American wildcelery (Vallisneria americana Michx.) is a valuable submersed aquatic plant that was negatively affected by pollution and urban runoff in the lower Detroit River for much of the 20th century. Following 25 years of water-pollution and urban-runoff abatement initiated in the early 1970s, we postulated that water clarity had increased and that this would allow restoration of wildcelery in the lower Detroit River. In addition, water clarity increased in the late 1980s due to water filtration and particulate removal by exotic dreissenid mussels (Dreissena polymorpha and D. bugensis), which could contribute to potential wildcelery restoration. We sampled wildcelery in 1996–97 and compared these data to wildcelery data from 1950–51 and 1984–85. Over the 48-year period of comparison, areal density of wildcelery tubers decreased 72% (from 51.2 million to 14.4 million tubers) between 1950–51 and 1984–85 then increased 251% (from14.4 million to 50.5 million tubers) between 1984–85 and 1996–97. As a result, overall areal abundance was about the same in 1950–51 as in fall 1996–97. However, tuber densities in spring 1996 were similar to historical low abundances in springs of 1984–85. Then between spring and fall 1996, tuber densities increased 333% and remained relatively abundant through October 1997 indicating the beginning of the restoration of wildcelery in the lower Detroit River. In addition, we believe further reductions of turbidity through continued pollution-abatement programs and water filtration by dreissenid mussels combined with habitat protection and active management of wildcelery will contribute even further to the restoration of wildcelery in the Detroit River in the 21st century.

Burrowing mayflies (Hexagenia limbata and H. rigida) recolonized sediments of the western basin of Lake Erie in the 1990s following decades of pollution abatement. We predicted that Hexagenia would also disperse eastward or expand from existing localized populations and colonize large regions of the other basins. We sampled zoobenthos in parts of the western and central basins yearly from 1997–2005, along the north shore of the eastern basin in 2001–2002, and throughout the lake in 2004. In the island area of the western basin, Hexagenia was present at densities ≤1,278 nymphs/m² and exhibited higher densities in odd years than even years. By contrast, Hexagenia became more widespread in the central basin from 1997–2000 at densities ≤48 nymphs/m² but was mostly absent from 2001–2005. Nymphs were found along an eastern basin transect at densities ≤382/m² in 2001 and 2002. During the 2004 lake-wide survey, Hexagenia was found at 63 of 89 stations situated throughout the western basin (≤1,636 nymphs/m², mean = 195 nymphs/m², SE = 32, N = 89) but at only 7 of 112 central basin stations, all near the western edge of the basin (≤708 nymphs/m²), and was not found in the eastern basin. Hexagenia was found at 2 of 62 stations (≤91 nymphs/m²) in harbors, marinas, and tributaries along the south shore of the central basin in 2005. Oxygen depletion at the sediment-water interface and cool temperatures in the hypolimnion are probably the primary factors preventing successful establishment throughout much of the central basin. Hexagenia can be a useful indicator of lake quality where its distribution and abundance are limited by anthropogenic causes.

Deepwater sculpin (Myoxocephalus thompsonii) were abundant in Lake Ontario in the 1920s and at least common into the 1940s. By the 1960s they were rare and, thereafter, some considered the population extirpated even though a synoptic survey of the lake in 1972 produced three, relatively large (148–165 mm total length, TL), and presumably old, specimens from the northern half of the lake. Deepwater sculpin were absent from annual survey catches in the 1980s and did not reappear until 1996, when three were caught in northern Lake Ontario. Isolated collections of deepwater sculpin continued during 1998–2004. Catches during 1996–2004 included five smaller individuals, 89–118 mm TL. In 2005, catches increased sharply, with 18 deepwater sculpin collected from southern waters and one from northern waters. Moreover, young, small sculpin were dominant in 2005—16 of the 19 sculpins averaged 68 ± 12 mm total length (± 1 s.d.). The young fish observed since 1996 could have originated from reproduction by the small in-lake population, from downstream drift of planktonic larvae from Lake Huron, or both. The presence of juveniles is a clear sign that conditions for survival of young deepwater sculpin are becoming more favorable, perhaps because of reduced abundance of alewife (Alosa pseudoharengus), a pelagic planktivore linked to depression of deepwater sculpin in Lake Michigan, and also low abundances of burbot (Lota lota) and lake trout (Salvelinus namaycush), benthic piscivores.

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 procedures, 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.

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.

