Search USGS⌕ Search

SEARCH · Search USGS

Results for “Fisheries”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,675 records · Page 93Linked to original sources
USGS2025

Angler dynamics in the St. Clair-Detroit River System after decades of change

Habitat and water quality were historically degraded within the St. Clair-Detroit River System (SCDRS). Beginning in 2004, extensive habitat restoration projects were implemented remediating losses of fish spawning beds and shoreline areas. Monitoring of post-restoration activities documented recovering fish populations; however, angler response remains unknown. Extensive creel surveys were conducted pre-restoration (2002–2004), but post-restoration (2012 and later) surveys were intermittent. The goal of this project was to examine both to create a comprehensive picture of the effects of restoration on angling. We calculated catch and harvest rates and inspected answers to supplemental questions collected by state and provincial agencies. We estimated economic impact of angling with a combination of lodging and gas expenses. Post-restoration, catch rates were higher, but harvest rates were variable for Lake St. Clair and the Detroit River. The 2017 open water boat fishery on Lake St. Clair was worth ∼$26 million. Increased fishing opportunities resulting from continued habitat and population recovery are leading to increased catch rates and likely attracting anglers to the area.

Michigan, Ontario↗
USGS2025

Drowned river mouth lakes are winter foraging habitats for the expanding Lake Michigan cisco Coregonus artedi population

Characterizing fish movements is required for understanding habitat use, energy flow, and trophic structure and can inform fisheries management. Drowned river mouth (DRM) lakes are productive inland habitats in the Laurentian Great Lakes basin used by migratory fishes. Despite recognition of their ecological connections to the Great Lakes, the value of DRM lakes as seasonal habitats is not well understood for many fishes. One such species, cisco Coregonus artedi , has recently expanded in Lake Michigan from near extirpation to higher relative abundances in the northeastern portion of the lake. Cisco are recreationally harvested in some DRM lakes during winter, but little is known about cisco movement patterns and ecology. In winter 2022 and 2023, we collected cisco from three DRM lakes along the eastern shores of Lake Michigan (Lake Charlevoix, Portage Lake, Muskegon Lake) to characterize genetics, morphometrics, and diets. We also implanted telemetry tags in 20 cisco collected in Lake Charlevoix to examine movement patterns and determine DRM lake residency (i.e., seasonal vs. year-round). We found no consistent genetic or morphometric differentiation across DRM lakes, suggesting that recolonization began from a single stock. Fish were the only diet item found in cisco guts collected during winter months. Movement patterns from Lake Charlevoix indicated strong spawning site fidelity to Grand Traverse Bay as well as non-spawning site fidelity. However, given the presence of cisco in southern DRM lakes and some site-specific differences in morphometrics, managers could benefit from further research to determine whether spawning occurs in southern Lake Michigan.

Journal of Great Lakes Research↗
USGS2026

A post-restoration evaluation of fish spawning on Coreyon Reef in Saginaw Bay, Lake Huron

Habitat diversity is important to fisheries for promoting resiliency to interannual environmental variation. Historical land use change resulting in increased sedimentation has impaired fish rock reef habitats in Saginaw Bay, Lake Huron. Pursuant to the recovery of Saginaw Bay’s walleye population, and to benefit other species, came the decision to restore the offshore habitat Coreyon Reef, a 0.8 ha rock reef complex. Following a pre-restoration assessment in 2014–2016 and construction in 2019, we conducted a comprehensive assessment from fall 2020 to spring 2022 to document the restored habitat’s viability for fish spawning. This assessment featured two objectives: (1) to evaluate reproductive usage by lake whitefish and walleye, and (2) to evaluate their corresponding egg incubation environment. We sampled directly on Coreyon Reef and at nearby unrestored control sites for comparison, with gears standardized to the pre-restoration assessment. We confirmed spawning of lake whitefish and walleye on the restored reef less than 2 years post-construction. Relative to the pre-restoration assessment, peak egg deposition increased substantially for walleye and marginally for lake whitefish. However, concurrent reproductive utilization at nearby unrestored sites was consistent or even greater than directly on the restored site. Dissolved oxygen concentration was sufficient for embryo development, but invasive round goby were abundant and consumed eggs. The fish assemblage at our sampling sites was consistent before and after restoration. We predict eggs deposited on the restored site have improved survival relative to unrestored sites, as the new reef structure may protect incubating embryos from predation and sedimentation.

