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At least 1,333 records · Page 74Linked to original sources
USGS2021

Evaluating the role of active management in mature Douglas-fir (Pseudotsuga menziesii) stands for songbird conservation

Forest birds, particularly those associated with late-successional forests, are of widespread conservation interest. Although birds are among the more widely studied taxa of forest wildlife, relatively few studies have examined the long-term effects of active management (i.e., intentional stand density reduction) on the forest bird assemblage. This is an important omission, as changes in stand structure and composition over the decades following harvesting may influence wildlife utilization of forest stands. We developed an observational study to evaluate forest bird response to stand structural development multiple decades following harvesting with differing levels of overstory density reduction, and in unmanaged stands. We focused, in particular, on songbirds and cavity excavating species associated with old-growth Douglas-fir forests, and the active management strategies that we examined – thinning and structural retention harvesting – were selected based on their potential to accelerate stand structural development. Our 18 mature stands (age range: 107–187 years) were located in the western hemlock zone of western Oregon, and bird surveys were conducted an average of 41 years and 22 years post-harvest in thinned and retention harvest stands, respectively. Poisson generalized linear models were formulated to evaluate the effects of management condition on forest birds. Although five species were associated with specific management conditions, relative abundance was not statistically different between unmanaged, thinned and retention harvest stands for a majority of the species in our analysis. Species richness was also relatively invariant across management conditions. Our results do suggest that retention harvesting adversely affects some songbird species associated with old-growth forests – Pacific-slope flycatcher ( Empidonax difficilis ) and Pacific wren ( Troglodytes pacificus ) for example - but our findings also indicate that retention harvesting has long-term benefits for birds associated with early-successional forests. This includes migrant species that have experienced significant population declines in Western North America over recent decades, such as Wilson’s and MacGillivray’s warblers ( Cardellina pusilla and Geothlypis tolmiei , respectively). Overall, our results imply that for many species of forest birds, including those associated with old-growth forests, managers have some flexibility in overstory density management where long-term species persistence is an objective. Equally significant, our results provide strong support for the application of variable retention harvesting as a tool for the conservation of bird species associated with early-successional forests, while also reinforcing the value of mature structural legacies for bird species associated with late-successional forests. While also reinforcing the value of mature structural legacies for birds associated with late-successional forests.

Oregon↗
USGS2015

Will the effects of sea-level rise create ecological traps for Pacific Island seabirds?

More than 18 million seabirds nest on 58 Pacific islands protected within vast U.S. Marine National Monuments (1.9 million km 2 ). However, most of these seabird colonies are on low-elevation islands and sea-level rise (SLR) and accompanying high-water perturbations are predicted to escalate with climate change. To understand how SLR may impact protected islands and insular biodiversity, we modeled inundation and wave-driven flooding of a globally important seabird rookery in the subtropical Pacific. We acquired new high-resolution Digital Elevation Models (DEMs) and used the Delft3D wave model and ArcGIS to model wave heights and inundation for a range of SLR scenarios (+0.5, +1.0, +1.5, and +2.0 m) at Midway Atoll. Next, we classified vegetation to delineate habitat exposure to inundation and identified how breeding phenology, colony synchrony, and life history traits affect species-specific sensitivity. We identified 3 of 13 species as highly vulnerable to SLR in the Hawaiian Islands and quantified their atoll-wide distribution (Laysan albatross, Phoebastria immutabilis ; black-footed albatross, P . nigripes ; and Bonin petrel, Pterodroma hypoleuca ). Our models of wave-driven flooding forecast nest losses up to 10% greater than passive inundation models at +1.0 m SLR. At projections of + 2.0 m SLR, approximately 60% of albatross and 44% of Bonin petrel nests were overwashed displacing more than 616,400 breeding albatrosses and petrels. Habitat loss due to passive SLR may decrease the carrying capacity of some islands to support seabird colonies, while sudden high-water events directly reduce survival and reproduction. This is the first study to simulate wave-driven flooding and the combined impacts of SLR, groundwater rise, and storm waves on seabird colonies. Our results highlight the need for early climate change planning and restoration of higher elevation seabird refugia to prevent low-lying protected islands from becoming ecological traps in the face of rising sea levels.

