J. Great Lakes Res. 21 (Supplement 1):128-151Internat. Assoc. Great Lakes Res., 1995

Progress Toward Lake Trout Restoration in Lake Michigan

Mark E. Holey,! Ronald W. Rybicki,2 Gary W. Eck,3 Edward H. Brown Jr.,3 J. Ellen Marsden,4Dennis S. Lavis,s Michael L. Toneys,6 Tom N. Trudeau,' and Ross M. Horrall (retired)8

Iu.S. Fish and Wildlife Service, Green Bay Fishery Resources Office1015 Challenger Court, Green Bay, Wisconsin 54311

2Michigan Department ofNatural Resources, Fisheries Division65 Grant Street, Charlevoix, Michigan 49720

3National Biological Service, Great Lakes Science Center1451 Green Road, Ann Arbor, Michigan 48105

4111inois Natural History Survey, Lake Michigan Biological StationBox 634, 400 17th St., Zion, lllinois 60099

5u.S. Fish & Wildlife Service, Ludington Biological Station229 South Jebavy Drive, Ludington, Michigan 49431

6Wisconsin Department ofNatural Resources, 110 South Neenah AvenueSturgeon Bay, Wisconsin 54235

71llinois Department of Conservation, Lake Michigan Program9511 Harrison Street, Des Plaines, lllinois 60016

8Marine Studies Center, University ofWisconsin-MadisonMadison, Wisconsin 53706

ABSTRACT. Progress toward lake trout restoration in Lake Michigan is described through 1993.Extinction of the native lake trout fishery by sea lamprey predation, augmented by exploitation andhabitat destruction, resulted in an extensive stocking program of hatchery-reared lake trout that beganin 1965. Sea lamprey abundance was effectively controlled using selective chemical toxicants. The ini­tial stocking produced a measurable wild year class of lake trout by 1976 in Grand Traverse Bay, butfailed to continue probably due to excessive exploitation. The overall lack of successful reproductionlakewide by the late 1970s led to the development and implementation in 1985 of a focused inter­agency lakewide restoration plan by a technical committee created through the Lake Committee struc­ture of the Great Lakes Fishery Commission. Strategies implemented in 1985 by the plan included set­ting a 40% total mortality goal lakewide, creating two large refuges designed to encompasshistorically the most productive spawning habitat and protect trout stocked over their home range,evaluating several lake trout strains, and setting stocking priorities throughout the lake. Target levelsfor stocking in the 1985 Plan have never been reached, and are much less than the estimated lakewiderecruitment of yearlings by the native lake trout stocks. Since 1985, over 90% of the available laketrout have been stocked over the best spawning habitat, and colonization of the historically productiveoffshore reefs has occurred. Concentrations of spawning lake trout large enough for successful repro­duction, based on observations of successful hatchery and wild stocks, have developed at specific reefs.Continued lack of recruitment at these specific sites suggests that something other than stock abun­dance has limited success. Poor survival of lake trout eggs, assumed to be related to contaminant bur­den, occurred in the late 1970s and early 1980s, but survival has since increased to equal survival inthe hatchery. A recent increase in lamprey wounding rates in northern Lake Michigan appears to berelated to the uncontrolled build-up of lampreys in the St. Marys River a tributary of Lake Huron. Ifleft uncontrolled, further progress toward restoration in the Northern Refuge may be limited.

INDEX WORDS: Lake trout, Lake Michigan, fish populations, restoration, sea lamprey.

128

Progress Toward Lake Trout Restoration in Lake Michigan 129

70 ~----------,----=----:---~---;::;-::-:-::-:-:-::--­--- Michigan -+- Superior - Huron - - Ontario

tial institutional structure that developed across the GreatLakes to address sea lamprey control and fisheriesrestoration basin-wide has been described by Smith et al.(1974), Fetterolf (1980), and Eshenroder (1987). Thepurpose of this paper is to describe how .la~e troutrestoration has been implemented for Lake MIchIgan andto evaluate our progress to date. To accomplish this, it isnecessary to consider the historical pre-lamprey condi­tions of the stocks as well as their condition today.

The Native Lake Trout Fishery of Lake Michigan

Brown et al. (1981) described the discrete stocks of laketrout that were exploited commercially in Lake Michigan,based on historical records such as U.S. Fish Commissionreports and interviews with commercial fishermen w~o

fished in the 1930s and 1940s when lake trout were stillabundant. Native lake trout were broadly separated intodeep-water and shallow-water forms that made up differ­ent stocks and stock complexes. A fat, deep-water form oflake trout, closely resembling the siscowet of Lake Supe­rior was found in the Beaver Island area of northern LakeMi~higan and in parts of Lake Huron in the mid-1800s buthad disappeared from Lake Michigan by the early 1900s(Strang 1855, Koelz 1926). The decline of this siscowet­like form was attributed to exploitation because, in themarkets of that time, its salted product was worth morethan double that of other forms. Stream spawning forms oflake trout, such as those reported in Lake Superior (Loftus1958), were not mentioned in any of the published ac­counts for Lake Michigan.

Three distinct stock complexes of lake trout were stillpresent in Lake Michigan in the early 1900s, and, basedon fishermen's accounts, may have persisted until all wereeliminated in the mid 1950s (Brown et al. 1981). The firstgroup included the shallow-water reef trout. These troutwere comparatively larger, leaner, and had a lower fatcontent than the deep-water forms and were generallymore abundant in the northern half of the lake. Theyspawned on shallow reefs and shoals generally a~ depthsranging from 1 to 23 m. The second form of native laketrout in Lake Michigan was described as the salmon orbay trout that existed entirely in Green Bay and at one lo­cation in the lake proper. Bay trout were small, lean, andvery red-fleshed and spawned about 10 days later thanshallow-water trout, in deeper water, over sand, gravel,and mud substrate. The third major form of lake trout wasthe deep-water trout, which was generally a smaller,deeper-bodied fish with a higher fat content than the shal­low-water trout. Deep-water lake trout in southern LakeMichigan spawned predominately on clay bottoms atdepths of 50-85 m in a zone extending from Milwaukeesouth and eastward around the lake to near St. Joseph,Michigan. Deep-water lake trout also spawned farthernorth on the Sheboygan, Northeast, East, and MilwaukeeReefs in the middle of the lake, between Milwaukee, Wis­consin and Whitehall, Michigan, over clay, gravel, andlimestone outcroppings at depths of 55-79 m (Fig. 2).

19601950194019301920oh--,...~~,.,--r~~---,~~~c-p-~~~~~""""-f-J1910

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INTRODUCTION

The native lake trout (Salvelinus namaycush) of LakeMichigan supported the largest lake trout fishery in theWorld before it was driven to extinction mainly by at­tacks from the exotic sea lamprey (Petromyzon marinus)in the 1940s and 1950s, exploitation, and habitat degra­dation (Eschmeyer 1957). Lake Michigan is only thethird largest of the Great Lakes, yet it consistently pro­duced more native lake trout per surface area and sus­tained higher annual catches than any of the other GreatLakes (Fig. 1). Lake trout preyed mainly on very abun­dant deep water ciscoes or "chubs" (Coregonus spp.),sculpins (Cottidae), and sticklebacks (Gasterosteidae)(Goode 1884, Van Oosten and Deason 1938, Hile 1953,Smith 1972). Burbot (Lota Iota), historically the onlyother open water predator, had similar predatory habitsbut were much less abundant than lake trout, which wereknown to prey occasionally on burbot (Milner 1874).This comparatively simple predator-prey system, withlake trout at its apex, was one of the most stable in theGreat Lakes (Hile 1953, Smith 1972). The stability wasan important factor in the lack of major fluctuations inthe commercial catch of lake trout during many decadesof high and frequently abusive exploitation (Hile 1953,Smith 1972). In 1927-1944, a period defined by Hile etal. (195la) as the "modem" fishery, the annual harvestof lake trout averaged 2,563 t.

Although the fish community of Lake Michigan andthose of other Great Lakes have been modified consider­ably by more than 100 years of fishing, habitat degrada­tion, and other limiting factors, the invasion by the sealamprey created an unprecedented crisis for managementagencies after it was first seen there in 1936. The essen-

FIG. 1. Commercial yield (kg/km2) of lake trout fromLake Michigan, Lake Superior, Lake Huron, and LakeOntario in 1910-1960 (Data from Baldwin et aI.1979).

130 Holey et al.

MM-3

District Boundary

State Boundary

N

I0 10 20 30 40

I ISTATUTE '-'ILES

FRANKFORT

• WHITEHALLWhite Lake

Stony Lake

• Ludington

I

Trt¥Jt Is Shoal 10Point aux BIIrques .~ /)

I 0:Gulll: la ~r

Boulder Ree~. • Richard's Reef

MM-~ N'FoxlsaS. ~oxls~

Fisherman IsCHARLEVOIX

Northport PointBellow Island

Traverse ShoalD TRAVERSE BAY (MM-4)

New Mission PointOld Misaion Point

Suttons PointTucker Point

Bowers HarborMarion lalandAcme

/(------­

Portage Lake Reef.

/

/- - - - - - - - -I

I

.' Sheboygan Reef,,WM-5

Northeast Reef.

II MM-6

Northeim Reef I+44° _88° I

IHavenSHEBOYGAN

GREEN BAY

SAUGATUCK

• campbell Power PlantPort Sheldon

• lake Michigan B8ach·St. Joseph

MM-7

MM-B

.'Milwaukee Reef

I • BridgmanMichiana Ree • lakeside

-,ND '.- MICHIGAN CITY

Bums Waterway Harbor

IL

WM-6

East Reel

• Julian's Reef

• Black Can Reef ,• Soutll Milwaukee Reef

(Bulishit Shoals) ,

-----------,• Wind Point Shoal

t-------,,- - - - -,

I

I

I

I

I

ICHICAGO

Wilmette.,

Glencoe.

WAUKEGAN

Fort Sheridan.

WMefishBay

MILWAUKEE

FIG. 2. Boundaries of statistical districts and locations of stocking, sampling, or spawning sites in Lake Michigan.

