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LAKE TROUT REHABILITATION
IN LAKE HURON
1997 PROGRESS REPORT ON
CODED-WIRE TAG RETURNS

PRESENTED AT THE
GREAT LAKES FISHERY COMMISSION
LAKE HURON COMMITTEE MEETING

Lake Huron Committee
MARCH 18-19, 1998

 

Lake Trout Rehabilitation in Lake Huron--1997
Progress Report on Coded Wire Tag Returns

Prepared by :
Jerry McClain
U.S. Fish and Wildlife Service
Alpena Fishery Resources Office
145 Water Street, Alpena, Michigan 49707
jerry_mcclain@fws.gov

Chuck Bowen and Jaci Savino
Biological Resources Division
Great Lakes Science Center
1451 Green Road, Ann Arbor, Michigan 48105
jacqueline_savino@usgs.gov

Contributors:
Mark Ebener
Inter-Tribal Fisheries and Assessment Program
Chippewa-Ottawa Treaty Fishery Management Authority
186 East 3 Mile Road
Sault Ste. Marie, Michigan 49783
qitfap@northernway.net

James Johnson
Michigan Department of Natural Resources
Alpena Great Lakes Research Station
160 East Fletcher St.
Alpena, Michigan 49707
johnsonje@michigan.gov

Lloyd Mohr
Ontario Ministry of Natural Resources
611 Ninth Avenue East
Owen Sound, Ontario. N4K3E4
lloyd.mohr@mnr.gov.on.ca

_______________

Presented at: Great Lakes Fishery Commission
Lake Huron Committee Meeting
Thunder Bay, ONT
March 18-19, 1998

Provisional data, not to be cited without permission.

BACKGROUND 

Stocking of hatchery reared lake trout was initiated in Lake Huron in 1973 following the implementation of sea lamprey (Petromyzon marinus) control. A single genotype (Marquette-Superior strain) was available to the hatchery program in the years 1973-1984 and the effort failed to establish stocks of naturally producing lake trout. Numerous hypotheses have been generated to explain the lack of progress. In addition to impacts of over fishing and sea lamprey wounding, genetic inadequacies and general fitness of the hatchery fish being stocked in Lake Huron were believed to be areas of major concern.

In March 1983, the Lake Huron Committee (LHC) of the Great Lakes Fishery Commission (GLFC) established the Lake Huron Technical Committee (LHTC) to plan a coordinated, lakewide lake trout rehabilitation strategy. The technical committee drafted a provisional rehabilitation plan in 1985 and amended it in 1986. In 1985, a multi-agency cooperative study was initiated to compare the relative performance of two alternative lake trout strains to that of the Marquette-Superior strain. A stocking strategy was initiated in the fall of 1985 to evaluate the performance of paired releases of Seneca, Marquette, and Jenny Lake strains of lake trout. All lake trout used in this experiment were externally marked with an excised adipose fin and implanted with binary coded wire tags (CWT) and released into areas subjected to different selective pressures. In northern Lake Huron, lake trout were stocked off Drummond Island in the Northern Refuge where the hatchery fish would be subjected to heavy sea lamprey predation. In central Lake Huron, lake trout were stocked in the waters surrounding the Six Fathom Bank reef where hatchery fish would experience moderate sea lamprey predation and no commercial or sport fishing pressure. The objective of these studies is to monitor the performance of alternative lake trout strains in Lake Huron. Strain performance is being measured in terms of growth, sea lamprey wounding, survival, contribution to the spawning stock, and contribution to wild progeny. The overall goal of this program is the selection of a preferred strain (s) that will help facilitate the recovery of lake trout in Lake Huron.

Beginning in 1992, and again in 1994 and 1996, additional lots of Lewis Lake fish were stocked in the nearshore waters of western Lake Huron to begin quantifying the movement and dispersal patterns of hatchery fish. All movement fish were fin clipped (Ad) and implanted with CWT to enable detailed evaluation of recovered data. The next and final lot of movement fish is scheduled for stocking in 1998. Tag recoveries will help biologists understand immigration and emigration between management zones and aid in the calculation of mortality rates and Total Allowable Catch (TAC) levels.

Post-release assessment of all Ad clipped lake trout stocked in Lake Huron is accomplished though the collaborative efforts of the Great Lakes Science Center (GLSC) and other federal, provincial, and state agencies, including the Michigan Department of Natural Resources (MDNR), Chippewa/Ottawa Treaty Fishery Management Authority (COFMA), Ontario Ministry of Natural Resources (OMNR), the Alpena Fisheries Resources Office (FRO), three National Fish Hatcheries (NFH), and sport fishing groups.

Lake Trout Strain Program

Genetic Strains - Historically, as many as 12 sub-populations or strains of lake trout stocks may have inhabited Lake Huron, each reflecting various degrees of adaptation to their local environment. However, with the exception of two remnant stocks in Georgian Bay, these variations have been lost forever. Restoration efforts over a 12 year period (1973-1984) using Marquette-Superior lake trout failed to establish stocks of naturally reproducing trout. Moreover, the use of a single genetic strain of lake trout may have actually hampered restoration efforts since Lake Superior fish evolved in a different environment and may not perform well in Lake Huron. Our lack of progress to date does not preclude rehabilitation since the high quality physicochemical conditions that were responsible for the wide variety of lake trout inhabiting Lake Huron still exist. Thus, the potential remains for establishing one or more genetic strains of lake trout that are better suited for survival in specific Lake Huron environments. To evaluate the restoration potential of these different strains, matched plantings of CWT lake trout were initiated. At present, the performance of five strains of lake trout are being monitored as part of the Lake Huron lake trout restoration program.

The Marquette-Superior strain or "lean" lake trout is native to the cold deep waters of Lake Superior. Hatchery broodstocks were first developed in 1950 from remnant stocks that survived sea lamprey predation. Prior to 1985, all of the lake trout stocked in Lake Huron were Marquette-Superior fish. The Marquette-Superior strain has served as the "backbone" of the federal hatchery system for more than four decades and continues to be stocked in all the Great Lakes. Given their extensive stocking history, this strain was selected to serve as the standard with which to compare the performance of the other strains. Thirteen consecutive year classes (1985-1997) of Marquette-Superior trout have been stocked in Lake Huron.

In 1889, Lewis and Shoshone Lakes in Yellowstone National Park were stocked with progeny reared from eggs originating in northern Lake Michigan (around Manistique, MI). Lake trout abundance soon increased through natural reproduction to the point were Lewis Lake fish were used to stock other high mountain lakes (e.g. Jenny Lake). However, concerns relative to over sampling and uncertainty of collecting gametes from high mountain lakes in the fall resulted in the development of two federal broodstock programs; first, the Jenny Lake program at Jackson Hole, Wyoming NFH in the early 1980's, and later in the mid 1980's, the Lewis Lake program at Saratoga, Wyoming NFH. Genetic testing of the Jenny Lake and Lewis Lake strains in the early 1980's indicated that the former had gone though a genetic bottleneck and lacked the heterozygocity possessed by the latter. When the Jenny Lake broodstock held at Jackson Hole NFH became infected with BKD and were destroyed in 1990, no effort was made to replace this strain. In 1989, the Lewis Lake broodstock matured at Saratoga NFH and began to supply eggs for the Lake Huron Program (1989-1996 year classes). Because of the shortage of Lewis Lake fish, the 1989 stocking of Wyoming strain trout consisted of a mixture of Jenny Lake (eggs provided for the program were obtained from the Story Wyoming state fish hatchery) and Lewis Lake fish.

One year class (1985) of Jenny Lake x Lewis Lake out-cross and four year classes (1986-1989) of Jenny Lake trout were stocked at Six Fathom Bank. Eight year classes (1989-1996) of Lewis Lake strain fish have been stocked on offshore reefs. The introduction of Lewis Lake strain fish to the Lake Huron program could prove helpful since they are probably genetically more like the original northern Lake Michigan lake trout than any other lake trout left in the United States.

Lake trout from Seneca Lake, New York, were also included in the Lake Huron program in an attempt to inject sea lamprey resistant strains into the system. Unlike their Great Lakes counterparts who quickly succumbed to this parasite, lake trout in Seneca Lake have coexisted with sea lamprey for centuries. Moreover, Seneca strain fish had been successfully stocked in Lake Champlain, New York in the early 1960's where they are reported to have survived and reproduced in the presence of sea lamprey. While no details were provided, New York biologists attributed their survival to the possibility that either this strain was less susceptible to attack or more resistant to sea lamprey predation.

Hatchery broodstocks (Seneca Lake strain) were developed for the lower Great Lakes at the Allegheny, Pennsylvania NFH in mid-1970 from eggs supplied by the New York State Department of Conservation. In the early 1980's a second broodstock program for supplying Seneca strain fish for the upper Great Lakes was started at Iron River NFH and provided four year classes (1985-1988) of this strain for the paired plant study. Unfortunately, these fish became infected with Epizootic Epitheliotropic Disease (EED) and were destroyed in February of 1988. Following the loss of this broodstock and until recently, the availability of Seneca Lake strain fish was not adequate to meet all the needs in the upper and lower Great Lakes and impacted the strain experiments in Lake Huron. Fortunately, Pendill's Creek/Hiawatha NFH has developed a disease- free broodstock that is now producing eggs and should meet all existing needs for Seneca Lake fish in Lake Huron.

The Lake Ontario strain of lake trout was introduced into the strain evaluation experiment because of the shortage of Seneca Lake fish. This strain was developed from gametes taken from feral Lake Ontario lake trout in mid-1980's. Fin clips were used to assist biologists in identifying what were presumed to be mature male and female Seneca lake trout. However, subsequent testing of the captive Lake Ontario broodstock has shown that some genetic contamination from Clearwater Lake and Marquette-Superior lake trout occurred during the selection. Only three year classes (1989, 1991-1992) of Lake Ontario strain lake trout were stocked in Lake Huron

Mid-lake Stocking - The Six Fathom Bank/Yankee Reef area was established as a high priority special rehabilitation area in the multi-agency Management Plan. However, the portion of this offshore area known as Six Fathom Bank was upgraded to full Refuge status by the Michigan Department of Natural Resources in 1996. In fall 1997, the Ontario Ministry of Natural Resources also closed their waters adjacent to the refuge to all commercial and sport harvest of lake trout. The prohibition of all harvest of lake trout from the waters within the Six Fathom Bank Refuge will help provide the protection necessary to increase survival and further our goal of restoring lake trout stocks in Lake Huron. Yankee Reef still retains its status as a high priority special rehabilitation area but is not currently being stocked.

Stocking lake trout on mid-lake reefs and the subsequent evaluation is an important element in the lakewide program for restoring self-sustaining populations of lake trout. The stocking of marked fish in these areas was designed to test the hypothesis that if lake trout are stocked in sufficient numbers as yearlings and are provided maximum protection from fishing, they will reproduce successfully and enough lake-produced progeny will survive to maturity to generate self-sustaining populations. To date, five strains of lake trout (Marquette-Superior, Jenny Lake, Lewis Lake, Seneca Lake and Lake Ontario) have been stocked on Six Fathom Bank. Through 1997, 2,335,618 coded-wire tagged lake trout have been stocked on this historically important spawning reef (Table 1).

