Factors Affecting Postrelease Survival of Coded‐Wire‐Tagged Lake Trout in Lake Michigan at Four Historical Spawning Locations

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The Northern Refuge of Lake Michigan was established in 1985 under the auspices of the Great Lakes Fishery Commission as part of an intensely managed effort to restore a self‐sustaining Lake Trout Salvelinus namaycush population to the lake. Despite the stocking of millions of Lake Trout into the refuge and survival of these stocked fish to adulthood, signs of natural recruitment by Lake Trout in the refuge have been very sparse. To ascertain whether low egg viability or poor fry survival could be limiting natural recruitment by Lake Trout in the refuge, hatching rates of eggs taken from Lake Trout caught in the Northern Refuge during October 2019 were determined in the laboratory. Moreover, survival rates of the hatched‐out fry were determined along with the thiamine concentrations in the fry. In addition, thiamine concentrations in eggs of ovulating Lake Trout caught in the Northern Refuge during 2019–2021 were determined. Egg hatching rate in the laboratory averaged 93%. Survival rate of Lake Trout fry up to 5 weeks after hatching averaged 97%. Mean (SE) thiamine concentrations in eggs of Lake Trout caught in 2019, 2020, and 2021 were 19.1 (3.6), 5.9 (1.3), and 6.2 (0.4) nmol/g, respectively; these levels are well above the threshold concentration of 2.3 nmol/g, above which the likelihood of experiencing mortality due to thiamine deficiency complex (TDC) is low. Thiamine concentrations in the Lake Trout fry at the end of the laboratory experiment averaged 11.2 nmol/g, and abnormal behavior in the fry was not observed. We conclude that TDC does not appear to represent a major impediment to Lake Trout rehabilitation in the Northern Refuge at present, although TDC may have contributed to the lack of detectable natural recruitment in the past.

Section: Figurementioning

confidence: 99%

Egg Hatchability and Egg Thiamine Concentrations in Lake Trout from the Northern Refuge of Lake Michigan

Madenjian

Keeler

Grivicich

et al. 2022

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“…One important consideration when building a propagation program is that of choosing appropriate strains that display high survival and growth to maximize the return on stocking investment while also preserving the genetic integrity of wild populations (if they are stocked in the same waters; Miller and Kapuscinski 2003; Jennings et al 2010). Information on the growth and survival of different strains to inform these choices is often provided through stocking evaluations, which generally employ physical tagging (e.g., fin clips, coded wire or passive integrated transponder tags) to track hatchery outplants (e.g., Younk and Strand 1992; McDougall et al 2014; Wagner et al 2017; Kornis et al 2019). However, genetic methods can be used to track different hatchery strains if the strains are sufficiently genetically diverged from each other (e.g., Homola et al 2019).…”

Section: Figurementioning

confidence: 99%

“…In addition to growth, survival is a major factor to be considered when choosing strains to stock. Differences in strain‐specific survival have been demonstrated in many fish species (e.g., Eldridge et al 2002; Negus et al 2012; Kornis et al 2019), with strains derived from local genetic backgrounds typically outperforming more divergent strains (Miller and Kapuscinski 2003). Differences in survival as a consequence of genetic strain have also been relatively well documented in Muskellunge.…”

Section: Figurementioning

confidence: 99%

Using Genetic Data to Estimate Capture Rate of Wisconsin and Leech Lake Strains of Muskellunge Stocked in Four Wisconsin Lakes

