Evidence of successful river spawning by lake trout (Salvelinus namaycush) in the Lower Niagara River,Lake Ontario

Restoration of a wild-produced lake trout Salvelinus namaycush population in Lake Ontario has not been successful despite the adult population often meeting or exceeding restoration targets. Lack of high-quality spawning habitat in Lake Ontario is suggested as one impediment to recruitment of wild lake trout, although the quantity and location of spawning habitat is poorly understood. If high-quality spawning habitat is limited in Lake Ontario, lake trout may be using uncommon spawning locations such as rivers. Anecdotal angler accounts point to the Niagara River as a lake trout spawning location. To better understand the potential of the Niagara River as a spawning location, egg and juvenile fish collections were conducted 12–14 river kilometers from the mouth of the Niagara River from 2010 to 2012; and mature female lake trout with surgically implanted acoustic tags were monitored from 2015 to 2019. Genetic analyses confirmed 60% of collected eggs and 93% of collected post-hatch juvenile fish in the Niagara River were lake trout. Tagged female lake trout returned to the Niagara River over consecutive years during the spawning season. The short duration of lake trout presence in the river (mean = 56 days/year) suggests female lake trout use the Niagara River primarily for spawning. Diversity in spawning locations may provide lake trout population’s resilience against environmental variability through a portfolio effect. Improved identification of riverine spawning locations, including their overall contribution to wild recruitment, may be a useful tool for managers to restore a wild-produced population of lake trout in Lake Ontario.     

Predation on emergent lake trout fry in Lake Champlain

The rehabilitation of extirpated lake trout (Salvelinus namaycush) in the Great Lakes and Lake Champlain has been hindered by various biological and physiological impediments. Efforts to restore a lake trout fishery to Lake Champlain include hatchery stocking and sea lamprey control. Despite these management actions, there is little evidence of recruitment of naturally-produced fish in annual fall assessments. Spawning occurs at multiple sites lake-wide in Lake Champlain, with extremely high egg and fry densities, yet sampling for juvenile lake trout has only yielded fin-clipped fish. To investigate this recruitment bottleneck, we assessed predation pressure by epi-benthic fish on emergent fry on two spawning reefs and the subsequent survival and dispersal of fry in potential nursery areas. Epi-benthic predators were sampled with 2-h gillnet sets at two small, shallow sites in Lake Champlain throughout the 24-h cycle, with an emphasis on dusk and dawn hours. In total, we documented seven different species that had consumed fry, with consumption rates from 1 to 17 fry per stomach. Rock bass and yellow perch dominated the near-shore fish community and were the most common fry predators. Predator presence and consumption of fry was highest between 19:00 and 07:00. Predators only consumed fry when fry relative abundance was above a threshold of 1 fry trap^− 1 day^− 1. We used an otter trawl to sample for post-emergent fry adjacent to the reef, but did not capture any age-0 lake trout. Due to the observed predation pressure by multiple littoral, species on shallow spawning reefs, lake trout restoration may be more successful at deep, offshore sites.     

Assessing habitat for lake sturgeon (Acipenser fulvescens) reintroduction to the Maumee River,Ohio using habitat suitability index models

Lake sturgeon (Acipenser fulvescens) were a candidate for reintroduction in the Maumee River, Ohio, where they were historically abundant, but are now functionally extirpated. Our objective was to determine if current habitat quality and quantity could support reintroduction efforts. We developed a spatially explicit habitat suitability index model for two lake sturgeon life stages: spawning adult and age-0 fish. To estimate habitat quality, substrate, water depth, and water velocity were assessed and integrated into suitability index values to delineate good, moderate, and poor areas for each life stage. Each habitat characteristic was mapped and combined to provide an overall assessment of habitat suitability, quantity, and location. Model results indicated 208 ha (10.2% of all habitat) of good adult spawning habitat (e.g., coarse substrates, depths between 0.3 and 8 m, and velocity between 0.5 and 1 m/s) and 529 ha (28.2% of all habitat) of good age-0 habitat (e.g., fine substrates, depths between 0.2 and 6 m, and velocity between 0.1 and 0.7 m/s). Good age-0 habitat was located mostly downstream of good spawning habitat, which will provide nursery areas for age-0 fish after hatch. Our models suggested habitat is not limiting for lake sturgeon and efforts to reintroduce this species into the Maumee River, and for the first time in the Lake Erie basin, were supported. The results of this work supported reintroduction efforts that began in 2018.     

Lake trout in northern Lake Huron spawn on submerged drumlins

Recent observations of spawning lake trout Salvelinus namaycush near Drummond Island in northern Lake Huron indicate that lake trout use drumlins, landforms created in subglacial environments by the action of ice sheets, as a primary spawning habitat. From these observations, we generated a hypothesis that may in part explain locations chosen by lake trout for spawning. Most salmonines spawn in streams where they rely on streamflows to sort and clean sediments to create good spawning habitat. Flows sufficient to sort larger sediment sizes are generally lacking in lakes, but some glacial bedforms contain large pockets of sorted sediments that can provide the interstitial spaces necessary for lake trout egg incubation, particularly if these bedforms are situated such that lake currents can penetrate these sediments. We hypothesize that sediment inclusions from glacial scavenging and sediment sorting that occurred during the creation of bedforms such as drumlins, end moraines, and eskers create suitable conditions for lake trout egg incubation, particularly where these bedforms interact with lake currents to remove fine sediments. Further, these bedforms may provide high-quality lake trout spawning habitat at many locations in the Great Lakes and may be especially important along the southern edge of the range of the species. A better understanding of the role of glacially-derived bedforms in the creation of lake trout spawning habitat may help develop powerful predictors of lake trout spawning locations, provide insight into the evolution of unique spawning behaviors by lake trout, and aid in lake trout restoration in the Great Lakes.     

Contribution of lake trout stocked as fry to an adult population in Lake Superior

Lake trout Salvelinus namaycush fry treated with heated water to create thermal marks in their otoliths were stocked at Sve's Reef in Minnesota waters of Lake Superior in 1994, 1995, and 1996. These fish began to reach maturity in 2000, and were vulnerable to annual assessment gill nets set at several locations along the Minnesota shoreline. Captured fish also included fin-clipped lake trout stocked as yearlings, and naturally reproduced (wild) lake trout. Otoliths from 3106 unclipped lake trout were aged and examined for thermal marks from 2000 to 2007, of which 1152 were from the target year classes (1994–1996). Thermal marks were found in otoliths from 64 fish, or 5.6% of those in the target year classes, demonstrating that stocked fry contributed to the adult lake trout population in Minnesota waters. Although numbers of recaptured fish were too low to demonstrate statistically significant differences, higher recapture rates of marked fish at Sve's Reef in fall and spawning assessments suggest that these fish may have imprinted at the stocking location and homed back to this area to spawn. Wild lake trout populations in Lake Superior may be approaching fully rehabilitated levels, but recovery in the lower Great Lakes has progressed more slowly, and evidence of success with fry stocking could benefit those populations.     

Acoustic estimates of abundance and distribution of spawning lake trout on Sheboygan Reef in Lake Michigan

Efforts to restore self-sustaining lake trout (Salvelinus namaycush) populations in the Laurentian Great Lakes have had widespread success in Lake Superior; but in other Great Lakes, populations of lake trout are maintained by stocking. Recruitment bottlenecks may be present at a number of stages of the reproduction process. To study eggs and fry, it is necessary to identify spawning locations, which is difficult in deep water. Acoustic sampling can be used to rapidly locate aggregations of fish (like spawning lake trout), describe their distribution, and estimate their abundance. To assess these capabilities for application to lake trout, we conducted an acoustic survey covering 22 km² at Sheboygan Reef, a deep reef ( < 40 m summit) in southern Lake Michigan during fall 2005. Data collected with remotely operated vehicles (ROV) confirmed that fish were large lake trout, that lake trout were 1–2 m above bottom, and that spawning took place over specific habitat. Lake trout density exhibited a high degree of spatial structure (autocorrelation) up to a range of ∼ 190 m, and highest lake trout and egg densities occurred over rough substrates (rubble and cobble) at the shallowest depths sampled (36–42 m). Mean lake trout density in the area surveyed (∼ 2190 ha) was 5.8 fish/ha and the area surveyed contained an estimated 9500–16,000 large lake trout. Spatial aggregation in lake trout densities, similarity of depths and substrates at which high lake trout and egg densities occurred, and relatively low uncertainty in the lake trout density estimate indicate that acoustic sampling can be a useful complement to other sampling tools used in lake trout restoration research.     

Evidence of lake trout (Salvelinus namaycush) spawning and spawning habitat use in the Dog River,Lake Superior

Lake trout spawn primarily in lakes, and the few river-spawning populations that were known in Lake Superior were believed to be extirpated. We confirmed spawning by lake trout in the Dog River, Ontario, during 2013–2016 by the collection of and genetic identification of eggs, and we describe spawning meso- and microhabitat use by spawning fish. Between 2013 and 2016, a total of 277 lake trout eggs were collected from 39 of 137 sampling locations in the river. The majority of eggs (220) were collected at the transition between the estuary and the river channel crossing the beach. Lake trout eggs were most often located near the downstream end of pools in areas characterized by rapid changes in depth or slope, coarse substrates, and increased water velocities, where interstitial flows may occur. Depths in wadeable areas where eggs were found averaged 0.9?m (range: 0.4 to 1.3?m) and substrate sizes consisted of large gravel, cobble, and boulder; comparable to spawning characteristics noted in lakes. Water velocities averaged 0.66?m·s^?1 (range: 0.33 to 1.7?m³·s^?1) at mid-depth. This information on spawning habitat could be used to help locate other remnant river-spawning populations and to restore river-spawning lake trout and their habitat in rivers that previously supported lake trout in Lake Superior. The Dog River population offers a unique opportunity to understand the ecology of a river spawning lake trout population.     

Does hatchery rearing of lake trout affect their reproductive behavior in the wild?

Stocking of hatchery-reared fishes has been used with variable success as a management action to promote the recovery of populations and species. The practice has been controversial for several reasons, including uncertainty about whether the hatchery rearing experience may affect reproduction after release. Fine-scale acoustic telemetry was used during three spawning seasons to test whether hatchery rearing affects the reproductive behavior of lake trout using a spawning shoal complex in northern Lake Huron. Within sex, wild- and hatchery-reared fish behaved similarly, but significant behavioral differences occurred between sexes. Lake trout of both sexes moved synchronously onto the spawning shoals at the completion of autumn thermal turnover and occupied the same spawning sites (confirmed visually by presence of fertilized eggs) on the shoals. Male lake trout tended to congregate directly on spawning sites, with duration of occupancy varying greatly among years. Female lake trout spent less time on spawning shoals than males and congregated less at spawning sites on shoals. Most fish visited multiple spawning sites among shoals per season, with many making multiple transits among individual spawning sites. We found no evidence to support the hypothesis that hatchery rearing impairs spawning behavior of lake trout and, therefore, conclude that behavior deficiencies on the spawning ground are likely not an impediment to rehabilitation of lake trout in northern Lake Huron. Our study narrows the field of possible impediments to lake trout rehabilitation in the Great Lakes and provides insights that expand the conceptual model of lake trout spawning behavior.     

Walleye in the Grand River,Ontario: an Overview of Rehabilitation Efforts,Their Effectiveness,and Implications for Eastern Lake Erie Fisheries

Walleye (Sander vitreus) from the Grand River (Ontario) are recognized as genetically and physiologically distinct from other Lake Erie stocks. The low abundance of these walleye in the early 1980s triggered rehabilitation efforts that included intensive research, transfers of walleye from the Thames River (Ontario), supplemental stocking from local hatcheries, construction of a fishway, and creation of additional spawning habitat. Walleye migrating from Lake Erie are currently hindered from reaching 90% of potential riverine spawning habitat by a dam 7 km upstream. Although increased walleye catch rates were reported following construction of a fishway in 1995, recent assessment has shown that access is still severely restrained. Catch rates of young-of-the-year walleye during fall surveys have increased notably since 1999, coincident with direct transfers of mature adults over the barrier. Recent successful year classes have contributed to a population dominated by young (< 5 y) fish. Genetic analyses show that fish culture contributed between 3% and 25% to five recent year classes of Grand River walleye. Facilitating access to spawning habitat above the Dunnville dam may be the most effective way to increase the productivity of this stock, with consequent strengthening of walleye fisheries and the fish community in the eastern basin of Lake Erie.     

