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 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 We review available data, much of it previously unpublished, before and after the population crash and discuss the possible factors contributing to the epizootics.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.

Nearshore ecosystem predictors of a bacterial infection in juvenile Chinook salmon

“…R. salmoninarum has been isolated from sea lamprey Petromyzon marinus from the Great Lakes (Eissa et al 2006) where epizootics of BKD have occurred among Chinook salmon (Holey et al 1998), and we have ob served R. sal moninarum in kidney tissue from adult Pacific lamprey Lampetra tridentata (Gairdner) from the Columbia River (L. Rhodes unpubl. obs.).…”

Measures of larval lake whitefish length and abundance as early predictors of year-class strength in Lake Michigan

“…10). Following the bacterial kidney disease (BKD) epizootic in the late 1980s (Holey et al 1998 The nutritional status of Chinook salmon continues to be of special concern because this fish is the dominant top predator in Lake Michigan, nutritional stress may have been responsible for the epizootic in this species in the late 1980s (Holey et al 1998), and the recent declines in mean weight of returning fish may indicate a declining food supply. Whole-body lipids are an important indicator of nutritional status (Adams 1999, Madenjian et al 2000, but lipids are expensive to measure.…”

“…A wellpublicized Chinook salmon die-off in Lake Michigan during the late 1980s resulted in more focus on fish health (Johnson and Hnath 1991). This epizootic was likely, but not entirely, a result of bacterial kidney disease (BKD), which is caused by the bacterium Renibacterium salmoninarum (Holey et al 1998). Although the exact etiology and precipitating factors for the BKD-Chinook salmon epizootics of the late 1980s are not completely understood, fishing effort by 1995 declined by more than 50%, resulting in substantial economic losses throughout the basin (Holey et al 1998).…”

“…Stress-mediated diseases, such as bacterial kidney disease (BKD), have strong regulatory influences on Chinook salmon populations in Lake Michigan (Holey et al 1998). Using consistent methods, gross (visual) signs of diseased organs have been recorded for fish captured in the open-water survey since 1994 and at weirs since 1991.…”

Pathological and immunological responses associated with differential survival of Chinook salmon following Renibacterium salmoninarum challenge

“…It is not known which factors contributed to the phenotypic divergence in R. salmoninarum survival between the 2 populations. However, the Lake Michigan population of Chinook salmon experienced large mortality events associated with R. salmoninarum in the late 1980s (Holey et al 1998), suggesting a possible role for pathogen-driven selection (Purcell et al 2008).…”