Mark E. Holey

Progress Toward Lake Trout Restoration in Lake Michigan

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 and habitat destruction, resulted in an extensive stocking program of hatchery-reared lake trout that began in 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, but failed to continue probably due to excessive exploitation. The overall lack of successful reproduction lakewide by the late 1970s led to the development and implementation in 1985 of a focused inter-agency 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 encompass historically 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 levels for stocking in the 1985 Plan have never been reached, and are much less than the estimated lakewide recruitment of yearlings by the native lake trout stocks. Since 1985, over 90% of the available lake trout have been stocked over the best spawning habitat, and colonization of the historically productive offshore 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 stotk 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 in the hatchery. A recent increase in lamprey wounding rates in northern Lake Michigan appears to be related to the uncontrolled build-up of lampreys in the St. Marys River a tributary of Lake Huron. If left uncontrolled, further progress toward restoration in the Northern Refuge may be limited.

Thiamine and Thiaminase Status in Forage Fish of Salmonines from Lake Michigan

Abstract Dietary sources of thiamine (vitamin B1) and thiamine-degrading enzymes (thiaminases) are thought to be primary factors in the development of thiamine deficiency among Great Lakes salmonines. We surveyed major forage fish species in Lake Michigan for their content of thiamine, thiamine vitamers, and thiaminase activity. Concentrations of total thiamine were similar (P ≤ 0.05) among most forage fishes (alewife Alosa pseudoharengus, bloater Coregonus hoyi, spottail shiner Notropis hudsonius, deepwater sculpin Myoxocephalus thompsonii, yellow perch Perca flavescens, ninespine stickleback Pungitius pungitius, and round goby Neogobius melanostomus) and slightly lower in rainbow smelt Osmerus mordax. Concentrations of total thiamine were all above the dietary requirements of coldwater fishes, suggesting the thiamine content of forage fish is not the critical factor in the development of thiamine deficiency in Lake Michigan salmonines. Thiamine pyrophosphate was the predominant form of thiamine in most ...

Chinook Salmon Epizootics in Lake Michigan: Possible Contributing Factors and Management Implications

Abstract Stability of the Lake Michigan fishery for chinook salmon Oncorhynchus tshawytscha at high levels became questionable after stocks declined dramatically following spring epizootics in which bacterial kidney disease (BKD) was a major factor. Initially stocked in 1967, favorable survival and growth of chinook salmon through the 1970s led to increases in abundance and in popularity with anglers. Returns of chinook salmon improved annually until the late–1980s, when, with little warning, spring epizootics reduced the abundance of adult salmon by 50% or more. Reduced abundance of alewives (Alosa pseudoharengus), coupled with an increase in chinook salmon density and heavy parasite infection rates were hypothesized to have reduced chinook salmon growth and fitness and to have increased their susceptibility to BKD. Evidence of slower growth exists and low food availability may be the stressor that triggered the epizootics. Chinook salmon were a major component of the economic development and subsequent ...

Relative abundance, site fidelity, and survival of adult lake trout in Lake Michigan from 1999 to 2001: Implications for future restoration strategies

Abstract We compared the relative abundance of lake trout Salvelinus namaycush spawners in gill nets during fall 1999–2001 in Lake Michigan at 19 stocked spawning sites with that at 25 unstocked sites to evaluate how effective site-specific stocking was in recolonizing historically important spawning reefs. The abundance of adult fish was higher at stocked onshore and offshore sites than at unstocked sites. This suggests that site-specific stocking is more effective at establishing spawning aggregations than relying on the ability of hatchery-reared lake trout to find spawning reefs, especially those offshore. Spawner densities were generally too low and too young at most sites to expect significant natural reproduction. However, densities were sufficiently high at some sites for reproduction to occur and therefore the lack of recruitment was attributable to other factors. Less than 3% of all spawners could have been wild fish, which indicates that little natural reproduction occurred in past years. Wound...

Lake Trout Movements in Northwestern Lake Michigan

Abstract We quantified the distance that lake trout Salvelinus namaycush moved in northwestern Lake Michigan and examined (1) the directional preference and (2) the effect of population density on movement. Lake trout were captured in spring and fall 1983–1996, tagged with Floy anchor tags, and recaptured during subsequent agency sampling and by commercial fishers and anglers during 1983–1997. Angler recaptures were used to quantify movements; these recaptures were standardized to 10,000 salmonid angler-hours (giving recaptures per effort (RPE)) to account for the spatial and temporal variation in recapture effort. Movement was inferred from the spatial and temporal differences in the distribution of RPE. The dispersal radius, an index of the area occupied by tagged lake trout, was defined as the area containing 90% of the total RPE. It was estimated by fitting the cumulative proportion of RPE versus distance from the tagging location to an exponential sigmoid model and using inverse prediction. We used l...

Lake Trout Restoration in the Great Lakes: Stock-Size Criteria for Natural Reproduction

Abstract We examined the question of whether the lake trout restoration program in the Great Lakes has developed brood stocks of adequate size to sustain natural reproduction. Stock size criteria were developed from areas of the Great Lakes where natural reproduction has been successful (defined as detection of age-1 or older recruits by assessment fishing). We contrasted them with stocks in areas with no natural reproduction. Based on the relative abundance of spawners measured in the fall and the presence or absence of natural reproduction in 24 areas of the Great Lakes, we found three distinct sets of lake trout populations. In seven areas of successful natural reproduction, the catch-per-unit-effort (CPE) of spawners ranged from 17 to 135 fish/305 m of gillnet. Stock sizes in these areas were used as a gauge against which stocks in other areas were contrasted. We conclude that stock densities of 17–135 fish/305 m of gill net are adequate for natural reproduction, provided that all other requirements are met. No natural reproduction has been detected in seven other areas, where CPEs of spawners ranged from only 3 to 5 fish/305 m. We conclude that spawning stocks of only 3–5 fish/305 m of net are inadequate to develop measurable natural reproduction. Natural reproduction has also not been detected in ten areas where CPEs of spawners ranged from 43 to 195 fish/305 m of net. We conclude that spawning stocks in these ten areas were adequate to sustain natural reproduction, but that some factor other than parental stock size prevented recruitment of wild lake trout.