Progress Toward Lake Trout Restoration in Lake Michigan 131

This midlake reef complex was said by many to be themost productive spawning area in the lake. Throughout1948-1952 and part of 1953 catch rates of small nativetrout in chub nets fished on Sheboygan Reef were similarto those of small trout in experimental chub nets fishedin 1930-31 before the sea lamprey invasion (Eschmeyer1957). By 1955, however, no lake trout catches were re­ported from that area.

Conclusive evidence that exploitation played a signifi­cant role in the final catastrophic decline of lake trout islacking. In fact, Hile et at. (1951 a) reported that, "Thedata ... fail completely to show a level of fishing inten­sity that would account for the recent decline in the laketrout fishery of Lake Michigan." Van Oosten (1949) re­ferred to the gradual long-term decline in production oflake trout in Lake Michigan in 1893-1938 as an exampleof depletion "in the face of greatly increased fishery in­tensity and expanded operations." However, Hile et at.(1951a) showed that fishing intensity declined in State ofMichigan waters at the end of that period (i.e., in1932-34) and remained below the 1929-1943 meanthrough 1937.

Coble et at. (1990) reanalyzed the historical lake troutcatch-effort statistics of Lake Michigan, and LakesHuron and Superior as well, to assess the role of fishingin the destruction of lake trout. Based on regressionanalysis of catch-per-effort (CPE) time series data, theirresults corroborated those of Hile et at. (1951a). Theyfound that instead of declining, catch per effort in large­mesh gillnets increased in State of Michigan waters ofLake Michigan from 1929 through 1946--seven years be­fore and 10 years after the sea lamprey was identified inthe lake. Coble et at. concluded that evidence of over­fishing before the impact of sea lampreys was found onlyin Lake Superior, as did Hile et at. (1951 b).

Though exploitation alone may not have caused thecatastrophic decline of Lake Michigan lake trout, it isstill possible that because of technological improvementsin gear, fishing effort was more effective in the 1930sand early 1940s and, together with fishing up of stocks,masked the lake trout decline in Lake Michigan as wellas Lake Huron (Pycha 1962, Eshenroder et at. 1995).Exploitation probably did reduce the resiliency of the na­tive lake trout stocks for surviving the increased mortal­ity from sea lamprey predation. Various stocks had beenfished down to a substantially lower level between thelate 1880s and 1930s and a number of local stocks appar­ently had been destroyed by fishing and habitat degrada­tion: e.g., pollution in lower Green Bay and inshore areasof the southern basin in general (Smith and Snell 1891).The drastic decline of whitefish in the southern half ofthe lake suggests that they were even more vulnerableand susceptible to exploitation than were lake trout(Smith 1908). The record-high production of lake troutin the late 1800s and early 1900s, which was followed bya gradual decline through the 1920s, apparently reflectedfishing down of the then surviving stocks to the lower

near-equilibrium level of the 1930s and early 1940s(Smith 1968, Hile et at. 1951a). These signs of attritionand the strong probability that yields to the fisherieswere near the maximum sustainable just before the sealamprey became a problem had probably reduced the po­tential resiliency of the stocks and, ultimately, theirchances of persisting except in a few isolated areas asoccurred in the Apostle Islands, Lake Superior, andGeorgian Bay, Lake Huron (Berst and Spangler 1973).

Development of the Lake Michigan Lake TroutRestoration Plan

The goals and objectives for the restoration of laketrout in Lake Michigan have evolved since the first massplanting of lake trout was made in 1965 under the aus­pices of the Great Lakes Fishery Commission (GLFC);the GLFC was formed in 1955 to coordinate fishery re­search and to develop measures to control sea lampreyswithin the Great Lakes (Fetterolf 1980).

The first group to focus on the specific lake troutrestoration needs of Lake Michigan was the Lake Michi­gan Study Group (LMSG), which was formed in 1966.The LMSG, although not officially a part of the GLFC'sLake Committee structure, was represented by biologistsfrom the four states bordering the lake, and the U.S. Bu­reau of Commercial Fisheries. The LMSG evaluated theeffectiveness of sea lamprey control and the large-scaleplanting of hatchery-reared trout to reestablish lake troutstocks.

The efficacy of the goal to restore self-sustainingstocks of lake trout was questioned as early as 1970, amere 5 years after initiation of the large-scale lake troutstocking program. The LMSG reported to the LakeMichigan Committee (LMC) of GLFC at the LMC's an­nual meeting in 1970, that "The Study Group is inclinedto believe that the high catch of lake trout combined withthe losses to the residual lamprey population may indeedprevent attainment of this objective (restoration), but atthe same time it was aware that restrictions on the sportfishery would conflict with the present objective of thestates of Michigan and Wisconsin to build up an inten­sive sport fishery as rapidly as possible. It, therefore, re­quests that the Lake Michigan Committee consider thisrequest at its meeting in March and decide whether anew objective should be established and recommendedto the Great Lakes Fishery Commission." Obviously,fisheries biologists were concerned that the restoration oflake trout in Lake Michigan was threatened by the exces­sive mortality caused by sea lamprey predation, the inci­dental harvest by the commercial fishery, and theincreasing targeted harvest by the developing sport fish­ery. The biologists also recognized that the restrictionsrequired to enhance the possibility for lake trout restora­tion would probably not have been supported given thesocial and political climate of the early 1970s.

In 1976, at the request of the LMSG, the LMC createdthe Lake Michigan Lake Trout Technical Committee

132 Holey et al.

FIG. 3. Boundaries of lake trout rehabilitation zonesin Lake Michigan.

target mortality rate applies to the entire lake; however,the likelihood of not exceeding that rate in a given regionwas one of the factors considered when the boundariesfor the restoration zones were determined. The authors ofthe plan recognized that, in order to hold mortality at orbelow the 40% goal in some areas of the lake, intensifi­cation of sea lamprey control or restrictions on lake troutharvest would be necessary.

To focus restoration in areas with the best lake trouthabitat and chances of success, the lake was divided intofour restoration zones; refuges, primary, secondary, anddeferred zones (Fig. 3). Two offshore refuges were cre­ated to encompass what were believed to be the mostproductive native lake trout spawning reef areas in LakeMichigan (Coberly and HorraH 1980, Brown et al. 1981,Goodyear et al. 1982, Organ et al. 1978). The Northern

(LMLTTC), and charged it with "developing a morecomprehensive data base, estimating vital population pa­rameters, and projecting theoretical allowable harvests oflake trout consistent with policies and goals of the Com­mission and member agencies." At its 1982 annual meet­ing, the LMC charged the LMLTTC with developing aformal restoration plan (LMC 1982). The content of theplan was influenced significantly by the proceedings oftwo major symposia held in the early 1980s: the StockConcept Symposium (STOCS) (Can. J. Fish. Aquat. Sci.,Vol. 38, No. 12) and A Conference On Lake Trout Re­search (CLAR), (GLFC Tech. Report. No. 40). In 1985,the LMC formally adopted and began implementation of"A Lakewide Management Plan For Lake Trout Rehabil­itation In Lake Michigan" (Plan) as developed byLMLTTC (1985).

The long range goal of the restoration plan is toachieve a self-sustaining lake trout population able toyield an annual harvest projected conservatively at500-700 thousand fish weighing 1,100 t (LMLTTC1985). This projection is conservative because of the lossof strains that were adapted to different habitats, thelarge stocks of exotic salmonines that now compete for agreatly altered and unstable forage base, and habitatdegradation. Three interim objectives were established tomeasure progress toward the restoration goal:

Within 10 Years; Achieve larger spawning popula­tions in refuges and high-priority zones that aresubject to no more than 40% annual mortality,Within 15 Years; Demonstrate routinely in trawland gillnet surveys the presence of lake-producedyoung of several year classes in refuges and highpriority zones,Within 20 Years; Show that spawning stocks ofhatchery-origin fish are being augmented by signif­icant numbers of wild spawners.

To achieve the interim objectives and the long termgoal, the plan called for a cap on total annual mortality,the classification and establishment of four restorationzones, specific stocking rates by zone, a study to evalu­ate the performance of several different lake troutstrains, experimentation with alternative stocking tech­niques, a monitoring program to determine long-termtrends in lake trout egg survival and the effects of conta­minants on survival, and a thorough assessment programto enable proper evaluation of progress.

The target or upper limit on total annual mortality ratefor lake trout in Lake Michigan is 40% (LMLTTC 1985),based on Healey's (1978) observations that lake troutpopulations with annual mortality in excess of 50% wereunable to sustain themselves through reproduction. TheTechnical Committee reasoned that reproductive ineffi­ciency of planted lake trout and other constraints notedabove would make a mortality limit higher than about40% unrealistic for attaining the restoration goal. The

GREEN BAY

SHEBOYGAN

MILWAUKEE

WAUKEGAN

CHICAGO

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_REFUGE

~PRIMARY

[I SECONDARY

DDEFERRED

.... .... . ..T GRAND HAVEN

SAUGATUCK

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o 10 ao _ 4Cl 10 •, , , , , , ,

Progress Toward Lake Trout Restoration in Lake Michigan 133

Refuge was established in 1985. It covers more than1,550 km2 in the Beaver Island area and contains a largecomplex of shallow-water (0-20 m) spawning reefs (Fig.3). Three specific reef sites, Boulder Reef, Richard'sReef, and Gull Island Shoal were chosen, based on his­torical records and habitat surveys (Edsall et al. 1989), toreceive all the lake trout stocked in the Northern Refuge(Fig. 2). The Southern or Midlake Refuge, in the south­central portion of the lake, was originally established in1984. It has been enlarged several times to its presentsize of more than 2,859 km2 and encompasses the com­plex of four large deep-water (45-80 m) spawning reefs(Fig. 3). Stocking in the Southern Refuge has been di­rected at the Sheboygan, Northeast, East, and Milwaukeereefs (Fig. 2). Regulations have been promulgated thatprohibit fishing and the possession of lake trout withinthese refuges. The stocking goal for each refuge is750,000 lake trout annually. The combination of no har­vest and high stocking rates was designed to address thehypothesis that (since stocking began in 1965) recruit­ment had been too low and exploitation too high to buildup adequate standing stocks of hatchery trout that couldspawn successfully (Eshenroder et al. 1984, Peck 1979,Rybicki and Keller 1978).