Michigan↗
USGS2026

Efficiency of down-looking cameras for detecting round goby (Neogobius melanostomus) over varying substrates in laboratory microcosms

Since invading the Laurentian Great Lakes in the late 1980s, round goby Neogobius melanostomus have become a dominant benthic prey species, resulting in a need to accurately monitor their population abundance to inform fisheries management. Camera-based methods for assessing round goby abundances have gained popularity, but their efficiencies for detecting round goby are poorly understood. We evaluated the efficiency of down-looking color monocular cameras for detecting round goby presence in microcosm enclosures with known numbers of fish. Detection efficiencies were compared between sand and cobble substrate during daylight hours using a generalized linear mixed-effects model. After accounting for trial effects, enclosure placement, and within-replicate temporal autocorrelation, round goby detection efficiency was 98.6% over sand (95% confidence limit (CL): 98.0–99.0%), and 55.3% over a single layer of cobble substrate (CL: 48.6–61.8%). The large difference in detectability between cobble and sand suggests that camera-based estimates of round goby abundances are likely to be biased low and have lower relative precision in high-structure habitats, but may be largely unbiased in low-structure habitats. Despite much lower relative detection efficiencies of cameras in high-structure cobble habitats, the efficiencies reported here still compare favorably to conventional methods like otter and beam trawling. Our results provide initial quantitative bounds on the possible degree of negative bias in camera-based estimates of round goby abundances in different substrates, but require further field verification across the diversity of substrates, interstitial infilling, and other structural attributes of habitat found in the Great Lakes.

Michigan↗
USGS2026

Spawning habitat suitability models for Lake Erie cisco (Coregonus artedi) during the historical period of pre- and post-population declines 1877–1957

Coregonine fishes play a key role in the food webs and fisheries of the Laurentian Great Lakes and are a major focus of basin-wide conservation efforts. In Lake Erie, management goals prioritize rebuilding spawning populations of cisco ( Coregonus artedi ). However, the historical distribution of cisco spawning habitat and the environmental conditions that influence early life-stage success remain poorly defined. We used a novel database of historical coregonine spawning observations as well as novel habitat variables to describe historical conditions to model and determine where and what habitat was historically most suitable for spawning cisco in Lake Erie. The environmental predictors that produced the best model included reefs, distance to rivers, historical substrate, coefficient of variation of ice duration, fetch, and circulation. The highest suitability occurred in areas of high reef probability, near river mouths, in rocky and sandy substrate, and in areas of low variability in historical ice, fetch, and circulation. Suitable spawning habitat is predicted mostly around reefs in the western basin as well as along the coast and near rivers lake-wide. Our model identifies important habitat features and allows managers to envision relevant scales and locations at which to focus restoration efforts.

Lake Erie↗
USGS2014

Collaborative modelling and integrated decision support system analysis of a developed terminal lake basin

A terminal lake basin in west-central Nevada, Walker Lake, has undergone drastic change over the past 90 yrs due to upstream water use for agriculture. Decreased inflows to the lake have resulted in 100 km 2 decrease in lake surface area and a total loss of fisheries due to salinization. The ecologic health of Walker Lake is of great concern as the lake is a stopover point on the Pacific route for migratory birds from within and outside the United States. Stakeholders, water institutions, and scientists have engaged in collaborative modeling and the development of a decision support system that is being used to develop and analyze management change options to restore the lake. Here we use an integrated management and hydrologic model that relies on state-of-the-art simulation capabilities to evaluate the benefits of using integrated hydrologic models as components of a decision support system. Nonlinear feedbacks among climate, surface-water and groundwater exchanges, and water use present challenges for simulating realistic outcomes associated with management change. Integrated management and hydrologic modeling provides a means of simulating benefits associated with management change in the Walker River basin where drastic changes in the hydrologic landscape have taken place over the last century. Through the collaborative modeling process, stakeholder support is increasing and possibly leading to management change options that result in reductions in Walker Lake salt concentrations, as simulated by the decision support system.

