its lowest point, remained higher than in Michigan in the late 1960's. Increased abundance in the 1970's was mostly of stocked lake trout, as in Michigan, and peak abundance also greatly exceeded the 1929-43 average. The abundance of stocked lake trout declined earlier than in Michigan, though not as much, and remained at 19% of the 1929-43 average.
Abundance of wild fish in Wisconsin increased irregularly from the 1970's through the early 1990's, but remained lower in 1993 than in Michigan and was only 53% of the 1929-43 average. Stocked lake trout were less important in the restoration of wild lake trout in Wisconsin than in Michigan. Because most spawning reefs in Wisconsin were farther offshore than in Michigan, they were not found by inexperienced stocked spawners. The increased abundance of wild lake trout in Wisconsin was largely due to reproduction by surviving wild fish in the 1960's and 1970's.
Direct measures of historical abundance do not exist for Minnesota or Ontario. The current abundance of lake trout in Minnesota is below that in Michigan and Wisconsin, but in Ontario it is probably similar to Michigan. Lake trout restoration is progressing in Minnesota but is behind that in Michigan or Wisconsin. Patterns of abundance in Minnesota since 1963 are similar to those in Michigan since 1959. Reproduction by stocked lake trout produced increased abundance of wild lake trout in Minnesota, as in Michigan (Hansen et al. 1995). Progress in lake trout restoration in Ontario is sufficient to eliminate stocking in most areas. Excessive fishery exploitation in the Michigan side of Whitefish Bay caused the deferral of lake trout stocking in the Ontario side. This deferral of lake trout restoration will continue until fishery management agencies in Michigan better regulate fishery exploitation.
Lake trout reestablished self-sustaining populations in much of Lake Superior, though few have reached former levels of abundance. Still, most of these populations are sufficiently large to support limited commercial and sport fishing. Current or proposed strategies for restoring wild lake trout in Lake Superior include controlling fishery exploitation, reducing sea lamprey populations, and reducing or eliminating stocking where self-sustaining populations exist.
Lake Michigan
Wild lake trout populations collapsed in Lake Michigan during the 1940's and the species became extirpated in the 1950's (Holey et al. 1995). Stocking began in the 1960's. The abundance of stocked lake trout increased in the late 1970's, then decreased in the northern part of the lake because of excessive fishery exploitation. Scattered evidence of lake trout reproduction, including eggs deposited on spawning grounds and newly hatched juvenile lake trout, has been found since the 1970's, although the only production of wild lake trout more than 1 year old was in Grand Traverse Bay during the late 1970's and early 1980's. Unfortunately, excessive fishery exploitation destroyed the wild lake trout produced in Grand Traverse Bay, preventing the establishment of a self-sustaining population (Holey et al. 1995). Current efforts to restore lake trout to Lake Michigan focus on stocking a variety of lake trout strains in offshore refuges that may afford protection from fishery exploitation, allowing restoration of wild populations to occur.
Lake Huron
Wild lake trout populations collapsed in Lake Huron in the 1940's and the species became extirpated in the main basin in the 1950's (Eshenroder et al. 1995). Stocking began in the 1970's. Abundance of stocked fish in southern Michigan waters increased steadily during the 1970's and 1980's, then decreased in response to reduced stocking. Abundance in northern Michigan waters increased briefly during the late 1970's and early 1980's, but decreased slowly after that because of excessive sea lamprey predation and fishery exploitation.
Natural reproduction occurred in Thunder Bay, Michigan, and South Bay, Ontario, but self-sustaining populations have not developed at either location. Restoration efforts now focus on reducing the number of sea lampreys and stocking a variety of lake trout strains on offshore reefs and in a refuge. The refuge, located in the northern part of the lake, may provide protection from fishery exploitation, and thereby may allow a self-sustaining population to become established.
Lake Erie
Wild lake trout populations collapsed in Lake Erie during the 1920's (Cornelius et al. 1995). Stocking began in the 1980's. Abundance of stocked lake trout increased steadily following initial chemical treatment of sea lampreys in 1986-87, although abundance of stocked lake trout decreased after 1990 for unexplained reasons. Current restoration efforts focus on controlling sea lampreys and stocking yearling lake trout. Research efforts focus on identifying causes of declining abundance of stocked fish and determining whether adult lake trout will aggregate at suitable spawning locations and reproduce successfully.
Lake Ontario
Wild lake trout populations collapsed in Lake Ontario between 1930 and 1960 (Elrod et al. 1995). Stocking began in the 1970's. Stocked lake trout subsequently survived to maturity, spawned, and deposited eggs that hatched into juveniles. These juveniles, however, evidently did not survive to later ages because fishery biologists have not yet discovered any older, wild-origin lake trout. Current restoration efforts focus on stocking strains of lake trout that reproduce most successfully. Research focuses on evaluating factors that limit survival of the fry, such as predation and contaminants.
For further information:
Michael J. Hansen
National Biological Service
Great Lakes Center
1451 Green Rd.
Ann Arbor, MI 48105
References
Cornelius, F.C., K.M. Muth, and R. Kenyon. 1995. Lake trout rehabilitation in Lake Erie: a case history. Journal of Great Lakes Res. In press.

Elrod, J.H., R. O'Gorman, C.P. Schneider, T.H. Eckert, T. Schaner, J.N. Bowlby, and L.P. Schleen. 1995. Lake trout rehabilitation in Lake Ontario. Journal of Great Lakes Res. In press.

Eschmeyer, P.H. 1968. The lake trout (Salvelinus namaycush). U.S. Fish and Wildlife Service, Fishery Leaflet 555. 8 pp.

Eshenroder, R.L., N.R. Payne, J.E. Johnson, C.A. Bowen II, and M.P. Ebener. 1995. Lake trout rehabilitation in Lake Huron. Journal of Great Lakes Res. In press.

 Hansen, M.J., J.W. Peck, R.G. Schorfhaar, J.H. Selgeby, D.R. Schreiner, S.T. Schram, B.L. Swanson, W.R. MacCallum, M.K. Burnham-Curtis, G.L. Curtis, J.W. Heinrich, and R.J. Young. 1995. Lake trout (Salvelinus namaycush) restoration in Lake Superior. Journal of Great Lakes Res. In press.

Hile, R., P.H. Eschmeyer, and G.F. Lunger. 1951. Status of the lake trout fishery in Lake Superior. Transactions of the American Fisheries Society 80:278-312.

Holey, M.E., R.W. Rybicki, G.W. Eck, E.H. Brown, Jr., J.E. Marsden, D.S. Lavis, M.L. Toneys, T.N. Trudeau, and R.M. Horrall. 1995. Progress toward lake trout restoration in Lake Michigan. Journal of Great Lakes Res. In press.

Pycha, R.L., and G.R. King. 1975. Changes in the lake trout population of southern Lake Superior in relation to the fishery, the sea lamprey, and stocking, 1950-70. Great Lakes Fishery Commission Tech. Rep. 28, Ann Arbor, MI. 34 pp.

Smith, B.R. 1971. Sea lampreys in the Great Lakes of North America. Pages 207-247 in M.W. Hardisty and I.C. Potter, eds. The biology of lampreys. Vol. 1. Academic Press, New York.


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