The rest of Lake Michigan outside the refuges wasclassified based on the availability of quality spawninghabitat, historic commercial lake trout production, andthe lakewide mortality goal (LMLTTC 1985). Primaryzones were established in the waters of northern Michi­gan and Wisconsin, and in a small area of Illinois (Fig.3). The quality of the spawning habitat in the primaryzones may equal that which exists in the refuges. Thedifference between a primary zone and a refuge is lessprotection from exploitation. In addition to the majorrefuges recommended in the plan, two smaller refugeswere created within the primary zones by independentactions of the states of Wisconsin and Illinois. The ClayBanks Refuge was created in 1986 to protect shallow­water near-shore spawning reefs between Sturgeon Bayand Algoma, Wisconsin (Fig. 3). Harvest restrictionswithin the Clay Banks Refuge are similar to those in thetwo major refuges. In 1985, Illinois created a smallrefuge that encompasses the Julians Reef spawning habi­tat, where sport fishing for lake trout is allowed but com­mercial fishing is prohibited (Fig. 3). The deferred zonecovers the extreme northern waters of Wisconsin andMichigan, and the waters of Green Bay (Fig. 3). The de­ferred zone contains the major commercial fishinggrounds for lake whitefish in Lake Michigan, whichoverlap some historically productive lake trout spawninghabitat. However, because the expected high incidentalcatches of lake trout in the whitefish and chub fisherieswould make the 40% mortality target unattainable, the1985 restoration plan postponed any restoration effortsin the deferred zone (LMLTTC 1985). The secondaryzone, which covers the remainder of the lake (Fig. 3),

has less quality spawning habitat than do the refuges andprimary zones.

Strategies to evaluate the potential of several strains oflake trout for establishing self-sustaining populations inLake Michigan were developed and implemented in boththe Northern and Southern refuges (Krueger et al. 1983).Since native Lake Michigan lake trout stocks were un­available, broodstocks were developed from donor popu­lations outside the basin that were established fromnative Lake Michigan stocks or occupied habitats similarto the habitats in the refuges. In the shallow-waterspawning habitat of the Northern Refuge the Marquette,Wyoming, and Domestic X Gull Island Shoal Hybridstrains were developed and stocked, beginning in 1986.The Marquette strain, developed from a Lake Superiorshallow-water spawning stock and used as the primarybroodstock to begin the stocking program in 1965(Krueger et al. 1983), was chosen as the control strainfor both refuges. The Wyoming-strain broodstock wasdeveloped from wild lake trout populations in LewisLake in Yellowstone National Park. The lake trout popu­lation in Lewis Lake was originally established from frythat were produced by wild lake trout from Lake Michi­gan in the late 1800s, shipped as fry to YellowstonePark, and stocked in Lewis Lake which at the time wasbarren (Krueger et al. 1983). The Domestic X Gull Is­land Shoal Hybrid strain was developed by crossing wildGull Island Shoal, Lake Superior males with Marquette­strain hatchery females to increase the wild adapted traitsin the hatchery broodstock. In the deep-water spawninghabitat of the Southern Refuge, the Marquette, Seneca,and Green Lake strains of lake trout were chosen forevaluation (Krueger et al. 1983). The Seneca-strainbroodstock was developed from deep water spawningpopulations of lake trout in Seneca Lake, New York. TheGreen Lake strain was developed from lake trout whoseorigin was from the midlake reef complex of LakeMichigan, which had been stocked in Big Green Lake,Wisconsin, specifically to try to induce spawning ondeep-reef areas in the lake (Hacker 1956). There were nospecific recommendations as to which strain to stock inthe primary and secondary Zones.

The recommended number of lake trout to be stockedin each restoration zone was based on the amount of sur­face area of water 80 m and shallower, the depth rangeconsidered to be lake trout habitat (LMLTTC 1985). Thestocking rate was set at 2.47 yearling trout per ha exceptin the refuges where the goal was 750,000 in each and inthe deferred zone where no stocking was recommended.To meet the stocking needs outlined in the 1985 plan,5.844 million fish would be required (Table 1). The entirelake trout production capabilities of the National FishHatchery system for stocking all three of the upper GreatLakes was only 5 to 6 million fish and there seemed littleprospect that new hatchery facilities would be built tomeet the stocking goals for the upper Great Lakes. In1988, the Lake Michigan Technical Committee (LMTC

134 Holey et al.

TABLE 1. Original (1985) and revised (1988) yearling lake trout stocking rates for Lake Michigan. Statisical dis-tricts are described in Figure 2.

1985 Plan 1988 Revision

Zone andStatistical Surface Area (ha) Number to Stock NumberDistrict of Water 0-80 m at 2.47 Fishlha Zone/Location (in priority rank) to Stock

REFUGES REFUGESNorthern MM-3 121,000 750,000 Northern 750,000Southern WM-5, MM-7 42,000 750,000 Southern 750,000

162,000 1,500,000 1,500,000

PRIMARY PRIMARY

MM-3 154,000 381,000 Clay Banks (WM-3) 196,000MM-4 73,000 181,000 Julians Reef (IL) 100,000MM-5 112,000 276,000 L. Traverse Bay Cement Plant (MM-3) 100,000WM-3 53,000 130,000 Acme (MM-4) 100,000WM-4 27,000 66,000 Lee's Reef (MM-4) 115,000IL 27.000 100.000 Old Mission Point (MM-4) 115,000

446,000 1,134,000 Good Harbor Reef (MM-5) 154,000Point Betsy (MM-5) 154,000Trout Island Shoal (MM-3) 100.000

1,134,000

SECONDARY SECONDARYMM-6 104,000 256,000 South Milwaukee Reef (MM-5) 100,000MM-7 126,000 312,000 Lakeside Reef (MM-8) 100,000MM-8 356,000 880,000 Stony Lake-White Lake Reefs (MM-7) 100,000WM-4 96,000 236,000 Saugatuck Reef (MM-8) 100,000WM-5 191,000 472,000 Michiana Reef (MM-8) 100,000WM-6 84,000 208,000 Northeim Reef (WM-4) 100,000IL 271,000 669,000 Portage Lake Reef (MM-6) 100,000IN 71.000 176.000 Ludington Reef (MM-6) 100,000

1,299,000 3,210,000 L. Mich. Beach-St. Joe Reefs (MM-8) 100,000900,000

DEFERRED DEFERREDGreen Bay 442,000MM-2 150,000MM-3 403,000WM-3 179,000

1,174,000

GRAND TOTAL 3,081,000 5,844,000 GRAND TOTAL 3,534,000

formerly the LMLTTC and renamed to reflect a broad­ened charge) modified the stocking goals for Lake Michi­gan to be more in line with the hatchery systemproduction capabilities (LMTC 1988). The stocking goalsfor the refuges and primary areas remained intact, but thestocking method in the primary zones changed fromshore stocking to offshore stocking by boat at specifichistoric spawning reef locations (Table 1). In the sec­ondary zones, a goal of 100,000 fish was set for each ofnine reef locations that had a record of historic spawning

activity (Table 1). The modified Lake Michigan stockinggoal called for a total of 3.534 million fish annually.

Studies to test stocking of early life history stages, suchas eggs and fry, as an alternative to the standard practiceof stocking hatchery-reared yearling fish were endorsed inthe 1985 plan as long as the studies would not interferewith the evaluation of results of the yearling stocking pro­gram (LMLTTC 1985). A fry-planting experiment hadbeen underway for a number of years on Horseshoe Reefin Green Bay (HorraH, personal communication). A pro-

Progress Toward Lake Trout Restoration in Lake Michigan 135

gram to monitor the hatchability and survivability of feralLake Michigan lake trout eggs was also proposed, becausepoor hatching success and survival of eggs from LakeMichigan lake trout in the laboratory was attributed totheir contaminant burden (Mac and Edsall 1991).

The draft Lake Michigan Plan, particularly its recom­mendations to establish refuges, provided valuable insightto State, Tribal, and Federal officials during the delibera­tions on the Treaty Fishery in the State of Michigan wa­ters of the Upper Great Lakes that led to a negotiatedsettlement in 1985. Adoption of the Northern Refuge inthe Consent Decree documents with boundaries nearly thesame as those in the Plan speeded acceptance of the Planby the State of Michigan. Other zones specified in theConsent Decree addressed regulatory needs peculiar totreaty fishing and differed somewhat from those devel­oped by the Technical Committee in its lakewide Plan.

Determination of the success of lake trout restorationin Lake Michigan is dependent on adequate assessment ofthe effectiveness of restoration strategies. An assessmentand evaluation plan was prepared by a subcommittee ofthe LMLTTC and appended to the 1985 plan (LMLTTC1985). The plan outlined specific assessment activitiesand data requirements that had been agreed on by thestate, tribal, and federal fisheries agencies around thelake. Trawls and graded-mesh gillnets (GMGN) wereidentified as the primary assessment gear for lake trout.Age III or younger lake trout are most vulnerable to thetrawl, and lake trout older than age III are most vulnera­ble to the GMGN. Although slight variations in gear maybe in use by some agencies, generally a standard gang ofGMGN included equal lengths of mesh sizes from 6.35 to15.24 cm stretch measure by 1.27 cm increments, fishedfor one night. To standardize assessment catches, thecatch per effort (CPE) from GMGN was expressed as thenumber caught per 305 m of a standard gang. Relativestock abundance and mortality rates were determinedfrom trout caught in GMGN fished in spring to late sum­mer, depending on the agency that conducted the survey.Spawning activity was measured by GMGN surveys dur­ing the fall spawning period (October to mid-November).