Nevada↗
USGS2014

Developing and testing temperature models for regulated systems: a case study on the Upper Delaware River

Water temperature is an important driver of many processes in riverine ecosystems. If reservoirs are present, their releases can greatly influence downstream water temperatures. Models are important tools in understanding the influence these releases may have on the thermal regimes of downstream rivers. In this study, we developed and tested a suite of models to predict river temperature at a location downstream of two reservoirs in the Upper Delaware River (USA), a section of river that is managed to support a world-class coldwater fishery. Three empirical models were tested, including a Generalized Least Squares Model with a cosine trend (GLScos), AutoRegressive Integrated Moving Average (ARIMA), and Artificial Neural Network (ANN). We also tested one mechanistic Heat Flux Model (HFM) that was based on energy gain and loss. Predictor variables used in model development included climate data (e.g., solar radiation, wind speed, etc.) collected from a nearby weather station and temperature and hydrologic data from upstream U.S. Geological Survey gages. Models were developed with a training dataset that consisted of data from 2008 to 2011; they were then independently validated with a test dataset from 2012. Model accuracy was evaluated using root mean square error (RMSE), Nash Sutcliffe efficiency (NSE), percent bias (PBIAS), and index of agreement (d) statistics. Model forecast success was evaluated using baseline-modified prime index of agreement (md) at the one, three, and five day predictions. All five models accurately predicted daily mean river temperature across the entire training dataset (RMSE = 0.58–1.311, NSE = 0.99–0.97, d = 0.98–0.99); ARIMA was most accurate (RMSE = 0.57, NSE = 0.99), but each model, other than ARIMA, showed short periods of under- or over-predicting observed warmer temperatures. For the training dataset, all models besides ARIMA had overestimation bias (PBIAS = −0.10 to −1.30). Validation analyses showed all models performed well; the HFM model was the most accurate compared other models (RMSE = 0.92, both NSE = 0.98, d = 0.99) and the ARIMA model was least accurate (RMSE = 2.06, NSE = 0.92, d = 0.98); however, all models had an overestimation bias (PBIAS = −4.1 to −10.20). Aside from the one day forecast ARIMA model (md = 0.53), all models forecasted fairly well at the one, three, and five day forecasts (md = 0.77–0.96). Overall, we were successful in developing models predicting daily mean temperature across a broad range of temperatures. These models, specifically the GLScos, ANN, and HFM, may serve as important tools for predicting conditions and managing thermal releases in regulated river systems such as the Delaware River. Further model development may be important in customizing predictions for particular biological or ecological needs, or for particular temporal or spatial scales.

Delaware, New York, Pennsylvania↗
USGS2010

Predicting potentially toxigenic Pseudo-nitzschia blooms in the Chesapeake Bay

Harmful algal blooms are now recognized as a significant threat to the Chesapeake Bay as they can severely compromise the economic viability of important recreational and commercial fisheries in the largest estuary of the United States. This study describes the development of empirical models for the potentially domoic acid-producing Pseudo-nitzschia species complex present in the Bay, developed from a 22-year time series of cell abundance and concurrent measurements of hydrographic and chemical properties. Using a logistic Generalized Linear Model (GLM) approach, model parameters and performance were compared over a range of Pseudo-nitzschia bloom thresholds relevant to toxin production by different species. Small-threshold blooms (???10cellsmL-1) are explained by time of year, location, and variability in surface values of phosphate, temperature, nitrate plus nitrite, and freshwater discharge. Medium- (100cellsmL-1) to large- threshold (1000cellsmL-1) blooms are further explained by salinity, silicic acid, dissolved organic carbon, and light attenuation (Secchi) depth. These predictors are similar to other models for Pseudo-nitzschia blooms on the west coast, suggesting commonalities across ecosystems. Hindcasts of bloom probabilities at a 19% bloom prediction point yield a Heidke Skill Score of -53%, a Probability of Detection ~75%, a False Alarm Ratio of ~52%, and a Probability of False Detection ~9%. The implication of possible future changes in Baywide nutrient stoichiometry on Pseudo-nitzschia blooms is discussed. ?? 2010 Elsevier B.V.

