SEARCH · USGS Science

Results for “Structure”

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

SourceResearch connectionFrom yearThrough year

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

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

USGS2018

Efficiently optimizing for dendritic connectivity on tree-structured networks in a multi-objective framework

We provide an exact and approximation algorithm based on Dynamic Programming and an approximation algorithm based on Mixed Integer Programming for optimizing for the so-called dendritic connectivity on tree-structured networks in a multi-objective setting. Dendritic connectivity describes the degree of connectedness of a network. We consider different variants of dendritic connectivity to capture both network connectivity with respect to long and short-to-middle distances. Our work is motivated by a problem in computational sustainability concerning the evaluation of trade-offs in ecosystem services due to the proliferation of hydropower dams throughout the Amazon basin. In particular, we consider trade-offs between energy production and river connectivity. River fragmentation can dramatically affect fish migrations and other ecosystem services, such as navigation and transportation. In the context of river networks, different variants of dendritic connectivity are important to characterize the movements of different fish species and human populations. Our approaches are general and can be applied to optimizing for dendritic connectivity for a variety of multi-objective problems on tree-structured networks.

Conference Paper↗

USGS2025

Red spruce forest stand structure and Virginia northern flying squirrel habitat suitability

The Virginia northern flying squirrel ( Glaucomys sabrinus fuscus ; VNFS) is a rare, Pleistocene-relict, disjunct subspecies of the northern flying squirrel. The squirrel occurs only in high-elevation red spruce ( Picea rubens ) forests of the central Appalachian Mountains of Virginia and West Virginia—a forest type that was substantially reduced by exploitative logging and wildfire in the 1890s–1930. Owing to its cryptic nature and difficulty of capture, managers have relied on an evolving series of predicted habitat suitability models that primarily have used topographic measures and red spruce cover class to assess potential occupancy on the landscape. Currently, VNFS is considered the sentinel species in the region whereby its predicted presence indicates red spruce forests with higher relative habitat integrity, and unsuitable habitat highlights where red spruce restoration or enhancement should occur. However, extant VNFS models only use red spruce percent composition and do not provide insights into forest structure, such as forest canopy height or basal area, that are needed by managers to implement restoration or assess effectiveness. We examined recent historical VNFS observations from nest-box surveys and radiotelemetry data (natural dens and foraging points) relative to random pseudoabsence points across red spruce cover classes from the most current VNFS predicted probability habitat model. Using generalized linear models in an information-theoretic approach, we found that within each red spruce composition class, suitable VNFS habitat was related to increased forest canopy height (m), basal area (m 2 ·ha −1 ), quadratic mean diameter (cm), and stem density (number of trees ha −1 ), indicating that, within red spruce and mixed red spruce–northern hardwood forests, VNFS is associated most with mature forest conditions. Accordingly, our results could be recombined with habitat suitability models to prioritize where, for example, red spruce forest structural enhancement would facilitate shifting a given stand to a higher probability condition for VNFS use.

Maryland, Virginia, West Virginia↗

USGS2008

Diagnosis of an intense atmospheric river impacting the pacific northwest: Storm summary and offshore vertical structure observed with COSMIC satellite retrievals

This study uses the new satellite-based Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission to retrieve tropospheric profiles of temperature and moisture over the data-sparse eastern Pacific Ocean. The COSMIC retrievals, which employ a global positioning system radio occultation technique combined with "first-guess" information from numerical weather prediction model analyses, are evaluated through the diagnosis of an intense atmospheric river (AR; i.e., a narrow plume of strong water vapor flux) that devastated the Pacific Northwest with flooding rains in early November 2006. A detailed analysis of this AR is presented first using conventional datasets and highlights the fact that ARs are critical contributors to West Coast extreme precipitation and flooding events. Then, the COSMIC evaluation is provided. Offshore composite COSMIC soundings north of, within, and south of this AR exhibited vertical structures that are meteorologically consistent with satellite imagery and global reanalysis fields of this case and with earlier composite dropsonde results from other landfalling ARs. Also, a curtain of 12 offshore COSMIC soundings through the AR yielded cross-sectional thermodynamic and moisture structures that were similarly consistent, including details comparable to earlier aircraft-based dropsonde analyses. The results show that the new COSMIC retrievals, which are global (currently yielding ???2000 soundings per day), provide high-resolution vertical-profile information beyond that found in the numerical model first-guess fields and can help monitor key lower-tropospheric mesoscale phenomena in data-sparse regions. Hence, COSMIC will likely support a wide array of applications, from physical process studies to data assimilation, numerical weather prediction, and climate research. ?? 2008 American Meteorological Society.