Sea Lamprey Control

The control of sea lampreys was the first step neces­sary to restore lake trout in any of the Great Lakes. InLake Michigan, sea lamprey spawning runs had beenconfirmed in 79 streams by the end of 1949 (Smith andTibbles 1980) and initial attempts to control the burgeon­ing sea lamprey population were targeted on these mi­grations; first with mechanical weirs (seven wereinstalled in streams along the west and south shore) andlater with more effective electromechanical weirs (65 ofthese combination electrical barrier and mechanical trapswere installed and operational by 1958). The develop­ment of a chemical lampricide to destroy the stream­dwelling larval phase of the sea lamprey (Applegate etal. 1961) hastened the abandonment of weirs, which had

a limited effect because of a variety of mechanical, phys­ical and biological problems, and many were operatedonly for a few years. Experimental chemical treatment oftributaries of Lake Michigan was begun in 1960 and, bythe end of 1965, most lamprey producing streams hadbeen treated once. The completion of this first round oftreatments caused the number of adult lampreys capturedat index electric weirs to decline by 80-90% by 1966.

Sea lamprey predation on fish populations in LakeMichigan has declined significantly over the last twodecades in most parts of the lake, although the averagesize of parasitic adults has doubled and their potential tokill small hosts increased six-fold (Kitchell 1990). Lam­prey marking (wounding and scarring) rates on many fishspecies are low, particularly in comparison with markingrates on the same species in other lakes (Table 2).

Trends in fresh (Type AI) lamprey wounding on laketrout (King 1980) in 1971-1992 varied among areas ofthe lake, but generally remained below 5% and the high­est rates occurred early in the period in northern Wiscon­sin and, in later years, in the northern Michigan section ofthe lake. Since 1984, marking rates (as measured by thenumber of Type AI, All and AlII marks per 100 fish)throughout the lake have generally increased across allsizes of fish (Fig. 4). The average lakewide sea lampreywounding rate was 5.4 wounds per 100 fish in 1992, thehighest since 1984 (Ebener 1993). Overall, lamprey-in­duced mortality, computed from statistical relations be­tween the number of wounds per fish and the probabilityof a lake trout surviving a single lamprey attack (Swinkand Hanson 1986, Swink 1990), is low in Lake Michigan,and averages less than 7% in most years, 1984-1992. Thelakewide rate has, however, increased annually from4.1 % in 1988 to 6.3% in 1992 - mainly the result of in­creasingly heavy predation on large fish in the northernMichigan region of the lake where mortality has ex­ceeded 14% each year since 1989 (Fig. 5). This region isadjacent to northern Lake Huron where lamprey-induced(and natural) mortality on lake trout has exceeded 45%because of the sea lamprey production in the St. MarysRiver, the largest uncontrolled source of sea lampreys inthe Great Lakes (GLFC 1993). Further movement intoLake Michigan of the uncontrolled St. Marys River lam­prey population will jeopardize the continued build-up oflake trout spawning stocks in the Northern Refuge.

The current objective for sea lamprey control in LakeMichigan is to reduce the present populations by inte­grating existing and new technologies. An IntegratedManagement of Sea Lamprey (lMSL) initiative will seekto further refine the objective for sea lamprey abundanceand define the optimal sea lamprey control program tomeet that objective. Integration of other control methodsincluding intensified chemical treatments, additional sealamprey barrier construction, increased trapping, andpossibly sterile male releases will be used to further re­duce populations to appropriate economic-injury levelsdictated through IMSL processes.

136 Holey et ale

TABLE 2. Average number ofsea lamprey wounds per 100 lake trout, whitefish, and bloater chubs ofall sizes fromU.S. waters ofLakes Michigan, Superior, and Huron, 1986-1992.

FishSpecies Lake 1986 1987 1988 1989 1990 1991 1992

Lake trout* Michigan 3.9 2.7 3.4 3.8 4.2 4.8 5.4Superior 4.7 5.1 4.1 9.0 7.0 5.9 6.5Huron 11.5 15.3 8.0 12.7 7.8 19.6 21.5

Whitefish Michigan 0.5 0.0 0.0 0.0 0.0 0.0Superior 0.0 0.3 0.0 0.0 0.0 0.1Huron 0.9 0.9 0.0 0.1 0.1 0.4

Bloater chub Michigan 0.0 0.0 0.0 0.0Huron 0.7 1.2 1.9 1.2 4.1 1.7

*Lake trout ~ 17 inches Lake Superior, ~ 21 inches Lake Michigan, ~ 14 inches Lake Huron.

~N. Wisconsin IZLIs. Wisconsin/Illinois OS. Michigan/lndiana .N. Michigan

16

:5 14e; 12:Y..!!l

8 10~(/) 8DC::J0 63:>-OJCi 4Eco--! 2

01984 1985 1986 1987 1988 1989 1990 1991 1992

25~~20 .co~E 15

DOJU

~ 10·.<:;

~0­Ej

1986 1988 1990 1992

FIG. 4. Lamprey wounding rates on lake trout (AI,All, AlII marks/lOO lake trout) in Lake Michigan,August-November 1984-1992.

Performance of Hatchery-Reared Lake Trout

Stocking

Stocking hatchery-reared yearling lake trout has beenone of the primary management actions to reestablishlake trout in Lake Michigan. The first stocking protocolfor lake trout was formulated by the Special Committeeon Lake Trout Rehabilitation in 1958 (GLFC 1958). TheCommittee established that only fin-clipped, yearlinglake trout would be planted in the spring of the year fromeither dockside or in Great Lakes tributaries, but the pro-

FIG. 5. Conditional lamprey-induced mortality (%)on large lake trout (> 734 mm) in Lake Michigan,1984-1992.

tocol encouraged the experimentation with fall plantsand other release techniques. The majority of the laketrout stocked in Lake Michigan have been supplied bythe U.S. Fish & Wildlife Service's fish hatchery system.During the development of the lake trout stocking pro­gram, however, eggs were supplied by broodstocks heldat the Marquette, Michigan State Fish Hatchery. The firstyearling plants, totalling 1.07 million fish, were made in1965 across the northern one-third of the lake (GLFC1965). The numbers of lake trout stocked in Lake Michi­gan increased steadily until the early 1970s, when they

Progress Toward Lake Trout Restoration in Lake Michigan 137

leveled off at about 2.4 million fish. Subsequent planti­ngs have generally fluctuated about that level (Fig. 6).The largest plants of lake trout have been made since theimplementation of the 1985 Plan.

The current 3.534-million-fish lakewide stocking goalfor lake trout has never been achieved (Fig. 6). Mortali­ties of epidemic proportions in the federal and statehatchery system that supplied lake trout to the upperGreat Lakes began in 1983 (John Quam, U.S. Fish &Wildlife Service, personal communication) and resultedin the lowest number of lake trout stocked into LakeMichigan since 1965 (Fig. 6). A new viral disease, neverbefore encountered in lake trout hatcheries, was identi­fied as the cause of mortality. By 1986, all fish includingbroodstocks in three federal hatcheries and three statehatcheries were destroyed and the facilities were com­pletely disinfected.

Lake Superior lake trout of shallow-reef spawningheritage have constituted the vast majority of the troutplanted in Lake Michigan since 1965 (Fig. 7). The strainexperiment adopted by the 1985 Plan was temporallyabandoned in Lake Michigan after 1986, because of thedisinfection of the Iron River National Fish Hatchery andthe loss of all the broodstocks that had been developedfor the experiment. The Northern Refuge was stockedwith a full compliment of the strains called for in 1986,before the broodstocks were destroyed (Fig. 8). The dis­ease outbreak in the hatchery system eliminated any pos­sibility of producing the Domestic-Gull Island ShoalHybrid because wild gametes could no longer be broughtinto the hatchery system without a disease clearance,which requires a two-year quarantine period. In order tomaintain the recommended stocking density of therefuge experiments during the rebuilding of the desired

4----,--------.=----------=.---------------,• Northern Refuge D Southern Refuge

~ Primary D Secondary

[7J Deferred Green Bay ~ Deferred N. Michigan

3

Dill.:::c.uo+-'

(/)2(/)

co

1

58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 PLAN

Year Class

FIG. 6. Numbers of lake trout of the 1958-1991 year classes stocked (yearling equivalents where2.4 fall fingerlings =1 yearling after Elrod et aI. 1988) by restoration zone in Lake Michigan, andthe revised stocking goal for rehabilitation. Numbers stocked in the deferred restoration zone areshown for Green Bay and northern Lake Michigan waters separately. A year class was usuallystocked as yearlings, 1 year later.

138 Holey et al.

4----,--iiiiiii'""-::----------;=T=;;-----------=...-------------,• Green Lake I!ZJ Wyoming ~ Marquette

o Gull Is Outcross ~ Seneca 0 Clearwater

58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90

Year Class

FIG. 7. Numbers of lake trout stocked (yearling equivalents where 2.4 fall fingerlings =I yearlingafter Elrod et al.1988) by strain and by the 1958-1991 year classes in Lake Michigan. A year classwas usually stocked as spring yearlings.

broodstock strains, other available strains were used inboth refuges. Consequently, only Marquette-strain fishwere stocked in the Northern Refuge in 1987 and 1988(Fig. 8). Wyoming-strain lake trout became availablefrom the Saratoga National Fish Hatchery in Wyomingin 1989 and were stocked in increasing numbers through1992 when they accounted for half of the fish stocked inthe Northern Refuge (Fig. 8). Isle Royale-strain laketrout, from a broodstock developed by Minnesota De­partment of Natural Resources from wild lake trout cap­tured near Isle Royale, and Seneca-strain fish werestocked in small numbers in the Northern Refuge in1990. The Marquette strain has made up 64% of all thetrout stocked in the Northern Refuge since stocking wasbegun in 1986. Only Marquette-and Seneca-strain fishwere available for stocking in the Southern Refuge whenthe Plan was first implemented in 1985. The Green Lakestrain, though used extensively in 1967-1976 to stock

the southern portion of the lake (Fig. 9), was not avail­able because the broodstock was discontinued from thehatchery system in 1976 (Krueger et al. 1983). Subse­quently, the Wisconsin Department of Natural Resources(WDNR), Illinois Department of Conservation, and theU.S. Fish and Wildlife Service (USFWS) have workedcooperatively to rebuild a Green Lake broodstock fromeggs of feral (i.e., hatchery-reared) Green Lake fish re­captured in Lake Michigan (Kincaid et al. 1993). Tomaintain high stocking numbers in the Southern Refuge,Domestic x Gull Island Shoal hybrid fish were stocked in1986, Wyoming strain fish were stocked in 1990-1992and Lake Ontario-strain fish were stocked in 1990-1992(Fig. 9). The Lake Ontario-strain broodstock was devel­oped from feral Lake Ontario spawners in 1982 and1983. This strain was used because 60 to 80% of its ge­netic makeup was from the deep-spawning Seneca strain(Charles Krueger, Cornell University, personal commu-

