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At least 775 records · Page 43Linked to original sources

USGS2023

Seasonal spatial ecology of Lake Trout in Lake Erie

Objective Lake Trout Salvelinus namaycush are native coldwater apex predators that play an important role in maintaining ecosystem functionality and diversity in the Laurentian Great Lakes. Following population collapses, rehabilitation efforts were widely initiated in the Great Lakes to reestablish self‐sustaining Lake Trout populations. Lake Erie may pose a challenge to these rehabilitation efforts due to limited availability of appropriate oxythermal habitat. Our goal was to investigate seasonal habitat use of adult Lake Trout in Lake Erie to inform management and rehabilitation efforts. Methods We used acoustic telemetry in Lake Erie, which was equipepd with a lake‐wide acoustic receiver grid, to quantify Lake Trout seasonal region occupancy, dispersal distances, bottom depth occupancy, space use extent, and space use overlap. Result We found that 32% of fish tagged in the eastern basin and all fish from the western basin dispersed more than 100 km from their tagging location, which represents a greater proportion of the population moving long distances than what has been previously documented in the Great Lakes. During stratification, Lake Trout were detected almost exclusively in the offshore eastern basin in areas where water depth exceeded 25 m. During nonstratified seasons, fish used other regions of the lake, occupying areas of highly variable depths. During fall, most fish tagged in the eastern basin occupied habitat along the southern shore of the eastern basin. Fish tagged in the western basin returned to this region in the fall of subsequent years despite occupying the offshore eastern basin during stratification and having depth occupancy, home range size, and overlap similar to that of eastern basin‐tagged fish. Fish size was positively correlated with receiver depth during winter and spring, and with home range overlap during spring and summer. Conclusion The results of this study can begin to inform management decisions regarding stocking locations, harvest regulations, and habitat restoration to facilitate the continued rehabilitation of this important native species.

Lake Erie↗

USGS2007

Revisiting submarine mass movements along the U.S. Atlantic Continental Margin: Implications for tsunami hazards

Interest in the generation of tsunamis by submarine mass movements has warranted a reassessment of their distribution and the nature of submarine landslides offshore of the eastern U.S. The recent acquisition and analysis of multibeam bathymetric data over most of this continental slope and rise provides clearer view into the extent and style of mass movements on this margin. Debris flows appear to be the dominant type of mass movement, although some translational slides have also been identified. Areas affected by mass movements range in size from less than 9 km2 to greater than 15,200 km2 and reach measured thicknesses of up to 70 m. Failures are seen to originate on either the open-slope or in submarine canyons. Slope-sourced failures are larger than canyonsourced failures, suggesting they have a higher potential for tsunami generation although the volume of material displaced during individual failure events still needs to be refined. The slope-sourced failures are most common offshore of the northern, glaciated part of the coast, but others are found downslope of shelf-edge deltas and near salt diapirs, suggesting that several geological conditions control their distribution.

Atlantic Ocean↗

USGS2022

U.S. Atlantic margin gas hydrates

The minimum distribution of gas hydrates on the U.S. Atlantic margin is from offshore South Carolina northward to the longitude of Shallop Canyon on the southern New England margin. Few wells have logged or sampled the gas hydrate zone on this margin, meaning that the presence of gas hydrates is inferred primarily based on seismic data that reveal bottom simulating reflections, mostly at water depths greater than 2000 m. The highest hydrate saturations most likely exist in sandy sediments of the Whale Prospect offshore New Jersey, New York, and the western part of Cape Cod, an area characterized by strong bottom simulating reflections. Such reflections are also imaged on the well-studied Blake Ridge, where fine-grained sediments host lower hydrate saturations that have been constrained by drilling. Within the section of the margin stretching from south of Cape Hatteras to nearly Hudson Canyon, the diagnostic seismic reflections are hard to discern, making inferences about gas hydrate distributions more uncertain. The recognition of as-yet unmapped bottom simulating reflections or top of gas features seaward of the 2000 m bathymetric contour (e.g., Cape Fear Slide, Currituck slide, beneath deepwater gas seeps) within the Mid-Atlantic Bight expands the area of probable gas hydrates on this margin.