Monthly Weather Review↗

USGS2018

Genetic diversity and structure from Antillean manatee (Trichechus manatus manatus) in the southern Gulf of Mexico: Comparison between connected and isolated populations

Antillean manatees ( Trichechus manatus manatus ), a subspecies of the West Indian manatee, is listed as endangered species in the Red List of Threatened Species of the International Union for Conservation of Nature. The aims of this research were to survey on the possible regional genetic structure in the southern Gulf of Mexico and to compare genetic status of a landlocked population in Laguna de las Ilusiones (IL) with individuals from localities with no barriers to displacement and breed (open population [OP]). We analyzed 45 manatee skin samples collected from different locations in Tabasco ( n = 38, including 19 from IL), Veracruz ( n = 3), Campeche ( n = 2), and Chiapas ( n = 2). The genomic DNA was isolated and PCR amplifications were performed for each sample using 28 microsatellite loci, previously designed for West Indian manatees and described as polymorphic for this species. Two clusters ( k = 2) were identified by STRUCTURE. The analysis of both a priori populations (IL and OP) indicate that the global values of F ST and R ST ( F ST =0.049, R ST =0.077) were significant. The H E for IL was 0.38 ± 0.03 and for OP was 0.49 ± 0.01. The average number of alleles N A for IL was 2.21 ± 0.09 and for OP was 2.32 ± 0.09. The overall inbreeding coefficient was F IS =−0.013 for analyzed populations. Genetic diversity was low. The IL population had slightly lower genetic diversity compared with OP, which could be explained by isolation of that small group, so conservation plans for IL should be considered as priority.

Tropical Conservation Science↗

USGS2008

Genetic structure along an elevational gradient in Hawaiian honeycreepers reveals contrasting evolutionary responses to avian malaria

Background. The Hawaiian honeycreepers (Drepanidinae) are one of the best-known examples of an adaptive radiation, but their persistence today is threatened by the introduction of exotic pathogens and their vector, the mosquito Culex quinquefasciatus. Historically, species such as the amakihi (Hemignathus virens), the apapane (Himatione sanguinea), and the iiwi (Vestiaria coccinea) were found from the coastal lowlands to the high elevation forests, but by the late 1800's they had become extremely rare in habitats below 900 m. Recently, however, populations of amakihi and apapane have been observed in low elevation habitats. We used twelve polymorphic microsatellite loci to investigate patterns of genetic structure, and to infer responses of these species to introduced avian malaria along an elevational gradient on the eastern flanks of Mauna Loa and Kilauea volcanoes on the island of Hawaii. Results. Our results indicate that amakihi have genetically distinct, spatially structured populations that correspond with altitude. We detected very few apapane and no iiwi in low-elevation habitats, and genetic results reveal only minimal differentiation between populations at different altitudes in either of these species. Conclusion. Our results suggest that amakihi populations in low elevation habitats have not been recolonized by individuals from mid or high elevation refuges. After generations of strong selection for pathogen resistance, these populations have rebounded and amakihi have become common in regions in which they were previously rare or absent. ?? 2008 Eggert et al; licensee BioMed Central Ltd.

BMC Evolutionary Biology↗

USGS2018

New insights into the phylogenetics and population structure of the prairie falcon (Falco mexicanus)

Background Management requires a robust understanding of between- and within-species genetic variability, however such data are still lacking in many species. For example, although multiple population genetics studies of the peregrine falcon ( Falco peregrinus ) have been conducted, no similar studies have been done of the closely-related prairie falcon ( F. mexicanus ) and it is unclear how much genetic variation and population structure exists across the species’ range. Furthermore, the phylogenetic relationship of F. mexicanus relative to other falcon species is contested. We utilized a genomics approach (i.e., genome sequencing and assembly followed by single nucleotide polymorphism genotyping) to rapidly address these gaps in knowledge. Results We sequenced the genome of a single female prairie falcon and generated a 1.17 Gb (gigabases) draft genome assembly. We generated maximum likelihood phylogenetic trees using complete mitochondrial genomes as well as nuclear protein-coding genes. This process provided evidence that F. mexicanus is an outgroup to the clade that includes the peregrine falcon and members of the subgenus Hierofalco. We annotated > 16,000 genes and almost 600,000 high-quality single nucleotide polymorphisms (SNPs) in the nuclear genome, providing the raw material for a SNP assay design featuring > 140 gene-associated markers and a molecular-sexing marker. We subsequently genotyped ~ 100 individuals from California (including the San Francisco East Bay Area, Pinnacles National Park and the Mojave Desert) and Idaho (Snake River Birds of Prey National Conservation Area). We tested for population structure and found evidence that individuals sampled in California and Idaho represent a single panmictic population. Conclusions Our study illustrates how genomic resources can rapidly shed light on genetic variability in understudied species and resolve phylogenetic relationships. Furthermore, we found evidence of a single, randomly mating population of prairie falcons across our sampling locations. Prairie falcons are highly mobile and relatively rare long-distance dispersal events may promote gene flow throughout the range. As such, California’s prairie falcons might be managed as a single population, indicating that management actions undertaken to benefit the species at the local level have the potential to influence the species as a whole.

BMC Genomics↗

USGS2024

Population structure of Desmophyllum pertusum found along the United States eastern continental margin

Objective The connectivity and genetic structuring of populations throughout a region influence a species’ resilience and probability of recovery from anthropogenic impacts. By gaining a comprehensive understanding of population connectivity, more effective management can be prioritized. To assess the connectivity and population genetic structure of a common cold-water coral species, Desmophyllum pertusum ( Lophelia pertusa ), we performed Restriction-site Associated DNA Sequencing (RADseq) on individuals from nine sites ranging from submarine canyons off New England to the southeastern coast of the United States (SEUS) and the Gulf of Mexico (GOM). Fifty-seven individuals and 3,180 single-nucleotide polymorphisms (SNPs) were used to assess genetic differentiation. Results High connectivity exists among populations along the SEUS, yet these populations were differentiated from those to the north off New England and in Norfolk Canyon along the North Atlantic coast of the United States, as well as those in the GOM. Interestingly, Norfolk Canyon, located just north of North Carolina, and GOM populations exhibited low levels of genetic differentiation, corroborating previous microsatellite analyses and signifying gene flow between these populations. Increasing sample sizes from existing populations and including additional sampling sites over a larger geographic range would help define potential source populations and reveal fine-scale connectivity patterns among D. pertusum populations.

Atlantic coastal margin↗

USGS2010

Recorded motions of the 6 April 2009 Mw 6.3 L'Aquila, Italy, earthquake and implications for building structural damage: Overview

The normal-faulting earthquake of 6 April 2009 in the Abruzzo Region of central Italy caused heavy losses of life and substantial damage to centuriesold buildings of significant cultural importance and to modern reinforcedconcrete- framed buildings with hollow masonry infill walls. Although structural deficiencies were significant and widespread, the study of the characteristics of strong motion data from the heavily affected area indicated that the short duration of strong shaking may have spared many more damaged buildings from collapsing. It is recognized that, with this caveat of shortduration shaking, the infill walls may have played a very important role in preventing further deterioration or collapse of many buildings. It is concluded that better new or retrofit construction practices that include reinforcedconcrete shear walls may prove helpful in reducing risks in such seismic areas of Italy, other Mediterranean countries, and even in United States, where there are large inventories of deficient structures. ?? 2010, Earthquake Engineering Research Institute.

Earthquake Spectra↗

USGS2014

Estimating structural collapse fragility of generic building typologies using expert judgment

The structured expert elicitation process proposed by Cooke (1991), hereafter referred to as Cooke’s approach, is applied for the first time in the realm of structural collapse-fragility assessment for selected generic construction types. Cooke’s approach works on the principle of objective calibration scoring of judgments coupled with hypothesis testing used in classical statistics. The performance-based scoring system reflects the combined measure of an expert’s informativeness about variables in the problem area under consideration, and their ability to enumerate, in a statistically accurate way through expressing their true beliefs, the quantitative uncertainties associated with their assessments. We summarize the findings of an expert elicitation workshop in which a dozen earthquake-engineering professionals from around the world were engaged to estimate seismic collapse fragility for generic construction types. Development of seismic collapse fragility functions was accomplished by combining their judgments using weights derived from Cooke’s method. Although substantial effort was needed to elicit the inputs of these experts successfully, we anticipate that the elicitation strategy described here will gain momentum in a wide variety of earthquake seismology and engineering hazard and risk analyses where physical model and data limitations are inherent and objective professional judgment can fill gaps.

Conference Paper↗

USGS1996

Structure, stratigraphy, and petroleum geology of the Little Plain basin, northwestern Hungary

The basement of the Little Plain (Kisalfold) basin is composed of two parts: an eastern part comprised of folded and overthrusted Triassic and Paleozoic rocks of the Pelso block (Transdanubian Central Range) compressed in the Early Cretaceous, and a western part consisting of stacked nappes of the Austroalpine zone of Paleozoic rocks, significantly metamorphosed during Cretaceous and later compression, overriding Jurassic oceanic rift-zone rocks of the Penninic zone. The evolution of the basin began in the late Karpatian-early Badenian (middle Miocene) when the eastern part of the basin began to open along conjugate sets of northeast- and northwest-trending normal faults. Neogene rocks in the study area, on the average, contain less than 0.5 wt. % total organic carbon (TOC) and, therefore, are not considered effective source rocks. Locally, however, where TOC values are as high as 3 wt. %, significant amounts of gas may have been generated and expelled. Although potential stratigraphic traps are numerous in the Neogene section, these potential traps must be downgraded because of the small amount of hydrocarbons discovered in structural traps to date. With the exception of the Cretaceous, the Mesozoic section has not been actively explored. Large anticlinal and overthrust structures involving pre-Cretaceous strata remain undrilled.

Little Plain basin↗

USGS1974

Structural framework of United States Atlantic outer continental shelf north of Cape Hatteras

To assess the area’s hydrocarbon potential, regional geologic and geophysical studies are being conducted by the U.S. Geological Survey to determine the structural framework of the United States Atlantic outer continental shelf (AOCS) north of Cape Hatteras. Preliminary interpretations of geophysical data suggest that the buried ridge under the eastern edge of the AOCS in the Baltimore Canyon trough area is deeper and farther west than previously suspected. Although it is not observed under the seaward extension of the Cape Fear arch, this ridge can be traced from the south side of the Baltimore Canyon trough northeastward toward the eastern edge of the Georges Bank trough. In the Baltimore Canyon trough area, the ridge seems to be fault controlled and to form the eastern edge of a Mesozoic depocenter in which approximately 12 km of relatively undisturbed post-Paleozoic sediments accumulated. Below a depth of 6 km, rocks previously considered to be crystalline basement instead may be carbonate and/or evaporite sequences of Jurassic age or older which overlie an even deeper crystalline basement. More than 8 km of sediments are present beneath the continental shelf on Georges Bank. The preliminary regional geophysical studies indicate that thick marine sedimentary sections and geologic structures favorable for the accumulation of petroleum apparently exist under the AOCS off the northeastern part of the United States.

Atlantic outer continental shelf↗

USGS1985

Seismic structure and stratigraphy of northern edge of Bahaman-Cuban collision zone

Common-depth-point (CDP) seismic reflection data in the southwestern Bahamas reveal the northern edge of the tectonized zone that resulted from the late Mesozoic-early Cenozoic collision of Cuba and the Bahamas. Two seismic facies are present: a basin facies and a shallow-water carbonate-platform facies. In Santaren Channel, between Cay Sal and the Great Bahama Bank, a 5-sec thick group of coherent flat-lying reflections is inferred to represent an accumulation of deep-water basinal carbonate deposits approximately 10 km thick. At the southern end of Santaren Channel and in Nicholas Channel toward the west, the basinal carbonate section thins abruptly and overlies zones that lack coherent reflections. These structureless zones, which are attended by positive gravity anoma ies, are inferred to represent shallow-water carbonate-platform materials. Neither seismic facies has associated short wavelength magnetic anomalies. A 10-km broad anticline occurs at the south end of Santaren Channel. Platform carbonates in the core of this structure overlie Early Cretaceous and older basinal carbonate deposits and are onlapped by Late Cretaceous and Cenozoic basinal facies. The structure is inferred to be a hanging-wall anticline at the northern limit of the Cuban fold-thrust belt formed in the Late Cretaceous. In eastern Nicholas Channel, a 40-km broad, tilted block of platform carbonate material appears to have been uplifted prior to the latest Cretaceous. This feature is onlapped by Upper Cretaceous and Cenozoic deposits. A depositional-erosional carbonate-platform edge of Early Cretaceous age occurs in western Nicholas Channel at its juncture with the Straits of Florida. An Early Cretaceous platform margin at this location indicates that a deeper water embayment extended northward into the Straits of Florida, around northern Cay Sal Bank, and back into Santaren Channel during the Early Cretaceous.

American Association of Petroleum Geologists Bulle↗

USGS2024

Crystal structure refinement and Mössbauer spectroscopy of an ordered, triclinic clinochlore

The crystal structure of a natural, ordered IIb-4 triclinic clinochlore has been refined in space group C 1¯ from 4282 unique X-ray intensity measurements of which 3833 are greater than 3 times the statistical counting error (3σ). Unit cell parameters are a = 5.3262(6) Å; b = 9.226(1) Å; c = 14.334(3) Å; α = 90.56(2)°; β = 97.47(2)°; and γ = 89.979(9)°, which represents the greatest deviation from monoclinic symmetry yet recorded for a triclinic chlorite. The final weighted R is 0.059 for reflections with I > 3σ and 0.064 for all reflections. The chemical formula is (Mg 0.966 Fe 0.034 ) M1 (Mg 0.962 Fe 0.038 ) M2 2 (Si 2.96 Al 1.04 )O 10 (OH) 2 (Mg 0.996 Fe 0.004 ) M3 2 (Al 0.841 Fe III 0.102 Cr 0.004 Ti 0.004 ) M4 (OH) 6 , which is consistent with electron microprobe (EMP), wet chemical analyses, Mössbauer spectroscopy and X-ray structure refinement. The high degree of ordering of the divalent versus trivalent octahedral cations in the interlayer is noteworthy, with Fe III and Al in M4 and virtually no Fe in M3. In the 2:1 layer, M1 and M2 each contain similar amounts of Fe. The 2 tetrahedral sites have nearly identical mean oxygen distances and volumes, and thus show no evidence of long-range cation ordering.

Clays and Clay Minerals↗

USGS2009

Hierarchical spatial genetic structure of Common Eiders ( Somateria mollissima ) breeding along a migratory corridor

Documentation of spatial genetic discordance among breeding populations of Arctic-nesting avian species is important, because anthropogenic change is altering environmental linkages at micro- and macrogeographic scales. We estimated levels of population subdivision within Pacific Common Eiders ( Somateria mollissima v-nigrum ) breeding on 12 barrier islands in the western Beaufort Sea, Alaska, using molecular markers and capture—mark—recapture (CMR) data. Common Eider populations were genetically structured on a microgeographic scale. Regional comparisons between populations breeding on island groups separated by 90 km (Mikkelsen Bay and Simpson Lagoon) revealed structuring at 14 microsatellite loci ( F ST = 0.004, P < 0.01), a nuclear intron ( F ST = 0.022, P = 0.02), and mitochondrial DNA (Φ ST = 0.082, P < 0.05). The CMR data ( n = 34) did not indicate female dispersal between island groups. Concordance between genetic and CMR data indicates that females breeding in the western Beaufort Sea are strongly philopatric to island groups rather than to a particular island. Despite the apparent high site fidelity of females, coalescence-based models of gene flow suggest that asymmetrical western dispersal occurs between island groups and is likely mediated by Mikkelsen Bay females stopping early on spring migration at Simpson Lagoon to breed. Alternatively, late-arriving females may be predisposed to nest in Simpson Lagoon because of the greater availability and wider distribution of nesting habitat. Our results indicate that genetic discontinuities, mediated by female philopatry, can exist at microgeographic scales along established migratory corridors.

The Auk↗

USGS2010

Subspecies status and population genetic structure in Piping Plover ( Charadrius melodus )

Piping Plover (Charadrius melodus) is a migratory shorebird that is listed as endangered in Canada and the U.S. Great Lakes and as threatened throughout the rest of its breeding and winter range. We undertook a comprehensive molecular-genetic investigation to (1) address subspecific taxonomy, (2) characterize population genetic structure, and (3) infer past bottlenecks and demographic processes in this species. Analyses included individuals from 23 U.S. states and Canadian provinces and were based on mitochondrial DNA sequences (580 base pairs, n = 245) and 8 nuclear microsatellite loci (n = 229). Our findings provide support for separate Atlantic and Interior subspecies (C. m. melodus and C. m. circumcinctus, respectively). Birds from the Great Lakes region were allied with the Interior subspecies and should be referred to as C. m. circumcinctus. Population genetic analyses illustrated stronger genetic structure among Atlantic than among Interior birds, which may reflect reduced natal- and breeding-site fidelity of Interior individuals. Furthermore, analyses suggested that Interior birds previously experienced genetic bottlenecks, whereas there was no evidence of such patterns in the Atlantic subspecies. We interpret these results in light of 25 years of range-wide census data. Overall, differences between Interior and Atlantic Piping Plovers may reflect differences in spatiotemporal stability of nesting habitat between regions. ?? 2010 The American Ornithologists' Union.

The Auk↗

USGS2000

Associations among fish assemblage structure and environmental variables in Willamette Basin streams, