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James J Willacker, Jr.

I am an Ecologist specializing in aquatic and trophic ecology at the USGS Forest and Rangeland Ecosystem Science Center in Corvallis, OR

I am broadly interested in aquatic ecology and in particular the application of trophic ecology to questions of ecotoxicology, evolution, physiology, and conservation biology. My current research focuses on understanding the interplay among ecological, biogeochemical, and physiological processes that govern contaminant accumulation in biota, particularly fishes and other aquatic taxa. My work is also aimed at quantifying ecological risk and toxicological impacts associated with contaminants, particularly mercury.

Professional Experience

  • 2013 - Present: Ecologist, USGS Forest and Rangeland Ecosystem Science Center, Corvallis, OR

  • 2009 - 2013: Doctoral Researcher, University of Alaska Fairbanks, Fairbanks, AK

  • 2009 - 2012: Instructor, Alaska Community Action on Toxics, Anchorage, AK

  • 2007 - 2009: Aquatic Ecologist, Environmental and Natural Resource Institute, Anchorage, AK

Education and Certifications

  • Ph.D., Biological Sciences, University of Alaska, Fairbanks, AK (2013)

  • M.S., Biological Sciences, University of Alaska, Anchorage, AK (2009)

  • B.S., Environmental and Forest Biology- Summa cum laude, State University of New York College of Environmental Science and Forestry (2006)

Honors and Awards

  • Outstanding Graduate Researcher Award, Environment and Natural Resources Institute, University of Alaska, Anchorage, AK. (2011)

  • Valedictorian, SUNY ESF (2007)

  •  University Scholar, SUNY (2007)

  • Faculty Honors, Department of Environmental and Forest Biology, SUNY ESF (2007)

  • Robin Hood Oak Award, SUNY ESF (2006)

Science and Products

If you are unable to access or download a product, email fresc_outreach@usgs.gov a request, including the full citation, or call (541) 750-1030.

Filter Total Items: 20

The influence of short-term temporal variability on the efficacy of dragonfly larvae as mercury biosentinels

Mercury (Hg) exposure to fish, wildlife, and humans is widespread and of global concern, thus stimulating efforts to reduce emissions. Because the relationships between rates of inorganic Hg loading, methylmercury (MeHg) production, and bioaccumulation are extremely complex and challenging to predict, there is a need for reliable biosentinels to understand the distribution of Hg in the environment
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Ecosystems Mission Area, Environmental Health Program, Forest and Rangeland Ecosystem Science Center

In-reservoir physical processes modulate aqueous and biological methylmercury export from a seasonally anoxic reservoir

Anoxic conditions within reservoirs related to thermal stratification and oxygen depletion lead to methylmercury (MeHg) production, a key process governing the uptake of mercury in aquatic food webs. Once formed within a reservoir, the timing and magnitude of the biological uptake of MeHg and the relative importance of MeHg export in water versus biological compartments remain poorly understood. W
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Ecosystems Mission Area, Water Resources Mission Area, Forest and Rangeland Ecosystem Science Center, Idaho Water Science Center, Upper Midwest Water Science Center, Mercury Research Laboratory

Small mammal shooting as a conduit for lead exposure in avian scavengers

Lead (Pb) exposure is a widespread wildlife conservation threat. Although commonly associated with Pb-based ammunition from big-game hunting, small mammals (e.g., ground squirrels) shot for recreational or pest-management purposes represent a potentially important Pb vector in agricultural regions. We measured the responses of avian scavengers to pest-shooting events and examined their Pb exposure
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Ecosystems Mission Area, Forest and Rangeland Ecosystem Science Center

Fish habitat use and food web structure following pond and plug restoration of a Montane Meadow in the Sierra Nevada, California

Montane meadows are areas of high biodiversity and provide many important ecosystem services; however, degradation of 40–60% of these habitats in the Sierra Nevada region of California has left many of these areas impaired. The “pond-and-plug” meadow-restoration technique is 1 type of treatment implemented to restore montane meadows. The objectives of this technique are to re-water the meadow and
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Ecosystems Mission Area, Forest and Rangeland Ecosystem Science Center

