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Grand Rapids, MN, United States

Larson J.H.,U.S. Geological Survey | Maki R.P.,Voyageurs National Park | Knights B.C.,U.S. Geological Survey | Gray B.R.,U.S. Geological Survey
Ecotoxicology | Year: 2014

Mercury (Hg) contamination of fisheries is a major concern for resource managers of many temperate lakes. Anthropogenic Hg contamination is largely derived from atmospheric deposition within a lake’s watershed, but its incorporation into the food web is facilitated by bacterial activity in sediments. Temporal variation in Hg content of fish (young-of-year yellow perch) in the regulated lakes of the Rainy–Namakan complex (on the border of the United States and Canada) has been linked to water level (WL) fluctuations, presumably through variation in sediment inundation. As a result, Hg contamination of fish has been linked to international regulations of WL fluctuation. Here we assess the relationship between WL fluctuations and fish Hg content using a 10-year dataset covering six lakes. Within-year WL rise did not appear in strongly supported models of fish Hg, but year-to-year variation in maximum water levels (∆maxWL) was positively associated with fish Hg content. This WL effect varied in magnitude among lakes: In Crane Lake, a 1 m increase in ∆maxWL from the previous year was associated with a 108 ng increase in fish Hg content (per gram wet weight), while the same WL change in Kabetogama was associated with only a 5 ng increase in fish Hg content. In half the lakes sampled here, effect sizes could not be distinguished from zero. Given the persistent and wide-ranging extent of Hg contamination and the large number of regulated waterways, future research is needed to identify the conditions in which WL fluctuations influence fish Hg content. © 2014, Springer Science+Business Media New York (outside the USA). Source

Pittman H.T.,Clemson University | Pittman H.T.,University of Arkansas | Bowerman W.W.,Clemson University | Bowerman W.W.,University of Maryland University College | And 3 more authors.
Ecotoxicology | Year: 2011

Bald eagles (Haliaeetus leucocephalus) have been utilized as a biosentinel of aquatic ecosystem health in the Great Lakes Region since the early 1960s. Bald eagle populations have been monitored at Voyageurs National Park (VNP), Minnesota, since 1973. For the past 20 years, researchers have collected feathers from nestling bald eagles to assess their dietary exposure to mercury (Hg) on Rainy, Kabetogama, and Namakan lakes in VNP. Mercury is an environmental pollutant with both natural and anthropogenic sources, and negatively affects many species of wildlife. In a previous study, geometric mean concentrations of Hg in feathers of nestling bald eagles were greater at VNP (20 mg/kg Dry Weight (DW)) than in nestling feathers from other Great Lakes subpopulations (~7 mg/kg DW), for the period 1985-1989. Current geometric mean concentrations have declined by 77.4% since 1989 at VNP. While all samples from 1985 to 1989 had detectable concentrations of Hg, 10% of current samples had concentrations below the reportable detection limit (0.001 mg/kg DW, n = 180). The major lakes at VNP are impounded, and Hg concentrations also declined greatly after the lake level stabilization order by the International Joint Commission was implemented in 1999. Mercury concentrations in feathers of nestling bald eagles from 1989 to 2010 ranged from ND (<0.001) to 34.97 mg/kg DW. The highest single concentration in a nestling was from Namakan Lake in 2010. The five-year geometric means for Rainy, Kabetogama, and Namakan lakes for 2006-2010 were 6.08, 1.07, and 5.56 mg/kg DW (n = 28, n = 32, n = 27) respectively. Although Hg concentrations in feathers of nestlings greatly declined after the change in water level management in 1999 and are lower than 1989 concentrations, recent samples suggest a gradual increase. Continued monitoring of nestling feather concentrations will be essential to assess this increase, to determine the source of Hg, to determine if there are changes to methylation potential, and to evaluate and optimize water level management. © 2011 Springer Science+Business Media, LLC. Source

