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At least 1,027 records · Page 57Linked to original sources
USGS1980

Trends in the distribution of recent foraminifera in San Francisco Bay

Much of the bathymetry of the southern part of San Francisco Bay reflects the drainage pattern of late Pleistocene streams. Holocene estuarine silt and clay cover most of the bay floor; relict eolian and deltaic sand occurs along the eastern shore; sandy patches are present in the main channel owing to higher tidal current velocities. Organic content is high along the western shore, where tidal flats are extensive, and in the slough at the mouth of Coyote Creek where wastewaters discharge. Thirty-one species of benthonic foraminifera were identified in surficial sediments of San Francisco Bay estuary; of these, 20 species were stained red by rose Bengal and are considered as live. Water depth, sediment textural characteristics, salinity, organic matter, sediment pH, and biological competition were considered as factors that might affect distribution of foraminifera. Four ecologic zones based on observed trends in the distribution and abundance of several species correlate well with some environmental factors. Four groups based on the Q-mode analysis of frequency counts of foraminiferal assemblages are reasonably similar to the four ecologic zones. These zones, showing restricted depth ranges, are: Inner Coastal Zone, where Elphidium incertum obscurum and Trochammina infiata are prominent; Outer Coastal Zone, dominated by Ammonia beccarii tepida and Elphidium incatum; Deep Bay Zone, where Elphidietla hannai, Elphidium incertum clavatum, Hopkinsina pacifica, and Bolivina spp. appear in abundance; and Deep Channel Zone, where Elphidiella hannai is most abundant. In the Inner Coastal Zone, salinity due to large fluctuations is a limiting factor for many species. Substrate textural characteristics are primary determinants of the distribution of agglutinated foraminifers. The percentage of organic matter in the sediment correlates well with the abundance of Elphidium incertum obscurum, a ubiquitous species in San Francisco Bay. Sediment pH is not critical. Biologic competition can be estimated by comparing the percentage of a species with the number of species present in the assemblage, as shown for Ammonia beccarii tepida and Elphidiella hannai.

California↗
USGS2015

Status and trends of prey fish populations in Lake Michigan, 2014

The U.S. Geological Survey Great Lakes Science Center has conducted lake-wide surveys of the fish community in Lake Michigan each fall since 1973 using standard 12-m bottom trawls towed along contour at depths of 9 to 110 m at each of seven index transects. The resulting data on relative abundance, size and age structure, and condition of individual fishes are used to estimate various population parameters that are in turn used by state and tribal agencies in managing Lake Michigan fish stocks. All seven established index transects of the survey were completed in 2014. The survey provides relative abundance and biomass estimates between the 5-m and 114-m depth contours of the lake (herein, lake-wide) for prey fish populations, as well as burbot, yellow perch, and the introduced dreissenid mussels. Lake-wide biomass of alewives in 2014 was estimated at 1.6 kilotonnes (kt, 1 kt = 1000 metric tonnes), which was a record low and only 16% of the average biomass estimated since 2005. Moreover, the age distribution of alewives remained truncated with no alewife exceeding an age of 5. Record low biomass was also observed for nearly every other prey fish species: bloater (0.3 kt), rainbow smelt (0.02 kt), slimy sculpin (0.09 kt), deepwater sculpin (1.0 kt) and ninespine stickleback (0.004 kt). Round goby was the only prey fish species to avoid a record-low biomass estimate (2.04 kt); the 2014 estimate was 58% of the average lakewide biomass observed since 2006 when round gobies became relatively abundant in our catches. Burbot lake-wide biomass (0.5 kt in 2014) has remained below 3 kt since 2001. No age-0 yellow perch (i.e., < 100 mm) were captured during the survey, which is indicative of a poor year-class. Lake-wide biomass estimate of dreissenid mussels in 2014 was 23.9 kt, not different from 2013 (23.2 kt). Overall, the total lake-wide prey fish biomass estimate (sum of alewife, bloater, rainbow smelt, deepwater sculpin, slimy sculpin, round goby, and ninespine stickleback) in 2014 was only 5.1 kt, compared to the previous record-low prey fish biomass of 15.2 kt in 2012. In 2014, alewives and round gobies constituted 71% of this total, following a trend of dominance by these species since 2012.