Journal of Marine Systems↗
USGS2014

Comparative biogeochemistry-ecosystem-human interactions on dynamic continental margins

The ocean’s continental margins face strong and rapid change, forced by a combination of direct human activity, anthropogenic CO 2 -induced climate change, and natural variability. Stimulated by discussions in Goa, India at the IMBER IMBIZO III, we (1) provide an overview of the drivers of biogeochemical variation and change on margins, (2) compare temporal trends in hydrographic and biogeochemical data across different margins (3) review ecosystem responses to these changes, (4) highlight the importance of margin time series for detecting and attributing change and (5) examine societal responses to changing margin biogeochemistry and ecosystems. We synthesize information over a wide range of margin settings in order to identify the commonalities and distinctions among continental margin ecosystems. Key drivers of biogeochemical variation include long-term climate cycles, CO 2 -induced warming, acidification, and deoxygenation, as well as sea level rise, eutrophication, hydrologic and water cycle alteration, changing land use, fishing, and species invasion. Ecosystem responses are complex and impact major margin services including primary production, fisheries production, nutrient cycling, shoreline protection, chemical buffering, and biodiversity. Despite regional differences, the societal consequences of these changes are unarguably large and mandate coherent actions to reduce, mitigate and adapt to multiple stressors on continental margins.

Journal of Marine Systems↗
USGS2021

Tolerance of northern Gulf of Mexico eastern oysters to chronic warming at extreme salinities

The eastern oyster, Crassostrea virginica , provides critical ecosystem services and supports valuable fishery and aquaculture industries in northern Gulf of Mexico (nGoM) subtropical estuaries where it is grown subtidally. Its upper critical thermal limit is not well defined, especially when combined with extreme salinities. The cumulative mortalities of the progenies of wild C. virginica from four nGoM estuaries differing in mean annual salinity, acclimated to low (4.0), moderate (20.0), and high (36.0) salinities at 28.9 °C (84 °F) and exposed to increasing target temperatures of 33.3 °C (92 °F), 35.6 °C (96 °F) or 37.8 °C (100 °F), were measured over a three-week period. Oysters of all stocks were the most sensitive to increasing temperatures at low salinity, dying quicker (i.e., lower median lethal time, LT 50 ) than at the moderate and high salinities and resulting in high cumulative mortalities at all target temperatures. Oysters of all stocks at moderate salinity died the slowest with high cumulative mortalities only at the two highest temperatures. The F1 oysters from the more southern and hypersaline Upper Laguna Madre estuary were generally more tolerant to prolonged higher temperatures (higher LT 50 ) than stocks originating from lower salinity estuaries, most notably at the highest salinity. Using the measured temperatures oysters were exposed to, 3-day median lethal Celsius degrees (LD 50 ) were estimated for each stock at each salinity. The lowest 3-day LD 50 (35.1–36.0 °C) for all stocks was calculated at a salinity of 4.0, while the highest 3-day LD 50 (40.1–44.0 °C) was calculated at a salinity of 20.0.

Louisiana, Texas↗
USGS2010

Source and fate of inorganic solutes in the Gibbon River, Yellowstone National Park, Wyoming, USA: I. Low-flow discharge and major solute chemistry

