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705 Alewife in the Great Lakes: Old Invader–New Millennium Robert O’Gorman, Charles P. Madenjian, Edward F. Roseman, Andrew Cook, and Owen T. Gorman Alewives (Alosa pseudoharengus) are unique among the many exotic species that have invaded and successfully colonized the Laurentian Great Lakes. Their burgeoning numbers could not only be reduced by management actions, but also the method used to reduce the populations, annual releases of hatchery-reared trout and salmon (salmonines), created a net economic benefit to the region by creating multi-million dollar recreational fisheries (Bence and Smith 1999; Connelly and Brown 2009). The largest of the hatcheries maintained, Alewife-based fisheries were in Lakes Ontario, Huron, and Michigan, the three lakes with an abundance of Alewife and salmonine habitats. Large scale releases of salmonines began in the 1970s, and, by the 1990s, management agencies faced a dilemma.Anglerswantedtomaintain,andinsomecasesexpand,theAlewife-basedfisheriesbycontinuing or increasing stocking of Chinook Salmon (Oncorhynchus tshawytscha). Although Chinook Salmon were favored by anglers because they grew to a large size during their four years in the lake, they also consumed more Alewives than any of the other salmonines (Stewart et al. 1981). Alewife populations, however, were not only reduced, but scientific studies suggested that they could collapse, due to predation pressure from the stocked salmonines (Stewart et al. 1981; Jones et al. 1993). Moreover, management agencies were committed to the restoration of native fishes, and numerous studies had implicated Alewife in the decline of native fishes (see O’Gorman and Stewart 1999 for a review). Thus, the management dilemma of the 1990s—continued stocking of Chinook Salmon would risk collapsing Alewife populations and the fisheries dependent on them, while increasing the likelihood of restoring some native fishes, whereas reduced stocking of Chinook Salmon would allow Alewife populations and the fisheries to persist, while reducing the likelihood of restoring some native fishes. ThefirstdecadeofthenewmillenniumsawmanyadvancesinourunderstandingofAlewifepopulation dynamics in the Great Lakes and their role in Great Lakes fish communities. The dilemma of the 1990s was, to some extent, resolved by studies that showed the link between numbers of Chinook Salmon stocked and predation pressure on Alewife had become increasingly tenuous in the 1990s because of the rising proportion of naturally produced salmon in Lakes Ontario, Huron, and Michigan (Claramunt et al. 2008; Connerton et al. 2009; Johnson et al. 2010). Indeed, naturally produced fish made up the majority of Robert O’Gorman et al. 706 some Chinook Salmon year classes. Moreover, survival of stocked Chinook Salmon was shown somewhat dependent on Alewife abundance (Johnson et al. 2007; Warner et al. 2008), debunking the notion that stocking was a wholly depensatory mortality factor for Alewife because it completely decoupled predator abundance from prey availability (Stewart et al. 1981). Nonetheless, Madenjian et al. (2005b) showed that Chinook salmon predation on Alewife represented a major regulator of Alewife abundance in Lake Michigan, validating the conclusions of Stewart et al. (1981) who were the first to point out the potential for Alewife population collapse from salmonine predation. The role of climate in Alewife recruitment was clarified (O’Gorman et al. 2004; Madenjian et al. 2005b), and additional evidence was amassed on the deleterious effect of Alewife on native fishes (Fielder et al. 2007; Riley et al. 2007; Madenjian et al. 2008; Schaeffer et al. 2008). Understanding how Alewives have affected native fishes requires knowledge of their seasonal distribution and role in the food web; we describe both herein. We also describe the two ways in which climate affects Alewife population dynamics—precipitating die-offs and influencing recruitment. Finally, we chronicle the history of Alewife populations in the five Great Lakes and the various approaches taken by natural resource agencies to manage Alewives. Seasonal Distribution The seasonal movements of Alewives are such that, during the course of a year, Alewives will have occupied all areas of the Great Lakes, from littoral waters near shore to waters in mid-lake (Graham 1956; Wells 1968a). In late spring and early summer, sexually immature Alewives spread out across the lake as waters warm, whereas sexually mature Alewives spawn at night near shore not only along the open lake shore, but also in bays, harbors, and the lower reaches of rivers. In summer, Alewives occupy the lakes’ warm epilimnion, both nearshore and offshore, and are largely absent from the cold hypolimnion, although, under certain conditions, some can be found in the thermocline (Wells 1968a; Olson et al. 1988; Johannsson and O’Gorman 1991; but see Janssen and Brandt 1980). Young-of-year (YOY) Alewives are...

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