Delaware, Maryland, New Jersey, New York, North Ca↗

USGS1988

Observed oil and gas field size distributions: A consequence of the discovery process and prices of oil and gas

If observed oil and gas field size distributions are obtained by random samplings, the fitted distributions should approximate that of the parent population of oil and gas fields. However, empirical evidence strongly suggests that larger fields tend to be discovered earlier in the discovery process than they would be by random sampling. Economic factors also can limit the number of small fields that are developed and reported. This paper examines observed size distributions in state and federal waters of offshore Texas. Results of the analysis demonstrate how the shape of the observable size distributions change with significant hydrocarbon price changes. Comparison of state and federal observed size distributions in the offshore area shows how production cost differences also affect the shape of the observed size distribution. Methods for modifying the discovery rate estimation procedures when economic factors significantly affect the discovery sequence are presented. A primary conclusion of the analysis is that, because hydrocarbon price changes can significantly affect the observed discovery size distribution, one should not be confident about inferring the form and specific parameters of the parent field size distribution from the observed distributions. ?? 1988 International Association for Mathematical Geology.

Mathematical Geology↗

USGS1984

Ferrelo fan, California: Depositional system influenced by Eustatic sea level changes

Remnants of an Eocene fan system are preserved onshore at San Diego and in the central part of the southern California borderland. Even though faults and erosion have truncated its margins, geophysical data and exploratory wells indicate that remaining parts of the fan extend beneath an offshore area nearly 400-km long and 40- to 100-km wide. Environments representing fluvial, fan-delta, shelf-channel, overlapping inner- to outer-fan, and basin-plain facies are recognized or inferred. Three progradational cycles onshore and two distinct pulses of sand accumulation offshore are attributable to eustatic low sea-level stands rather than to tectonic uplift or shifts in depositional patterns. ?? 1984 Springer-Verlag New York Inc.

Geo-Marine Letters↗

USGS2012

Near-field tsunami edge waves and complex earthquake rupture

The effect of distributed coseismic slip on progressive, near-field edge waves is examined for continental shelf tsunamis. Detailed observations of edge waves are difficult to separate from the other tsunami phases that are observed on tide gauge records. In this study, analytic methods are used to compute tsunami edge waves distributed over a finite number of modes and for uniformly sloping bathymetry. Coseismic displacements from static elastic theory are introduced as initial conditions in calculating the evolution of progressive edge-waves. Both simple crack representations (constant stress drop) and stochastic slip models (heterogeneous stress drop) are tested on a fault with geometry similar to that of the M w = 8.8 2010 Chile earthquake. Crack-like ruptures that are beneath or that span the shoreline result in similar longshore patterns of maximum edge-wave amplitude. Ruptures located farther offshore result in reduced edge-wave excitation, consistent with previous studies. Introduction of stress-drop heterogeneity by way of stochastic slip models results in significantly more variability in longshore edge-wave patterns compared to crack-like ruptures for the same offshore source position. In some cases, regions of high slip that are spatially distinct will yield sub-events, in terms of tsunami generation. Constructive interference of both non-trapped and trapped waves can yield significantly larger tsunamis than those that produced by simple earthquake characterizations.

Pure and Applied Geophysics↗

USGS2007

Landward and eastward shift of Alaskan polar bear denning associated with recent sea ice changes

Polar bears (Ursus maritimus) in the northern Alaska region den in coastal areas and on offshore drifting ice. We evaluated changes in the distribution of polar bear maternal dens between 1985 and 2005, using satellite telemetry. We determined the distribution of maternal dens occupied by 89 satellite collared female polar bears between 137°W and 167°W longitude. The proportion of dens on pack ice declined from 62% in 1985–1994 to 37% in 1998–2004 ( P = 0.044) and among pack ice dens fewer occurred in the western Beaufort Sea after 1998. We evaluated whether hunting, attraction to bowhead whale remains, or changes in sea ice could explain changes in den distribution. We concluded that denning distribution changed in response to reductions in stable old ice, increases in unconsolidated ice, and lengthening of the melt season. In consort, these changes have likely reduced the availability and quality of pack ice denning habitat. Further declines in sea ice availability are predicted. Therefore, we expect the proportion of polar bears denning in coastal areas will continue to increase, until such time as the autumn ice retreats far enough from shore that it precludes offshore pregnant females from reaching the Alaska coast in advance of denning.