Changes in a population of rainbow smelt (Osmerus mordax) in the Apostle Islands region of Lake Superior were chronicled over a 32-yr time series, 1974–2005. At the beginning of the time series, rainbow smelt was the predominant prey species, abundance of lake herring (Coregonis artedi) was very low, and the dominant predator was stocked lake trout (Salvelinus namaycush). Following a period of successful lake trout stocking in the 1970s, the rainbow smelt population declined sharply in 1980, largely through mortality of adult fish and subsequent poor recruitment. In the succeeding 4 years, rainbow smelt populations reached historic low levels, resulting in reduced food resources for both wild and stocked lake trout. During 1985–1990 lake herring stocks began a spectacular recovery following the appearance of a very strong 1984 year class and subsequent 1988, 1989, and 1990 year classes. Rainbow smelt benefited from the high abundance of young lake herring as an alternate prey source for lake trout and showed a partial recovery in the late 1980s. However, a growing lake trout population coupled with an 8-yr period of low herring reproduction after 1990 resulted in a diminished rainbow smelt population dominated by age-1 and 2 fish and showing a pattern of alternating recruitment attributed to cannibalism. Low productivity of rainbow smelt and intermittent production of herring over the past decade has left lake trout populations with a diminished prey base. Although lake trout recovery benefited from the presence of rainbow smelt as a prey resource, the Lake Superior fish community was fundamentally altered by the introduction of rainbow smelt.

The burbot Lota lota population in Lake Erie increased dramatically between 1995 and 2003, due mainly to control of the sea lamprey Petromyzon marinus, which began in the late 1980s. We estimated total length- and weight-at-age at capture for burbot caught in annual gillnet surveys of eastern Lake Erie during August 1994–2003. Mean total length was generally greater for burbot age 4–9 years that were caught in New York waters than in either Ontario or Pennsylvania waters of Lake Erie. Similarly, mean weight was greater for burbot at ages 4 through 6 years in New York waters than in either Ontario or Pennsylvania waters. Age-9 burbot caught in Ontario waters had greater mean weight and mean total length than did age-9 burbot caught in Pennsylvania waters. One possible explanation for greater length- and weight-at-age for New York burbot may be greater abundance of prey fishes, particularly rainbow smelt Osmerus mordax and round goby Neogobius melanostomus in New York waters. Total lengths at ages 4–10 years were generally greater for burbot caught in Lake Erie during 1994–2003 than those from published studies of other large lakes in North America that we considered, including for Lake Erie in 1946. The regional differences in size-at-age have important management ramifications, particularly because a commercial fishery targeting burbot has been considered for Ontario waters of Lake Erie.

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 wall-eye 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.

The Saginaw Bay walleye population (Sander vitreus) has not fully recovered from a collapse that began in the 1940s and has been dependent on stocking with only limited natural reproduction. Beginning in 2003, and through at least 2005, reproductive success of walleye surged to unprecedented levels. The increase was concurrent with ecological changes in Lake Huron and we sought to quantitatively model which factors most influenced this new dynamic. We developed Ricker stock-recruitment models for both wild and stock fish and evaluated them with second-order Akaike's information criterion to find the best model. Independent variables included adult alewife (Alosa pseudoharengus) abundance, spring water temperatures, chlorophyll a levels and total phosphorus levels. In all, 14 models were evaluated for production of wild age-0 walleyes and eight models for stocked age-0 walleyes. For wild walleyes, adult alewife abundance was the dominant factor, accounting for 58% of the variability in age-0 abundance. Production of wild age-0 fish increased when adult alewives were scarce. The only other plausible factor was spring water temperature. Predictably, alewife abundance was not important to stocked fish; instead temperature and adult walleye abundance were more significant variables. The surge in reproductive success for walleyes during 2003–2005 was most likely due to large declines in adult alewives in Lake Huron. While relatively strong year classes (age-1 and up) have been produced as a result of increased age-0 production during 2003–2005, the overall magnitude has not been as great as the initial age-0 abundance originally suggested. It appears that over-winter mortality is higher than in the past and may stem from higher predation or slower growth (lower condition for enduring winter thermal stress). From this it appears that low alewife abundance does not assure strong walleye year classes in Saginaw Bay but may be a prerequisite for them.

Walleye (Sander vitreus) stocks in Nipigon Bay and Black Bay historically numbered as the largest stocks in Lake Superior, but collapsed in the 1960s due to overfishing, habitat loss, and other pressures. We used microsatellite DNA analyses to assess the success and relative contributions of past rehabilitation stocking to walleye in Nipigon Bay, and to investigate the relationship between historical and contemporary populations in Black Bay. Based on the genetic data, juvenile stocking and adult transfers from four source populations into Nipigon Bay differed substantially in their contributions to the reestablished population. The genetic data also indicated that natural reproduction was occurring and identified survivors from the former Nipigon Bay population. Similar genetic analysis of scale samples from the historical Black Bay fishery and present-day walleye from a major tributary (Black Sturgeon River) showed that the historical and contemporary samples comprise one genetic stock, which is significantly different from neighboring native and introduced populations. These findings suggest that walleye restoration efforts in Lake Superior are working, and highlight the utility of and options for adaptive management approaches for restoring extirpated populations.