The Gibbon River in Yellowstone National Park (YNP) is an important natural resource and habitat for fisheries and wildlife. However, the Gibbon River differs from most other mountain rivers because its chemistry is affected by several geothermal sources including Norris Geyser Basin, Chocolate Pots, Gibbon Geyser Basin, Beryl Spring, and Terrace Spring. Norris Geyser Basin is one of the most dynamic geothermal areas in YNP, and the water discharging from Norris is much more acidic (pH 3) than other geothermal basins in the upper-Madison drainage (Gibbon and Firehole Rivers). Water samples and discharge data were obtained from the Gibbon River and its major tributaries near Norris Geyser Basin under the low-flow conditions of September 2006. Surface inflows from Norris Geyser Basin were sampled to identify point sources and to quantify solute loading to the Gibbon River. The source and fate of the major solutes (Ca, Mg, Na, K, SiO 2 , Cl, F, HCO 3 , SO 4 , NO 3 , and NH 4 ) in the Gibbon River were determined in this study and these results may provide an important link in understanding the health of the ecosystem and the behavior of many trace solutes. Norris Geyser Basin is the primary source of Na, K, Cl, SO 4 , and N loads (35–58%) in the Gibbon River. The largest source of HCO 3 and F is in the lower Gibbon River reach. Most of the Ca and Mg originate in the Gibbon River upstream from Norris Geyser Basin. All the major solutes behave conservatively except for NH 4 , which decreased substantially downstream from Gibbon Geyser Basin, and SiO 2 , small amounts of which precipitated on mixing of thermal drainage with the river. As much as 9–14% of the river discharge at the gage is from thermal flows during this period.

Wyoming↗
USGS2022

Estimating the pelagic ocean’s benefits to humanity can enhance ocean governance

The human footprint on the global ocean is ever-increasing, particularly with new ways to grow food in the ocean, new technologies in marine energy production as a way to resolve climate change, and transport and commerce expanding across the ocean. Yet, human activities in the ocean have long been managed using a sectoral approach (e.g., fisheries, biodiversity protection, energy production, shipping) rather than a holistic integration of sector interactions, trade-offs, costs, and benefits. Coordination across sectors is now more critical than ever, not only because of the expanding human footprint but also because of climate change impacts on the ocean. Sustainable global ocean use can support the Blue Economy while also reversing negative climate impacts on the ocean. Advancements in science and technology, along with increasing momentum on global commitments to sound ocean governance, and science diplomacy internationally can support sustainable ocean use with accurate and timely information about the status and trends in the ocean’s ecosystem services (benefits) to society. Near-real time information about ecosystem services’ dynamics is critical to policymaking for a sustainable Blue Economy that works for nature and people in an ever-changing ocean. Here, we propose seven principles for ecosystem service assessments, essentially to international science diplomacy, for consideration by global marine policy communities.

Marine Policy↗
USGS2014

Total mercury concentrations in lionfish (Pterois volitans/miles) from the Florida Keys National Marine Sanctuary, USA

Strategies to control invasive lionfish in the western Atlantic and Caribbean are likely to include harvest and consumption. Until this report, total mercury concentrations had been documented only for lionfish from Jamaica, and changes in concentrations with increasing fish size had not been evaluated. In the Florida Keys, total mercury concentrations in dorsal muscle tissue from 107 lionfish ranged from 0.03 to 0.48 ppm, with all concentrations being less than the regulatory threshold for limited consumption. Mercury concentrations did not vary consistently with standard lengths or wet weights of lionfish. In 2010, lionfish from the upper Keys had mean concentrations that were 0.03–0.04 ppm higher than lionfish from the middle Keys, but mean concentrations did not differ consistently among years and locations. Overall, total mercury concentrations in lionfish were lower than those in several predatory fishes that support commercial and recreational fisheries in Florida.

Florida↗
USGS2016

Resetting the bar: Establishing baselines for persistent contaminants after Hurricane Sandy in the coastal environments of New Jersey and New York, USA

In the immediate aftermath of natural disasters, public health officials and other first responders engage in many activities to protect the public and ecosystems in the affected area. These activities include critical tasks designed to minimize adverse consequences resulting from chemical and microbial contaminant exposures, such as acute disease incidence and transmission. However, once these urgent priorities have been met and situations requiring immediate attention have been stabilized, questions regarding the potential longer term threats to humans and ecosystems associated with persistent contaminant exposures remain. Research conducted to address these questions is frequently challenged by the lack of available baseline contaminant information collected before the event for comparison and perspective. In addition, deployments of field crews and collection of environmental samples typically occur days, weeks, or months after the event. Consequently, during and in the aftermath of disasters, public health agencies commonly advise the public to disinfect water, avoid contact with disturbed infrastructure (such as sewer lines), and (or) refrain from use of recreational waters, with the general focus on acute health threats; however, the persisting effects of such releases on local recreational waters, fisheries, and other estuarine habitats are often undetermined.