Never Give a Sucker an Even Break

Abstract Suckers are thought to be harmful to other species of fish because of predation on eggs and fry and from competition, mainly for food. This belief has led to many sucker removal projects to enhance sport fisheries. In a review of the literature, we found that (1) although suckers eat eggs and fry of some fishes, there was no evidence that such predation is harmful to prey populations; (2) studies suggesting competition for food failed to demonstrate that food was limiting (which is necessary for competition to occur); (3) evidence is equivocal that sport fish populations fare better in the absence of suckers or after sucker removal programs. Reasons for the poor evidence that suckers are detrimental are the complexity of species interactions in aquatic communities, particularly interactive segregation (Nilsson 1967), as well as the lack of removal projects in which sucker removal alone was the sole variable. Guidelines are suggested for studies designed to elucidate the role of suckers in fish co...

PCBs, Liver Lesions, and Biomarker Responses in Adult Walleye (Stizostedium vitreum vitreum) Collected from Green Bay, Wisconsin

Adult walleye were collected from several locations in the Lower Fox River and Green Bay, Wisconsin (the assessment area) and two relatively uncontaminated reference locations (Lake Winnebago and Patten Lake, Wisconsin) between July and October in 1996 and 1997. Whole body and liver samples collected in 1996 were analyzed for total PCBs and PCB congeners. Follow-up sampling in 1997 included examination of liver histopathology, measurement of ethoxyresorufin-O-deethylase (EROD) activity, immunological evaluation of kidney and blood samples, measurement of plasma vitellogenin, and examination of tissues for parasites as well as bacterial and viral infections. Mean PCB concentrations in whole body and liver samples were elevated in assessment area walleye (4.6-8.6 and 4.1-7.9 mg/kg wet weight, respectively) compared to PCB concentrations in reference areas (e.g., 0.04 mg/kg in walleye fillets from Lake Winnebago). Mean total PCB concentrations were 87% higher in walleye collected from eastern Green Bay than in western Green Bay, a finding consistent with spatial patterns of PCB contamination in bay sediments and with walleye data collected by Connolly et al. (1992). We observed a significant (p < 0.01) elevation in the prevalence (26%) of hepatic preneoplastic foci of cellular alteration (FCA) and neoplasms in 5 to 8 year old walleye collected from the assessment area, compared to reference area fish (6% prevalence). Walleye from the assessment area also contained multiple FCA and hepatic tumors per liver sample, whereas no tumors and a reduced prevalence of FCA were observed in reference area walleye. Both tumors and FCA were more prevalent in female fish than in male fish. There were no remarkable effects on immunological parameters in assessment area walleye, although hematocrit was elevated and blood monocyte counts were 40% lower than those of reference area fish. EROD activity was similar in assessment area and reference area walleye. Plasma vitellogenin was elevated in female walleye from eastern Green Bay, but was not detected in male fish from this location. Assessment area walleye exhibited a higher prevalence and intensity of gill parasites, whereas intestinal parasites and bacterial infections were similar in assessment area and reference area fish. The results of this investigation demonstrate significant elevation in hepatic preneoplastic lesions and hepatocellular adenomas and carcinomas in assessment area walleye exposed to elevated concentrations of PCBs. These histopathological lesions are consistent with long-term exposure to tumor promoters such as PCBs.

Genetic Evaluation of a Great Lakes Lake Trout Hatchery Program

Abstract Efforts over several decades to restore lake trout Salvelinus namaycush in U.S. waters of the upper Great Lakes have emphasized the stocking of juveniles from each of six hatchery broodstocks. Retention of genetic diversity across all offspring life history stages throughout the hatchery system has been an important component of the restoration hatchery and stocking program. Different stages of the lake trout hatchery program were examined to determine how effective hatchery practices have been in minimizing the loss of genetic diversity in broodstock adults and in progeny stocked. Microsatellite loci were used to estimate allele frequencies, measures of genetic diversity, and relatedness for wild source populations, hatchery broodstocks, and juveniles. We also estimated the effective number of breeders for each broodstock. Hatchery records were used to track destinations of fertilized eggs from all spawning dates to determine whether adult contributions to stocking programs were proportional to ...

Performance of Two Strains of Lake Trout Stocked in the Midlake Refuge of Lake Michigan

Abstract To evaluate the performance of Seneca and Marquette strains of lake trout Salvelinus namaycush for restoring stocks in southern Lake Michigan, we compared relative abundance (fish per lift of 305 m of gill net), survival (slope of the decline in natural logarithms of relative abundance), growth (von Bertalanffy growth curves), and wounding rates by sea lamprey Petromyzon marinus of the 1984 and 1985 year-classes captured at ages 3–16 in fall gill-net assessments on the Sheboygan Reef and the Milwaukee nearshore area during 1987–2000. Marquette strain lake trout survived at a significantly higher rate than Seneca strain lake trout prior to age 3 but at similar rates after age 3. The 1984 year-class of lake trout survived at a significantly higher rate than the 1985 year-class of lake trout prior to age 3 but at similar rates after age 3. Emigration of lake trout from the Sheboygan Reef to the nearshore Milwaukee area was similar for the Marquette and Seneca strains but was higher for the 1984 year...