Alaska↗

USGS2012

Terrestrial and marine trophic pathways support young-of-year growth in a nearshore Arctic fish

River discharge supplies nearshore communities with a terrestrial carbon source that is often reflected in invertebrate and fish consumers. Recent studies in the Beaufort Sea have documented widespread terrestrial carbon use among invertebrates, but only limited use among nearshore fish consumers. Here, we examine the carbon source and diet of rapidly growing young-of-year Arctic cisco ( Coregonus autumnalis ) using stable isotope values (δ 13 C and δ 15 N) from muscle and diet analysis (stomach contents) during a critical and previously unsampled life stage. Stable isotope values (δ 15 N and δ 13 C) may differentiate between terrestrial and marine sources and integrate over longer time frames (weeks). Diet analysis provides species-specific information, but only from recent foraging (days). Average δ 13 C for all individuals was −25.7 ‰, with the smallest individuals possessing significantly depleted δ 13 C values indicative of a stronger reliance of terrestrial carbon sources as compared to larger individuals. Average δ 15 N for all individuals was 10.4 ‰, with little variation among individuals. As fish length increased, the proportion of offshore Calanus prey and neritic Mysis prey increased. Rapid young-of-year growth in Arctic cisco appears to use terrestrial carbon sources obtained by consuming a mixture of neritic and offshore zooplankton. Shifts in the magnitude or phenology of river discharge and the delivery of terrestrial carbon may alter the ecology of nearshore fish consumers.

Polar Biology↗

USGS2015

Estimating the abundance of the Southern Hudson Bay polar bear subpopulation with aerial surveys

The Southern Hudson Bay (SH) polar bear subpopulation occurs at the southern extent of the species’ range. Although capture–recapture studies indicate abundance was likely unchanged between 1986 and 2005, declines in body condition and survival occurred during the period, possibly foreshadowing a future decrease in abundance. To obtain a current estimate of abundance, we conducted a comprehensive line transect aerial survey of SH during 2011–2012. We stratified the study site by anticipated densities and flew coastal contour transects and systematically spaced inland transects in Ontario and on Akimiski Island and large offshore islands in 2011. Data were collected with double-observer and distance sampling protocols. We surveyed small islands in James Bay and eastern Hudson Bay and flew a comprehensive transect along the Québec coastline in 2012. We observed 667 bears in Ontario and on Akimiski Island and nearby islands in 2011, and we sighted 80 bears on offshore islands during 2012. Mark–recapture distance sampling and sight–resight models yielded an estimate of 860 (SE = 174) for the 2011 study area. Our estimate of abundance for the entire SH subpopulation (943; SE = 174) suggests that abundance is unlikely to have changed significantly since 1986. However, this result should be interpreted cautiously because of the methodological differences between historical studies (physical capture–recapture) and this survey. A conservative management approach is warranted given previous increases in duration of the ice-free season, which are predicted to continue in the future, and previously documented declines in body condition and vital rates.

Polar Biology↗

USGS2017

Evaluation of a method using survey counts and tag data to estimate the number of Pacific walruses ( Odobenus rosmarus divergens ) using a coastal haulout in northwestern Alaska

Increased periods of sparse sea ice over the continental shelf of the Chukchi Sea in late summer have reduced offshore haulout habitat for Pacific walruses ( Odobenus rosmarus divergens ) and increased opportunities for human activities in the region. Knowing how many walruses could be affected by human activities would be useful to conservation decisions. Currently, there are no adequate estimates of walrus abundance in the northeastern Chukchi Sea during summer–early autumn. Estimating abundance in autumn might be possible from coastal surveys of hauled out walruses during periods when offshore sea ice is unavailable to walruses. We evaluated methods to estimate the size of the walrus population that was using a haulout on the coast of northwestern Alaska in autumn by using aerial photography to count the number of hauled out walruses (herd size) and data from 37 tagged walruses to estimate availability (proportion of population hauled out). We used two methods to estimate availability, direct proportions of hauled out tagged walruses and smoothed proportions using local polynomial regression. Point estimates of herd size (4200–38,000 walruses) and total population size (76,000–287,000 walruses) ranged widely among days and between the two methods of estimating availability. Estimates of population size were influenced most by variation in estimates of availability. Coastal surveys might be improved most by counting walruses when the greatest numbers are hauled out, thereby reducing the influence of availability on population size estimates. The chance of collecting data during peak haulout periods would be improved by conducting multiple surveys.