Northern Refuge Stocking - The Drummond Island Refuge (Northern Refuge) site was selected: 1) To establish identifiable stocks of lake trout for monitoring sea lamprey attack and resultant mortality rates. A differential response to sea lamprey predation by the respective strains (Marquette-Superior, Seneca Lake, and Lake Ontario) would provide a measure of strain specific response to sea lamprey and provide a means to evaluate the efficacy of control measures considered for the St. Mary’s River in northern Lake Huron; 2) Stocking on this refuge was also a provision of the 1985 Consent Agreement between the Native American Tribes affected by the Treaty of 1836, the State of Michigan, the U.S. Government and various sportfishing groups. This agreement provided for the stocking of lake trout in the refuge until the year 2000. Since the fall of 1985, a total of 1,356,440 coded-wire tagged lake trout has been stocked at this site (Table 2).

Nearshore Stocking - Beginning in 1992, and again in 1994 and 1996, experimental lots of lake trout were stocked at four nearshore sites in western Lake Huron to begin identifying the movement and dispersal patterns of these hatchery fish. A total of four alternate year classes of Lewis Lake strain lake trout will be stocked for this study. In 1992 and 1994, lots of 60,000 fish each were stocked at Point Aux Barques, Sturgeon Point, Middle Island, and Adams Point. In 1996, eight lots of 30,000 lake trout were stocked at the same four nearshore locations (Table 3). The NFH’s have altered their current program to improve the quality of lake trout stocked in the Great Lakes. The number of lots of nearshore fish were increase from four to eight in order to compare the relative survival of the new treatment groups. Tag recovery from assessment, commercial, and sport fisheries will aid in determining the extent and direction of movement from the stocking site. For some time there has been speculation that a significant amount of immigration is occurring in MH-1, complicating the calculation of mortality rates and Total Allowable Catch (TAC) levels. Data recovered from this study should greatly enhance those calculations.

 

Table 1. Plants of lake trout marked with adipose fin clip and coded-wire tag at Six Fathom Bank Refuge.

¹JL=Jenny Lk; LL=Lewis Lk; MQ=Marquette; SEN=Seneca Lk; ONT=Ontario
²ALL=Allegheny NFH; IRR=Iron River NFH; JR=Jordan River NFH; PC=Pendills Creek NFH

 

Table 2. Plants of lake trout marked with adipose fin clip and coded-wire tag at Northern Refuge.

 ¹ JL=Jenny Lk; MQ=Marquette; SEN=Seneca Lk; ONT= Ontario
² IRR=Iron River NFH; JR=Jordan River NFH; PC=Pendills Creek NFH

  

1997 LAKEWIDE CODED-WIRE TAG RECOVERIES

A total of 970 coded-wire tags were recovered in 1997 from fish stocked in U.S. waters of Lake Huron since 1985; 205 by COTFMA, 309 by OMNR, 52 by FWS and NBS, 84 by MDNR, and 320 were recovered from the Michigan sport fishery. A few twelve- year- old lake trout from the 1985 year class stocked at Six Fathom Bank and in the Northern Refuge are still present in the catch. Additionally, a substantial number of returns representing both the 1991 and 1993 year class stocked for the movement study were available from the respective fisheries for analysis. Return data will be discussed for each study separately in the following sections of this report and represents total lakewide recovery of the individual lots.

In 1997, returns of the Lake Ontario (1989, 1991, and 1992 year classes)) and Lewis Lake (1989, 1990, 1991, and 1992 year classes) fish continue to increase as more cohorts become vulnerable to assessment gear. Both strains have been stocked at Six Fathom Bank and in the Northern Refuge beginning in 1989 and eight year old fish are present in the catch at both locations. Returns of Lake Ontario trout are expected to decrease rapidly over the next few years given the missing 1990 year class and that no year classes were stocked after 1992.

 

Table 3. Plants of lake trout marked with adipose fin clips and coded-wire tags along the western shore of Lake Huron.

 ¹ LL= Lewis Lake
² JR= Jordan River NFH
³ Enhanced quality/size
⁴ Standard quality/size

 

Recoveries from Six Fathom Bank -

A total of 310 coded-wire tags were recovered from lake trout stocked at Six Fathom Bank between 1985 and 1997. This number represents total lakewide recoveries from all agencies, regardless of location, season, or gear in 1997. The percentage recovered by age was 1.3% age II, 4.8% age III, 19.7% age IV, 34.5% age V, 18.4% age VI, 8.4% age VII, 3.2% age VIII, 2.9% age IX, 1.3% age X, 4.5% age XI, and 1.0 age XII. Total returns by strain in 1997 (all ages combined) was 1.0% Jenny Lake, 15.5% Lake Ontario, 18.1% Seneca Lake, 34.2% Lewis Lake, and 31.2% Marquette-Superior. Once again significant differences between strains in the age at return were observed and will be discussed in the Summary of Six Fathom Bank Recoveries, 1989-1997.

Recoveries from the Northern Refuge -

In 1997 a total of 198 coded-wire tags were recovered from lake trout stocked in the Northern Refuge since 1985. This number represents total lakewide recoveries from all agencies, regardless of location, season, or gear in 1997. The percent return by age was 4.0% age II, 6.6% age III, 0% age IV, 40.9% age V, 20.2% age VI, 10.0% age VII, 10.6% age VIII, 4.5% age IX, 3.0% age X, and 0.5% age XII.. Total recovery by strain (all ages combined) was 0.0% Jenny Lake, 41.9% Lake Ontario, 18.7% Seneca Lake, and 39.4% Marquette-Superior. Significant trends in strain specific survival rates continued to be evident in 1997 and will be discussed in more detail in the Summary of Northern Refuge Recoveries, 1989-1997.