Progress Toward Lake Trout Restoration in Lake Michigan 139

800 ,-----------------------,

600DS)looen.g 400cro(/)::>o

Lf-

200 -

PLAN 85 86 87 88 89 90 91 92

800

700

D 600~g 500en.g 400crocg 300o.cf- 200

100

a80 81 82 83 84 85 86 87 88 89 90 91 92 PLAN

D Gull Is OutX ~Wyoming • Marquette ~ Isle Royale ~ Seneca o Green Lake ~ Seneca

1711 Gull Is OutX 0 Wyoming

• Marquette

DL. Ontario

FIG. 8. Numbers of lake trout stocked (yearlingequivalents where 2.4 fall fingerlings =1 yearling afterElrod et aI. 1988) by strain in the Northern Refuge ofLake Michigan in 1985-1992.

nication). A small number of pure Seneca-strain fishwere stocked in the Southern Refuge in 1990 (Fig. 9).Green Lake-strain lake trout, from the redevelopingbroodstock, were stocked in small numbers in 1992. Afull complement (250,000) of Green Lake strain wasavailable in 1993-1994 (John Quam, USFWS, personalcommunication). Anticipating that major restoration ef­forts would be focused in the Midlake Reef area, WDNRdiverted some of its allocation of stocked lake trout,which were all Marquette-strain fish, from near shoresites to the Midlake Reef area in 1980-1984. Conse­quently, from 1980 to 1992 the Marquette strain hasmade up 65% of the 7.1 million fish the Southern Refugehas received (Fig. 9).

The 1985 Plan has had a dramatic effect on wherelake trout have been planted, and has directed the avail­able lake trout into the highest quality lake trout habitat.Almost the entire shoreline, including that of Green Bay,was stocked at some time in 1965-1984 (Fig. 6). Duringthat period, 53% of the lake trout were stocked into whatis now designated as secondary or deferred restorationzones, and only 9% were stocked in the area of the pre­sent refuges. Since the implementation of the Plan in1985, 90% of the lake trout have been stocked in eitherrefuges (56%) or primary (34%) areas, and only 10%have gone to the secondary and deferred zones com­bined. The method of stocking has also been modifiedsubstantially in recent years. The majority (76%) of thelake trout stocked in 1985-1991 were transported byboat and released directly above the target reef areas, as

FIG. 9. Numbers of lake trout stocked (yearlingequivalents where 2.4 fall fingerlings =1 yearling afterElrod et aI. 1988) by strain in the Southern Refuge inLake Michigan 1980-1992.

compared to only 27% in 1965-1984. Ferries were usedin the early years to stock fish over reef areas; however,because of the need for stocking substantial numbers intorefuge areas, the USFWS obtained and outfitted a vessel,the R/V Togue, for the sole purpose of stocking laketrout in Lakes Michigan and Huron.

Two alternative stocking methods have been tried inLake Michigan. The University of Wisconsin-Madisonstocked 5.14 million lake trout sac fry on HorseshoeReef in northern Green Bay in 1981-1987 and 220,000more on Northeast Reef, one of the four reefs in the mid­lake-reef complex, in 1982 (Ross Horrall, University ofWisconsin, retired, personal communication, and Fig. 2).Assessment surveys and onboard monitoring of commer­cial chub and whitefish fishing in Wisconsin waters havefailed to detect any survivors of those fry plants(Michael Toneys, WDNR, personal communication). Ar­tificial turf incubators (Swanson 1982) were used tostock lake trout eggs on Jacksonport Deep Reef nearJacksonport, Wisconsin in 1988, 1989, and 1992 (Fig. 2).The WDNR cooperated with commercial fishers to ob­tain 850,000 eggs in 1988 and 1.79 million eggs in 1989for the incubator experiment. In 1992, the USFWS col­laborated with the same two groups to stock 2.3 millioneggs. Survival of lake trout hatched from these eggstockings have not been verified to date. Evaluation ofthe egg-stocking technique in Lake Michigan cannot becompleted until after 1994 when survivors from the 1988egg stocking should be mature for the first time.

140 Holey et al.

Mortality and Harvest

High exploitation by sport and tribal commercial fish­eries that have developed on hatchery-reared lake troutcontinues to be an important limiting factor for therestoration of lake trout in Lake Michigan. Total annualmortality rates have not been below the target 40% goalexcept in a few locations. Excessive mortality is of great­est concern for lake trout restoration in eastern LakeMichigan, especially the northern waters. The excessivemortality has been attributed to sport and tribal commer­cial harvest (Rybicki 1991). A sport fishery developedfor lake trout as soon as the first lake trout grew to acatchable size in the early 1970s (Hansen et ai. 1990). In1978, Native American tribal commercial fishers beganexercising their treaty fishing rights in the ceded watersof Lake Michigan in the State of Michigan set forth inthe Treaty of 1836, and developed fisheries for bothwhitefish and lake trout. Both sport and tribal fisheriesdeveloped in Michigan waters in the 1970s just as thefirst stocked year classes were beginning to mature.Total annual mortality of lake trout caught in the springin graded-mesh gillnets on the eastern shore has neverbeen below the 40% target, and in 1975-1989 it in­creased from 46.4% to 77.7% in northern Michigan wa­ters of the lake, from 51.3% to 66.2% in central waters,and from 53.9% to 60.7% in southern waters (Table 3).

Total annual mortality rates have reached the 40% tar-

get in the Wisconsin primary zone and in Illinois waters(Table 3). As in northern Michigan waters, mortality inthe Wisconsin primary zone, measured from summergraded-mesh-gillnet surveys, steadily increased from 32to 38% in the 1970s to a high of 80% in 1985. Sincethen, however, the mortality (measured by graded meshgillnet surveys and spring pound-net surveys) hassteadily declined to very near the 40% level. Mortality inIllinois waters, measured from summer graded-meshgillnet surveys, has dropped steadily from above 50% inthe late 1970s to the low 20% level in 1991 (Table 3).That level of mortality appears to be unrealistically low,but recently the sport harvest of lake trout in Illinois wa­ters has been less than 6,000 fish (Brofka and Marsden1993), and estimated incidental losses of lake trout incommercial gillnets have declined greatly since 1986(Hess 1992). Mortality rates in the secondary zones inWisconsin measured at assessment summer graded­mesh-gillnet survey sites near Manitowoc and Milwau­kee have varied within the range of 40-60%.

In addition to the refuges that were created as a resultof the Plan, other sport and commercial fishing regula­tions have been modified by all management agencies toimprove the survival of lake trout and other stocked troutand salmon. The commercial harvest of lake trout wasbanned by all four states shortly after the stocking pro­gram began in 1965. Large-mesh gillnets were totallybanned in all Michigan waters in 1970, and in Wisconsin

TABLE 3. Annual mortality rates for lake trout caught in spring or summer graded mesh gill nets in Lake Michi­gan by region.

Year MM3+4 MM5+6 MM7+8 Saugatuck

Clay Banks

Gill PoundNets Net Manitowoc Milwaukee Illinois

SheboyganReef

1975 46.4 51.3 53.91976 49.1 47.2 49.91977 48.8 45.8 55.2 38.0 50.01978 55.6 48.2 55.3 34.0 67.01979 68.1 51.0 46.3 32.0 58.01980 56.0 57.2 48.4 58.0 48.01981 66.9 61.3 54.5 39.0 54.0 44.01982 64.5 57.8 52.0 54.0 44.01983 76.2 61.7 57.0 44.0 39.01984 69.0 62.1 80.0 56.0 53.0 46.01985 67.0 62.0 57.0 38.0 57.0 60.0 69.0 40.01986 68.0 55.9 60.1 42.0 43.0 62.0 57.0 44.0 42.01987 77.5 67.8 67.5 41.0 43.0 53.0 60.0 45.0 35.0 88.81988 77.7 66.2 60.7 48.0 47.0 50.0 47.0 31.0 84.81989 45.0 27.0 41.0 38.0 57.0 36.0 85.71990 44.0 46.0 41.0 51.0 27.0 58.11991 44.0 43.5 25.0 61.11992 40.1 345 27.0 40.7

Source of information: MM3+4, MM5+6, MM7+8, Rybicki (1991); Saugatuck, NBS; Clay Banks, Manitowoc, Milwau­kee, and Sheboygan, WDNR; Illinois, IDOC. Statistical districts are described in Figure 2.

Progress Toward Lake Trout Restoration in Lake Michigan 141

waters south of Baileys Harbor (approximately 90% ofthe state's waters) in 1978. The use of large-mesh gill­nets declined again in the remaining Wisconsin watersopen to that gear type with the implementation of indi­vidual whitefish quotas in 1989. Total large-mesh effortin Wisconsin waters has dropped from 155,000 km in1977 to an annual average of 7,600 km in the early1980s to an annual average of 4,300 km since 1989(WDNR, unpublished data). The estimated incidental killof lake trout in the fishery by large-mesh gillnets hasdropped from an average of 24,000 in the early 1980s to8,000 since 1989 (WDNR, unpublished data). State-li­censed commercial fishers are presently managed bylimited-entry rules in all four states. Small-mesh gillnetsare currently restricted to a low-profile type (less than 20meshes deep) for commercial fishers in Indiana, Illinois,and a portion of Wisconsin waters. Michigan banned itsstate-licensed commercial fishers from using small-meshgillnets in 1976.

Regulations have been implemented to limit the har­vest of lake trout by sport angling. The daily bag limitwas reduced from five to two in all states except Indiana,where it remains at five. The year-round season wasshortened to 1 May-Labor Day by Wisconsin in 1985.Michigan shortened the season from 1 May to 15 Augustin 1984, but extended it to Labor Day in 1989. In 1992,Michigan increased the minimum size limit (MSL) forlake trout from 254 mm to 610 mm for Michigan watersnorth of the 45th parallel. For 1992, at least, the largerMSL appears to have reduced the sport harvest of laketrout in that area by 50% (0. Rakoczy, MDNR,Charlevoix, MI, personal communication). Whether theincreased MSL continues to limit the sport harvest oflake trout in northern Michigan waters, and decreasestotal mortality, remains to be seen.