Polar Biology↗

USGS2013

Rapid fluctuations in flow and water-column properties in Asan Bay, Guam: implications for selective resilience of coral reefs in warming seas

Hydrodynamics and water-column properties were investigated off west-central Guam from July 2007 through January 2008. Rapid fluctuations, on time scales of 10s of min, in currents, temperature, salinity, and acoustic backscatter were observed to occur on sub-diurnal frequencies along more than 2 km of the fore reef but not at the reef crest. During periods characterized by higher sea-surface temperatures (SSTs), weaker wind forcing, smaller ocean surface waves, and greater thermal stratification, rapid decreases in temperature and concurrent rapid increases in salinity and acoustic backscatter coincided with onshore-directed near-bed currents and offshore-directed near-surface currents. During the study, these cool-water events, on average, lasted 2.3 h and decreased the water temperature 0.57 °C, increased the salinity 0.25 PSU, and were two orders of magnitude more prevalent during the summer season than the winter. During the summer season when the average satellite-derived SST anomaly was +0.63 °C, these cooling events, on average, lowered the temperature 1.14 °C along the fore reef but only 0.11 °C along the reef crest. The rapid shifts appear to be the result of internal tidal bores pumping cooler, more saline, higher-backscatter oceanic water from depths >50 m over cross-shore distances of 100 s of m into the warmer, less saline waters at depths of 20 m and shallower. Such internal bores appear to have the potential to buffer shallow coral reefs from predicted increases in SSTs by bringing cool, offshore water to shallow coral environments. These cooling internal bores may also provide additional benefits to offset stress such as supplying food to thermally stressed corals, reducing stress due to ultraviolet radiation and/or low salinity, and delivering coral larvae from deeper reefs not impacted by surface thermal stress. Thus, the presence of internal bores might be an important factor locally in the resilience of select coral reefs facing increased thermal stress.

Coral Reefs↗

USGS2025

Quantifying benthic flux of Mysis biomass through diel vertical migration at the ecosystem scale

Mysis diluviana is a macroinvertebrate that couples benthic and pelagic habitats on a daily timescale through diel vertical migration (DVM). However, quantifying how much Mysis biomass is exchanged between benthic and pelagic habitats at an ecosystem scale is difficult because of sampling limitations and variability in Mysis DVM behavior related to light and depth. Although Mysis are benthic-pelagic migrators, a portion remains pelagic during the day offshore in Lake Ontario, partially contradicting the assumption of population-level DVM over deep areas. To estimate the amount of biomass transferred from benthic to pelagic habitat via DVM in Lake Ontario, we estimated the portion of pelagic biomass at night originating from benthic habitat as the difference between night and day pelagic estimates from net tows along a bathymetric depth gradient. We then modeled the portion as a function of depth, extrapolated these depth-dependent estimates to an existing lake wide night-pelagic dataset, and summed amounts across depth strata. We estimated more biomass was transferred from benthic to pelagic habitat at intermediate lake depths (100–160 m) despite greater offshore (> 180 m) night-pelagic biomass. Our results suggest ways to improve estimates of Mysis habitat coupling and how to account for important factors such as depth and light for modeling Mysis DVM behavior at the population- and ecosystem-levels.

