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At least 991 records · Page 55Linked to original sources
USGS2016

A brackish diatom, Pseudofrustulia lancea gen. et sp. nov. (Bacillariophyceae), from the Pacific coast of Oregon (USA)

Light and electron microscope observations show that a brackish diatom taxon should be classified as a new species of a new genus; Pseudofrustulia lancea gen . et sp . nov . We propose separating Pseudofrustulia from other similar genera such as Frickea , Frustulia , Amphipleura , Muelleria , and Envekadea on the basis of its thickened axial ribs, raphe endings, axial costae, morphology of helictoglossa, size of striae on valve surfaces, and areolae on the inner side between its axial ribs and raphe. Girdle bands may be another diagnostic feature for the separation of Pseudofrustulia from related taxa, but more detailed observations using SEM images are required to determine if bands are diagnostic.

Oregon↗
USGS2007

Long-term performance of Aanderaa optodes and sea-bird SBE-43 dissolved-oxygen sensors bottom mounted at 32 m in Massachusetts Bay

A field evaluation of two new dissolved-oxygen sensing technologies, the Aanderaa Instruments AS optode model 3830 and the Sea-Bird Electronics, Inc., model SBE43, was carried out at about 32-m water depth in western Massachusetts Bay. The optode is an optical sensor that measures fluorescence quenching by oxygen molecules, while the SBE43 is a Clark polarographic membrane sensor. Optodes were continuously deployed on bottom tripod frames by exchanging sensors every 4 months over a 19-month period. A Sea-Bird SBE43 was added during one 4-month deployment. These moored observations compared well with oxygen measurements from profiles collected during monthly shipboard surveys conducted by the Massachusetts Water Resources Authority. The mean correlation coefficient between the moored measurements and shipboard survey data was >0.9, the mean difference was 0.06 mL L −1 , and the standard deviation of the difference was 0.15 mL L −1 . The correlation coefficient between the optode and the SBE43 was >0.9 and the mean difference was 0.07 mL L −1 . Optode measurements degraded when fouling was severe enough to block oxygen molecules from entering the sensing foil over a significant portion of the sensing window. Drift observed in two optodes beginning at about 225 and 390 days of deployment is attributed to degradation of the sensing foil. Flushing is necessary to equilibrate the Sea-Bird sensor. Power consumption by the SBE43 and required pump was 19.2 mWh per sample, and the optode consumed 0.9 mWh per sample, both within expected values based on manufacturers’ specifications.

Massachusetts↗
USGS1998

Epizootic vacuolar myelinopathy of the central nervous system of bald eagles ( Haliaeetus leucocephalus ) and American coots ( Fulica americana )

Unprecedented mortality occurred in bald eagles ( Haliaeetus leucocephalus ) at DeGray Lake, Arkansas, during the winters of 1994-1995 and 1996-1997. The first eagles were found dead during November, soon after arrival from fall migration, and deaths continued into January during both episodes. In total, 29 eagles died at or near DeGray Lake in the winter of 1994-1995 and 26 died in the winter of 1996-1997; no eagle mortality was noted during the same months of the intervening winter or in the earlier history of the lake. During the mortality events, sick eagles were observed overflying perches or colliding with rock walls. Signs of incoordination and limb paresis were also observed in American coots ( Fulica americana ) during the episodes of eagle mortality, but mortality in coots was minimal. No consistent abnormalities were seen on gross necropsy of either species. No microscopic findings in organs other than the central nervous system (CNS) could explain the cause of death. By light microscopy, all 26 eagles examined and 62/77 (81%) coots had striking, diffuse, spongy degeneration of the white matter of the CNS. Vacuolation occurred in all myelinated CNS tissue, including the cerebellar folia and medulla oblongata, but was most prominent in the optic tectum. In the spinal cord, vacuoles were concentrated near the gray matter, and occasional swollen axons were seen. Vacuoles were uniformly present in optic nerves but were not evident in the retina or peripheral or autonomic nerves. Cellular inflammatory response to the lesion was distinctly lacking. Vacuoles were 8-50 microns in diameter and occurred individually, in clusters, or in rows. In sections stained by luxol fast blue/periodic acid-Schiff stain, the vacuoles were delimited and transected by myelin strands. Transmission electron microscopy revealed intramyelinic vacuoles formed in the myelin sheaths by splitting of one or more myelin lamellae at the intraperiodic line. This lesion is characteristic of toxicity from hexachlorophene, triethyltin, bromethalin, isonicotinic acid hydrazide, and certain exotic plant toxins; however, despite exhaustive testing, no etiology was determined for the DeGray Lake mortality events. This is the first report of vacuolar myelinopathy associated with spontaneous mortality in wild birds.