Predicting physical and geomorphic habitat associated with historical lake whitefish and cisco spawning locations in Lakes Erie and Ontario

The Great Lakes basin was historically populated by multiple, coevolved coregonine species, but much of that diversity has been lost. In Lakes Erie and Ontario, both lake whitefish (Coregonus clupeaformis) and cisco (Coregonus artedi) occurred in high numbers before habitat degradation, overfishing, invasive species, and other factors caused significant declines. There is growing interest in restoring these populations, and suggested actions include restoration of critical habitats such as spawning habitat. Unfortunately, our current understanding of lake whitefish and cisco spawning habitat characteristics and locations in these lakes is limited. To highlight areas of potential importance for conservation and restoration, we used random forest models and data on historical spawning locations to predict lake whitefish and cisco spawning habitats based on hypothesized key factors including wind fetch, ice cover duration, distance from 1st and 6th order tributaries, and lake bottom substrate. Our model accurately predicted spawning habitat locations for 71% and 54% of cases for lake whitefish and cisco, respectively. Fetch was the most important variable in the lake whitefish model, with spawning habitats being most likely to occur in regions of low to moderate fetch. Cisco spawning habitats were most likely to occur in areas of relatively low fetch near a 1st order stream. We used these models to predict spawning habitat locations for both species across Lakes Erie, Ontario, and St. Clair. Our results improve our understanding of lake whitefish and cisco spawning habitat characteristics and will aid in the spatial prioritization of actions to restore these native fishes.     

Potential Spawning Habitat for Lake Trout on Julian's Reef,Lake Michigan

Julian's Reef is an historical spawning ground for lake trout (Salvelinus namaycush) in southwestern Lake Michigan. It is a designated lake trout refuge and is the focus of lake trout restoration efforts in Illinois waters of the lake. We studied the reef to determine its potential as spawning habitat for stocked lake trout. We used side-scan sonar and a remotely operated vehicle equipped with a video camera to survey and map 156 ha of lake bed on the southeast portion of the reef, where an earlier study revealed the presence of loose-rock substrate potentially suitable for use by spawning lake trout. Our survey showed that the substrate on the reef that most closely resembled that described in the literature as suitable for spawning by stocked lake trout in the Great Lakes was rubble patches with interstitial depths greater than 20 cm. These rubble patches occupied about 2 ha of the 13-ha expanse of bedrock and rubble substrate near the reef crest in the surveyed area. We estimated that these rubble patches, if fully used by spawning lake trout, could accommodate egg deposition by at least 1,300–3,300 2.7-kg females.     

Potential Strategies for Recovery of Lake Whitefish and Lake Herring Stocks in Eastern Lake Erie

Lake Erie sustained large populations of ciscoes (Salmonidae: Coregoninae) 120 years ago. By the end of the 19^th century, abundance of lake whitefish (Coregonus clupeaformis) had declined drastically. By 1925, the lake herring (a cisco) population (Coregonus artedii) had collapsed, although a limited lake herring fishery persisted in the eastern basin until the 1950s. In the latter part of the 20^th century, the composition of the fish community changed as oligotrophication proceeded. Since 1984, a limited recovery of lake whitefish has occurred, however no recovery was evident for lake herring. Current ecological conditions in Lake Erie probably will not inhibit recovery of the coregonine species. Recovery of walleye (Sander vitreus) and efforts to rehabilitate the native lake trout (Salvelinus namaycush) in Lake Erie will probably assist recovery because these piscivores reduce populations of alewife (Alosa psuedoharengus) and rainbow smelt (Osmerus mordax), which inhibit reproductive success of coregonines. Although there are considerable spawning substrates available to coregonine species in eastern Lake Erie, eggs and fry would probably be displaced by storm surge from most shoals. Site selection for stocking or seeding of eggs should consider the reproductive life cycle of the stocked fish and suitable protection from storm events. Two potential sites in the eastern basin have been identified. Recommended management rocedures, including commercial fisheries, are suggested to assist in recovery. Stocking in the eastern basin of Lake Erie is recommended for both species, as conditions are adequate and the native spawning population in the eastern basin is low. For lake herring, consideration should be given to match ecophenotypes as much as possible. Egg seeding is recommended. Egg seeding of lake whitefish should be considered initially, with fingerling or yearling stocking suggested if unsuccessful. Spawning stocks of whitefish in the western basin of Lake Erie could be utilized.     