Lake Michigan↗
USGS2012

Status and trends of prey fish populations in Lake Michigan, 2012

The U.S. Geological Survey Great Lakes Science Center has conducted lake-wide surveys of the fish community in Lake Michigan each fall since 1973 using standard 12-m bottom trawls towed along contour at depths of 9 to 110 m at each of seven index transects. The resulting data on relative abundance, size and age structure, and condition of individual fishes are used to estimate various population parameters that are in turn used by state and tribal agencies in managing Lake Michigan fish stocks. All seven established index transects of the survey were completed in 2012. The survey provides relative abundance and biomass estimates between the 5-m and 114-m depth contours of the lake (herein, lake-wide) for prey fish populations, as well as burbot, yellow perch, and the introduced dreissenid mussels. Lake-wide biomass of alewives in 2012 was estimated at 9 kilotonnes (kt, 1 kt = 1000 metric tonnes), which continues the trend of unusually low alewife biomass since 2004 but represented a 20% increase from the 2011 estimate. The age distribution of alewives larger than 100 mm was dominated (i.e., 84%) by age-2. Record low biomass was observed for several species, including bloater (0.4 kt), rainbow smelt (0.1 kt), deepwater sculpin (1.5 kt), and ninespine stickleback (0.01 kt). Slimy sculpin lake-wide biomass was 0.73 kt in 2012, which was the third consecutive year revealing a decline. Estimated biomass of round goby increased by 79% to 3 kt. Burbot lake-wide biomass (0.5 kt in 2012) has remained below 3 kt since 2001. Numeric density of age-0 yellow perch (i.e., < 100 mm) was only 2 fish per ha, which is indicative of a relatively poor year-class. Lake-wide biomass estimates of dreissenid mussels have continued to increase from 2010, from 12 to 95 kt in 2012. Overall, the total lake-wide prey fish biomass estimate (sum of alewife, bloater, rainbow smelt, deepwater sculpin, slimy sculpin, round goby, and ninespine stickleback) in 2012 was 15 kt, which represented the lowest total biomass of the time series.

Lake Michigan↗
USGS2009

Status and trends of the Lake Huron deepwater demersal fish ommunity, 2008

The U.S.Geological Survey Great Lakes Science Center has conducted trawl surveys to assess annual changes in the deepwater demersal fish community of Lake Huron since 1973. Since 1992, surveys have been carried out using a 21 m wing trawl towed on-contour at depths ranging from 9 to 110 m on fixed transects. Sample sites include five ports in U.S. waters with less frequent sampling near Goderich, Ontario. The 2008 fall bottom trawl survey was carried out between October 24 and November 20, 2008 and sampled only the three northern U.S. ports at DeTour, Hammond Bay, and Alpena due to mechanical problems with the research vessel and prolonged periods of bad weather. Therefore, all data presented for 2008 are based on samples collected from these ports. Compared to previous years, alewife populations in Lake Huron remain at low levels after collapsing in 2004. Age-0 alewife density and biomass appears to have increased slightly but overall levels remain near the nadir observed in 2004. Density and biomass of adult and juvenile rainbow smelt showed a decrease from 2007 despite record-high abundance of juveniles observed in 2005, suggesting recruitment was low. Numbers of adult and juvenile bloater were low despite recent high year-classes. Abundances for most other prey species were similar to the low levels observed in 2005 - 2007. We captured one wild juvenile lake trout in 2008 representing the fifth consecutive year that wild lake trout were captured in the survey. Based on pairwise graphical comparisons and nonparametric correlation analyses, dynamics of prey abundance at the three northern ports followed lakewide trends since 1992. Density of benthic macroinvertebrates was at an all-time low in 2008 since sampling began in 2001. The decline in abundance was due to decreases in all taxonomic groups and a large reduction in recruitment of quagga mussels. Density of Diporeia at northern ports in 2008 was the lowest observed. Diporeia were found only at 73-m sites of three ports sampled in northern Lake Huron. While no lakewide estimate of prey biomass was calculated due to the limited spatial scope of the 2008 survey, existing data suggest prey biomass remains depressed. Prey available to salmonids during 2009 will likely be small alewives, small rainbow smelt and small bloaters. Predators in Lake Huron will continue to face potential prey shortages.

