The combined destructive effects of overfishing, habitat destruction, and invasive species, especially alewife (Alosa pseudoharengus) and sea lamprey (Petromyzon marinus) led to the loss of the native top predator lake trout (Salvelinus namaycush) from most of the Great Lakes by 1960. Alewife populations then exploded, creating nuisance die-offs. Public demands for action, coupled with control of sea lamprey, allowed fishery managers to consider stocking Pacific salmon to control alewife and establish a recreational fishery. This effort was successful, reducing alewife numbers and creating a recreational fishery that is estimated at $7 billion annually. This fishery management regime may no longer be viable as new invasive species continue to alter the ecosystem. Fishery managers face an interesting dilemma: whether to manage in the short term for a popular and economically important sport fishery or to embrace ecosystem change and manage primarily for native fish species that appear to be better suited to ongoing ecosystem changes. Such dilemmas occur in great lakes around the world as fishery managers seek to balance economic pressure with changes in their respective ecosystems, often brought about by invasive species.

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 hardship of the sportfishing industry on Lake Michigan. Sustaining the chinook salmon fishery at previous levels may require managing for high abundance of alewives, which may be inconsistent with overall fish community management goals. The future sustainability and role of chinook salmon needs to be reevaluated in the context of the entire Lake Michigan fish community. * Corresponding author: markholey@mail.fws.gov so abruptly. The crash of the chinook salmon population also resulted in a significant decline in angling effort.The dynamics of BKD within Lake Michigan are poorly understood. Coho salmon Oncorhynchus kisutch, steelhead Oncorhynchus mykiss, and chinook salmon have shown clinical signs of BKD, but chinook salmon was the only Lake Michigan salmonine to experience epizootics and high mortalities. This paper describes the rise and fall of the chinook salmon population and fishery in Lake Michigan. We review available data, much of it previously unpublished, before and after the population crash and discuss the possible factors contributing to the epizootics. How the future management of chinook salmon in Lake Michigan may change because of the species susceptibility to BKD is also discussed.

The Laurentian Great Lakes Basin provides an ecological system to evaluate the potential effect of climate change on dynamics of fish populations and the management of their fisheries. This review describes the physical and biological mechanisms by which fish populations will be affected by changes in timing and duration of ice cover, precipitation events and temperature regimes associated with projected climate change in the Great Lakes Basin with a principal focus on the fish communities in shallower regions of the basin. Lake whitefish Coregonus clupeaformis, walleye Sander vitreus and smallmouth bass Micropterus dolomieu were examined to assess the potential effects of climate change on guilds of Great Lakes cold, cool and warm-water fishes, respectively. Overall, the projections for these fishes are for the increased thermally suitable habitat within the lakes, though in different regions than they currently inhabit. Colder-water fishes will seek refuge further north and deeper in the water column and warmer-water fishes will fill the vacated habitat space in the warmer regions of the lakes. While these projections can be modified by a number of other habitat elements (e.g. anoxia, ice cover, dispersal ability and trophic productivity), it is clear that climate-change drivers will challenge the nature, flexibility and public perception of current fisheries management programmes. Fisheries agencies should develop decision support tools to provide a systematic method for incorporating ecological responses to climate change and moderating public interests to ensure a sustainable future for Great Lakes fishes and fisheries.

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