Evidence of Lake Trout Reproduction at Lake Michigan's Mid-lake Reef Complex

The Mid-Lake Reef Complex (MLRC), a large area of deep (> 40 m) reefs, was a major site where indigenous lake trout (Salvelinus namaycush) in Lake Michigan aggregated during spawning. As part of an effort to restore Lake Michigan's lake trout, which were extirpated in the 1950s, yearling lake trout have been released over the MLRC since the mid-1980s and fall gill net censuses began to show large numbers of lake trout in spawning condition beginning about 1999. We report the first evidence of viable egg deposition and successful lake trout fry production at these deep reefs. Because the area's existing bathymetry and habitat were too poorly known for a priori selection of sampling sites, we used hydroacoustics to locate concentrations of large fish in the fall; fish were congregating around slopes and ridges. Subsequent observations via unmanned submersible confirmed the large fish to be lake trout. Our technological objectives were driven by biological objectives of locating where lake trout spawn, where lake trout fry were produced, and what fishes ate lake trout eggs and fry. The unmanned submersibles were equipped with a suction sampler and electroshocker to sample eggs deposited on the reef, draw out and occasionally catch emergent fry, and collect egg predators (slimy sculpin Cottus cognatus). We observed slimy sculpin to eat unusually high numbers of lake trout eggs. Our qualitative approaches are a first step toward quantitative assessments of the importance of lake trout spawning on the MLRC.     

Lake Trout (Salvelinus Namaycush) Spawning Habitat in Seneca Lake,New York

Lake trout from Seneca Lake provide an important source of stock for Great Lakes rehabilitation but the lake trout in Seneca Lake have been hatchery supported, themselves, for many years. Hatchery catch data show a continued decline in lake trout population and this is assumed to reflect changes in hatchery stocking, fishing pressure, and lamprey predation. A commensurate increase in the smelt population, since 1973, may have also contributed to the decrease of natural recruitment by lake trout. No indication of reduced egg survival was found in the hatchery which might be related to lake contamination effects. Our survey observations (1980–81) indicate that the lower parts of deep water cobble gravels have become much degraded by fine particulates, making such sites unsuitable for spawning lake trout. It is thought that natural replacement in Seneca Lake is strongly dependent on successful hatch of eggs laid at depths of 25 to 35 m, but the observed relationship between egg deposition and optimal thermal conditions seems to be anomalous. Since no controlling relationship was found between long-term decline of the lake trout population and climatic variation, it is believed that degradation of lake spawning sites has strongly influenced natural recruitment.     

Evidence of Lake Whitefish Spawning in the Detroit River: Implications for Habitat and Population Recovery