Lake Huron↗
USGS2014

Summary of preliminary step-trend analysis from the Interagency Whitebark Pine Long-termMonitoring Program—2004-2013

In mixed and dominant stands, whitebark pine ( Pinus albicaulis ) occurs in over two million acres within the six national forests and two national parks that comprise the Greater Yellowstone Ecosystem (GYE). Currently, whitebark pine, an ecologically important species, is impacted by multiple ecological disturbances; white pine blister rust ( Cronartium ribicola ), mountain pine beetle ( Dendroctonus ponderosae ), wildfire, and climate change all pose significant threats to the persistence of whitebark pine populations. Substantial declines in whitebark pine populations have been documented throughout its range. Under the auspices of the Greater Yellowstone Coordinating Committee (GYCC), several agencies began a collaborative, long-term monitoring program to track and document the status of whitebark pine across the GYE. This alliance resulted in the formation of the Greater Yellowstone Whitebark Pine Monitoring Working Group (GYWPMWG), which consists of representatives from the U.S. Forest Service (USFS), National Park Service (NPS), U.S. Geological Survey (USGS), and Montana State University (MSU). This groundbased monitoring program was initiated in 2004 and follows a peer-reviewed protocol (GYWPMWG 2011). The program is led by the Greater Yellowstone Inventory and Monitoring Network (GRYN) of the National Park Service in coordination with multiple agencies. More information about this monitoring effort is available at: http://science. nature.nps.gov/im/units/gryn/monitor/whitebark_pine.cfm. The purpose of this report is to provide a draft summary of the first step-trend analysis for the interagency, long-term monitoring of whitebark pine health to the Interagency Grizzly Bear Study Team (IGBST) as part of a synthesis of the state of whitebark pine in the GYE. Due to the various stages of the analyses and reporting, this is the most efficient way to provide these results to the IGBST.

Natural Resource Data Series↗
USGS1993

Status and population trends of Hawaii's native waterbirds, 1977-1987

Status and population trends of Hawaiis ’ native waterbirds were examined from 1977 through 1987. Waterbird population fluctuations were analyzed in relation to rainfall and land use dynamics. Numbers of Hawaiian Duck (Koloa) ( Anus wyvilliana ) and Hawaiian Common Moorhen ( Gallinula chloropus sandvicensis ) appeared stable over time; however, surveys were limited. Increase in Black-crowned Night-Heron ( Nycticorux nycticorux ) abundance appeared linked to expansion of aquaculture, particularly on Oahu, and not to climatic events. Annual rainfall patterns help explain and predict population fluctuations and anomalous distribution patterns involving Hawaiian American Coots ( Fulica americana alai ), moorhens, and Hawaiian Black-necked Stilts ( Himantopus mexicanus knudseni ). Coot, stilt, and moorhen populations fluctuated with climatic events, and intraisland dispersal to ephemeral wetlands occurred. Stilts exhibited regular inter-island migratory behavior, but coots dispersed in relation to major rainfall events. Seasonal fluctuation recorded for coots by past observers is the result of survey techniques not accounting for seasonal dispersal patterns.

Hawai'i↗
USGS2017

Global nonfuel mineral exploration trends 2001-2015

The mission of the U.S. Geological Survey (USGS) National Minerals Information Center (NMIC) is to collect, analyze and disseminate information on the domestic and international supply of and demand for minerals and mineral materials essential to the U.S. economy and national security. Understanding mineral exploration activities and trends assists government policy makers, minerals industry decision makers and research entities in identifying where future sources of mineral supply are likely to be discovered, the amount and type of these resources and factors that may affect exploration and development.

Mining Engineering↗
USGS1980

Lateral trends and vertical sequences in estuarine sediments, Willapa Bay, Washington