Recoveries from the nearshore movement study

The 1991 and 1993 year classes of Lewis Lake strain lake trout stocked for evaluation of movement patterns of hatchery fish are now both vulnerable to all fisheries gear, and contributed heavily to the 1997 catch in Lake Huron. In 1997 a total of 413 coded-wire tags were recovered from lake trout stocked for the nearshore movement study and represented over 40% of the total lakewide CWT returns. A majority of these returns were provided by the Michigan sport fishery (54.7%). Lakewide returns from each of the four stocking sites were as follows: 13.1% from Adams Point, 21.5% from Middle Island, 36.8% from Sturgeon Point, and 28.6% from Pt. Aux Barques. Since 1993 a total of 1,489 CWTs have been returned from the three year classes stocked in this study. Of this total, 1,214 (81.5%) represent the 1991 year class, 268 (18.0%) the 1993 year class, and 7 (0.5%) returned in 1997 from the 1995 year class. Detailed discussion of these recoveries will be presented in the Summary of Lake Trout Movement, 1997.

 

1997 ASSESSMENT OF THE OFFSHORE LAKE TROUT STOCKS

Since June 1986, the Great Lakes Science Center (GLSC) has conducted spring assessments of lake trout, burbot, and prey fish stocks in the Six Fathom Bank lake trout refuge. Assessment of the spawning stock to determine relative abundance and sexual maturity of lake trout on Six Fathom Bank was initiated in October 1991 and continued through 1996. Due to inclement weather no spawning survey was conducted in the fall of 1997. Since 1993, these fall surveys have been conducted as a cooperative project with GLSC and FWS personnel aboard the FWS vessel M/V Togue. Assessment of lake trout on Yankee Reef, located 15 miles southwest of Six Fathom Bank, was added in 1992 to determine if immigration of coded-wire tagged lake trout from Six Fathom Bank was occurring. In 1993, fry surveys were added to the spring assessments in an effort to identify lake trout nursery areas and determine if reproduction was occurring.

Spring assessment- A total of 344 lake trout were caught in 13,500 feet of graded mesh gill nets (2-6 inch) fished at Six Fathom Bank (8,100 ft) and Yankee Reef (5,400 feet). Catches of all lake trout increased significantly at both Six Fathom Bank (CPUE=14.7 trout/1000 ft.of net) and Yankee Reef (CPUE=41.7). The majority (67.1%) of the fish netted at Yankee Reef were age V (RP-LV fin clip) Lewis Lake trout stocked as fall fingerling on Yankee Reef in 1992.

The overall offshore CPUE for just CWT fish captured at Six Fathom Bank in 1997 was 3.1 trout/1000ft, compared to 2.2 in 1996, 12.4 in 1995 and 7.2 in 1994. Of the 52 Ad clipped lake trout captured in 1997, 42 coded-wire tags were recovered and strains identified. The CPUE’s by strain, all ages combined, were 0.0 Jenny Lake/1000 feet, 2.0 Lewis Lake/1000 feet, 1.0 Marquette-Superior/1000 feet, 1.2 Lake Ontario/1000 feet, and 1.0 Seneca Lake/1000 feet. Catch rates of Seneca Lake strain at this offshore site are expected to be low and clearly reflect the impact of three missing year classes (1989, 1991 and 1992). The maximum age of Lake Ontario and Lewis Lake trout on these remote offshore reefs is now VIII and enable better evaluation of these strains performance. In 1996 age IV and V (1991 and 1992 year classes) of Lewis Lake strain lake trout represented 44.5 % of the total spring catch (CWT fish only). In 1997 these same cohorts, as age V and VI, accounted for 16.7% of the catch. These same cohorts of Lake Ontario strain accounted for only 10.3 % of the spring catch in 1996 but accounted for 21.4% of the catch (CWT only) in 1997. Although preliminary, it appears that the Lewis Lake strain may not survive well beyond age V as has been the case with the Marquette strain. With only three cohorts of Ontario strain fish available for evaluation it is doubtful that definitive conclusions can be drawn relative to their long term performance and survival, especially as it relates to comparisons with the closely related Seneca Lake strain. In the past, strain-specific trends in spring catch rates have not held up as the cohorts matured and recruited to the spawning population at Six Fathom Bank. Research conducted in Lake Ontario has shown that Seneca strain fish inhabit deeper, colder water than Marquette-Superior lake trout . Greater overlap in bathythermal distribution of Marquette-Superior lake trout and sea lamprey in the fall could account for the lower survival rates in Marquette-Superior fish. It is possible that the Lewis Lake strain is also subjected to similar habitat overlap.

Based on data from the 42 CWTs recovered in 1997, offshore sea lamprey wounding rates (AI-III marks per 100 fish) by strain, regardless of age, were 18.8 for Lewis Lake, 0.0 for Marquette-Superior, 0.0 for Lake Ontario, and 0.0 for Seneca Lake.

Spring YOY Surveys- Beam trawls were fished to determine the relative abundance, diet, genetic origin and bathymetric and hatch-date distribution of wild progeny of Six Fathom Bank and Yankee Reef. This activity is part of a four year study designed to characterize the early life history of YOY lake trout on deep offshore spawning reefs. Attempts at capturing age 0 (1997 year class) lake trout in the waters surrounding Six Fathom Bank with a 3 meter beam trawl in June and July were relatively unsuccessful. A total of 2.88 hectares were trawled in June at the three reefs on Six Fathom Bank and two sites at Yankee Reef with no YOY lake trout captured. Subsequent trawling surveys at Six Fathom Bank on July 23 and 25 (4.12 ha) produced 2 YOY lake trout for a CPUE of 0.48 fry/ha. CPUE’s for lake trout progeny had increased steadily during the 1993-95 period and appeared to be related to spawning stock density measured the previous fall. However, with decreasing numbers of older (age VII-X) spawners, particularly the Seneca Lake strain, this stock recruitment relationship appears to be breaking down.