A national-scale assessment of mercury bioaccumulation in United States National Parks using dragonfly larvae as biosentinels through a citizen-science framework

We conducted a national-scale assessment of mercury (Hg) bioaccumulation in aquatic ecosystems using dragonfly larvae as biosentinels, by developing a citizen science network to facilitate biological sampling. Implementing a carefully designed sampling methodology for citizen scientists, we developed an effective framework for landscape-level inquiry that might otherwise be resource limited. We as
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Ecosystems Mission Area, Patuxent Wildlife Research Center, Eastern Ecological Science Center, Forest and Rangeland Ecosystem Science Center, Upper Midwest Water Science Center, Western Ecological Research Center (WERC), Mercury Research Laboratory

Mercury bioaccumulation in freshwater fishes of the Chesapeake Bay watershed

Chemical contaminants are a threat to the Chesapeake Bay watershed, with mercury (Hg) among the most prevalent causes of impairment. Despite this, large-scale patterns of Hg concentrations, and the potential risks to fish, wildlife, and humans across the watershed, are poorly understood. We compiled fish Hg data from state monitoring programs and recent research efforts to address this knowledge g
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Ecosystems Mission Area, Eastern Ecological Science Center, Chesapeake Bay Activities, Forest and Rangeland Ecosystem Science Center

Mercury and selenium concentrations in fishes of the Upper Colorado River Basin, southwestern United States: A retrospective assessment

Mercury (Hg) and selenium (Se) are contaminants of concern for fish in the Upper Colorado River Basin (UCRB). We explored Hg and Se in fish tissues (2,324 individuals) collected over 50 years (1962–2011) from the UCRB. Samples include native and non-native fish collected from lotic waterbodies spanning 7 major tributaries to the Colorado River. There was little variation of total mercury (THg) in
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Ecosystems Mission Area, Colorado Water Science Center, Southwest Biological Science Center

Timber harvest alters mercury bioaccumulation and food web structure in headwater streams

Timber harvest has many effects on aquatic ecosystems, including changes in hydrological, biogeochemical, and ecological processes that can influence mercury (Hg) cycling. Although timber harvest’s influence on aqueous Hg transformation and transport are well studied, the effects on Hg bioaccumulation are not. We evaluated Hg bioaccumulation, biomagnification, and food web structure in 10 paired c
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Ecosystems Mission Area, Water Resources Mission Area, Forest and Rangeland Ecosystem Science Center, Oregon Water Science Center, Upper Midwest Environmental Sciences Center, Upper Midwest Water Science Center, Mercury Research Laboratory

Mercury bioaccumulation in estuarine fishes: Novel insights from sulfur stable isotopes

Estuaries are transitional habitats characterized by complex biogeochemical and ecological gradients that result in substantial variation in fish total mercury concentrations (THg). We leveraged these gradients and used carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) stable isotopes to examine the ecological and biogeochemical processes underlying THg bioaccumulation in fishes from the San Franc
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Ecosystems Mission Area, Forest and Rangeland Ecosystem Science Center

Reservoirs and water management influence fish mercury concentrations in the western United States and Canada

Anthropogenic manipulation of aquatic habitats can profoundly alter mercury (Hg) cycling and bioaccumulation. The impoundment of fluvial systems is among the most common habitat manipulations and is known to increase fish Hg concentrations immediately following impoundment. However, it is not well understood how Hg concentrations differ between reservoirs and lakes at large spatial and temporal sc
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Ecosystems Mission Area, Contaminant Biology, Environmental Health Program, Forest and Rangeland Ecosystem Science Center, John Wesley Powell Center for Analysis and Synthesis

Assessing potential health risks to fish and humans using mercury concentrations in inland fish from across western Canada and the United States