Larson

Hill

Rowe

et al. 2020

Many inland fisheries are supported by stocking hatchery-produced fish, and fisheries managers often face difficult decisions regarding strain selection. Stocking evaluations that are designed to quantify differences in strain performance provide valuable data for designing stocking programs. Here, we used genetic tools to investigate the capture rate of two strains of Muskellunge that were stocked in Wisconsin lakes. We genotyped a total of 1,011 Muskellunge at 13 microsatellites and used the data from five reference populations to assign fish that were stocked in four Wisconsin lakes to their strain of origin. The strains that were stocked in these lakes were derived from Wisconsin populations in the upper Chippewa River and Wisconsin River drainages and from Leech Lake, Minnesota. The Muskellunge from Leech Lake demonstrated much lower capture rates than the Wisconsin strain, but the results were variable, with a 10% capture rate of fish from the Leech Lake strain in Lake Monona and a 2% capture rate in Lake Wissota, despite similar stocking rates (~25%) in both lakes. We hypothesized that the higher capture rates of Muskellunge from the Wisconsin strain could be due the adaptative advantages of the Wisconsin strain in these waters and suggest that managers continue to stock the nearest native (i.e., Wisconsin) strain to achieve the highest return on investment. Stocking hatchery-produced fish is one of the most common tools employed by fisheries managers to rebuild and sustain inland fisheries (Halverson 2008). One important consideration when building a propagation program is that of choosing appropriate strains that display high survival and growth to maximize the return on stocking investment while also preserving the genetic integrity of

“…The investment in rehabilitating the Lake Trout Salvelinus namaycush population in Lake Michigan has included (1) more than 50 years of effort; (2) stocking millions of Lake Trout into the lake each year; (3) annual control of the Sea Lamprey Petromyzon marinus population; (4) extensive coordination and collaboration between many state, federal, and tribal agencies; (5) regulations on Lake Trout harvest; and (6) billions of dollars (Holey et al 1995; Bronte et al 2008; Dexter et al 2011; Kornis et al 2019; Lake Trout Working Group [LTWG] 2022). The Lake Trout was an apex native predator in Lake Michigan (Smith 1968), and therefore it played a critical role in the structure and function of the lake's ecosystem (Estes et al 2011; Madenjian 2022).…”

Section: Introductionmentioning

confidence: 99%

Lake Trout population dynamics in the Northern Refuge of Lake Michigan: Importance of stocking rate

Madenjian,

Dieter,

Desorcie

et al. 2023

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ObjectiveThe Northern Refuge of Lake Michigan was established under the auspices of the Great Lakes Fishery Commission in 1985 as an additional step toward restoring a self‐sustaining Lake Trout Salvelinus namaycush population to the lake. The overall goal of our study was to assess progress toward Lake Trout rehabilitation in the Northern Refuge through 2021.MethodsWe conducted annual (1992–2021) gill‐net surveys in the fall to assess the adult population and beam trawl surveys in the spring to assess naturally reproduced age‐0 Lake Trout.ResultSpawner abundance averaged 45 fish • 305 m of gill net−1 • day−1 during 1992–1999, just 4 fish • 305 m of gill net−1 • day−1 during 2000–2014, and then 67 fish • 305 m of gill net−1 • day−1 during 2018–2021. Sea Lamprey Petromyzon marinus wounding rate decreased by nearly 90% between the 2000–2014 and 2015–2021 periods. The average annual mortality rate of adult Lake Trout decreased from 43% during the 1990s and 2000s to 22% during 2015–2021. All of these population dynamics were partly driven by changes in Lake Trout stocking rates, which declined by roughly 50% during 1994–1996 but then increased roughly twofold during 2006–2010 and remained at this higher level during 2010–2018. In 2021, early signs of natural recruitment of Lake Trout became evident. Beam trawling during June 2021 yielded a wild age‐0 Lake Trout, the first ever caught since the surveys began in 1992. In addition, 15 (4% of total catch) of the Lake Trout caught in the fall 2021 gill‐net survey were unclipped (wild) fish. Estimated ages of these wild fish indicated that natural recruitment had begun sometime around 2015.ConclusionWith Alewife Alosa pseudoharengus abundance in Lake Michigan at record low levels, Sea Lamprey wounding rate greatly reduced, and Lake Trout spawner abundance at relatively high levels, the outlook for Lake Trout rehabilitation in the Northern Refuge holds promise.