Fall Spawning surveys - Due to prolonged inclement weather in the fall of 1997, no spawning survey was conducted.

Summary of Offshore Recoveries: 1989 - 1997 - Biological data on growth, movement, diet, and wounding of all strains stocked at this offshore reef complex have been collected since 1986. A number of significant events have been documented since the initiation of the strain comparison studies and have been reported over the past few years. Male and female lake trout in spawning condition were first observed in the fall of 1991, just six years after the initial stocking. Surveys in 1994 and 1995 produced the first evidence that offshore stocks can successfully reproduce and that progeny can survive past the swim-up stage. Aggregations of spawning lake trout on this historically important reef complex have continued to expand with CPUE’s exceeding those reported for any other location in Lake Huron.

Analysis of coded-wire tag returns (1989-1997) from fish stocked at Six Fathom Bank has indicated superior survival of the Seneca Lake strain when compared with the other test strains. The age distribution of the respective strains best illustrates the superior performance of the Seneca Lake strain in terms of being able to survive beyond the age of first maturity (Figure 1). In this region of Lake Huron female lake trout reach full maturity at age 8. To date, the Seneca Lake strain is by far the most abundant strain encountered in these older age classes. Seneca fish survive better on these offshore reefs because for any given size they are less likely to be attacked and they are more likely to survive a sea lamprey attack than the other strains of lake trout.

Figure 1. Age distribution of 1990-1997 lakewide returns of coded-wire tags from lake trout stocked at Six Fathom Bank Refuge, Lake Huron

 

Evidence of differential sea lamprey wounding trends - The genetic strain and size of lake trout appears to influence the frequency of attacks (AI-III) by sea lamprey in central Lake Huron (Figure 2). Very few wounds were found on Seneca Lake strain trout <532 mm T.L. and although wounding increases in successively larger size categories, it never reaches levels recorded with the other strains with which it is being compared. The early avoidance of sea lamprey attack combined with lower overall

wounding rates provide evidence that the Seneca Lake strain may possess one or more strain related behavioral attributes that effectively increase their chances for survival. Although wounding of the other comparison strains tends to also be low in fish <531 mm, it rapidly increases in the larger size categories (10.0 - 66.7 wounds per 100 fish). These greater wounding rates obviously have a significant influence on survival and strain specific trends observed in age class distribution (Figure 1).

While cohorts of the Lewis Lake and Lake Ontario strains are just now maturing to the point where similar long term comparisons can be made, it appears early on that they are not as successful at avoiding sea lamprey wounding as is the Seneca Lake strain. As the 1989 and subsequent cohorts mature, a more definitive comparison can be made.

 

Figure 2. Sea lamprey wounding rates (AI-III wounds per 100 fish, all seasons combined) for Six Fathom Bank lake trout in seven length groups: 1990-1997.

 

Six Fathom Bank Food Web Observations - To assess the potential for competition, adult lake trout and burbot have been sampled concurrently each spring from 1991 to 1997 at Six Fathom Bank and 1991-1996 at Adams Point. Similar numbers of lake trout were captured at Six Fathom Bank (N = 1107) and Adams Point (N = 1129), but more burbot were captured at Six Fathom Bank (N = 1107) than at Adams Point (N = 209) during this period. About 24% of all stomachs sampled were empty; 627 burbot and 965 lake trout collected at Six Fathom Bank had full stomachs and 169 burbot and 926 lake trout at Adams Point had full stomachs. Diet analysis provided prey species frequency and lengths. In fish with full stomachs, 40-45% of fish prey were unidentifiable. Biomass of each prey species eaten was based on regressions from length to weight provided in the literature or from data obtained in concurrent studies in the Lake Huron. Burbot diets included a number of invertebrate as well as fish prey, but frequency of invertebrate prey was generally <1% of total diet. As predators of similar size may be most apt to overlap in diet preferences, predators were divided into similar size-group intervals (10 cm) for diet comparisons.

In initial analyses of fish diets at each site, we combined the data set across years to examine general trends and the potential for competition. Based on mean weights of identifiable fish prey per predator with full stomach, lake trout and burbot primarily ate alewife at Six Fathom Bank (Figure 3). Rainbow smelt were next in importance for lake trout, but sculpin (slimy and deepwater) were next in importance for burbot. Schoener's index of overlap for each length group between lake trout and burbot based on weight of prey eaten was: 0.81 (<43 cm), 0.79 (43-53), 0.74 (53-63), and 0.81 (63-73). Generally, values for Schoener's index greater than 0.60 are considered biologically significant. Therefore, lake trout and burbot diets are very similar at Six Fathom Bank. Schoener's index of overlap based on frequency of prey in diet was: 0.71 (<43 cm), 0.61 (43-53), 0.55 (53-63), and 0.69 (63-73). Although not as dramatic, diets of lake trout and burbot based on frequency of prey still exhibited overlaps.

Figure 3. Diets of lake trout and burbot at Six Fathom Bank, shown as percent by weight, summarized for the years 1991-1997 from spring assessment surveys.

 

Similar analysis with lake trout and burbot sampled at Adams Point showed somewhat different diets (Figure 4). Lake trout ate primarily rainbow smelt and alewife. The smallest lake trout had a more diverse diet that also included ninespine stickleback and slimy sculpin. Fewer burbot were sampled for diets at Adams Point, but their diets were more diverse than at Six Fathom Bank. Rainbow smelt and alewife were also important in burbot diets. In addition, slimy sculpin, ninespine stickleback, and bloater provided 10-50% of the diet. Schoener's index of overlap for each length group between lake trout and burbot based on weight of prey eaten was: 0.58 (<43 cm), 0.55 (43-53), 0.57 (53-63), and 0.46 (63-73). Hence, lake trout and burbot diets were not as similar as at Six Fathom Bank. However, Schoener's index of overlap based on frequency of prey in diet was: 0.70 (<43 cm), 0.53 (43-53), 0.61 (53-63), and 0.25 (63-73). In this analysis, the smallest burbot and lake trout demonstrate a potential for diet overlap and competition.