Willapa Bay is a sizable estuary on the southern coast of Washington- Relatively unmodified in a geologic sense by human activity the bay provides an excellent example of modern depositional facies in an estuarine setting. Studies of these deposits indicate that consistent lateral trends exist in sediment texture and sedimentary structures. The texture changes from sandy at the mouth of the bay to muddy in its upper parts. In any part of the bay , sediment is coarsest in the channel bottoms, where lag deposits accumulate. The sediment tends to fine in an upslope direction and is finest in supratidal flat deposits of silt and clay. The nature of sedimentary structures depends on the combination of physical and biological processes and sediment textures. Bedforms exist wherever the bed is sandy. In the main tidal channels sandwaves and dunes up to 4 meters high occur. In tributary channels and at the margins of the main channel, at shallower depths and under less intense currents , the structures are generally less than a meter high. Current ripples occur in t he sandy bed of all of the tidal channels and in runoff channels cross the tidal flat. Symmetric long-crested ripples are produced by wave action over the sandy intertidal flat. Internal structures in the bay's sediment depend not only on the nature of the bedform but also on the rate of bioturbation relative to physical processes. Under fields of large sandwaves or dunes, medium- to large-scale tabular and trough crossbedding predominates. This crossbedding generally is unidirectional, reflecting the locally dominant current (ebb or flood). Ripple bedding predominates elsewhere in sandy sediment within the channels. Where sand transport is diminished, as on the floor of the upper tributary channels, bioturbation exceeds the rate of production of physical structures and bedding is destroyed. The depositional banks in such areas tend to be sites of rapid sediment accumulation and bedding in the form of interlayered sand (commonly ripple bedded) and mud persists. On intertidal flats the sediment accumulates slowly and bioturbation erases nearly all physical structures. Bedding is preserved only where deposition is locally rapid , as in topographic depressions or on the depositional banks of runoff channels, or where faunal activity is inhibited, as beneath mounds of blue-green algae. The rate of sedimentation is slower still on the supratidal flats, but the general paucity of faunal activity allows the preservation of thin alternations of fine sand , silt or clay. The lateral migration of the tidal channels produces vertical sequences in which topographically higher facies are superposed on one another. Near the mouth of the estuary the upward sequence: lag deposit — crossbedded sand — ripple or planar-bedded sand is typical. The crossbedding shows a general upward decrease in thickness and a progression from trough to tabular units. In the main tidal channel - in the central estuary and in sandy tributary channels, the typical vertical sequence resembles that near the mouth , with the exception that the sequence is capped by bioturbated sandy or muddy tide flat deposits. In the upper estuary , where muddy sediment predominates, a typical sequence shows the progression-. bioturbated lag deposit — gently dipping interlaminated sand and mud layers of the accretionary bank — bioturbated mud flat deposits — thinly laminated fine supratidal deposits.

Oregon, Washington↗
USGS2014

Population trends of smallmouth bass in the upper Colorado River basin with an evaluation of removal effects

Smallmouth bass Micropterus dolomieu were rare in the upper Colorado River basin until the early 1990’s when their abundance dramatically increased in the Yampa River sub-basin. Increased abundance was due primarily to colonization from Elkhead Reservoir, which was rapidly drawn down twice, first to make improvements to the dam (1992) and a second time for reservoir expansion (2005), and allowed escapement of resident bass to the river through an unscreened outlet. Elkhead Reservoir is located on Elkhead Creek, a tributary of the Yampa River. The rapid Elkhead Reservoir drawdown in 1992 was followed by a period of drought years with low, early runoff in the Yampa River sub-basin that benefitted smallmouth bass reproduction. This combination of factors allowed smallmouth bass to establish a self-sustaining population in the Yampa River. Subsequently, successful recruitment allowed smallmouth bass to disperse upstream and downstream in the Yampa River and eventually move into the downstream Green River. Smallmouth bass were also likely introduced, by unknown means, into the upper Colorado River and have since dispersed in this sub-basin. The rapid increase of smallmouth bass in the upper Colorado River basin overlapped with significant reductions in native fish populations in some locations. The threat to these native fishes initiated intensive mechanical removal of smallmouth bass by the Upper Colorado River Endangered Fish Recovery Program. In general, three factors explain fluctuating patterns in smallmouth bass density in the upper Colorado River basin in the last decade: reductions due to electrofishing removal, bass recovery after exploitation due to recruitment and immigration, and changes due to environmental factors not related to electrofishing and other management actions. Our analyses indicated that smallmouth bass densities were substantially reduced in most years by 7 electrofishing removal efforts. Less often, but dramatically in some cases, environmental effects were also responsible for significant declines in smallmouth bass densities in some reaches. Abundant year classes of young smallmouth bass produced in low flow and warm years such as 2007 have potential to overwhelm removal efforts, and the year class persists for one or more years. Nonetheless, it appears that increased electrofishing removal efforts from 2007 to 2011 resulted in sustained reductions in density of smallmouth bass sub-adults and adults throughout the upper basin despite environmental conditions that favored smallmouth bass reproduction in some years (e.g. 2007 and 2009), subsequent recruitment into sub-adult and adult age classes, and movement of smallmouth bass which previously (prior to increases in electrofishing removal efforts) allowed densities to recover in some reaches. We recommend that removal efforts continue in most areas of the upper basin but that the Recovery Program consider allocating effort based on population trends and suspected areas of highest smallmouth bass reproduction. For instance, reproduction, recruitment, and movement of smallmouth bass allowed densities to recover in some reaches, particularly Little Yampa Canyon. Smallmouth bass population recovery implies that areas such as Little Yampa Canyon itself or adjacent reaches (especially upstream), may provide important habitat for age-0 production. We recommend continued assessment of smallmouth bass populations in reaches where reproduction or age-1 nurseries are suspected, such as Little Yampa Canyon and the adjacent upstream reach. It may also be necessary to expand monitoring to areas surrounding suspected sources of smallmouth bass reproduction and increase electrofishing removal effort in these reaches.

Colorado, Utah↗
USGS2018

Sediment supply to San Francisco Bay, water years 1995 through 2016: Data, trends, and monitoring recommendations to support decisions about water quality, tidal wetlands, and resilience to sea level rise

Knowledge of the status and trends of sediment supply to San Francisco Bay is critically important for management decisions about dredging, marsh restoration, flood control, contaminants, water clarity (in relation to primary production), and sea level rise. Several sitespecific studies of sediment supply to San Francisco Bay have been conducted, but no synthesis of recent studies is available. The purpose of this report is to synthesize the best available data and knowledge to answer a few of the key study questions related to sediment supply to the Bay (listed below). This synthesis report was prepared jointly by the Regional Monitoring Program for Water Quality in San Francisco Bay (RMP) and the U. S. Geological Survey (USGS) with funding from both organizations. The project is meant to be a step in the development of a more comprehensive sediment management and monitoring strategy for the Bay. What are the magnitudes and sources of fine and coarse sediment transported to San Francisco Bay? Net sediment supply to San Francisco Bay from terrestrial sources during the most recent 22- year period (water years [WY] 1995-2016) was 1.9+/-0.8 Mt/yr (1 Mt is one million metric tonnes or 1 billion kilograms). Sixty-three percent of the sediment supply was from small tributaries that drain directly to the Bay. Net supply from the Central Valley (measured at Mallard Island) was 37% of the total supply. Bedload supply, after accounting for dredging, removals, storage in flood control channels, and errors in measurements was indistinguishable from zero. For a 30-year “climate normal” reference period of WY 1981-2010 (a period assumed to be representative of current climatic conditions), we estimate the total sediment supply would be 2.0 Mt/yr of which 70% would come from small tributaries. The delivery points are Mallard Island for sediment from the Delta and the head of tide of each small tributary or outfall for sediment from the small tributaries. The finding that, on average, small tributaries have supplied more sediment to the Bay than the Delta is important but not new (McKee et al., 2013). During the Gold Rush and perhaps through to the 1980s, 80% or more of the supply was estimated to be from the Central Valley (Porterfield, 1980). But land and water management have continued to evolve (Krone, 1996) and the sediment wave associated with the Gold Rush has diminished (Schoellhamer, 2011). In addition, the coastal mountains of California and around the Bay are steep, tectonically active and composed of relatively erodible marine sedimentary and metasedimentary rocks, in contrast to the Central Valley watershed that is dominated by highly indurated granitic, metasedimentary, and metavolcanic rocks in the western-facing slopes of the Sierra Nevada Mountains (McKee et al., 2013). Also, water management is quite different between the Central Valley rivers and small tributaries. About 48% of the Central Valley watershed is upstream from dams that are designed to capture, delay and diminish discharge from spring snowmelt and so eliminate or damp many of the peak flows that are normally crucial for sediment transport. Another factor contributing to the importance of small tributaries for sediment supply is the way that they deliver sediment. Annual discharge from small tributaries is very small in comparison to the volume of the Bay (around one-fifth of a Bay volume on average), and the load that small tributaries supply is delivered through hundreds of channels and outfalls via wetland sloughs to the mudflats on the margin of the Bay. Therefore, the majority of this sediment delivered from Bay Area small tributaries is more likely to be trapped in these tidal channels or the margins of the Bay. In contrast, supply from the Central Valley enters the Bay through one large river channel at the head of the estuary (functionally adjacent to Mallard Island, near Pittsburg, CA) with an average annual discharge volume that is more than twi

California↗
USGS1989

Trends in wintering canvasback populations at Catahoula Lake, Louisiana

Aerial survey data (1968-1989) and water gauge readings (1958-1989) were examined to detennine trends in and relationships between canvasback (Aythya valisineria) populations and water levels at Catahoula Lake, Louisiana. Wintering canvasback populations at Catahoula Lake have increased over the past 21 years. A peak population estimate of 78,000 canvasbacks was recorded in January 1988. There was a significant relationship between increases in wintering canvasback numbers and increased November water levels. No significant changes in December or January water levels nor relationships between wintering canvasback numbers and December or January water levels could be detected. In recent years, Catahou1a Lake has become one of the most important canvasback wintering areas in North America. We conclude that the increased availability of open water feeding habitat has been a major factor in the increased usage of Catahoula Lake by canvasbacks.

Louisiana↗
USGS2019

Status and trends of pelagic prey fish in Lake Huron, 2018

Scientists from the U.S. Geological Survey’s Great Lakes Science Center conducted integrated acoustic and mid-water trawl surveys of Lake Huron annually from 2004-2018. The 2018 survey was conducted during September and included transects in Lake Huron’s main basin, Georgian Bay, and North Channel. Mean lake-wide pelagic fish density was 1532 fish/ha and mean pelagic fish biomass was 4151 g/ha in 2018, which represents 128% and 108% of the long-term mean, respectively. Mean lake-wide biomass was 24% lower in 2018 and mean lake-wide fish density was 3.3% lower in 2018 as compared to 2017. Lake-wide density and biomass of small alewife (< 100 mm) increased significantly in 2018 and was due primarily to increased abundance in the western main basin. Lake-wide density of small rainbow smelt (< 90 mm) increased in 2018 and was a result of increased abundance in the eastern main basin, Georgian Bay, and the North Channel. Biomass of large rainbow smelt (> 90 mm) increased in 2018 and was a result of increased biomass in the main basin and Georgian Bay. Density of small bloater (< 120 mm) declined in the western main basin but increased in other regions of Lake Huron. Biomass of large bloater (> 120 mm) remained at levels similar to 2017 in most regions of Lake Huron. Emerald shiner density and biomass increased in 2018 due to increased abundance in the main basin south and main basin west regions. Density and biomass of large cisco (> 200 mm) declined marginally between 2017 and 2018, but cisco biomass and density has shown an increasing trend in the North Channel and Georgian Bay since 2011.

Lake Huron↗
USGS2008

Spatial and temporal trends in nitrate concentrations in the eastern San Joaquin Valley regional aquifer and implications for fertilizer management

Ground-water withdrawals in the San Joaquin Valley totaled 64 million m 3 /day (19 million ac-ft) in 2000, supplying about 45% of agricultural irrigation demand and about 80% of municipal supply (Hutson et al., 2004). Most of the population and ground-water use are in the eastern San Joaquin Valley, where reliance on ground water is expected to increase as a result of rapid population growth and limited surface water supplies. Protection of ground-water quality for future use requires monitoring and understanding the mechanisms controlling the long-term quality of ground water in the regional aquifer system. Nitrate has been widely detected above background concentrations in ground water in the eastern San Joaquin Valley. Nitrate concentrations (reported as nitrogen in this paper) were above the MCL of 10 mg/L in 24% of domestic wells screened in the shallow part of the aquifer that were sampled during 1993–95 (Dubrovsky et al., 1998) and the Central Valley is one of the top three regions in the state in terms of the number of public drinking-water wells exceeding the MCL for nitrate (California State Water Resources Control Board, 2002). To assess spatial and temporal trends in nitrate concentrations in the eastern San Joaquin Valley and to evaluate the long-term effects of nitrogen fertilizer use on ground-water quality in this region, data were evaluated at multiple spatial scales. Data from regional-scale monitoring networks were used to map the regional occurrence of nitrate and to determine whether shallow ground water containing elevated nitrate is migrating to deeper parts of the aquifer system. At the local scale, mean ground-water ages from analysis of age-dating tracers were combined with concentrations of nitrate to reconstruct nitrate inputs in recharge through time and to compare with estimated nitrogen applications. Ground-water flow and transport simulations of a typical public-supply well screened from about 100 to 400 ft below the water table were used to evaluate long-term concentrations beneath agricultural areas under different nitrogen management scenarios.

California↗
USGS2020

2018 Kaua'i forest bird population estimates and trends

Kaua‘i's native forest birds have experienced steep declines since the beginning of systematic surveys in 1981, and declines have accelerated in recent decades. This report details the analysis of the most recent surveys conducted in 2018. Incorporating the new survey results, long-term trends continue to show sharp declines for all native honeycreeper species with the exception of ‘apapane (Himatione sanguinea), which has stable numbers in core areas of its range. Kaua‘i ‘elepaio (Chasiempis sclateri) continued to decline in the outer portions of its range but increased in the core areas of its range. Abundance estimates of forest birds ranged from slightly higher to slightly lower in most species, indicating a relatively stable period from 2012–2018, and a pause from the rapid declines seen in earlier periods. Many native species now exist in very low numbers, and variation in estimates from survey to survey will increase.

Hawaii↗
USGS2019

Current trends and future directions in swan research: Insights from the 6th International Swan Symposium

Given their popularity with researchers and public alike, together with their welldocumented importance in aquatic and terrestrial ecosystems, fundamental and applied research on swans continues to develop in the 21st century. The 6th International Swan Symposium (6th ISS), was held at the Estonian University of Life Sciences in Tartu, Estonia, in October 2018. The symposium brought together 101 delegates from 17 countries, with presentations on a range of topics on Cygnus and Coscoroba species, including monitoring, habitat and resource use, demography, movements and migration, and threats and conservation. The proceedings of the 6th ISS in this special issue of Wildfowl include select papers on swan research presented at the 6th ISS, covering a wide range of species, systems and issues. This paper presents a synthesis of the 6th ISS and an overview of current trends and future directions in swan research. Despite progress on many topics, southern hemisphere swan species continue to receive less attention than their northern hemisphere counterparts, whilst facing many of the same pressures. It is clear that, given the challenges facing swan researchers in the twenty-first century, international cooperation will continue to be vital. Swans are highly mobile animals and many populations undertake migrations spanning thousands of kilometres, and crucially do not recognise human geographic and political borders. Such international collaborations will be particularly important in coordinating future monitoring and conservation activities. The IUCN-SSC/Wetlands International Swan Specialist Group (SSG) will continue to facilitate international collaborations and communication among the global network of swan researchers, through its activities, website and annual newsletter. Given the substantial challenges and knowledge gaps documented here, there is no doubt that swan researchers will continue to benefit from regular symposia to share information and develop collaborations towards understanding and addressing emerging conservation issues. As such, we recommend holding International Swan Symposia every 4–5 years.

Wildfowl↗
USGS2021

Status and trends of pelagic and benthic prey fish populations in Lake Michigan, 2020

Lakewide acoustic (AC) and bottom trawl (BT) surveys are conducted annually to generate indices of pelagic and benthic prey fish densities in Lake Michigan. The BT survey had been conducted each fall from 1973 through 2019 using 12-m trawls at depths ranging from 9 to 110 m and included 70 fixed locations distributed across seven transects; this survey estimates densities of seven prey fish species (i.e., alewife, bloater, rainbow smelt, deepwater sculpin, slimy sculpin, round goby, ninespine stickleback) as well as for age-0 yellow perch and large burbot. The AC survey, which serves to estimate densities of three prey fish species (i.e., alewife, bloater, and rainbow smelt), had been conducted each late summer/early fall from 2004-2019. The data generated from these surveys are used to estimate various population parameters that are, in turn, used by state and tribal agencies in managing Lake Michigan fish stocks. The 2020 COVID-19 pandemic severely limited the Lake Michigan pelagic and benthic prey fish surveys. While the AC survey was not conducted, 32 tows across three of seven standard BT transects (Saugatuck, Waukegan and Port Washington) were completed during an abbreviated survey. Total prey fish biomass density from the abbreviated BT survey was 1.91 kg/ha, continuing a recent trend of historically low estimates below the long-term (i.e., 1973-2020) average of 34.94 kg/ha. Mean biomass of yearling and older (YAO) alewives in 2020 was 0.025 ± 0.017 kg/ha, tied for the lowest ever recorded on the BT survey. No age-0 alewife were captured in the bottom trawl and of the limited number (n=16) of alewife collected, none were older than age four. Bloater (1.39 kg/ha) and deepwater sculpin (0.47 kg/ha) accounted for greatest proportion of biomass in the BT survey, while biomass density of slimy sculpin, round goby and rainbow smelt were all ≤ 0.01 kg/ha. While caution must be taken when interpreting the results of the abbreviated BT survey, the estimates suggest that prey fish densities remain well below historical values.

Lake Michigan↗
USGS2022

Status and trends of the Lake Huron prey fish community, 1976-2020

The USGS Great Lakes Science Center (GLSC) has assessed annual changes in the offshore prey fish community of Lake Huron since 1973. Assessments are based on a bottom trawl survey conducted in October and an acoustics-midwater trawl survey conducted in September-October. In 2020, USGS-GLSC vessels were not permitted to cross into Canada due to the COVID-19 pandemic, so prey fish surveys sampled only sites in U.S. (Michigan) waters of Lake Huron. This prevented USGS from providing information about the current status and trends of prey fish communities in Georgian Bay and the North Channel. Prey fish biomass in U.S. waters of Lake Huron in 2020 remained below levels observed prior to community-wide declines that began in the early to mid-1990s. Fish community biomass was dominated by two species, Bloater (Coregonus hoyi) and Rainbow Smelt (Osmerus mordax). While both surveys found Bloater biomass in the main basin had declined from levels observed in 2019, Bloater still comprised over three-quarters of prey fish biomass in Lake Huron in 2020. Biomass and abundance for other prey fish species were within the range observed over the past five years. Current low biomass of invasive species like Alewife (Alosa pseudoharengus) and Rainbow Smelt is consistent with fish community objectives focused on restoration of native fish communities. Reduced lake productivity, predation by a recovering piscivore community, and shifts in food web dynamics that favor fish production in nearshore environments may prevent prey fish biomass in offshore areas from returning to levels observed prior to the early 1990’s. However, the dominance of Bloater in bottom trawl catches and acoustic surveys suggests that current lake conditions are conducive to the recovery of some native species.

Lake Huron↗
USGS2018

Migration trends for king and common eiders and yellow-billed loons past Point Barrow in a rapidly changing environment

Most of the king ( Somateria spectabilis ) and common eiders ( S. mollissima v-nigra ) nesting in northern Alaska and northwestern Canada migrate past Point Barrow, Alaska, during the spring and fall migration. Yellow-billed loons ( Gavia adamsii ) also migrate past Point Barrow and are a species of international conservation concern. Spring migration counts of eiders have been conducted approximately every ten years at Point Barrow since 1976, and indicated that both eider species experienced population declines of approximately 50% between 1976 and 1996, and that the declines had stabilized by 2004. Population estimates derived from migration counts have not been previously estimated for yellow-billed loons. We conducted spring counts of eiders and loons in 2015 and 2016 to obtain population estimates to compare with those from 1994, 1995, 2003, and 2004 in order to evaluate long-term and current trends. We estimated (95% confidence intervals) that 796,419 (304,011) king and 96,775 (39,913) common eiders passed Point Barrow in 2015, and 322,381 (145,833) king and 130,390 (34,548) common eiders passed Point Barrow in 2016. Both and king and common eider population estimates increased from 1994 through 2016, however, the increase over time was not significant (F < 5.07, P > 0.087, df = 1). Our population estimates for king eiders were very different between the two years of this study, possibly due to a very short and intense migration peak in 2016, resulting in a population count that was biased low because sampling periods did not adequately capture the peak of migration. The numbers of common eiders were similar between the two years, as well as for the 12 years since the previous count. Photo analysis of flocks indicated that observer counts were on average 4% lower than photo counts (paired t-test; |t| = 3.26, df = 297, P < 0.001) for flocks less than 1400 individuals (observer count). Estimates of yellow-billed loon populations were very variable and are biased low as numbers of loons passing Pt. Barrow were still high when our counts ended in late May. It is important that counts continue to be conducted for these species of conservation and subsistence importance, but that techniques be refined to reduce bias and variability, and to find solutions to the increasing difficulty of conducting a count from the shore-fast ice in spring.

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