Fish represent high quality protein and nutrient sources, but Hg contamination is ubiquitous in aquatic ecosystems and can pose health risks to fish and their consumers. Potential health risks posed to fish and humans by Hg contamination in fish were assessed in western Canada and the United States. A large compilation of inland fish Hg concentrations was evaluated in terms of potential health ris
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Ecosystems Mission Area, Contaminant Biology, Cooperative Research Units, Environmental Health Program, Forest and Rangeland Ecosystem Science Center, John Wesley Powell Center for Analysis and Synthesis

Mercury risk to avian piscivores across western United States and Canada

The widespread distribution of mercury (Hg) threatens wildlife health, particularly piscivorous birds. Western North America is a diverse region that provides critical habitat to many piscivorous bird species, and also has a well-documented history of mercury contamination from legacy mining and atmospheric deposition. The diversity of landscapes in the west limits the distribution of avian pisciv
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Ecosystems Mission Area, Contaminant Biology, Environmental Health Program, Forest and Rangeland Ecosystem Science Center, John Wesley Powell Center for Analysis and Synthesis

Non-USGS Publications**

Willacker Jr., J.J., Sobczak, W.V., Colburn, E.A., 2009, Stream macroinvertebrate communities in paired hemlock and deciduous watersheds: Northeastern Naturalist, v. 16, no. 1, p. 101-112, https://doi.org/10.1656/045.016.0108.
Willacker Jr., J.J., von Hippel, F.A., Wilton, P.R., Walton, K.M., 2010, Classification of threespine stickleback along the benthic–limnetic axis: Biological Journal of the Linnean Society, v. 101, p. 595-608, https://doi.org/10.1111/j.1095-8312.2010.01531.x.
Kenney, L.A., von Hippel, F.A., Willacker Jr., J.J., O'Hara, T.M., 2012, Mercury concentrations of a resident freshwater forage fish at Adak Island, Aleutian Archipelago, Alaska: Environmental Toxicology and Chemistry, v. 31, no. 11, p. 2647-2652, https://doi.org/10.1002/etc.1990.
Walton, K.M., Spalinger, D.E., Harris, N.R., Collins, W.B., Willacker Jr., J.J., 2013, High spatial resolution vegetation mapping for assessment of wildlife habitat: Wildlife Society Bulletin, v. 37, no. 4, p. 906-915, https://doi.org/10.1002/wsb.344.
Willacker Jr., J.J., von Hippel, F.A., Ackerly, K.L., O'Hara, T.M., 2013, Habitat-specific foraging and sex determine mercury concentrations in sympatric benthic and limnetic ecotypes of threespine stickleback: Environmental Toxicology and Chemistry, v. 32, no. 7, p. 1623-1630, https://doi.org/10.1002/etc.2213.
Shedd, K.R., F.A. von Hippel, J.J. Willacker, T.R. Hamon, O.L. Schlei, J.K. Wenburg, J.L. Miller, and S.A. Pavey. 2015. Ecological release leads to novel ontogenetic diet shift in kokanee (Oncorhynchus nerka). Canadian Journal of Fisheries and Aquatic Sciences 72: 1718-1730.
Willacker, J.J. 2013. Ecological drivers of mercury accumulation in Threespine Stickleback fish. Doctor of Philosophy, University of Alaska Fairbanks, Fairbanks, AK, USA.
Willacker, J.J. 2009. Geometric morphometrics of Threespine Stickleback in the Cook Inlet Basin, Alaska. Master of Science, University of Alaska Anchorage, Anchorage, AK, USA.
Willacker, J.J., D. Rinella, and D. Bogan. 2008. Aquatic macroinvertebrate and diatom surveys in Tetlin National Wildlife Refuge, AK. Environmental and Natural Resources Institute Annual Progress Report to the U.S. Fish and Wildlife Service.
Willacker, J.J., D. Rinella, and D. Bogan. 2007. Macroinvertebrate abundance in the Eklutna River, AK: an estimate of food supply for rearing salmonids. Environmental and Natural Resources Institute Final Report to the Eklutna River Restoration Project, U.S. Army Corps of Engineers.

**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.

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A brook trout swimming in stream.