New Jersey, New York↗
USGS2024

Shifting sands: The influence of coral reefs on shoreline erosion from short-term storm protection to long-term disequilibrium

Climate change is exacerbating shoreline erosion and flooding, posing significant risks to coastal communities. Although traditional coastal defenses such as seawalls, dykes, and breakwaters offer protection from these hazards, their high environmental and economic costs are driving interest in cost-competitive nature-based solutions. Coral reef restoration is a nature-based solution that may be particularly apt to mitigate tropical coastal flooding and shoreline erosion while providing benefits to local tourism, fisheries, and nature. However, the novelty of this field requires studies demonstrating the benefits of reefs for coastal protection. While the flood protection benefits of reefs have been well-documented, their effects on shoreline erosion are comparatively less understood. Here, we investigate the effects of coral reefs on shoreline erosion by comparing tropical beach responses at short and long timescales, as well as identifying important reef structural features influencing coastal erosion rates. Our analyses leveraged two key datasets created in this study: the first derived from a literature review on short-term shoreline erosion due to storm events, and another compiling >80 years of long-term erosion rates, bathymetry, habitat, and wave energy for the Hawaiian Islands of Kauaʻi, Oʻahu, and Maui. Our analyses reveal three key findings regarding the effects of reefs on shoreline erosion. Firstly, we find evidence for the role of reefs in mitigating shoreline erosion during storm events, with coral reef-protected beaches experiencing 97 % less beach volume loss than unprotected beaches. Secondly, a linear regression analysis demonstrates that coral reef structure and wave energy are important predictors of long-term shoreline erosion rates, explaining 34 % of the variation across the Hawaiian Islands. Consistent with prior research, we find beaches protected by coral reefs with shallow reef crests, wide reef flats, calmer offshore conditions, and positioned farther from the shore exhibit lower erosion rates than others. Finally, when comparing historical erosion rates of protected and unprotected beaches in Hawai'i, we find a seemingly incongruous pattern where coral reef-protected beaches eroded up to 2x faster than beaches without reefs. While the cause of the enhanced erosion is yet to be fully understood, a combination of coral reef structural degradation and sea-level rise is likely shifting the equilibrium profiles of reef-protected beaches inshore. These results emphasize the role of coral reefs in reducing coastal erosion during storm events while revealing contrasting erosion patterns over long timescales. Future studies would ideally broaden the scope to include various regions, utilize advanced sediment transport models, and undertake field experiments to deepen our understanding of coral reef-coupled shoreline dynamics.

Nature-Based Solutions↗
USGS2004

Ecological and political issues surrounding decommissioning of offshore oil facilities in the Southern California Bight

To aid legislators, resource managers, and the general public, this paper summarizes and clarifies some of the issues and options that the federal government and the state of California face in decommissioning offshore oil and gas production platforms, particularly as these relate to platform ecology. Both local marine ecology and political climate play a role in decommissioning offshore oil production platforms. Compared to the relatively supportive political climate in the Gulf of Mexico for “rigs-to-reefs” programs, conflicting social values among stakeholders in Southern California increases the need for understanding ecological impacts of various decommissioning alternatives (which range from total removal to allowing some or all of platform structure to remain in the ocean). Additional scientific needs in the decommissioning process include further assessment of platform habitat quality, estimation of regional impacts of decommissioning alternatives to marine populations, and determination of biological effects of any residual contaminants. The principal management need is a ranking of environmental priorities (e.g. species-of-interest and marine habitats). Because considerable numbers of economically important species reside near oil platforms, National Oceanic and Atmospheric Administration Fisheries should consider the consequences of decommissioning alternatives in their overall management plans. Management strategies could include designating reefed platforms as marine protected areas. The overarching conclusion from both ecological and political perspectives is that decommissioning decisions should be made on a case-by-case basis.