Accurate lakewide harvest estimates for Lake Michi­gan were not available until 1985. Lakewide harvest oflake trout has decreased from 1,211 t (metric tons) in1985 to 581 t in 1992 (Fig. 10). Sport fishing has ac­counted for the majority of the lake trout removals. Re­cent lakewide declines in the sport harvest can beattributed primarily to the overall decrease in sport fish­ing effort on Lake Michigan as a result of the collapse ofthe chinook fishery in 1987 (LMTC 1993).

Abundance

Relative abundance of stocked lake trout has increasedas a result of restoration measures. The best method ofcomparing lake trout abundance lakewide is from springand summer assessment graded-mesh gillnetting CPEdata, since stock size has been estimated only for Michi­gan waters (Rybicki and Keller 1978, Rybicki 1983, Ry­bicki 1991). Relying on assessment CPE data haslimitations because of the year-to-year variability incatch, and, consequently, the overall trend information itprovides is more meaningful than year-to-year compar­isons. Spring and summer surveys will capture the

1,200

gj'1,000cc

.~ 800ill

S 600u;Q)>CiJ:r: 400

200

o1985 1986 1987 1988 1989 1990 1991 1992

FIG. 10. Harvest (metric tones) of lake trout fromLake Michigan in 1985-1992, by sport fisheries, tar­geted commercial fisheries, non-targeted commercialfisheries, and assessment fisheries.

broadest range of age groups, while the fall surveys cap­ture mostly mature lake trout.

Spring and summer assessment surveys show that theinitial stocking that was begun in 1965 produced similarrelative abundance throughout the lake in the 1970s andearly 1980s (Fig. 6 and Table 4). The decrease in CPE inMM 3 and MM 4 (Fig. 2) that started in the late 1970s andearly 1980s is attributed to tribal commercial and sport ex­ploitation (Table 4). The stocking emphasis that has beenplaced on the refuges and primary zones since 1985 hasresulted in increases in spring or summer CPE in therefuges and primary zones, with the exception of the ClayBanks (Table 4). Stocking levels in the Clay Banks areaafter 1985 were actually lower than in the late 1970s andearly 1980s, and have resulted in a decrease in summerCPE. The relative abundance of lake trout is not evenlydistributed among the four midlake reefs. The summerCPE of lake trout on Sheboygan Reef (the largest andshallowest of the four) increased from 44.4 in 1984 to169.5 in 1992. On the other three reefs, CPE exceeded 45only twice, both at the East Reef, in 1986-1992. The rela­tive abundance on the four midlake reefs is generally in­versely related to their depth. The CPEs on MilwaukeeReef (the deepest of the four) are some of the lowest in thelake. The redirected stocking has in most cases resulted ina decrease in lake trout CPEs in secondary zones.

Concentrations of mature lake trout in the fall spawn­ing season are a prerequisite for successful reproduction.Fall spawning surveys have been done on 30 reefs in1973-1992, but on only nine since 1985 (Table 5). Peck(1979) determined that to have a good to excellentchance for successful reproduction, a CPE of 25 or more

TABLE 4. Lake trout catch per effort (number/30S m ofgill net) during spring and summer surveys.

(north) Eastern Lake Michigan (south) (north) Western Lake Michigan (south) Midlake Reefs

Statistical DistrictSheboy- North- Milwau-

Sauga- Cana Clay Mani- Milwau- gan east East keeYear MM3 MM4 MM5 MM6 tuck Island Banks towoc kee Illinois Reef Reef Reef Reef

1975 4.5 10.1 19.8 41.41976 4.2 20.9 16.0 22.2 31.91977 12.4 25.2 19.0 37.9 27.6 49.2 39.51978 5.8 22.2 18.7 30.7 29.4 24.7 52.01979 5.6 9.5 32.5 19.2 29.1 61.9 86.8 ~1980 6.0 3.8 15.7 49.9 32.2 45.6 122.0 -1981 5.9 4.1 24.9 45.1 28.8 42.8 35.5 47.3 ~1982 3.4 10.2 13.3 38.1 57.9 57.2 62.5 85.2 tD-1983 1.7 8.8 12.9 46.8 52.9 43.3 60.7 =1984 3.1 6.8 14.0 21.3 26.9 10.1 82.1 48.3 35.4 :-1985 4.0 6.2 23.3 39.2 32.6 34.8 48.2 59.4 16.7 44.41986 5.9 5.3 42.9 11.9 36.4 9.8 104.8 22.4 17.8 17.8 59.3 9.5 24.11987 8.4 9.8 23.0 17.8 24.2 5.0 39.9 14.5 32.6 34.0 105.2 39.3 53.7 5.61988 11.3 30.3 24.3 9.4 22.5 10.5 74.7 15.0 14.5 11.7 149.6 16.6 77.2 6.71989 5.0 25.0 22.2 12.5 15.4 2.1 34.3 17.0 20.9 18.3 141.7 16.7 19.7 8.01990 12.7 12.4 18.8 11.7 18.5 24.4 12.3 19.4 74.0 10.0 34.3 11.11991 12.1 30.1 13.5 107.0 12.0 44.7 6.61992 44.6 29.1 21.3 169.5 22.6 43.1 4.91993 17.3 9.7 118.7 13.0 44.9 12.0

Source of information: MM3-MM8 from MDNR, Saugatuck from NBS, Illinois from moc, all others from WDNR. Statistical districts are described in Figure 2.

TABLES. Lake trout catch per effort (number/30S m ofgill net) during fall spawning surveys.

(south) Western lake Michigan (north) Mid-Lake Reefs

Wind South Black Whitefish Jackson- Sheboygan North-Julians Point Milwaukee Can Whitefish Clay Salona Point port Larsens Sheboygan Reef east

Year Reef Shoal Reef Reef Bay Banks Road Reef Shoal Reef Reef Deep Reef

1974 70.91975 71.5 29.11976 17.4 47.61977 12.51978 5.6 ~1979 10.7

~1980 79.3 109.8 7.5~

1981 45.3 35.0 20.7 <"l<"l

1982 98.0 133.5 12.0 Q31983 24.9 50.7 112.6 61.9 69.2 38.0 1.3

~1984 71.7 108.2 29.9 137.7 119.1 4.0 1.2 31.5 92.1 1.3 10.2 l::l

1985 45.8 62.6 3.2 72.1 44.9 10.6 1.2 5.2 74.5 .33 a.1986 30.0 90.4 109.4 67.7 91.2 7.0 71.4 7.8 ~1987 17.4 92.2 106.1 84.3 8.0 18.8 59.6 ~

1988 21.9 100.1 94.3 131.4 199.0 60.8~

1989 15.2 127.9 179.0 141.0 7.0 61.3 ~<=!

1990 21.4 79.9 143.2 156.8 136.3 27.4 ;:::....1991 113.8 94.0 137.1 153.0 142.6 7.9 :=tl1992 111.4 74.4 ~

<"l

S'(west) Northern Lake Michigan (east) a

::toPoint Seul Nau- Fisher- <=!

:::Aux Choix binway Northern Dahlia mans Irishman Traverse ....

:::Year Barques Point Reef Refuge Shoal Island Grounds Shoal

~1973 2.5 1,2 6.01 117.0 22.0

~1974 0 2.0 5.01 8.01975 3.03 2.0 4.01 2.5 1 6.0 $:1976 2.0 9.0 6.0

(").

:::l'"1992 45.5 r)Q'1993 25.0

l::l:::

(north) Grand Traverse Bay (south)

New Marion MarionNorthport Bellow Mission Suttons Tucker Bowers Island Island

Year Point Island Point Point Point Harbor North South

1976 43 103 126 138 6 46 86 23

Source of information: Western Lake Michigan and Mid-Lake Reef from WDNR, Northern Lake Michigan (1973-1976) and Grand Traverse Bay fromPeck (1979), 1992-1993 Northern Refuge from NBS ....1 = average of two surveys 2 = N.W. South Fox Island 3 = Richards Reef ...

(M

144 Holey et ale

in 114-mm-mesh gillnet was required, based on naturallyreproducing populations of lake trout on Gull IslandShoal in Wisconsin waters of Lake Superior and fromreefs near Marquette, Michigan. Selgeby et al. (1995) re­viewed published and unpublished records of lake troutspawning densities and found that at five locations in theGreat Lakes where successful recruitment has occurred,minimum and average CPE of spawners was 17 and 50.In 1973-1976, CPEs during the spawning season onLake Michigan reefs exceeded 17 at eleven sites; SalonaRoad in Wisconsin's primary zone, Larsens Reef inGreen Bay, and Fishermans Island and Traverse Shoalnear Charlevoix, and seven sites within Grand TraverseBay in Michigan's primary zone (Table 5 and Fig. 2).Only seven sites had spawning CPEs greater than 50, theaverage stock-size criterion for success determined bySelgeby et al. (1995). CPEs well in excess of 50 havebeen measured at several locations sampled since 1980,and they indicate that large concentrations of mature laketrout have been present along most of the west shore ofLake Michigan (Table 5). Large concentrations of adultlake trout do occur in the fall in areas, such as Milwau­kee, that have a low relative abundance in the summer(Tables 4 and 5) A spawning stock of lake trout has de­veloped in the Northern Refuge where CPEs have ex­ceeded 17, but not 50, in 1992 and 1993 (Table 5). Theoffshore stocking strategies in the Northern Refuge haveproduced a spawning stock of lake trout roughly 10times larger than it was in 1973-1975, when little stock­ing was done offshore.