Bioaccumulation of Mercury in Fish Varied by Species and Location in the Chesapeake Bay Watershed—Summary of Existing Data and a Roadmap for Integrated Monitoring

Fish mercury data from State monitoring programs and research studies within the Chesapeake Bay were compiled and summarized to provide a comprehensive overview of the variation in fish mercury concentrations among species and habitats within the watershed. These data are put into context with existing health benchmarks for humans, birds, and fish. Scientists also provide a roadmap for an...
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Ecosystems Mission Area, Contaminant Biology, Environmental Health Program, Toxic Substances Hydrology, Chesapeake Bay Activities
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Bioaccumulation of Mercury in Fish Varied by Species and Location in the Chesapeake Bay Watershed—Summary of Existing Data and a Roadmap for Integrated Monitoring

Fish mercury data from State monitoring programs and research studies within the Chesapeake Bay were compiled and summarized to provide a comprehensive overview of the variation in fish mercury concentrations among species and habitats within the watershed. These data are put into context with existing health benchmarks for humans, birds, and fish. Scientists also provide a roadmap for an...
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Landsat image of the south end of San Francisco Bay Estuary and associated wetlands

Scientists Identify Processes that Affect Fish Mercury Concentrations in Estuarine Wetlands

In a study designed to help resource managers when considering mercury exposure risk, scientists determined that sulfur cycling—a process closely related to mercury methylation rates—and ecological conditions that influence exposure are important factors affecting fish mercury concentrations in estuarine wetlands.
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Ecosystems Mission Area, Contaminant Biology, Environmental Health Program, Toxic Substances Hydrology
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Scientists Identify Processes that Affect Fish Mercury Concentrations in Estuarine Wetlands

In a study designed to help resource managers when considering mercury exposure risk, scientists determined that sulfur cycling—a process closely related to mercury methylation rates—and ecological conditions that influence exposure are important factors affecting fish mercury concentrations in estuarine wetlands.
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fish frozen in tubes

Contaminant Ecology Research Team (FRESC)

The FRESC Contaminant Ecology research program evaluates the distribution, movement, and ecological effects of environmental contaminants across the landscape and strives to provide relevant science in support of natural resource conservation, management, and decision making.
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Forest and Rangeland Ecosystem Science Center
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Contaminant Ecology Research Team (FRESC)

The FRESC Contaminant Ecology research program evaluates the distribution, movement, and ecological effects of environmental contaminants across the landscape and strives to provide relevant science in support of natural resource conservation, management, and decision making.
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USGS science for a changing world logo

Mercury cycling, bioaccumulation, and risk across western North America: a landscape scale synthesis linking long-term datasets

Mercury (Hg) is a serious environmental problem that is impacting ecological and human health on a global scale. However, local and regional processes are largely responsible for producing methylmercury, which drives ecological risk. This is particularly true in western North America where the combination of diverse landscapes, habitat types, climates, and Hg sources may disproportionally impact t
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John Wesley Powell Center for Analysis and Synthesis
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Mercury cycling, bioaccumulation, and risk across western North America: a landscape scale synthesis linking long-term datasets

Mercury (Hg) is a serious environmental problem that is impacting ecological and human health on a global scale. However, local and regional processes are largely responsible for producing methylmercury, which drives ecological risk. This is particularly true in western North America where the combination of diverse landscapes, habitat types, climates, and Hg sources may disproportionally impact t
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If you are unable to access or download a product, email fresc_outreach@usgs.gov a request, including the full citation, or call (541) 750-1030.