Windels S.K.,Voyageurs National Park
Wildlife Society Bulletin | Year: 2014

External marking of American beavers (Castor canadensis) is essential to studies of population dynamics and behavior of individuals. Application of metal ear tags is a common method used to mark beavers but rates and causes of ear-tag loss have been insufficiently documented. I live-trapped and tagged 627 beavers in Voyageurs National Park, Minnesota, USA, from 2006 to 2012 with a single, uniquely numbered no. 3 monel ear tag in each ear. Beavers recaptured or recovered via live-trapping (n=178), legal harvest outside of the park (n=55), or death (n=4) up to 6 years after initial release were inspected for tag loss. An additional 31 beavers were secondarily marked with radiotransmitters and used to test the assumption that loss of one ear tag was independent of loss of the other. Six percent (15 out of 237) of beavers lost a single ear tag. Overall probability of beavers losing a single ear tag was low (3.3%) and did not differ by sex, age class, or method of recapture-recovery. Tag loss was highest within 6 months of initial tagging, but probability of tag loss was not related to time between tagging and recovery up to 6 years after tagging. None of the radioed beavers lost both ear tags, supporting the assumption of independence of ear-tag loss among individual beavers. Ear-tag loss rates are sufficiently low that studies of American beavers that rely on mark- recapture methods do not need to account for bias from ear-tag loss. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. Source

Moen R.,University of Minnesota | Windels S.K.,Voyageurs National Park | Hansen B.,University of Minnesota
Natural Areas Journal | Year: 2012

Voyageurs National Park (VNP) is within the historical distribution of Canada lynx (Lynx canadensis), a federally threatened species. Sightings of lynx in and near VNP have existed since the 1970s, and three recent sightings have been confirmed with DNA analysis. However, population status and habitat suitability for lynx in VNP are unknown. We used remote cameras and snow-tracking to search for lynx in and near VNP in 2007 and 2008 and did not document lynx presence. We estimated the density of the lynx's primary prey, snowshoe hare (Lepus americanus), with hare pellet counts, extrapolated hare density to the landscape level, and compared habitat in VNP to habitat in lynx home ranges in northeastern Minnesota. Hare pellet densities in VNP were about half of hare pellet densities in lynx home ranges in northeastern Minnesota. Even though patches of high-density hare habitat exist in the VNP area, the low density of snowshoe hares at the landscape level would not support resident lynx, and most of the lynx recently documented in and near VNP are, therefore, probably transient animals. A female lynx with a kitten west of VNP in winter of 2010 was the only probable resident lynx confirmed near VNP from 2001 to 2010. Habitat management or natural disturbance processes that increase snowshoe hare densities would be required to support a resident lynx population in VNP. Source

Windels S.K.,Voyageurs National Park | Flaspohler D.J.,Michigan Technological University
Botany | Year: 2011

Canada yew (Taxus canadensis Marsh.) is a shade-tolerant evergreen shrub native to the understories of the boreal and deciduous forests of northeastern North America. Canada yew has a relatively unique growth form, with low sprawling branches capable of forming dense clusters of stems. Historic accounts suggest that before Euro-American settlement, Canada yew was a common plant across its range in many forest types and that it was locally abundant or dominant in 5%-20% of forest stands in the northern part of its range. Canada yew's range has declined during the last century as a result of browsing by native ungulates, fire, intensive forest management, and clearing of land for agriculture and other development. It is considered uncommon throughout most of its present North American range, except for often isolated populations in areas that remain free from heavy browsing pressure by moose and deer (e.g., islands, areas with heavy snow cover, or areas naturally low in ungulate abundance). Its decline has likely resulted in changes to abiotic and biotic conditions, including structure and composition of understory vegetation and concomitant effects on understory vertebrates. Increasing whitetailed deer populations and reduced snowfall as a result of climate change in eastern North America threaten to extirpate this species from additional parts of its range in the next century. Suggestions for future research are discussed. Source

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