High CPEs of lake trout have been measured on She­boygan Reef in the fall from 1983 to 1990, but they donot represent abundance of ripe fish (Table 5). Unlikenear-shore spawning areas where juvenile and adult laketrout segregate during the spawning season, immatureand mature lake trout mingle during the fall. Growth and,consequently, maturity are much slower for trout in theSouthern Refuge than for those in near-shore areas be­cause of the thermal habitat occupied. Of the more than2,900 lake trout caught on Sheboygan Reef in the fall,1983-1990, fewer than ten mature females have beennoted even though lake trout up to age X were captured(WDNR, unpublished data). Greater numbers of maturefemale lake trout that were stocked in the SouthernRefuge have been caught during near-shore spawningsurveys near Milwaukee than on Sheboygan Reef(WDNR, unpublished data). These data suggest that laketrout stocked in the Southern Refuge either emigrate toinshore areas before they mature or they mature in therefuge at age X or older. CPEs of lake trout in the fall onSheboygan Reef were greater at depths < 60 m than atdepths > 60 m, and were greater than catches from thedeeper Northeast Reef in the years sampled (Table 5).

Comparison of Lake Trout Strains

Evaluation of the performance of lake trout strainsstocked in both refuges is incomplete due to insufficient

numbers stocked at the implementation of the plan andinsufficient time for evaluation of the full performanceof the fish that have been stocked. Rybicki (1990) foundno significant differences in the relative survival rate,growth, or straying up to age 4 from trawl catches of the1985 year classes of the Domestic X Gull Island ShoalHybrid, Marquette, and the Wyoming strains of laketrout stocked in the Northern Refuge. All strains strayedoutside the refuge in similar proportions of 12-15%.Twenty-four percent of the sport harvest of 4-year-oldlake trout from the Little Traverse-Grand Traverse Bayarea and 14% from the Leland-Frankfort area consistedof strays from the Northern Refuge. Mature lake trout ofall three strains were sampled in the fall, 1992-1993, inthe Northern Refuge (NBS, Great Lakes Science Center,unpublished data).

Preliminary analysis of coded wire tag returns fromthe Marquette-and Seneca-strain fish stocked in theSouthern Refuge in 1985 and 1986 suggests that theMarquette strain is surviving better than the Senecastrain (LMC 1993). Both strains have also strayed out­side the refuge and significant numbers of each strainhave been caught in near-shore summer and fall graded­mesh-gillnet surveys and by sport anglers.

Natural Reproduction

Successful reproduction of hatchery-reared lake trouthas occurred in Lake Michigan (Dorr et al. 1981, Jude etal. 1981, Rybicki 1991, and Wagner 1981), but sustain­able recruitment of wild lake trout into assessment, sport,and commercial fisheries has failed to develop (Rybicki1991). Large concentrations of ripe lake trout in the fallat many locations have not resulted in successful repro­duction.

Fertilized eggs were found at several sites along thesouth-eastern shoreline in the early 1970s, in the GrandTraverse Bay area in the late 1970s, and along the south­western shoreline in the early 1990s (Table 2 and Fig. 2).This apparent clustering of spawning activity in part is areflection of the focus of research in these areas. Eggswere found at 19 of 25 sites sampled; six of these siteswere man-made structures. Whenever a concerted efforthas been made to sample eggs from reef areas associatedwith spawning concentrations of fish, fertilized eggshave been found, except at the Clay Banks (Edsall et al.1995) and Julians Reef (Horns et al. 1989, Horns 1991).

Lake trout fry have been captured at four of 15 sitessampled in Lake Michigan (Table 6 and Fig. 2). All foursites were man-made structures; the Traverse City PowerPlant intake crib, Elmwood Marina, Campbell PowerPlant intake, and Port of Indiana breakwall (Table 6).The prevalence of adults, eggs, and fry at man-madestructures suggests that either good spawning habitat isscarce in Lake Michigan or man-made structures ofclean, deep cobbles may act as a "super-stimulus" to at­tract stocked lake trout. Natural spawning sites were his­torically sufficient to support an abundant native

Progress Toward Lake Trout Restoration in Lake Michigan 145

TABLE 6. Reputed spawning sites of stocked lake trout in Lake Michigan. An x indicates that eggs or fry werefound. A zero indicates that an effort was made but no eggs or fry were found. Distances from the nearest stockingsite are given when known; an n indicates that the site was described as "near" to a stocking site.

Life stage Dist. fromcollected stocking

Site Depth Substrate egg fry Year site Reference

WEST SHOREClay Banks 6-16 m rubble, cobble x 1990-91 Okm 2Haven (just N of Sheboygan) 5-7 m rocks, cobbles 0 1970s 3just N of Milwaukee 10-13 m clay, rubble x* 1970s n 3Black Can Reef, Milwaukee 6-8 m gravel, cobble x 1991 5km 6Bullshit Shoal 6-10 m cobble x 1991-92 Okm 6Wind Point 7-8 m cobble, boulders x 1991 15 km 6Fort Sheridan 5m cobble x 1992 5km 6Glencoe 2.5 m bedrock, cobble 0 1991 6Julian's Reef 32-40 m bedrock, cobble 0 1985-90 n 4Wilmette WR2 buoy 6-11 m cobble x 1991-92 6Burns Waterway Harbor 12 m cobble x x 1990s n 6Michgan City, 2 mi west of city to50m x n 3

TRAVERSE BAY AREACharlevoix Harbor 2-8 m sand, gravel, cobbles x 0 1973-74 Okm 7, 8Fisherman Island 2-10 m rock, rubble, boulder 0 0 1974-76 9km 7, 8North Point (Northport Point) 2-18 m cobble, gravel x 0 1973-76 2km 7,8Bellow Island 2-18 m rubble ridges 0 0 1977 9km 7,8Traverse Shoal 5m rock, rubble x* 1973-75 n 7New Mission Point to 17 m boulder, cobble x 0 1976-77 7km 7, 8Suttons Point 2-12 m rock, rubble 0 1977 4km 7, 8Bowers Harbor 3-5 m boulders, cobble x 0 1976-77 lkm 7, 8Marion Island l-17km boulders, cobble 0 0 1977 4km 7, 8Elmwood Marina 0-7 m rubble breakwall x x 1977-79 lkm 7, 8Traverse City to 30 m rock x 0 1975-78 2km 7, 8Traverse City Power Plant 8-9 m intake crib x x 1977-78 2km 7, 8Clinch Park Marina 0-4m cobble, boulders x 0 1979-79 2km 7,8

EAST SHOREPort Sheldon, Campbell Power to 17 m intake structure x 1977-80 n 5

PlantSaugatuck 6-10 m rock, gravel x 1971+ n 1Bridgman, Cook Power Plant nearshore rip-rap x 1970s 5

*eggs found in stomach of a sculpin or lake troutReferences: 1 = Dorr et al. 1981,2 = Edsall et al. 1995,3 = Goodyear et al. 1982,4 = Horns et al. 1989,5 = Jude et al.1981,6 = Marsden 1994,7 = Peck 1979, 8 = Wagner 1981

population of lake trout. Degradation of spawning siteshas been suggested as a cause for reproductive failure,but that seems improbable in a lake as large as LakeMichigan.

Wild yearling and older lake trout have been detectedin Grand Traverse Bay and Platte Bay (Rybicki 1991)where several cohorts contained significantly greater fre­quencies of unmarked trout than the 2% expected due tofin clipping and fin regeneration error. He reported that

13% of the 1976 year class and 7% of the 1981 yearclass taken by assessment netting in 1983-1989 were at­tributed to natural recruitment in Grand Traverse Bay aswere 4% of the 1983 year class in Platte Bay.

The detection of egg deposition and fry production inthe early 1970s, and recruitment of wild lake trout intothe 1976 year class show that the first plantings of laketrout into Grand Traverse Bay spawned successfully.Based on the maturity schedule for Lake Michigan lake

146 Holey et al.

trout, seven year classes (1964-1970) could have con­tributed to the Grand Traverse Bay spawning stock in thefall of 1975 (Rybicki 1991). The stocking rate for thoseseven year classes averaged 2.09/ha. Successful repro­duction only in Grand Traverse Bay when significantspawning concentrations were present on other selectedreefs suggests that, at least at those sites, somethingother than stock size was limiting reproduction.

The absence of significant numbers of naturally pro­duced lake trout past the fry stage in Lake Michigan maybe due to the effects of contaminants on egg and fry sur­vival. Reduced hatchability and fry survivability fromhatching to post swim-up have been observed and corre­lated with organic environmental contaminants in LakeMichigan lake trout (Mac et al. 1985, Mac and Edsall1991). Survival of feral Lake Michigan lake trout eggs

was the poorest when compared with those from LakesSuperior and Huron during lab incubation experiments in1980 (Mac et al. 1985). Mortality during swim-up is themost important controlling factor of early life survival,even though a high inverse correlation existed betweenthe concentration of the PCB congener 3,3'4,4'-tetra­chlorobiphenyl (found in adult Lake Michigan lake trout)and the hatchability of Lake Michigan lake trout eggs in1985 (Mac and Edsall 1991). Trends in hatching success,fry survival and overall egg to fry survival since 1982,and in the contaminant body burden of Lake Michiganlake trout lead us to believe that contaminant relatedmortality will have a minimal impact on future egg andfry survival. Hatchability of Lake Michigan lake trouteggs in lab conditions generally increased from 1975 to1990 and has ranged from 65 to 98% (Fig. 11). Survival

100

80

eu>->'- 60::J(f)

'-0..c0

40+-0

euI~

20

o

I

/ \ -Jt lit II/ pi

/~

II

~~!\

..............

I I I I

74 76 78 80 82 84

Year

86 88 90 92

• Hatching lITO Swim-up + Total (egg to swim-up)

FIG. 11. Hatching rates, fry survival, and total egg to swim-up survival of feral Lake Michiganlake trout eggs, 1975-1992. Datafrom 1975-1989 were extrapolated from figures in Mac and Edsall1991. Data from 1990-1992 are for Clay Banks Reef, Wisconsin (Carol Edsall, NBS, Great LakesScience Center, personal communication).