Historic reports imply that the lower Detroit River was once a prolific spawning area for lake whitefish (Coregonus clupeaformis) prior to the construction of the Livingstone shipping channel in 1911. Large numbers of lake whitefish migrated into the river in fall where they spawned on expansive limestone bedrock and gravel bars. Lake whitefish were harvested in the river during this time by commercial fisheries and for fish culture operations. The last reported landing of lake whitefish from the Detroit River was in 1925. Loss of suitable spawning habitat during the construction of the shipping channels as well as the effects of over-fishing, sea lamprey (Petromyzon marinus) predation, loss of riparian wetlands, and other perturbations to riverine habitat are associated with the disappearance of lake whitefish spawning runs. Because lake whitefish are recovering in Lake Erie with substantial spawning occurring in the western basin, we suspected they may once again be using the Detroit River to spawn. We sampled in the Detroit River for lake whitefish adults and eggs in late fall of 2005 and for lake whitefish eggs and fish larvae in 2006 to assess the extent of reproduction in the river. A spawning-ready male lake whitefish was collected in gillnets and several dozen viable lake whitefish eggs were collected with a pump in the Detroit River in November and December 2005. No lake whitefish eggs were found at lower river sites in March of 2006, but viable lake whitefish eggs were found at Belle Isle in the upper river in early April. Several hundred lake whitefish larvae were collected in the river during March through early May 2006. Peak larval densities (30 fish/1,000 m³ of water) were observed during the week of 3 April. Because high numbers of lake whitefish larvae were collected from mid-and downstream sample sites in the river, we believe that production of lake whitefish in the Detroit River may be a substantial contribution to the lake whitefish population in Lake Erie.     

Does Lake Erie still have sufficient oxythermal habitat for cisco Coregonus artedi?

In Lake Erie, cisco (Coregonus artedi) once supported one of the most valuable freshwater fisheries on earth, yet overfishing caused their eventual extirpation from the lake. With warming lake temperatures, some have questioned whether Lake Erie still contains suitable oxythermal conditions for cisco. Using published oxythermal thresholds for adult cisco (which have more stringent requirements than juveniles) and oxythermal profiles from Lake Erie, we sought to answer two questions critical to cisco restoration science. First, is cisco habitat still available during the most restrictive periods? Second, what is the distribution of cisco habitat during these times? Beta regression was used to determine that cisco habitat was most limited during the month of August, and that August of 2010 was the most restrictive period in the time series. We then used Empirical Bayesian Kriging (EBK) to map the spatial extent of cisco habitat during these times. EBK maps revealed large areas of summer refugia for cisco in Lake Erie, even during the least favorable periods. Most of the Central and East Basins contain suitable habitat during the average August, yet during August of 2010, suitable conditions were limited to the eastern edge of the Central Basin and the deep waters of the East Basin. These findings aligned well with historical accounts of cisco landings. While suitable oxythermal habitat still exists for cisco in Lake Erie, future restoration efforts, if attempted, will partially depend on: 1) better management of nutrient inputs, 2) the realization of future climate scenarios, and 3) the ability of cisco to adapt to a changing lake.     

Modelling the effects of dam removal on migratory walleye (Sander vitreus) early life‐history stages

Many dams in the USA have outlived their intended purpose and an increasing number are being considered for removal. Yet, quantitative studies of the potential physical, biological and ecological responses are needed to assess dam removal decisions. In this paper, the responses of migratory walleye (Sander vitreus) to increased spawning habitat availability as a result of dam removal was studied by comparing scenarios with and without a high‐head dam in the Sandusky River (Ohio), a major tributary to Lake Erie. A conceptual, ecological model was proposed to define the relationship between hydrodynamics and walleye spawning, egg hatching, larval drift and survival. A mathematical, ecological model of the early life‐history stages was then developed and coupled with time series of depth and velocity predictions over the spawning grounds from a 1‐D hydrodynamic model. Model simulations were run for 1984–1993 for both the with‐ and without‐dam scenarios to assess the potential benefit of dam removal. The simulation results demonstrated that velocity, depth and water temperature are major factors influencing adult walleye spawning success. Without the dam, 10 times the amount of spawning habitat would be available for walleye to spawn. This increase in spawning habitat area resulted in up to five times the total egg deposition and seven times the larval output to the nursing grounds, based on the assumption that 5% of the walleye population of Lake Erie migrated up the Sandusky River to spawn. We concluded that the spawning habitat in the current condition (with the dam) is limiting and additional spawning habitat upstream could significantly increase the number of larval walleye drifting to Lake Erie. The model sensitivity analysis showed that the number of walleye migrating up the river in spring is the dominant factor for larval recruitment to the lake. Copyright © 2006 John Wiley & Sons, Ltd.     

The Sea Lamprey in Lake Erie: a Case History

Sea lampreys (Petromyzon marinus), first reported in Lake Erie in 1921, emigrated from Lake Ontario via the Welland Canal. It was not until the advent of pollution abatement, stream rehabilitation, and salmonid enhancement programs that sea lampreys proliferated. The Great Lakes Fishery Commission (GLFC), in co-operation with state, provincial, and federal fisheries agencies, implemented an integrated sea lamprey management (IMSL) plan for Lake Erie in 1986. Suppression of sea lampreys was nearly immediate, as indicated by declining larval-, parasitic-, and spawning-phase abundance, while survival of lake trout (Salvelinus namaycush) was markedly improved. Consistent with their vision statement, the GLFC began reducing lampricide use by the mid-1990s, while increasing reliance on alternative control methodologies. Reduction of treatment effort coincided with the development of new lampricide application techniques and treatment selection criteria, in addition to heightened regional concern for the impact of lampricide on non-target species. Subsequently, Lake Erie's sea lamprey numbers have rebounded, and marking rates on lake trout have approached pre-control levels. It is hypothesized that Lake Erie's rising abundance is primarily fuelled by untreated and residual larval populations, although some migration of parasitic-phase sea lampreys from Lake Huron is suspected. Model simulations infer that treatment effort on Lake Erie was sub-optimal from 1995 to 1998. Beginning in 1999, the GLFC enhanced measures to identify and control sources of sea lampreys. Based on historical abundance patterns and model results, it is anticipated that intensified management in Lake Erie will reduce sea lamprey numbers and provide an opportunity for lake trout restoration.     

Spring-Summer Diet of Lake Trout on Six Fathom Bank and Yankee Reef in Lake Huron

We examined the stomach contents of 1,045 lake trout (Salvelinus namaycush) caught on Six Fathom Bank and Yankee Reef, two offshore reef complexes in Lake Huron, during late spring and early summer 1998–2003. Lake trout ranged in total length from 213 to 858 mm, and in age from 2 to 14 years. In total, 742 stomachs contained food. On a wet-weight basis, alewife (Alosa pseudoharengus) dominated the spring-summer diet of lake trout on both of these offshore reef complexes. Alewives accounted for 75 to 90% of lake trout diet, depending on the lake trout size category. Size of alewives found in lake trout stomachs increased with increasing lake trout size. Faster growth of juvenile lake trout on Six Fathom Bank and Yankee Reef than on Sheboygan Reef in Lake Michigan was attributed to greater availability of small alewives on the offshore reefs in Lake Huron. Our findings indicated that alewives inhabited Six Fathom Bank and Yankee Reef during spring and summer months. Thus, our study provided support for the contention that alewives may have interfered with natural reproduction by lake trout on these offshore reef complexes in Lake Huron.     

Challenges to Deep-water Reproduction by Lake Trout: Pertinence to Restoration in Lake Michigan

Restoration efforts for lake trout Salvelinus namaycush in Lake Michigan are increasingly being focused on re-establishment of the species in deep water. This focus is based in part on examination of historical records of indigenous lake trout, which suggest that offshore reefs, especially deep reefs, sustained the greatest numbers of lake trout. This focus is also based on the increasing impact of non-indigenous species, such as alewife and round goby, on lake trout survival on shallow reefs. Development of a successful strategy for re-establishing deep-water lake trout in Lake Michigan will require a better understanding of the challenges to a species that evolved in shallow water and whose nearest relatives are shallow-water fishes. The challenges include an annual temperature cycle with fall warming rather than cooling, which may impact reproductive timing and embryo incubation. Deep water presents challenges to fry in that there is no apparent physiological mechanism for producing swim bladder gas and initial filling of the swim bladder at the surface has little impact on buoyancy once a fry returns to depth and the swim bladder is compressed. First feeding is a challenge because there is no local primary production to support a rich prey supply and the phenology of zooplankton prey abundance differs from that in small lakes. We propose that plans for restoration of lake trout into deepwater habitats in Lake Michigan must proceed in concert with research leading to a better understanding of extant deepwater strains in Lake Superior.