Mercury and biogeochemical parameters in surface water and sediment from U.S. National Parks, 2014-2015

Comma-separated values (.csv) file containing data related to mercury and biogeochemical parameters in surface water and aquatic sediment collected from U.S. National Parks in 2014-2015.
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Forest and Rangeland Ecosystem Science Center

Total mercury and methylmercury in biota from Cottage Grove Reservoir and the Coast Fork Willamette River, Oregon, 2021

Comma-separated values (.csv) file containing data related to mercury in biota from Cottage Grove Reservoir, and the rivers upstream of Cottage Grove Reservoir, Oregon.
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Forest and Rangeland Ecosystem Science Center

Biomass and methylmercury concentrations in biweekly biological samples from Brownlee and Oxbow Reservoir outflows, Snake River Hells Canyon Complex (Idaho-Oregon), 2018-2019

This dataset describes biomass and methylmercury concentrations in zooplankton, other invertebrates, fish, and coarse and fine detritus samples collected at the outflow locations of Brownlee and Oxbow Reservoirs in the Snake River Hells Canyon Complex. Based on the sampling locations, the sampled materials were presumed to have flowed through the dam turbines or over the spillway, thereby represen
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Idaho Water Science Center

Total Mercury Concentrations in Dragonfly Larvae from U.S. National Parks (ver. 8.0, December 2022)

Comma-separated values (.csv) file containing data related to mercury concentrations in dragonfly samples from U.S. National Parks collected as part of the Dragonfly Mercury Project (DMP)
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Forest and Rangeland Ecosystem Science Center

Mercury Bioaccumulation in US National Parks Using Dragonfly Larvae as Biosentinels, 2009-2018

Comma-separated values (.csv) files containing data related to a National-scale assessment of mercury bioaccumulation in the US National Parks using dragonfly larvae as biosentinels through a citizen science framework.
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Forest and Rangeland Ecosystem Science Center

Total Mercury Concentrations in Smallmouth Bass from Chesapeake Bay Tributaries, USA Dataset, 2013-2017

This dataset includes fish scientific name, fish common name, site identification codes, latitude, longitude, site name, sample identification codes, collection date, tissue type, percent moisture content in fish samples, and wet and dry total mercury concentrations in fish tissues.
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Land Management Research Program, Chesapeake Bay Activities, Forest and Rangeland Ecosystem Science Center

Fish tissue mercury and selenium concentrations in Upper Colorado River Basin: 1962-2011

These data were compiled to study mercury and selenium concentrations in fish species and assemblages in lotic waterbodies across the Upper Colorado River Basin. Data were compiled from State and Federal agencies. This data table contains raw concentration data, as well as standardized concentrations corrected for differences based on sample type (i.e., tissue type), species-specific bioaccumulati
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Southwest Biological Science Center

Trask River Watershed Study Area Forestry Bioaccumulation Dataset, 2011-2015

This dataset includes timber harvest treatments; mercury concentrations in aquatic macroinvertebrates, salamanders, and riparian songbirds; carbon and nitrogen stable isotopes in aquatic macroinvertebrates and salamanders; and Bayesian estimates of food web length, basal resource diversity, and isotopic niche size for individual feeding guilds.
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Forest and Rangeland Ecosystem Science Center

Mercury Condition Index Tool

The Mercury Condition Index Tool uses existing data of mercury concentrations in invertebrates, fish, and birds within national parks to estimate a park level Condition Index (and associated uncertainty) for mercury, based on its potential risk to fish and wildlife health. The tool employs a series of logic steps to convert provided data into standardized units, based upon both basic stoichiometr
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Ecosystems Mission Area, Species Management Research Program, Forest and Rangeland Ecosystem Science Center
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Short-Term Variability Does Not Impact the Efficacy of Dragonfly Larvae as Mercury Biosentinels

Measuring the amount of mercury in dragonfly larvae is one way scientists can determine how much contamination is in aquatic food webs.

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Fish Habitat Use and Food Web Structure Following Pond-and-Plug Meadow Restoration

The ‘‘pond-and-plug’’ meadow-restoration technique, in which ponds are formed by excavating the floodplain and plugging incised channels with the...

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Mercury Bioaccumulation in the Chesapeake Bay Watershed

Despite the prevalence of mercury contamination in the Chesapeake Bay, large-scale patterns of mercury concentrations, and potential risks to fish...

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Timber Harvest Alters Mercury Bioaccumulation and Food Webs in Headwater Streams

Land use change is an important driver of global mercury cycling. Timber harvest is a common land use that can alter associated aquatic ecosystems...

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