Progress Toward Lake Trout Restoration in Lake Michigan 147

of fry from hatching to post-swim-up in the lab was verylow (less than 25% in 1978-1981), but increased dramat­ically to 60% or greater since 1982. The overall survivalof feral Lake Michigan lake trout eggs in the lab fromfertilization to post swim-up was lowest, 10-20%, duringthe time when successful reproduction was first beingmeasured in Grand Traverse Bay. Increased survival ofeggs from feral Lake Michigan lake trout has closelycorresponded with a detected decrease in total PCB bodyburden in adult lake trout (Stow et ai. 1995).

Recent information suggests that predation on emer­gent lake trout fry by alewives (Krueger et ai. 1995),which occupy inshore and nearshore waters in May,June, and July, may limit successful lake trout recruit­ment. Given the high abundance of alewives in LakeMichigan (Eck and Brown 1985, Hatch et ai. 1981),alewife predation on emergent lake trout could easily ex­plain the lack of successful reproduction on a broadlakewide scale.

Comparison of Hatchery-Reared Lake TroutTo Native Stocks

Lake Michigan's native stocks are not directly compa­rable with today's introduced fish because the native fishwere well adapted to their environments and were pre­sumably more efficient at reproducing themselves(Brown et at. 1981). Some additional insight into theproblem of rehabilitating lake trout in Lake Michiganmight be gained by estimating the size, age structure,and reproductive potential of the native trout populationduring the 1927-1944 period. At the very least, such anexercise can provide some indication of the characteris­tics that a rehabilitated lake trout population in LakeMichigan should possess. Then, by reexamining the fac­tors that led to the demise of the native trout, we may de­velop some perspective on the efficacy of the presentLake Michigan lake trout rehabilitation program.

To estimate the size and age structure of the averagelake trout population in 1927-1944, we assumed: (1) thatthe population was at equilibrium; (2) that Silliman's es­timates of F (0.5) and M (0.2) in analog computer simu­lations of the fishery were reasonable (Silliman 1969);(3) that recruitment to the fishery was knife-edged at age6 (Van Oosten 1950); (4) that hypothetical survival ratesof age groups not susceptible to fishing were 0.8, 0.8,0.75,0.7, and 0.6 for fish age 5, 4, 3, 2, and 1; and (5)that mortality was evenly distributed throughout theyear. We then derived our estimates of stock size and agedistribution from the following relations:

Oosten 1950), Nx = number of fish in the exploitablestock, u = exploitation rate (0.357), F = instantaneousfishing mortality rate, A = annual mortality rate, Z = in­stantaneous total mortality rate, and R = number of age-6recruits to the exploitable stock each year. Numbers offish in age groups 5 to 1 were estimated from their as­sumed survival rates by working backwards from the es­timated number of age-6 fish.

Given the above, we estimated that the average stockof native lake trout in Lake Michigan in 1927-1944 con­tained a total of about 32 million fish of age 1 and olderat the beginning of each year (Fig. 12). The native troutat that time were roughly six times more abundant thanthe artificially maintained population that in 1979, ayear in which the lake trout population was perhapslarger than it is now because of higher stocking rates inthe 1970s, was estimated to be about 5.3 million fish(Eck and Wells 1983, Stewart and Iberra 1991). In part,the difference can be explained by an average stockingrate from 1965 to 1979 of about 2.5 million yearlings asopposed to the 10 to 11 million yearlings that the nativefish woold have had to produce to keep their populationat equilibrium (Fig. 12). In addition, estimated survivalrates of the hatchery fish, especially of the newly plantedyearlings, are much lower than those that we assumedfor the native trout.

The reproductive potential (i.e., number of eggs pro­duced) of the native stock was estimated by assumingthat all native fish were mature at age 7 (Cable 1956),that one-half of the mature fish were female, and that

12,--------------------,

1061

L(f)

LL

"6Gi.0E::JZ

FIG. 12. Estimated age distribution and size of theLake Michigan native lake trout stock in 1927-1944, aperiod ofassumed population equilibrium with the fish­ery. See text for details.

Cn = Cw/Wa,

Nx = Cn I u, and u = FxA I Z, and, at equilibrium,

R = NxxA

where Cn = catch in numbers, Cw = catch in weight, Wa= average weight of a fish in the catch (1.68 kg, Van

2 3 4

Age (years)

5 6 >=7

148 Holey et ale

each female produced 1500 eggslkg (Eschmeyer 1955).Therefore,

Ab = (C I u) - N6xW6,

Sb = Abxexp(-ZxlO/12), and

E = (Sb I 2) x 1,500

where Ab = adult biomass at the beginning of the year,N = number of age-6 fish in the exploitable stock at theb:ginning of the year, W6 = mean weight of age-6 fish(0.64 kg, Van Oosten and Eschmeyer 1956), Sb = spawn­ing biomass, i.e., adult biomass adjusted for mortalityduring the year, and E = number of eggs produced. Theresulting estimate of 2.4 billion eggs is probably an un­derestimate because egg production is not adjusted foradult growth during the year (growth data are not avail­able for adult native lake trout) nor is it adjusted forwhether or not fishermen reported their catch as dressedor whole-fish weight (round). If most of the catch wasreported as dressed weight, as we believe was the com­mon practice, egg production would have to be expandedby a factor of 1.24 (NBS, Great Lakes Science Center,unpub. data).

From estimates of egg production and numbers of age­l fish, we estimated that the survival rate from egg toage 1 for the native stock was about 0.004. If we appliedthis survival rate to the estimated number of eggs pro­duced by the 1979 stock of lake trout (392.5 million), 1.6million yearling lake trout should have been produced in1979 had natural reproduction been successful. Obvi­ously, it was not.

Eschmeyer (1957) stated that failure of natural repro­duction in 1949 contributed to the rapid demise of LakeMichigan's lake trout. The decline in lake trout abun­dance because of sea lamprey predation began in 1945,but substantial numbers of young were produced eachyear until 1950. The decline in abundance of the 1950year class, when compared to that of 1949, was so abruptthat reproductive failure in the fall of 1949, rather thanincreased lamprey predation, appeared to be thecausative factor. Yet, the abundance of mature nativetrout in 1949 was still 26% of the average abundance in1929-1943 (Hile et al. 1951a). Based on our estimate ofstock size for about the same period, the standing stockof adult trout in 1949 would have probably have equalledthe biomass of adult fish present in Lake Michigantoday. Although these figures involve much supposition,one wonders why planted lake trout are expected to re­plenish themselves when their lakewide spawning poten­tial may be at a level that was associated withreproductive failure of the native stocks.

SUMMARY

Sea lamprey control effectively reduced the adult lam­prey population, resulted in the lowest wounding rates onlake trout in the three Upper Great Lakes, and enabled

lake trout restoration to proceed. The recent increase inthe lamprey-marking rate on lake trout in the northernwaters of Lake Michigan appears to be linked to the un­controlled increase of lampreys from the St. Marys Riverin northern Lake Huron. If the St. Marys River lampreypopulation remains uncontrolled, maintaining lake troutspawning stocks in the Northern Refuge will probably bejeopardized.

Stocking has been successful in building localizedlake trout spawning stocks large enough to result in suc­cessful natural reproduction. Stocked lake trout havespawned successfully, but successful spawning has beenextremely limited. Hatchery-reared lake trout produced ameasurable amount of wild progeny of the 1976 and1983 year classes in Grand Traverse Bay, and viableeggs have been sampled at several other locations. Wide­spread success of the initial stocking program throughthe late 1970s and early 1980s was hampered by pooregg and fry survival presumably from contaminants, andfrom the lack of colonization of the offshore reefs wherethe best spawning habitat is located. The onset of thestocking program also coincided with major changes inthe Lake Michigan fish community; the explosion ofalewives and their possible predation on emergent laketrout, the collapse of the native bloater chub and yellowperch stocks, and the beginning of a massive stockingprogram of Pacific salmon and other stream trout, someof which may have constrained successful lake trout re­production.

The adoption of the 1985 rehabilitation plan has re­sulted in successful stocking of the available lake trout inthe best available spawning habitat. Since the implemen­tation of the 1985 Plan, 90% of the available lake trouthave been stocked into the refuges and primary zones,compared with only 37% in 1965-1984. Colonization ofthe historically productive offshore reefs, now within theNorthern and Southern Refuge boundaries, would nothave happened without the 1985 Plan-it was accom­plished by transporting lake trout offshore and stockingthem on or near the reefs.

Even though stocking has produced adequate numbersof spawners for successful reproduction on specificreefs, the number of lake trout stocked has been inade­quate for rehabilitation lakewide. Current stocking levelsare only one fourth of the estimated yearling recruitmentof the former native lake trout population. Numbers oflake trout stocked have never reached the initial 5.844million recommendation of the LMTC or the present3.534 million goal that was adjusted down to reflecthatchery production levels.

Evaluation of the restoration strategies implementedunder the 1985 Plan is a prerequisite for the managementagencies to meet the needs of lake trout rehabilitation asthey change. Factors limiting successful reproductioncan not be identified without adequate assessment effort.Presently, there are only three assessment surveys forevaluation of lake trout restoration on the eastern shore

Progress Toward Lake Trout Restoration in Lake Michigan 149

of Lake Michigan, one of which is in the NorthernRefuge. Management of the Lake Michigan fish commu­nity is a complex socioeconomic as well as biologicalissue. Pressures on the fisheries agencies, since restora­tion efforts began, to react to the shift from a mainlycommercial to mainly sport-based fishery, the socioeco­nomic problems created by windrows of dead alewivesalong the shoreline, the redevelopment of a tribal fishery,and the recent decline in the chinook salmon fisheryhave made it difficult for managers to remained focusedon lake trout restoration. The lag time between the onsetand results of lake trout restoration strategies adds to thefocus problem. Rehabilitation strategies similar to thosein the 1985 Plan, have resulted in progress toward reha­bilitation in Lakes Superior (Hansen et ai. 1995), Ontario(Elrod et ai. 1995), and Huron (Eshenroder et ai. 1995)as reported at this conference. Continued commitment bythe management agencies to the strategies in the 1985Plan should result in the successful reproduction of laketrout in Lake Michigan.

ACKNOWLEDGMENTS

We thank Pat McKee, Rich Hess, and DanMakauskus for reviewing the manuscript and compilingunpublished data. We thank Martha Kneuer for assis­tance with graphics.

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