Lake Ontario↗

USGS2006

Temporal trends of young-of-year fishes in Lake Erie and comparison of diel sampling periods

We explored temporal trends of young-of-year (YOY) fishes caught in bottom trawl hauls at an established offshore monitoring site in Lake Erie in fall during 1961–2001. Sampling was conducted during morning, afternoon, and night in each year. Catches per hour (CPH) of alewife ( Alosa pseudoharengus ) YOY were relatively low and exhibited no temporal trend. This result was consistent with the species’ intolerance to Lake Erie’s adverse winter water temperatures. Gizzard shad ( Dorosoma cepedianum ) YOY decreased sharply after 1991, which was consistent with recent oligotrophication of the lake. Following the establishment in 1979 and rapid increase of white perch ( Morone americana ) YOY, white bass ( Morone chrysops ) and freshwater drum ( Aplodinotus grunniens ) YOY decreased. Trout-perch ( Percopsis omiscomaycus ) YOY decreased during 1986–1991, but recovered to previous levels during 1991–2001. The recovery coincided with the resurgence of mayflies ( Ephemoptera ) in the lake. CPH of spottail shiner ( Notropis hudsonius ) and emerald shiner ( N. atherinoides ) YOY exhibited no temporal trend between 1961 and the late 1970s to early 1980s. CPH of yellow perch ( Perca flavescens ) YOY decreased during 1961–1988, and walleye ( Sander vitreum ) YOY increased overall during the time series. These observations were consistent with published studies of adults in the region. CPH of 4 of the 10 species of YOY considered were greatest during night. CPH for walleye YOY was higher in the morning than in the afternoon, but there was no significant difference between night and morning abundances. The results suggest that (1) CPH of YOY fishes may be a useful monitoring tool for Lake Erie, and (2) offshore monitoring programs that do not include night sampling periods may underestimate recruitment for several common species.

Environmental Monitoring and Assessment↗

USGS2005

Evidence for competitive dominance of Pink salmon (Oncorhynchus gorbuscha) over other Salmonids in the North Pacific Ocean

Relatively little is known about fish species interactions in offshore areas of the world's oceans because adequate experimental controls are typically unavailable in such vast areas. However, pink salmon (Oncorhynchus gorbuscha) are numerous and have an alternating-year pattern of abundance that provides a natural experimental control to test for interspecific competition in the North Pacific Ocean and Bering Sea. Since a number of studies have recently examined pink salmon interactions with other salmon, we reviewed them in an effort to describe patterns of interaction over broad regions of the ocean. Research consistently indicated that pink salmon significantly altered prey abundance of other salmon species (e.g., zooplankton, squid), leading to altered diet, reduced total prey consumption and growth, delayed maturation, and reduced survival, depending on species and locale. Reduced survival was observed in chum salmon (O. keta) and Chinook salmon (O. tshawytscha) originating from Puget Sound and in Bristol Bay sockeye salmon (O. nerka). Growth of pink salmon was not measurably affected by other salmon species, but their growth was sometimes inversely related to their own abundance. In all marine studies, pink salmon affected other species through exploitation of prey resources rather than interference. Interspecific competition was observed in nearshore and offshore waters of the North Pacific Ocean and Bering Sea, and one study documented competition between species originating from different continents. Climate change had variable effects on competition. In the North Pacific Ocean, competition was observed before and after the ocean regime shift in 1977 that significantly altered abundances of many marine species, whereas a study in the Pacific Northwest reported a shift from predation- to competition-based mortality in response to the 1982/1983 El Nino. Key traits of pink salmon that influenced competition with other salmonids included great abundance, high consumption rates and rapid growth, degree of diet overlap or consumption of lower trophic level prey, and early migration timing into the ocean. The consistent pattern of findings from multiple regions of the ocean provides evidence that interspecific competition can significantly influence salmon population dynamics and that pink salmon may be the dominant competitor among salmon in marine waters. ?? Springer 2005.

Reviews in Fish Biology and Fisheries↗

USGS1981

Patterns of groundwater salinity changes in a deep continental-oceanic transect off the southeastern Atlantic coast of the U.S.A.

Investigations of formation-fluid salinities in a transect from western Georgia to the edge of the Blake Plateau off the coast of Georgia show surprisingly similar hydrochemical features offshore and onshore. A fresh-brackish wedge of groundwater (<25 g/kg total dissolved solids) lies beneath the shelf to a depth of ∼ 900 m. On land, brackish waters extend to a maximum depth of ∼ 1.2 km below sea level in Lowndes County, Georgia. In deeper horizons, hypersaline brines (> 100 g/kg) occur in Lower Cretaceous (?) strata. These strata have a pronounced evaporitic (anhydritic) character in the offshore segment. Strong salinity gradients in interstitial waters signify buried evaporite deposits at drill sites beneath the Blake Plateau.

Florida, Georgia, South Carolina↗

USGS1978

A sediment-dispersal model for the South Texas continental shelf, northwest Gulf of Mexico

Textural-distribution patterns of sea-floor sediments on the South Texas continental shelf between Matagorda Bay and the U.S.-Mexico international boundary were evaluated as part of a regional environmental-studies program. Sediment textural gradients support a conceptual model for the regional sediment-dispersal system, which is characterized by both net offshore transport and net south-trending coastwise transport components on a wind-dominated shelf. Coastwise transport results in the net southward migration of both palimpsest sandy mud composing the ancestral Brazos-Colorado delta flank in the northern sector, and modern mud composing the central sector; these migrating sediments are encroaching southward onto immobile relict muddy sands composing the ancestral Rio Grande delta in the southern sector. In the proposed model, the suspension transport of modern silt-enriched mud derived mainly from coastal sources is the dominant dispersal mechanism. Net offshore transport is attributed both to diffusion, and to the advective ebb-tide discharge of turbid lagoonal-estuarine waters from coastal inlets. Net southward transport is attributed mainly to advection by seasonally residual coastwise drift currents reflecting a winter-dominated hydraulic regime. Frequent winter storms characterized by relatively high-speed northerly winds that accompany the passage of cold fronts appear to be dominant regional dispersal agents.

Texas↗

USGS1983

K-Ar ages and the opening of the South Atlantic Ocean: Basaltic rock from the Brazilian margin

New K-Ar ages for 13 samples of basalt, gabbro, wehrlite, and trachyandesite drilled from the Brazilian continental shelf and coastline yield information about the timing of the opening of the South Atlantic and the nature of the crust seaward from the Brazil margin. The oldest basalt is 138.1 ± 3.5 m.y. "> 138.1 ± 3.5m.y. old and from offshore at 24.5°S; it represents Serra Geral flood basalt on attenuated crust in the Santos basin. Basalts from the coastline at 19.5°S are mixed with terrigenous graben sediments, and their ages confirm that rifting was underway before 130 m.y. Offshore sites in the Campos basin, ∼22°–23°S, 41°W, have basalt ranging from 124 to 112 m.y. in age and mostly continental flood basalt in composition. One 112-m.y. basalt, however, is MORB-like and could therefore represent oceanic lithosphere mixed with continental crust about 50 km from the shoreline at ∼22.5°S. Other samples reveal compositionally varied intraplate, passive-margin magmatism occurring 75-43 m.y. ago. They correlate with profuse contemporary alkalic magmatism on the southeastern Brazil coast and probably represent reactivation of zones of “weakness” (i.e., fracture zone-lineaments).

Marine Geology↗

USGS1983

A system for measuring bottom profile, waves and currents in the high-energy nearshore environment

A new data-acquisition system capable of measuring waves, currents and the nearshore profile in breaking waves as high as 5 m has been developed and successfully field-tested. Components of the mechanical system are a sled carrying a vertical mast, a double-drum winch placed landward of the beach, and a line that runs from one drum of the winch around three blocks, which are the corners of a right triangle, to the other drum of the winch. The sled is attached to the shore-normal side of the triangular line arrangement and is pulled offshore by one drum of the winch and onshore by the other. The profile is measured as the sled is towed along the shore-normal transect using an infrared rangefinder mounted landward of the winch and optical prisms mounted on top of the sled's mast. A pressure sensor and two-axis electromagnetic current meter are mounted on the frame of the sled. These data are encoded on the sled and telemetered to a receiving/recording station onshore. Preliminary results suggest that near-bottom offshore-flowing currents during periods of high-energy swell are important in forcing changes to the configuration of the nearshore profile.

Marine Geology↗