Thus far in our analyses, we find that burbot and lake trout diets and diet overlaps differ with site and presumably prey availability. Areas such as Six Fathom Bank with a less diverse prey base and larger populations of burbot, would have more potential for diet overlap and competition with lake trout. Further analyses will continue to explore the potential for competition at a more local level, i.e., based on concurrent sampling.

 

Figure 4. Diets of lake trout and burbot at Adams Point, shown as percent by weight, summarized for the years 1991-1997 from spring assessment surveys.

 

1997 LAKE TROUT ASSESSMENT IN THE NORTHERN REFUGE

Since 1989, the Inter-tribal Fisheries and Assessment Program has conducted spring and fall lake trout assessment in the Northern Refuge of Lake Huron to monitor the coded-wire tag study at that site. The study in this region of the lake will aid managers in evaluating the efficacy of sea lamprey control efforts in the St. Marys River and examine the relative performance of the test strains in an area of greatest sea lamprey populations.

Spring Assessment - A total of 50 lake trout were caught in 15,700 feet of graded mesh gill nets (2-6 inch) fished in the Northern Refuge in May of 1997. The overall CPUE was 3.2 fish/1000ft compared to 14.6/1000 ft in 1996, 6.3/1000 ft in 1995, 8.3/1000 ft in 1994, 2.0/1000 ft in 1993, and 6.6/1000 ft in 1992. Of the 50 fish caught, 31 coded-wire tags were recovered. Strain composition of those containing coded-wire tags, regardless of age, was 48.4% Lake Ontario, 38.7% Marquette-Superior, 9.7% Seneca Lake, and 3.2% Lewis Lake. By age, regardless of strain, 6.5 % were age II, 6.5% were age III, 0% were age IV, 58.1% were age V, 16.1% were age VI, 3.2% were age VII, 3.2 % were age VIII, 0% were age IX, 3.2% were age X, and 3.2% were age XI.

 Fall Spawning Surveys - A total of 160 lake trout were caught in 14,800 feet of graded mesh gill nets (2-6 inch) fished in the Northern Refuge in October of 1997 to assess the spawning aggregations at this location. Fall assessment at the Northern Refuge is conducted somewhat differently than at Six Fathom Bank. Larger mesh panels (4.5-6.0 inch) are fished in shallow waters on the reefs. Smaller mesh nets are fished in deep water adjacent to the reefs. This practice increases the overall CPUE but reduces the mean age captured by strain. The overall CPUE was 10.8 fish/1000 ft. Of the 160 fish caught, 88 coded-wire tags were recovered. Strain composition of those containing coded-wire tags, regardless of age, was 43.2% Lake Ontario (mean age =6.7), 29.5% Seneca Lake (mean age =7.7), 23.9% Marquette-Superior (mean age =3.7), 2.3% Lewis Lake (mean age =5.0), and 1.1% Jenny Lake (mean age 8.0). The average age of all fish captured was 6.3 compared to 5.3 in 1996 and 5.7 in 1995.

Returns from each cohort and strain of lake trout captured in the fall survey is illustrated in Figure 5. Although the overall catch rate of spawning aggregations at the Northern Refuge is significantly lower than at Six Fathom Bank, the superior ability of the Seneca Lake (and Lake Ontario) strain to survive to spawning age is nowhere more evident. Only 6.8% of fish age 5 and older were Marquette-Superior strain, whereas 27.3% were Seneca Lake, and 43.2% were Lake Ontario. In spite of excessive mortality resulting from large sea lamprey populations and harvest in waters adjacent to the refuge, Seneca Lake strain fish from the second plant (1987 year class) are still present in the spawning population. Additionally, the 1989 year class of Ontario strain continues to perform quite well and accounted for 20.4% of the total catch and 56.2% of fish age 7 and older. Seneca Lake and Ontario strain fish accounted for 93.3% of all spawners age 7 and older.

Figure 5. Age and strain of coded-wire tagged lake trout captured during spawning surveys at the Northern Refuge, October 7-11, 1997.

 

Summary of Northern Refuge Recoveries, 1989 - 1995 - Progress on establishing identifiable stocks of specific strains of lake trout for monitoring sea lamprey wounding and the efficacy of future control efforts on the St. Marys River is on schedule. Marquette-Superior, Seneca Lake, and Lake Ontario strain lake trout in and adjacent to the Northern Refuge have been monitored since 1986. Six years after the initial stocking of 180,000 fall fingerling lake trout (1985 year class), male and female trout in spawning condition were observed congregating over nearshore reefs in the refuge.

Analysis of coded-wire tag returns (1989-1997) from fish stocked at the Northern Refuge has indicated superior performance of the Seneca Lake strain when compared with the other test strains. The age distribution of the respective strains best illustrates the superior performance of the Seneca Lake strain in terms of being able to survive beyond the age of first maturity (Figure 6). In this region of Lake Huron female lake trout reach full maturity at age 8. To date, the Seneca Lake strain is by far the most abundant strain represented in fish older than age 5. Dramatic differences in strain related survival are clearly apparent in lake trout stocked in this region of Lake Huron. Spring surveys tend to capture younger lake trout that in many cases are predominantly Marquette-Superior strain fish. Conversely, fall spawning surveys represented by older fish are almost entirely composed of Seneca Lake and Lake Ontario strains.

 

 Figure 6. Age distribution of 1989-1997 lakewide returns of coded-wire tags from lake trout stocked at the Northern Refuge, Lake Huron.

 

Wounding by sea lampreys in northern Lake Huron also appeared to be related to the genetic strain and size of lake trout (Figure 7). Marquette-Superior strain lake trout are attacked earlier (size and age) and to a greater degree than are either the Seneca Lake or Lake Ontario strains. The earlier wounding and apparent high mortality among this strain suggests that sea lamprey may be a major factor limiting this strain’s ability to survive to spawning age and, ultimately, produce wild progeny (Figure 6). The oldest Lake Ontario strain fish stocked at the Northern Refuge are now age 8, and although wounding data indicate that this strain is somewhat intermediate, in terms of sea lamprey wounding, between the Seneca Lake and Marquette-Superior strains they are surviving to age 8 at comparable rates to the Seneca strain. While

continued monitoring of the three cohorts stocked in the Northern Refuge will be required to make a final determination, it appears that the avoidance and/or resistance characteristics reported for the Seneca Lake strain may be possessed by this strain as well. The ability of the Seneca Lake strain to reach sexual maturity in the presence of large sea lamprey populations provides compelling evidence for increased use of this strain in the Lake Huron lake trout rehabilitation program, especially in the northern regions of the lake.

Figure7. Sea lamprey wounding rates (AI-III wounds per 100 fish, all seasons combined) for Northern Refuge lake trout in seven length groups: 1989-1997.

 

 

SUMMARY OF LAKE TROUT MOVEMENT, 1997

Catch records of lake trout in northern Lake Huron has suggested that there is substantial south to north movement of stocked lake trout from MH-2 to MH-1. Calculation of mortality and development of Total Allowable Catch (TAC) estimates are significantly complicated by immigration and emigration. In an effort to quantify post-stocking movements, coded-wire tagged lake trout have been stocked at strategic locations along the western shore of Lake Huron. Study objectives were to: 1) determine the extent of migration to MH-1 from MH-2 and beyond, 2) better define movement for improved delineation of management units, and 3) better define seasonal inshore/offshore movement patterns of feral lake trout. Thus far, three alternate year classes (1991, 1993, and 1995) of Lewis Lake strain trout have been stocked in lots of 60,000 each at Adams Point (MH-2), Middle Island (MH-2), Sturgeon Point (MH-3), and Point Aux Barques (MH-4). Beginning in 1995, adequate numbers of coded-wire tag recoveries were available from these study groups to begin the evaluation of movement patterns. In this report we have updated the 1996 analysis with return data from 1997 assessment, sport, and commercial fisheries from all regions of Lake Huron.

In addition, there is also interest in evaluating the movement/dispersal patterns of lake trout stocked at Six Fathom Bank and in the Northern Refuge. The trends indicating superior performance of the Seneca Lake strain at these two locations could be misinterpreted if there were significant strain specific differences in movement/dispersal patterns.

Nearshore Movement Study -Since 1993, a total of 1,489 coded-wire tags have been recovered from plants of the 1991, 1993, and 1995 year classes of these study fish. Most of the recoveries (1214) are from the 1991 year class which became increasingly vulnerable to the various fisheries (assessment, commercial, and sport) in 1995, 1996 and 1997. The discussion that follows should be considered preliminary and is biased geographically by the effort employed at specific fishing sites(all sources). In addition, no attempt has been made to adjust the returns by the amount of effort at each site. Efforts to adjust for these biases will be made in future years as the number of returns increases. However, as Lake Huron lake trout are exposed to fishing effort of varying degrees and types in most nearshore regions, trends in movement from the stocking location are apparent and will be discussed for each location separately.

Adams Point - A total of 307 coded-wire tag recoveries have been made from fish stocked at Adams Point. Recoveries of were plotted by grid of recapture to illustrate dispersal from planting site (Figure 8). Numbers of recaptures shown in the figure represents only those for which grid data were available (268) and may represent individual grid recaptures, or in some cases clusters of recaptures from 2 or 3 adjacent grids for visual clarity. Of the four sites stocked for this study, Adams Point fish tended to remain more closely associated with the stocking location than the other three. Of the tags recovered, 33.6 % were from the Adams Point index site, 20.9 % had moved north, and 45.5% had moved south. It would appear that more north to south movement of Adams Point fish is indicated in this summary than was reported in the 1995 and 1996 summary. However, this apparent trend is probably biased by the sportfishing effort in the Alpena to Presque Isle areas where increased returns in 1997 are reported. Adjustment of return data to CPUE will be necessary to better define the movement patterns of these fish.

Figure 8. Dispersal pattern of coded-wire tagged Lewis Lake strain lake trout stocked at Adams Point, as defined by location of tag recovery,1993 - 1997

 

Middle Island -A total of 295 coded-wire tag recoveries have been made from fish stocked at Middle Island. Recoveries were plotted by grid of recapture to illustrate dispersal from planting site (Figure 9). Numbers of recaptures shown in the figure represents only those for which grid data were available (276) and may represent individual grid recaptures, or in some cases clusters of recaptures from 2 or 3 adjacent grids for visual clarity. More extensive movement from stocking site is observed with Middle Island fish. A fairly substantial number of fish moved northwest along the shoreline and were recovered in areas common with recovery sites of Adams Point fish (MH-1). Only 30.1 % of the total recoveries of Middle Island fish are associated with the stocking site while 29.0 % moved north and 44.6 % south. Many of the fish that were recovered north of the stocking site (18.5 %) were captured along with Adams Point fish at that index site.

Figure 9. Dispersal pattern of coded-wire tagged Lewis Lake strain lake trout stocked at Middle Island, as defined by location of tag recovery,1993 -1997.