PLoS ONE↗
USGS2012

Bathymetry and digital elevation models of Coyote Creek and Alviso Slough, South San Francisco Bay, California

In 2010, the U.S. Geological Survey (USGS), Pacific Coastal and Marine Science Center completed three cruises to map the bathymetry of the main channel and shallow intertidal mudflats in the southernmost part of south San Francisco Bay. The three surveys were merged to generate comprehensive maps of Coyote Creek (from Calaveras Point east to the railroad bridge) and Alviso Slough (from the bay to the town of Alviso) to establish baseline bathymetry prior to the breaching of levees adjacent to Alviso and Guadalupe Sloughs as part of the South Bay Salt Pond Restoration Project ( http://www.southbayrestoration.org ). Since 2010, the USGS has conducted fourteen additional surveys to monitor bathymetric change in this region as restoration progresses. The bathymetric surveys were conducted using the state-of-the-art research vessel R/V Parke Snavely outfitted with an interferometric sidescan sonar for swath mapping in extremely shallow water. This publication provides high-resolution bathymetric data collected by the USGS. For the 2010 baseline survey we have merged the bathymetry with aerial lidar data that were collected for the USGS during the same time period to create a seamless, high-resolution digital elevation model (DEM) of the study area. The series of bathymetric datasets are provided at 1 m resolution and the 2010 bathymetric/topographic DEM at 2 m resolution. The data are formatted as both X, Y, Z text files and ESRI Arc ASCII files that are accompanied by Federal Geographic Data Committee (FGDC) compliant metadata.

California↗
USGS2020

Evaluating dewatering approaches to protect larval Pacific lamprey

Executive Summary Larval Pacific lamprey live for several years burrowed in nearshore sediments where they filter feed on detritus and organic matter. Dewatering of larval habitat can occur as a result of flow-management practices, construction projects, or seasonal closures of irrigation diversions. Effective management of dewatering events requires guidance on approaches to protect lamprey, such as dewatering rates and light conditions (day or night) that allow lamprey the best opportunity to relocate water and avoid being stranded. We conducted controlled laboratory experiments comparing five dewatering rates (1, 1.8, 4, 8, and 16 inches per hour [in/h]) and two light conditions (light and dark) to evaluate their effectiveness in protecting larval lamprey. We used a tank with a simulated shoreline at a 10-percent slope filled with river sediment and manipulated the outflow to control the rate of dewatering until water was covering only the sediment in the lowest tank section, at the bottom of the slope. Following dewatering, larvae were classified as either stranded (in or on the substrate outside the watered area) or safe (relocated to the wetted area at the lower end of the tank). All study groups experienced high rates of stranding. The lowest stranding rates were for 1 in/h, in both light (77 percent) and dark (80 percent). Faster dewatering rates generally produced higher percentages of stranded fish, and both the dark and light trials at 16 in/h stranded all larvae. At each of the five dewatering rates, trials conducted in the dark stranded the same or higher proportions of fish than the corresponding trial conducted in the light, so there was no clear advantage to dewatering during dark conditions. The largest contribution to stranding rates for all study groups was the high number of larvae (50–80 percent) that did not initiate movement in response to dewatering and remained in the uppermost tank section where they were stocked at the start of the trials. The proportion of larvae that emerged from the sediment during dewatering trials was approximately 30 percent, and fish that emerged were consistently smaller than those that remained burrowed. Combining all dewatering rates, emergence was 31.3 percent for groups under dark conditions and 30.7 percent for groups under light conditions. We recorded the timing of emergence for 58 larvae and their median time to emerge (after the surface of the sediment in the uppermost tank section was dewatered) was 0.62 hour (h) (range 0–4.5 h). We measured larval movement rates and found that large fish moved faster than small fish. Differences in larval movement rate based on light condition were significant only for large fish, which had a significantly faster rate during light conditions. Larval lamprey moved, over short distances, at rates that exceeded the fastest dewatering rate we tested. The mean movement rates for groups ranged from 19.0 to 44.4 centimeters per minute [cm/min]) and the fastest dewatering rate (16 in/h) is equivalent to less than 1 cm/min. Only the slowest movement rate measured, 6.6 cm/min for one individual lamprey, was slower than the fastest dewatering rate. We also investigated lamprey responses to a series of dewatering and rewatering events. Individual larvae were held in cylinders and exposed to four cycles of dewatering and rewatering using dewatering rates of 1 and 16 in/h and a rewatering rate of 2 in/h. Each dewatering rate was tested under both dark and light conditions. The location of fish, either on the surface of the sediment or burrowed, was recorded after each dewatering event for four rounds. The most common individual fish response for all study groups was to remain burrowed through all four rounds, and there were large differences in response between small and large larvae. Overall for small larvae, combining all groups, 14 of 28 fish emerged, and of those, 8 died and 1 was lethargic. The 1-in/h rate had 7 of the 8 mortalities, split about equally between the dark (3 fish) and light (4 fish) trials. All but one fish that died emerged from the sediment at some point during the four rounds of dewatering. Large larvae predominantly remained burrowed in all four rounds and did not experience any mortality. None of the large fish emerged for more than a single round, and emergence occurred only in the first and second rounds. Larvae emerged more quickly as the number of dewatering events increased. The mean time to emerge after the surface of the sediment in the tube was dewatered, combing all four groups, was 42 minutes (min) in round 1 (14 fish), 16 min in round 2 (5 fish), 11 min in round 3 (3 fish), and 8 minutes in round 4 (3 fish). When all groups and rounds of dewatering were combined, the overall mean time to emerge was 29 min (25 fish) and ranged from 1 min to 2 hours after the surface of the sediment was dewatered. Larvae burrowed deeper during the 1-in/h trials than the 16-in/h trials, and few fish were deeper than about 23 centimeters (cm). Large larvae burrowed deeper than small larvae. Small larvae were most concentrated from 0 to 7.6 cm (83.7 percent), and large fish were concentrated from 15.2 to 22.8 cm (43.3 percent). The second dewatering event resulted in greater mean burrowing depth than the first event, but trends after the second event were less clear. Larval size played a role in lamprey responses to dewatering, having a significant effect on emergence, movement rate, and vertical distribution. The sediment used for laboratory testing or occupied by lamprey in the field appears to affect lamprey response to dewatering and deserves greater attention in future studies. Larvae were more active in the dark, but darkness did not consistently provide better outcomes (e.g., more emergence or reduced stranding) compared to daylight. An improved understanding of the cues that prompt larvae to emerge from the sediment, combined with the ability to manage dewatering rates, would be useful to guide future dewatering events to minimize negative effects to lamprey.