Arkansas↗
USGS2021

A subset of CyberShake ground-motion time series for response-history analysis

This manuscript describes a subset of CyberShake numerically simulated ground motions that were selected and vetted for use in engineering response-history analyses. Ground motions were selected that have seismological properties and response spectra representative of conditions in the Los Angeles area, based on disaggregation of seismic hazard. Ground motions were selected from millions of available time series and were reviewed to confirm their suitability for response-history analysis. The processes used to select the time series, the characteristics of the resulting data, and the provided documentation are described in this article. The resulting data and documentation are available electronically.

California↗
USGS2022

Comparisons of the NGA-Subduction ground motion models

In this article, ground-motion models (GMMs) for subduction earthquakes recently developed as part of the Next Generation Attenuation-Subduction (NGA-Sub) project are compared. The four models presented in this comparison study are documented in their respective articles submitted along with this article. Each of these four models is based on the analysis of the large NGA-Sub database. Three of the four current models are developed for a global version as well as separate regionalized models. The fourth model was developed based on earthquakes only from Japan, and as such is applicable only for Japan. As part of this comparison study, a general discussion on the parameterization of the four models and the regionalization of the three models is provided. The specific strengths and or weaknesses or the technical decisions and justifications of any one model are not part of this comparison. A selected suite of deterministic attenuation curves and spectra are presented for the models along with a selected suite of currently used subduction models. A limited number of comparisons are presented in this article with a larger number of comparisons and the digital values provided in the electronic attachment. In addition to these scenario calculation comparisons, the results from a standard probabilistic seismic hazard analysis (PSHA) for two sites located in the Pacific Northwest Region in the state of Washington are presented. These calculations highlight the potential impact of using the new GMMs. Based on the comparisons presented here, a general understanding of these new GMMs can be obtained with the expectation that the implementation of a specific seismic hazard study should incorporate similar and additional comparisons and sensitivity studies pertinent to the site of interest.

Earthquake Spectra↗
USGS2000

The United States Board on Geographic Names: Standardization or regulation?

The United States Board on Geographic Names was created in 1890 to standardize the use of geographic names on federal maps and documents, and was established in its present form in 1947 by public law. The Board is responsible for geographic name usage and application throughout the federal government and its members must approve a name change or new name before it can be applied to federal maps and publications. To accomplish its mission, the Board has developed principles, policies, and procedures for use in the standardization process. The Board is also responsible legally for the promulgation of standardized names, whether or not these names have ever been controversial, and today this is accomplished by the universal availability of electronic databases for domestic and foreign names. This paper examines the development of Board policies and the implementation of these policies to achieve standardization with a view to relating these policies and activities to questions of standardization or regulation.

Names↗
USGS2018

Proposed nomenclature for samarskite-group minerals: new data on ishikawaite and calciosamarskite

The current definition of samarskite-group minerals suggests that ishikawaite is a uranium rich variety of samarskite whereas calciosamarskite is a calcium rich variety of samarskite. Because these minerals are chemically complex, usually completely metamict, and pervasively altered, their crystal chemistry and structure are poorly understood. Warner and Ewing (1993) proposed that samarskite is an A 3+ B 5+ O 4 mineral with an atomic arrangement related to α-PbO 2 . X-ray diffraction analyses of the recrystallized type specimen of ishikawaite and the Ca-rich samarskite reveal that they have the same structure as samarskite-(Y) recrystallized at high temperatures. Electron microprobe analyses show that the only significant difference between samarskite-(Y), ishikawaite, and calciosamarskite lies in the occupancy of the A -site. The A -site of samarskite-(Y) is dominated by Y+ REE whereas the A -site of ishikawaite is dominantly U+Th and calciosamarskite is dominantly Ca. Additionally, a comparison of these data to those of Warner and Ewing (1993) show that in several cases Fe 2+ or Fe 3+ are dominant in the A -site. We propose that the name samarskite-( REE +Y) should be used when one of these elements is dominant and that the mineral be named with the most abundant of these elements as a suffix. The name ishikawaite should be used only when U+Th are dominant and the name calciosamarskite should only be used when Ca is the dominant cation at the A -site. Finally, because of the inability to quantify the valence state of iron in these minerals, the exact nature of the valence state of iron in these minerals could not be determined in this study.

Mineralogical Magazine↗
USGS2018

Zinc- and Y-group-bearing senaite from St Peters Dome, and new data on senaite from Dattas, Minas Gerais, Brazil

A Zn- and Y-group-bearing senaite, formulated as AM 21 O 38 (Pb 0.63 Na 0.46 Ba 0.11 ) Σ1.20 (Ti 14.64 Zn 1.74 Y‒group REE 0.70 Mn 0.38 Nb 0.20 Sn 0.03 Zr 0.03 Th 0.02 ) Σ20.9 O 38 , a member of the crichtonite group, is a newly characterized phase associated with murataite at the St Peters Dome area, Colorado. The Zn- and Y-group-bearing senaite is uranium-free and nonmetamict, but otherwise is comparable to known senaites and davidites in X-ray diffraction pattern, symmetry, and structure. The REE distribution shows a strong dominance of Y and the Y-group REE which are present in M (1). Megascopically, the mineral is black, submetallic, and opaque; in polished section it appears to be white and moderately bright compared with murataite. Cleavage is absent but twinning on {52 0} is present. Senaite and hitherto unreported zinc-bearing senaite from Dattas, Diamantina, Minas Gerais, Brazil, have the following respective structural formulas as determined by electron microprobe: (Pb 0.76 Sr 0.20 La 0.08 Ce 0.07 Ba 0.04 ) Σ1.15 (Ti 12.89 Mn 0.88 Y 0.59 Zn 0.12 Mg 0.07 Nb 0.03 Cr 0.02 Th 0.02 ) Σ20.61 O 38 and (Pb 0.89 Ba 0.15 Ce 0.02 Sr 0.02 ) Σ1.08 (Ti 14.57 Zn 1.76 Na 0.63 Mn 0.50 Y 0.28 Nb 0.14 Mg 0.04 Cr 0.02 ) Σ20.83 O 38

Dattas, Minas Gerais↗
USGS2018

Uranoan thorite in lithophysal rhyolite - Topaz Mountain, Utah, U.S.A.

Uranoan thorite crystals have been found occurring as a sparse constituent in lithophysae in 6.1 to 6.8 Ma alkali rhyolite flows at Thomas Mountain, Utah, USA. The crystals are associated with sandidine, quartz, topaz, hematite, magnetite, and calcite; they are leek to dark grass green, transparent, well-formed, euhedral prisms, showing development of forms {100}, {101}, and {111}. The mineral is both optically isotropic, with a refractive index of 1.86(1), and X-ray amorphous, indicating its metamict state. Electron microprobe analysis yields: SiO 2 17.3, ThO 2 56.8, UO 2 25.4, total 99.5%, and a structural formula of (Th 0.72 U 0.31 ) Σ1.03 Si 0.97 O 4 . This appears to be the first reported occurrence of thorite in volcanic rocks of rhyolitic composition, and may account for part or all of the Th reported in alkali rhyolites and so-called ‘topaz-rhyolites’ of the western USA.

Utah↗
USGS2018

REE partitioning between apatite and melt in a peralkaline volcanic suite, Kenya Rift Valley

Electron microprobe analyses are presented for fluorapatite phenocrysts from a benmoreite-peralkaline rhyolite volcanic suite from the Kenya Rift Valley. The rocks have previously been well characterized petrographically and their crystallization conditions are reasonably well known. The REE contents in the M site increase towards the rhyolites, with a maximum britholite component of ~35 mol.%. Chondrite-normalized REE patterns are rather flat between La and Sm and then decrease towards Yb. Sodium and Fe occupy up to 1% and 4%, respectively, of the M site. The major coupled substitution is REE 3+ + Si 4+ ??? Ca 2+ + P 5+ . The substitution REE 3+ + Na + ??? 2Ca 2+ has been of minor importance. The relatively large Fe contents were perhaps facilitated by the low fo 2 conditions of crystallization. Zoning is ubiquitous and resulted from both fractional crystallization and magma mixing. Apatites in some rhyolites are relatively Y-depleted, perhaps reflecting crystallization from melts which had precipitated zircon. Mineral/glass (melt) ratios for two rhyolites are unusually high, with maxima at Sm (762, 1123). ?? 2008 The Mineralogical Society.

Mineralogical Magazine↗
USGS2018

Compositional variation in the chevkinite group: new data from igneous and metamorphic rocks

Electron microprobe analyses are presented of chevkinite-group minerals from Canada, USA, Guatemala, Norway, Scotland, Italy and India. The host rocks are metacarbonates, alkaline and subalkaline granitoids, quartz-bearing pegmatites, carbonatite and an inferred K-rich tuff. The analyses extend slightly the range of compositions in the chevkinite group, e.g. the most MgO-rich phases yet recorded, and we report two further examples where La is the dominant cation in the A site. Patchily- zoned crystals from Virginia and Guatemala contain both perrierite and chevkinite compositions. The new and published analyses are used to review compositional variation in minerals of the perrierite subgroup, which can form in a wide range of host rock compositions and over a substantial pressure- temperature range. The dominant substitutions in the various cation sites and a generalized substitution scheme are described.

Mineralogical Magazine↗
USGS2018

Major element and oxygen isotope geochemistry of vapour-phase garnet from the Topopah Spring Tuff at Yucca Mountain, Nevada, USA

Twenty vapour-phase garnets were studied in two samples of the Topopah Spring Tuff of the Paintbrush Group from Yucca Mountain, in southern Nevada. The Miocene-age Topopah Spring Tuff is a 350 m thick, devitrified, moderately to densely welded ash-flow tuff that is zoned compositionally from high-silica rhyolite to latite. During cooling of the tuff, escaping vapour produced lithophysae (former gas cavities) lined with an assemblage of tridymite (commonly inverted to cristobalite or quartz), sanidine and locally, hematite and/or garnet. Vapour-phase topaz and economic deposits associated commonly with topaz-bearing rhyolites (characteristically enriched in F) were not found in the Topopah Spring Tuff at Yucca Mountain. Based on their occurrence only in lithophysae, the garnets are not primary igneous phenocrysts, but rather crystals that grew from a F-poor magma-derived vapour trapped during and after emplacement of the tuff. The garnets are euhedral, vitreous, reddish brown, trapezohedral, as large as 2 mm in diameter and fractured. The garnets also contain inclusions of tridymite. Electron microprobe analyses of the garnets reveal that they are almandine-spessartine (48.0 and 47.9 mol.%, respectively), have an average composition of (Fe 1.46 Mn 1.45 Mg 0.03 Ca 0.10 )(Al 1.93 Ti 0.02 )Si 3.01 O 12 and are comparatively homogeneous in Fe and Mn concentrations from core to rim. Composited garnets from each sample site have δ18O values of 7.2 and 7.4‰. The associated quartz (after tridymite) has δ 18 O values of 17.4 and 17.6‰, values indicative of reaction with later, low-temperature water. Unaltered tridymite from higher in the stratigraphic section has a δ 18 O of 11.1‰ which, when coupled with the garnet δ 18 O values in a quartz-garnet fractionation equation, indicates isotopic equilibration (vapour-phase crystallization) at temperatures of ~600°C. This high-temperature mineralization, formed during cooling of the tuffs, is distinct from the later and commonly recognized low-temperature stage (generally 50–70°C) of calcite, quartz and opal secondary mineralization, formed from downward-percolating meteoric water, that locally coats fracture footwalls and lithophysal floors.

Nevada↗
USGS2007

Microbial sulfate reduction and metal attenuation in pH 4 acid mine water

Sediments recovered from the flooded mine workings of the Penn Mine, a Cu-Zn mine abandoned since the early 1960s, were cultured for anaerobic bacteria over a range of pH (4.0 to 7.5). The molecular biology of sediments and cultures was studied to determine whether sulfate-reducing bacteria (SRB) were active in moderately acidic conditions present in the underground mine workings. Here we document multiple, independent analyses and show evidence that sulfate reduction and associated metal attenuation are occurring in the pH-4 mine environment. Water-chemistry analyses of the mine water reveal: (1) preferential complexation and precipitation by H2S of Cu and Cd, relative to Zn; (2) stable isotope ratios of 34S/32S and 18O/16O in dissolved SO4 that are 2-3 ??? heavier in the mine water, relative to those in surface waters; (3) reduction/oxidation conditions and dissolved gas concentrations consistent with conditions to support anaerobic processes such as sulfate reduction. Scanning electron microscope (SEM) analyses of sediment show 1.5-micrometer, spherical ZnS precipitates. Phospholipid fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) analyses of Penn Mine sediment show a high biomass level with a moderately diverse community structure composed primarily of iron- and sulfate-reducing bacteria. Cultures of sediment from the mine produced dissolved sulfide at pH values near 7 and near 4, forming precipitates of either iron sulfide or elemental sulfur. DGGE coupled with sequence and phylogenetic analysis of 16S rDNA gene segments showed populations of Desulfosporosinus and Desulfitobacterium in Penn Mine sediment and laboratory cultures. ?? 2007 Church et al; licensee BioMed Central Ltd.

Geochemical Transactions↗
USGS2016

Combined exposure of diesel exhaust particles and respirable Soufrière Hills volcanic ash causes a (pro-)inflammatory response in an in vitro multicellular epithelial tissue barrier model

Background There are justifiable health concerns regarding the potential adverse effects associated with human exposure to volcanic ash (VA) particles, especially when considering communities living in urban areas already exposed to heightened air pollution. The aim of this study was, therefore, to gain an imperative, first understanding of the biological impacts of respirable VA when exposed concomitantly with diesel particles. Methods A sophisticated in vitro 3D triple cell co-culture model of the human alveolar epithelial tissue barrier was exposed to either a single or repeated dose of dry respirable VA (deposited dose of 0.26 ± 0.09 or 0.89 ± 0.29 μg/cm 2 , respectively) from Soufrière Hills volcano, Montserrat for a period of 24 h at the air-liquid interface (ALI). Subsequently, co-cultures were exposed to co-exposures of single or repeated VA and diesel exhaust particles (DEP; NIST SRM 2975; 0.02 mg/mL), a model urban pollutant, at the pseudo-ALI. The biological impact of each individual particle type was also analysed under these precise scenarios. The cytotoxic (LDH release), oxidative stress (depletion of intracellular GSH) and (pro-)inflammatory (TNF-α, IL-8 and IL-1β) responses were assessed after the particulate exposures. The impact of VA exposure upon cell morphology, as well as its interaction with the multicellular model, was visualised via confocal laser scanning microscopy (LSM) and scanning electron microscopy (SEM), respectively. Results The combination of respirable VA and DEP, in all scenarios, incited an heightened release of TNF-α and IL-8 as well as significant increases in IL-1β, when applied at sub-lethal doses to the co-culture compared to VA exposure alone. Notably, the augmented (pro-)inflammatory responses observed were not mediated by oxidative stress. LSM supported the quantitative assessment of cytotoxicity, with no changes in cell morphology within the barrier model evident. A direct interaction of the VA with all three cell types of the multicellular system was observed by SEM. Conclusions Combined exposure of respirable Soufrière Hills VA with DEP causes a (pro-)inflammatory effect in an advanced in vitro multicellular model of the epithelial airway barrier. This finding suggests that the combined exposure to volcanic and urban particulate matter should be further investigated in order to deduce the potential human health hazard, especially how it may influence the respiratory function of susceptible individuals (i.e. with pre-existing lung diseases) in the population.

Particle and Fibre Toxicology↗
USGS2017

Estimating incision healing rate for surgically implanted acoustic transmitters from recaptured fish

Background Intracoelomic implantation of electronic tags has become a common method in fishery research, but rarely are fish examined by scientists after release to understand the extent that surgical incisions have healed. Walleye ( Sander vitreus ) are a valuable, highly exploited fishery resource in the Laurentian Great Lakes. Here, fishery capture of walleye with internal acoustic transmitters combined with a high reward program provided multiple opportunities to examine photographs and quantify the status of surgical incisions. Walleye ( n = 926) from reef and river spawning populations in Lake Erie and Lake Huron were implanted with acoustic transmitters during spring spawning events from 2011 to 2016. Incisions were closed with polydioxanone monofilament using two to three interrupted sutures. Out of 276 recaptured fish, 60 incision sites were clearly visible in photographs, and these were scored by two independent readers for incision closure, inflammation, and the presence of sutures. Results While incision sites were completely closed by 61 days post-release (95% CI 44–94), sutures remained for up to 866 days. Sutures were expelled serially during a protracted period, and the probability of observing at least one suture in a recaptured fish declined below 50% after 673 days (95% CI 442–1016). Inflammation at the incision increased during the first 71 days and then declined monotonically, remaining detectable at low levels. Conclusion Our results emphasized that sutures remained in free-ranging fish past the time when they were beneficial for incision healing. Most dissolvable sutures have been designed for use in endotherms where the body temperature and internal milieu differ dramatically from the conditions experienced by fishes in temperate climates. Identification of new suture materials for fish that facilitate healing while absorbing or dissolving in a reasonable period (e.g., a few weeks to three months) in colder temperatures (e.g., <12 °C) would be beneficial to mitigate potential adverse impacts from inflammation at the incision.

Animal Biotelemetry↗
USGS2019

Acoustic tag retention rate varies between juvenile green and hawksbill sea turtles

Background Biotelemetry has become a key tool for studying marine animals in the last decade, and a wide range of electronic tags are now available for answering a range of research questions. However, comparatively, less attention has been given to attachment methods for these tags and the implications of tag retention on study design, especially when designing a comparative study looking at multiple species. Here, we reported our findings on acoustic tag retention rates for juveniles of two species of marine turtle: the green sea turtle (Chelonia mydas) and the hawksbill sea turtle (Eretmochelys imbricata). We captured both species twice annually (spring and fall) from 2012 through 2017, as part of a capture–mark–recapture study at Buck Island Reef National Monument, St. Croix, U.S. Virgin Islands. We assessed tag retention rates using physical recaptures of turtles previously outfitted with an acoustic tag. Results We deployed 72 acoustic tags on 60 juvenile greens and 37 acoustic tags on 29 hawksbills. We estimated the half-life for tags on greens to be 150 days (95% CI 117–188 days), whereas the half-life for tags on hawksbills was 1077 days (95% CI 870–2118 days), a marked difference. We observed that tag attachment holes, drilled into the posterior marginal scutes, migrated laterally towards the outer edge of the marginals in both species. Green turtles tended to exhibit tear-outs, as their attachment holes wore and/or tags grew near the edge of their scutes, whereas hawksbills tended to maintain the structure of these holes and did not exhibit these tear-outs. Conclusions We conclude that hawksbills can be tagged with long-battery-life acoustic tags for long-term studies of habitat use and movement patterns, whereas greens are likely to shed their tags in the 1st year, making long-term studies difficult. This study is the first clear evidence that tagging protocols should vary between species of hard-shelled turtles. Furthermore, shed tags on the seafloor continue to be detected by acoustic receivers, creating a challenge in data filtering before analysis. We encourage future research into an efficient method for filtering these data points prior to analysis.

Animal Biotelemetry↗
USGS2025

Linking bathythermal habitat selection to management of a migratory freshwater fish

Background For migratory fishes, habitat selection in dimensions of temperature and depth may be jointly used to define the bathythermal niche. Seasonal and long-term changes in the availability of bathythermal habitat can cause behavioral responses that have consequences for managing interjurisdictional fisheries that target migratory fishes. Management of such fisheries typically relies on standardized surveys to provide knowledge of stock status, yet changes in fish behavior may complicate interpretation of survey results. For example, changes in bathythermal habitat selection could uncouple fish availability from surveys designed to intercept migrating fish in predefined bathythermal habitats. Methods We applied electronic tagging methods to Lake Erie walleye ( Sander vitreus ) to address spatial management and stock assessment questions regarding bathythermal habitat. Specifically, we sought to determine if bathythermal habitat use varied in relation to body size, season, and time of day, with a particular focus on how these may influence availability to fisheries-independent surveys conducted during September-November. Results As predicted, bathythermal habitat distribution fluctuated substantially throughout the year, was most limited during spawning months, and most expansive during fall migration. During the summer stratified months, walleye primarily selected epilimnetic habitats, despite the prevailing notion that colder hypolimnetic waters would be preferred during this time. Conclusions While our results did not support a previous hypothesis that smaller fish were more available to assessment survey gears, our results did support previous assertions that walleye were more active and available to suspended gill nets during late crepuscular periods in fall. Considering uncertainties in water quality and long-term warming trends, our case study could improve decisions regarding spatial management of this species in the context of independent water quality management objectives.

Detroit River, Lake Erie, Lake St. Clair↗
USGS1960

A comprehensive system of automatic computation in magnetic and gravity interpretation

In the interpretation of magnetic and gravity anomalies, downward continuation of fields and calculation of first and second vertical derivatives of fields have been recognized as effective means for bringing into focus the latent diagnostic features of the data. A comprehensive system has been devised for the calculation of any or all of these derived fields on modern electronic digital computing equipment. The integral for analytic continuation above the plane is used with a Lagrange extrapolation polynomial to derive a general determinantal expression from which the field at depth and the various derivatives on the surface and at depth can be obtained. It is shown that the general formula includes as special cases some of the formulas appearing in the literature. The process involves a "once for all depths" summing of grid values on a system of concentric circles about each point followed by application of the appropriate one or more of the 19 sets of coefficients derived for the purpose. Theoretical and observed multilevel data are used to illustrate the processes and to discuss the errors. The coefficients can be used for less extensive computations on a desk calculator.

Geophysics↗