Abundance Indices for Determining the Status of Lake Trout Restoration in Michigan Waters of Lake Superior

Self Cite

In the 1950s, populations of lake trout Salvelinus namaycush in Lake Superior collapsed because of excessive exploitation and predation by sea lampreys Petromyzon marinus. Restoration began in the 1950s with the stocking of juvenile, hatchery‐reared lake trout and controls on fisheries and sea lampreys. Partial restoration was declared in 1996 because wild fish made up most of the populations in many areas, especially in Michigan waters, so stocking was dramatically curtailed in most areas. We evaluated the production of age‐7 lake trout (recruits) by age‐8 and older wild and stocked parental lake trout (spawners). Using Ricker stock–recruitment models, we also evaluated the effects of large‐mesh (114‐mm stretch measure) gill‐net effort on wild lake trout recruitment in Michigan waters of Lake Superior during 1970–1998. In general, the density of wild lake trout spawners increased, whereas that of stocked lake trout spawners decreased in all management areas investigated. The density of recruits was best described by the combined density of wild and stocked parents, which suggested similar reproductive contributions for both. Recruitment rates declined significantly with increasing spawner density in four of the five management areas and suggested that carrying capacities were reached and exceeded, which may serve as an indicator of population restoration. We conclude that both wild and stocked lake trout have contributed to the recruitment of lake trout in Michigan waters of Lake Superior. Large‐mesh gill‐net fishing effort varied in all Michigan management areas but did not account for the significant variation in wild lake trout recruitment. We conclude that levels of large‐mesh gill‐net fishing effort during 1970–1998 were not having an appreciable effect on wild lake trout recruitment in Michigan waters of Lake Superior.

Section: Relative Abundancesupporting

confidence: 83%

Section: Management Implicationsmentioning

confidence: 99%

Recruitment Dynamics of the 1971–1991 Year‐Classes of Lake Trout in Michigan Waters of Lake Superior

Richards

Hansen

Bronte

et al. 2004

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“…The decline in density of stocked lake trout in every management unit reflected a continuing trend toward wild fish predomination; in contrast, stocks in western Lake Superior before the 1990s consisted of mostly stocked lake trout (Lawrie and Rahrer 1973;Lawrie 1978;MacCallum and Selgeby 1987;Hansen et al 1995aHansen et al , 1995b. By the end of the study period, the percentage of spawners that were wild ranged from 71% in WI-1 to 95% in MN-3.…”

Section: Relative Abundancementioning

confidence: 96%

Recruitment Dynamics of Lake Trout in Western Lake Superior during 1988–1995

Corradin

Hansen

Schreiner

et al. 2008

Self Cite

Stocks of lake trout Salvelinus namaycush in Lake Superior are recovering from historical collapse. Stocking, control of sea lampreys Petromyzon marinus, and harvest restrictions have aided lake trout recovery, but the contribution of stocked lake trout to contemporary recruitment has not been quantified in western Lake Superior. Using variants of the Ricker stock-recruit model, we evaluated the production of age-7 lake trout (recruits) by examining age-8 and older wild and stocked parental lake trout (spawners). We found that density of wild lake trout spawners and recruits increased during 1980-2003, whereas the density of stocked spawners decreased in all management areas. Two competing models best described recruit density of the 1988-2003 year-classes: (1) wild and stocked parents each contributed to recruitment but stocked parents contributed negatively and (2) only wild parents contributed to recruitment. Recruitment rates declined significantly with increasing spawner density in four of five management areas, which suggests that recruitment is density dependent in much of western Lake Superior. We conclude that stocked lake trout did not contribute significantly to lake trout rehabilitation in western Lake Superior during 1980-1995.

“…Angler catch rate of Lake Trout increased linearly from about 0.025 fish/angler-hour in 2002 to about 0.048 fish/angler-hour in 2011 (Figure 2). Assuming that the angler catch rate is proportional to abundance (Hansen et al 1995), this trend suggests that the Lake Trout population almost tripled in size over that time period. We found a similar rate of increase in Lake Trout abundance estimated by mark-recapture in 2002 (Crockett et al 2006) and by SPIN in 2011.…”

Section: Lake Trout Population Modelingmentioning

confidence: 98%

Managing for Coexistence of Kokanee and Trophy Lake Trout in a Montane Reservoir

Pate

Johnson

Lepak

et al. 2014

Kokanee Oncorhynchus nerka and Lake Trout Salvelinus namaycush are stocked for sportfishing in lakes and reservoirs throughout the western United States and Canada. However, where the two species co‐occur, unsustainable levels of predation by Lake Trout can lead to declines in kokanee abundance and declines in Lake Trout growth and body condition. Such declines occurred in Blue Mesa Reservoir, Colorado. In 2009, managers began removing Lake Trout (<740 mm TL) in an attempt to sustain the hatchery‐dependent kokanee population while still providing a trophy Lake Trout fishery. To evaluate this and other strategies for achieving the dual management goals, we developed age‐structured kokanee and Lake Trout population models and linked them to a bioenergetics model of Lake Trout predation. We found that the existing level of Lake Trout removal (0.23; ages 4–9) is insufficient to prevent further decline and ultimately the extirpation of the kokanee population. If removal of age‐4–9 Lake Trout is intensified to 0.38, the kokanee population would persist; however, removal would have to be increased to 0.63 to allow a return to historic kokanee abundance. Focusing removal on age‐4 Lake Trout (0.78) would allow for persistence of kokanee and would leave more trophy Lake Trout for anglers, suggesting that the two goals are compatible under some circumstances. However, management costs of balancing kokanee with trophy Lake Trout are high and put both fisheries at risk unless Lake Trout abundance is controlled. Received October 31, 2013; accepted May 5, 2014