Ocean and Coastal Management↗
USGS2021

Using bottom trawls to monitor subsurface water clarity in marine ecosystems

Biophysical processes that affect subsurface water clarity play a key role in ecosystem function. However, subsurface water clarity is poorly monitored in marine ecosystems because doing so requires in-situ sampling that is logistically difficult to conduct and sustain. Novel solutions are thus needed to improve monitoring of subsurface water clarity. To that end, we developed a sampling method and data processing algorithm that enable the use of bottom trawl fishing gear as a platform for conducting subsurface water clarity monitoring using trawl-mounted irradiance sensors without disruption to fishing operations. The algorithm applies quality control checks to irradiance measurements and calculates the downwelling diffuse attenuation coefficient, K d , and optical depth, ζ – apparent optical properties (AOPs) that characterize the rate of decrease in downwelling irradiance and relative irradiance transmission to depth, respectively. We applied our algorithm to irradiance measurements, obtained using bottom-trawl-mounted archival tags equipped with a photodiode collected during NOAA’s Alaska Fisheries Science Center annual summer bottom trawl surveys of the eastern Bering Sea continental shelf from 2004 to 2018. We validated our AOPs by quantitatively comparing surface-weighted K d from tags to the multi-sensor K d (490) product from the Ocean Colour Climate Change Initiative project (OC-CCI) and qualitatively evaluating whether tag K d was consistent with patterns of subsurface chlorophyll-a concentrations predicted by a coupled regional physical-biological model (Bering10K-BESTNPZ). We additionally examined patterns and trends in water clarity in the eastern Bering Sea. Key findings are: 1) water clarity decreased significantly from 2004 to 2018; 2) a recurrent, pycnocline-associated, maximum in K d occurred over much of the northwestern shelf, putatively due to a subsurface chlorophyll maximum; and 3) a turbid bottom layer (nepheloid layer) was present over a large portion of the eastern Bering Sea shelf. Our study demonstrates that bottom trawls can provide a useful platform for monitoring water clarity, especially when trawling is conducted as part of a systematic stock assessment survey.

Alaska↗
USGS2013

Fate of geothermal mercury from Yellowstone National Park in the Madison and Missouri Rivers, USA

Mercury is a worldwide contaminant derived from natural and anthropogenic sources. River systems play a key role in the transport and fate of Hg because they drain widespread areas affected by aerial Hg deposition, transport Hg away from point sources, and are sites of Hg biogeochemical cycling and bioaccumulation. The Madison and Missouri Rivers provide a natural laboratory for studying the fate and transport of Hg contributed by geothermal discharge in Yellowstone National Park and from the atmosphere for a large drainage basin in Montana and Wyoming, United States of America (USA). Assessing Hg in these rivers also is important because they support fishery-based recreation and irrigated agriculture. During 2002 to 2006, Hg concentrations were measured in water, sediment, and fish from the main stem, 7 tributaries, and 6 lakes. Using these data, the geothermal Hg load to the Madison River and overall fate of Hg along 378 km of the Missouri River system were assessed. Geothermal Hg was the primary source of elevated total Hg concentrations in unfiltered water (6.2–31.2 ng/L), sediment (148–1100 ng/g), and brown and rainbow trout (0.12– 1.23 µg total Hg/g wet weight skinless filet) upstream from Hebgen Lake (the uppermost impoundment). Approximately 7.0 kg/y of geothermal Hg was discharged from the park via the Madison River, and an estimated 87% of that load was lost to sedimentation in and volatilization from Hebgen Lake. Consequently, Hg concentrations in water, sediment, and fish from main-stem sites downstream from Hebgen Lake were not elevated and were comparable to concentrations reported for other areas affected solely by atmospheric Hg deposition. Some Hg was sequestered in sediment in the downstream lakes. Bioaccumulation of Hg in fish along the river system was strongly correlated (r 2 =0.76–0.86) with unfiltered total and methyl Hg concentrations in water and total Hg in sediment.

Montana, Wyoming↗