 

Sturgeon Point -A total of 508 coded-wire tag recoveries have been made from fish stocked at Sturgeon Point. Numbers of recaptures shown in the figure represents only those for which grid data were available (478). Tag recovery location illustrating apparent dispersal patterns are shown in Figure 10. As was the case with the previous two locations, some grouping of recovery grids was undertaken to reduce "cluttering". Although there continues to be some south-to-north movement of fish stocked at Sturgeon Point, for the first time we begin to see a shift to a north-to-south movement pattern developing with these fish. A large percentage of the Sturgeon Point fish were recovered through the sport fishery (71%) and location is again influenced by areas of greatest effort. The Alpena to Presque Isle area to the north, and the Harrisville to Oscoda area to the south accounted for a combined 43.5 % of the returns. Again, an increasing occurrence of these fish in the Ontario assessment and commercial fisheries (19.0%) is observed in the southern main basin. This pattern and direction of movement appears to be consistent with a major geological feature of the lake (the Ipperwash Scarp). In addition, there was a significant increase in returns of these fish in the sport fishery in the Thumb region of U.S. waters (9.2% of total returns).

Figure 10. Dispersal pattern of coded-wire tagged Lewis Lake strain lake trout stocked at Sturgeon Point, as defined by location of tag recovery, 1993 -1997.

 

Point Aux Barques -A total of 379 coded-wire tag recoveries have been made from fish stocked at Point Aux Barques. Figure 11 illustrates the dispersal pattern as defined by the location of tag recovery. Numbers of recaptures shown in the figure represents only those for which grid data were available. The southeasterly movement pattern that began developing with Sturgeon Point fish is most apparent with the Point Aux Barques fish. Recoveries from this lot of fish in the Ontario assessment and commercial fisheries in the southern main basin accounted for 53.6% of the 364 returns where grid of capture was reported. Very little northerly movement is observed with these fish and most is associated with the sport fishery in the Oscoda to Harrisville area..

Summary

A cursory examination of tag recovery data from the early phases of the nearshore movement study indicates site specific dispersal patterns between stocking location. It appears that habitat and/or other physical factors in the Adams Point and northern adjacent areas of the lake tend to hold and attract fish from both Adams Point and Middle Island. The significance of this movement, in terms of emigration from MH-2 to MH-1, appears to support more definitive analysis. At the Sturgeon Point region of the lake there appears to be a transition to a south easterly movement. Geological and/or other factors appear to be influencing the dispersal pattern. This trend is magnified at the Point Aux Barques location where the dispersal pattern indicates an extensive southeasterly movement of these fish.

Figure 11. Dispersal pattern of coded-wire tagged Lewis Lake strain lake trout stocked at Point Aux Barques, as defined by location of tag recovery, 1993 -1997.

 

Six Fathom Bank Movement/Dispersal -A total of 2767 identifiable coded-wire tags from fish stocked at Six Fathom Bank have been recovered in lakewide activities since 1990. Previous reports have discussed significant trends in strain specific performance that indicate superior performance by the Seneca Lake strain. In an effort to examine potential bias associated with differential dispersal patterns of the strains, we have examined coded-wire tag return data in regard to the intensity and location of those recoveries. At this point no attempt has been made to adjust these returns by the degree of effort at the respective sites. However, it should be understood that significantly more effort is employed outside Six Fathom Bank than within. Over one-third (42.4 %) of the total tag returns, regardless of strain, have come from within the boundaries of Six Fathom Bank, while 57.6 % have been recovered at other locations considered outside the site (Figure 12). This would tend to indicate that while there is substantial dispersal of Six Fathom Bank fish to other regions of Lake Huron, a majority of the fish stocked on the reef remain there. In terms of differences in strain specific dispersal patterns there appears to be no difference between strains in the degree to which they move away from the stocking site.

One of the general premises for stocking Six Fathom Bank as a high priority rehabilitation area was that if sufficient stock density was achieved, the area would act as an epicenter for lakewide lake trout rehabilitation. As Figure 12 illustrates, the effect is being realized. Lake trout stocked at Six Fathom Bank since 1985 are being recovered in nearly all regions of the main Lake Huron basin. This dispersal pattern offers considerable encouragement for the future of lake trout rehabilitation in Lake Huron, especially if future generations of naturally produced trout are realized at Six Fathom Bank.

Figure 12. Dispersal pattern of coded-wire tagged lake trout (strains combined) stocked at Six Fathom Bank, as defined by location of tag recovery, 1989 -1997.

 

 Northern Refuge Movement/Dispersal -A total of 2926 identifiable coded-wire tags from fish stocked in the Northern Refuge have been recovered since 1989. Trends indicating superior survivability of the Seneca Lake strain at Six Fathom Bank are even more striking in the Northern Refuge. Spawning age fish in the Northern Refuge are generally 90 - 95% Seneca Lake/Ontario strain (93.3% in 1997).

A significant proportion of the total tag returns from fish stocked in the Northern Refuge have come from U.S. (Tribal) and Canadian commercial fisheries. Areas of greatest commercial fishing pressure are adjacent to the boundaries of the Northern Refuge. Dispersal patterns of Northern Refuge fish indicate that most of the fish remain in northern Lake Huron and are closely associated with the extensive shoal areas surrounding the Drummond-Cockburn-Manitoulin Islands chain (Figure 13). Very few tag returns have come from outside the North Channel or northern main basin. The intense pressures of a large sea lamprey population being generated in the St. Marys River, coupled with substantial fishing pressure in this region of the lake, greatly diminish the longevity of lake trout here. This is especially true of the Marquette-Superior strain where few fish older than age 4 are encountered.

Figure 13. Dispersal pattern of coded-wire tagged lake trout (strains combined) stocked at the Northern Refuge, as defined by location of tag recovery, 1989 -1997.

 

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