Open-File Report↗
USGS2020

Evidence of energy and nutrient transfer from invasive pink salmon (Oncorhynchus gorbuscha) spawners to juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in northern Norway

Recent large influxes of non-native Pacific pink salmon ( Oncorhynchus gorbuscha ) to North European rivers have raised concern over their potential negative impacts on native salmonids and recipient ecosystems. The eggs and carcasses of semelparous pink salmon may provide a significant nutrient and energy subsidy to native biota, but this phenomenon has not been widely documented outside the species' native distribution. We analysed the stomach contents and stable isotope values (δ 15 N and δ 13 C) in muscle and liver tissues of juvenile Atlantic salmon ( Salmo salar ) and brown trout ( Salmo trutta ) to determine whether these native salmonids utilise marine-derived nutrients and energy provided by pink salmon eggs and carcasses in the subarctic river system Vesterelva, northern Norway. Although egg foraging and assimilation of marine-derived nutrients in fish body tissues were found to be minor at the population level, a few juvenile salmon and trout had recently eaten large quantities of pink salmon eggs. Some of these individuals also had high δ 15 N and δ 13 C values, indicating a long-term diet subsidised by marine-derived nutrients and energy from pink salmon eggs. Hence, our study provides novel evidence that the eggs of invasive pink salmon may provide an energetic, profitable food resource for juvenile native fish. More research is needed to understand the broader ecological implications for fishes and other biota in river ecosystems invaded by pink salmon.

Troms and Finnmark County↗
USGS2010

Movements of walruses radio-tagged in Bristol Bay, Alaska

Satellite radio-location data from 57 adult male Pacific walruses ( Odobenus rosmarus divergens ) were used to estimate haul-out fidelity, broadly describe seasonal foraging distributions, and determine the approximate timing of autumn migration from Bristol Bay, Alaska. Data were collected intermittently during 1987–91 and 1995–2000, primarily during the period from May to October. Transmitter longevity ranged from less than 1 day to 560 days (median 75 d). The four tagging sites were the only haul-outs that were commonly used in the bay from spring through autumn. Mean fidelity, defined as the chance that an animal will return to an area where it previously hauled out, was 0.56 (SE = 0.09). However, small sample sizes precluded comparisons of fidelity among years and among haul-outs by season. No tagged animals migrated out of the bay between spring and early autumn. Combined monthly locations suggest that foraging occurred primarily in the southern and eastern areas of the bay in spring and gradually shifted towards northwestern areas in late autumn and winter. Ninety-eight percent of the in-water locations were in waters under 60 m deep, which account for 76% of the study area. Some animals migrated out of the bay in late autumn and winter; others remained within the bay throughout the year. Those making long-range migrations departed the bay during November and December.

Alaska↗
USGS2009

Propagation of the myxozoan parasite Myxobolus cerebralis by different geographic and genetic populations of Tubifex tubifex: An Oregon perspective

Tubifex tubifex are obligate invertebrate hosts in the life cycle of Myxobolus cerebralis, the myxozoan parasite that causes whirling disease in salmonid fishes. This exotic parasite is established to varying degrees across Oregon's Columbia River system (Pacific Northwest, USA) and characteristics of local T. tubifex populations likely play a role in the pattern of disease occurrence. To better understand these patterns, we collected T. tubifex from three Oregon river basins (Willamette, Deschutes, and Grande Ronde), determined their genotype (mitochondrial 16S rDNA lineage and RAPD genotype) and exposed 10 different populations to M. cerebralis in the laboratory. Four mt lineages were identified: I, III, V and VI. Lineage III was found in all river basins but dominated both central and eastern sites. The RAPD assay further divided these lineages into geographic sub-populations; no RAPD genotype was common to all basins. There was a significant difference in prevalence of infection and level of parasite production among the populations we exposed to M. cerebralis that was attributed to genotypic composition. Only lineage III worms released actinospores and only populations dominated by this lineage amplified the parasite. These populations had the lowest survival, however, the lineage dominant before exposure remained dominant despite the high prevalence of infection. The distribution and infection dynamics of susceptible T. tubifex throughout Oregon may contribute to the differences in M. cerebralis occurrence; our studies further support the influence of oligochaete genotypes on the manifestation of whirling disease in salmonid populations. ?? 2009 Elsevier Inc. All rights reserved.

Journal of Invertebrate Pathology↗
USGS2008

Breeding and moulting locations and migration patterns of the Atlantic population of Steller's eiders Polysticta stelleri as determined from satellite telemetry

This study was designed to determine the spring, summer, autumn, and early winter distribution, migration routes, and timing of migration of the Atlantic population of Steller's eiders Polysticta stelleri. Satellite transmitters were implanted in 20 eiders captured in April 2001 at Vads??, Norway, and their locations were determined from 5 May 2001 to 6 February 2002. Regions where birds concentrated from spring until returning to wintering areas included coastal waters from western Finnmark, Norway, to the eastern Taymyr Peninsula, Russia. Novaya Zemlya, Russia, particularly the Mollera Bay region, was used extensively during spring staging, moult, and autumn staging; regions of the Kola, Kanin, and Gydanskiy peninsulas, Russia, were used extensively during spring and moult migrations. Steller's eiders migrated across the Barents and Kara seas and along the Kara Sea and Kola Peninsula coastal waters to nesting, moulting, and wintering areas. The majority of marked eiders (9 of 15) were flightless in near-shore waters along the west side of Novaya Zemlya. Eiders were also flightless in northern Norway and along the Kanin and at Kola Peninsula coasts. We compare and contrast natural history characteristics of the Atlantic and Pacific populations and discuss evolutionary and ecological factors influencing their distribution. © Journal of Avian Biology.

Journal of Avian Biology↗
USGS2003

Map of glacial limits and possible refugia in the southern Alexander Archipelago, Alaska, during the late Wisconsin glaciation

During the late Wisconsin glaciation (circa 26,000-13,000 carbon-14 yr BP) the Cordilleran glacier complex formed vast ice fields and large glaciers along the crest of the Coast Mountains. As these glaciers flowed west to the Pacific Ocean, they were joined by local glaciers originating on the higher reaches of the Alexander Archipelago (Mann and Hamiltion, 1995). This extensive volume of ice was channeled into deep troughs (present-day fiords) that formed major outlet glaciers, such as the glaciers that occupied Chatham Strait and Dixon Entrance. In several places along the coast, deep glacially scoured submarine troughs indicate that glaciers reached to the edge of the continental shelf. For instance, the glacier that extended into the Dixon Entrance trough is known to have extended to the edge of the continental shelf. Its retreat began sometime after 16,000-15,000 carbon-14 yr BP (Barrie and Conway, 1999).

Miscellaneous Field Studies Map↗
USGS2022

Limits to coseismic landslides triggered by Cascadia Subduction Zone earthquakes

Landslides are a significant hazard and dominant feature throughout the landscape of the Pacific Northwest. However, the hazard and risk posed by coseismic landslides triggered by great Cascadia Subduction Zone (CSZ) earthquakes is highly uncertain due to a lack of local and global data. Despite a wealth of other geologic evidence for past earthquakes on the Cascadia Subduction Zone, no landslides have been definitively linked to such earthquakes, even in areas otherwise highly susceptible to failure. While shallow landslides may not leave a lasting topographical signature in the landscape, there are thousands of deep-seated landslides in Cascadia, and these deposits often persist for hundreds of years and multiple earthquake cycles. Synthesizing newly developed inventories of dated large deep-seated landslides in the Oregon Coast Range, we use statistical methods to estimate the proportion of these types of landslides that could have been triggered during past great Cascadia Subduction Zone earthquakes. Statistical analysis of high-precision dendrochronology ages of landslide-dammed lakes and surface roughness-dated bedrock landslides reveal Cascadia Subduction Zone earthquakes may have triggered 0–15 % of large deep-seated landslides in the Oregon Coast Range over multiple earthquake cycles. Our results refine estimates from previous studies and further suggest that coseismic triggering accounts for a small fraction of the total deep-seated bedrock landslides mapped in coastal Cascadia. However, if the real rate of coseismic landslide triggering during CSZ earthquakes is near our estimated upper bound for the 1700 CSZ earthquake, we estimate up to 2400 coseismic large deep-seated landslides could occur in the Oregon Coast Range in a single earthquake. These findings suggest Cascadia is consistent with global observations from other subduction zones and that coseismic landslides may still represent a serious geohazard in the region.

Oregon↗
USGS2018

Genomic evolution, recombination, and inter-strain diversity of chelonid alphaherpesvirus 5 from Florida and Hawaii green sea turtles with fibropapillomatosis

Chelonid alphaherpesvirus 5 (ChHV5) is a herpesvirus associated with fibropapillomatosis (FP) in sea turtles worldwide. Single-locus typing has previously shown differentiation between Atlantic and Pacific strains of this virus, with low variation within each geographic clade. However, a lack of multi-locus genomic sequence data hinders understanding of the rate and mechanisms of ChHV5 evolutionary divergence, as well as how these genomic changes may contribute to differences in disease manifestation. To assess genomic variation in ChHV5 among five Hawaii and three Florida green sea turtles, we used high-throughput short-read sequencing of long-range PCR products amplified from tumor tissue using primers designed from the single available ChHV5 reference genome from a Hawaii green sea turtle. This strategy recovered sequence data from both geographic regions for approximately 75% of the predicted ChHV5 coding sequences. The average nucleotide divergence between geographic populations was 1.5%; most of the substitutions were fixed differences between regions. Protein divergence was generally low (average 0.08%), and ranged between 0 and 5.3%. Several atypical genes originally identified and annotated in the reference genome were confirmed in ChHV5 genomes from both geographic locations. Unambiguous recombination events between geographic regions were identified, and clustering of private alleles suggests the prevalence of recombination in the evolutionary history of ChHV5. This study significantly increased the amount of sequence data available from ChHV5 strains, enabling informed selection of loci for future population genetic and natural history studies, and suggesting the (possibly latent) co-infection of individuals by well-differentiated geographic variants.

Florida, Hawaii↗
USGS2016

Water temperature profiles for reaches of the Raging River during summer baseflow, King County, western Washington, July 2015

Re-introducing wood into rivers where it was historically removed is one approach to improving habitat conditions in rivers of the Pacific Northwest. The Raging River drainage basin, which flows into the Snoqualmie River at Fall City, western Washington, was largely logged during the 20th century and wood was removed from its channel. To improve habitat conditions for several species of anadromous salmonids that spawn and rear in the Raging River, King County Department of Transportation placed untethered log jams in a 250-meter reach where wood was historically removed. The U.S. Geological Survey measured longitudinal profiles of near-streambed temperature during summer baseflow along 1,026 meters of channel upstream, downstream, and within the area of wood placements. These measurements were part of an effort by King County to monitor the geomorphic and biological responses to these wood placements. Near-streambed temperatures averaged over about 1-meter intervals were measured with a fiber‑optic distributed temperature sensor every 30 minutes for 7 days between July 7 and 13, 2015. Vertical temperature profiles were measured coincident with the longitudinal temperature profile at four locations at 0 centimeters (cm) (at the streambed), and 35 and 70 cm beneath the streambed to document thermal dynamics of the hyporheic zone and surface water in the study reach.

Washington↗
USGS2024

Birdwatching preferences reveal synergies and tradeoffs among recreation, carbon, and fisheries ecosystem services in Pacific Northwest estuaries, USA

Coastal ecosystems provide multiple ecosystem services that are valued in diverse ways. The Nisqually River Delta (the Delta), an estuary in Puget Sound, Washington, U.S.A., is co-managed by the Nisqually Indian Tribe and the Billy Frank Jr. Nisqually National Wildlife Refuge. In an ecosystem services assessment, we used different service-appropriate methods including citizen science, statistical and geospatial models, and scenario analysis to evaluate three ecosystem services – recreational birdwatching, soil carbon accumulation and fishery production – indicated as priorities for the Refuge, Nisqually Indian Tribe, and surrounding communities. We developed a generalized additive mixed model set based on eBird mobile application birdwatching observations to understand the biological and landscape features that influence birdwatching and to project birdwatching visitation based on scenarios of Delta habitat change. We evaluated ecosystem service synergies and tradeoffs associated with habitat change for three coastal habitat types using scenario outputs from the birdwatching model and published results on Delta soil carbon accumulation and fishery production. The highest-ranked birdwatching models explained 88 % of the deviance and showed that visitation was greatest in winter months when distance to major cities was approximately 20 km. Recreational birdwatching increased with increasing area of forested wetland, emergent wetland, aquatic vegetation bed, open access, and total estuary. With increasing forested and emergent wetland area, recreational birdwatching, out-migrating juvenile Chinook salmon weight and soil carbon accumulation all increased. With increasing aquatic vegetation bed (resulting from sea level rise), recreational birdwatching increased, but salmon weight and soil carbon accumulation decreased. We identified practical ways in which ecosystem services may be incorporated into adaptive management frameworks that support climate adaptation decision making. This study illustrated how use of ecosystem services can help managers make decisions that have greater benefit for wildlife and people, communicate the societal value of decisions and increase local support and participation.

Washington↗
USGS2012

The influence of upper-crust lithology on topographic development in the central Coast Ranges of California

A fundamental geological tenet is that as landscapes evolve over graded to geologic time, geologic structures control patterns of topographic distribution in mountainous areas such that terrain underlain by competent rock will be higher than terrain underlain by incompetent rock. This paper shows that in active orogens where markedly weak and markedly strong rocks are juxtaposed along contacts that parallel regional structures, relatively high topography can form where strain is localized in the weak rock. Such a relationship is illustrated by the topography of the central Coast Ranges between the Pacific coastline and the San Andreas fault zone (SAFZ), and along the length of the Gabilan Mesa (the “Gabilan Mesa segment” of the central Coast Ranges). Within the Gabilan Mesa segment, the granitic upper crust of the Salinian terrane is in contact with the accretionary-prism mélange upper crust of the Nacimiento terrane along the inactive Nacimiento fault zone. A prominent topographic lineament is present along most of this lithologic boundary, approximately 50 to 65 km southwest of the SAFZ, with the higher topography formed in the mélange on the southwest side of the Nacimiento fault. This paper investigates factors influencing the pattern of topographic development in the Gabilan Mesa segment of the central Coast Ranges by correlating shortening magnitude with the upper-crust compositions of the Salinian and Nacimiento terranes. The fluvial geomorphology of two valleys in the Gabilan Mesa, which is within the Salinian terrane, and alluvial geochronology based on optically-stimulated luminescence (OSL) age estimates, reveal that the magnitude of shortening accommodated by down-to-the-southwest tilting of the mesa since 400 ka is less than 1 to 2 m. Our results, combined with those of previous studies, indicate that at least 63% to 78% of late-Cenozoic, northeast–southwest directed, upper-crustal shortening across the Gabilan Mesa segment has been accommodated within the Nacimiento terrane. This is significant because perpendicular to orogenic strike the Nacimiento terrane constitutes less than ¼ of the distance between the coast and the SAFZ, and the other ¾ (or greater) of the distance between the coast and the SAFZ is underlain by the granitic upper crust of the Salinian terrane. We propose that strain and mountain building are localized within the Nacimiento terrane because it consists predominantly of the relatively weak Franciscan Complex mélange, and because the upper crust of the Salinian terrane is composed of relatively strong granitic rocks. Our hypothesis is supported by the distribution of post-seismic surface uplift associated with the 2003, 6.5 M W San Simeon earthquake, which mimics the topography of the southwestern part of the Gabilan Mesa segment of the central Coast Ranges.

California↗
USGS2021

Evaluation of satellite imagery for monitoring Pacific walruses at a large coastal haulout

Pacific walruses ( Odobenus rosmarus divergens ) are using coastal haulouts in the Chukchi Sea more often and in larger numbers to rest between foraging bouts in late summer and autumn in recent years, because climate warming has reduced availability of sea ice that historically had provided resting platforms near their preferred benthic feeding grounds. With greater numbers of walruses hauling out in large aggregations, new opportunities are presented for monitoring the population. Here we evaluate different types of satellite imagery for detecting and delineating the peripheries of walrus aggregations at a commonly used haulout near Point Lay, Alaska, in 2018–2020. We evaluated optical and radar imagery ranging in pixel resolutions from 40 m to ~1 m: specifically, optical imagery from Landsat, Sentinel-2, Planet Labs, and DigitalGlobe, and synthetic aperture radar (SAR) imagery from Sentinel-1 and TerraSAR-X. Three observers independently examined satellite images to detect walrus aggregations and digitized their peripheries using visual interpretation. We compared interpretations between observers and to high-resolution (~2 cm) ortho-corrected imagery collected by a small unoccupied aerial system (UAS). Roughly two-thirds of the time, clouds precluded clear optical views of the study area from satellite. SAR was unaffected by clouds (and darkness) and provided unambiguous signatures of walrus aggregations at the Point Lay haulout. Among imagery types with 4–10 m resolution, observers unanimously agreed on all detections of walruses, and attained an average 65% overlap (sd 12.0, n 100) in their delineations of aggregation boundaries. For imagery with ~1 m resolution, overlap agreement was higher (mean 85%, sd 3.0, n 11). We found that optical satellite sensors with moderate resolution and high revisitation rates, such as PlanetScope and Sentinel-2, demonstrated robust and repeatable qualities for monitoring walrus haulouts, but temporal gaps between observations due to clouds were common. SAR imagery also demonstrated robust capabilities for monitoring the Point Lay haulout, but more research is needed to evaluate SAR at haulouts with more complex local terrain and beach substrates.

Alaska↗
USGS2011

LANDFIRE 2001 and 2008 Refresh Geographic Area Report--Pacific Southwest

The LANDFIRE National project (LF_1.0.0) was successfully completed in 2009. The goal of LANDFIRE National was to generate consistent 2001 vintage 30 meter spatial data sets for all 50 states for fire and other natural resource applications. This report highlights results from the continuation of LANDFIRE as a program to update the spatial data layers through 2008. The focus of this phase of the program was to improve the data products and account for vegetation change across the landscape caused by wildland fire, fuel and vegetation treatments, and (or) management. In addition, changes caused by insects and disease, storms, invasive plants, and other natural or anthropogenic events were incorporated when appropriate data were available. This report describes the LANDFIRE 2001/2008 Refresh effort to update existing map layers to reflect more current conditions, focusing primarily on vegetation changes. The effort incorporated user feedback and new data, producing two comprehensive Refresh data product sets: 1. LANDFIRE 2001 Refresh (LF_1.0.5) enhanced LANDFIRE map layers by incorporating user feedback and additional data to provide a foundation to update data to 2008. It was also designed to provide users with a data set to help facilitate comparisons between 2001 and 2008 (i.e. Refresh LF_1.1.0) data sets. 2. LANDFIRE 2008 Refresh (LF_1.1.0) updated map layers to reflect vegetation changes and disturbances that occurred between 1999 and 2008. In this report, we (1) address the background and provide details pertaining to why there are two Refresh data sets, (2) explain the requirements, planning, and procedures behind the completion and delivery of the updated products for each of the data product sets, (3) show and describe results, and (4) provide case studies illustrating the performance of LANDFIRE National, LANDFIRE 2001 Refresh and LANDFIRE 2008 Refresh (LF_1.1.0) data products on some example wildland fires.

Report↗
USGS2013

Genomic analysis of avian influenza viruses from waterfowl in Western Alaska, USA

The Yukon-Kuskokwim Delta (Y-K Delta) in western Alaska is an immense and important breeding ground for waterfowl. Migratory birds from the Pacific Americas, Central Pacific, and East Asian-Australasian flyways converge in this region, providing opportunities for intermixing of North American- and Eurasian-origin hosts and infectious agents, such as avian influenza virus (AIV). We characterized the genomes of 90 low pathogenic (LP) AIV isolates from 11 species of waterfowl sampled on the Y-K Delta between 2006 and 2009 as part of an interagency surveillance program for the detection of the H5N1 highly pathogenic (HP) strain of AIV. We found evidence for subtype and genetic differences between viruses from swans and geese, dabbling ducks, and sea ducks. At least one gene segment in 39% of all isolates was Eurasian in origin. Target species (those ranked as having a relatively high potential to introduce HP H5N1 AIV to North America) were no more likely than nontarget species to carry viruses with genes of Eurasian origin. These findings provide evidence that the frequency at which viral gene segments of Eurasian origin are detected does not result from a strong species effect, but rather we suspect it is linked to the geographic location of the Y-K Delta in western Alaska where flyways from different continents overlap. This study provides support for retaining the Y-K Delta as a high priority region for the surveillance of Asian avian pathogens such as HP H5N1 AIV.

Alaska↗
USGS2009

Linking marine and freshwater growth in western Alaska Chinook salmon Oncorhynchus tshawytscha

The hypothesis that growth in Pacific salmon Oncorhynchus spp. is dependent on previous growth was tested using annual scale growth measurements of wild Chinook salmon Oncorhynchus tshawytscha returning to the Yukon and Kuskokwim Rivers, Alaska, from 1964 to 2004. First-year marine growth in individual O. tshawytscha was significantly correlated with growth in fresh water. Furthermore, growth during each of 3 or 4 years at sea was related to growth during the previous year. The magnitude of the growth response to the previous year's growth was greater when mean year-class growth during the previous year was relatively low. Length (eye to tail fork, LETF) of adult O. tshawytscha was correlated with cumulative scale growth after the first year at sea. Adult LETF was also weakly correlated with scale growth that occurred during freshwater residence 4 to 5 years earlier, indicating the importance of growth in fresh water. Positive growth response to previous growth in O. tshawytscha was probably related to piscivorous diet and foraging benefits of large body size. Faster growth among O. tshawytscha year classes that initially grew slowly may reflect high mortality in slow growing fish and subsequent compensatory growth in survivors. Oncorhynchus tshawytscha in this study exhibited complex growth patterns showing a positive relationship with previous growth and a possible compensatory response to environmental factors affecting growth of the age class.

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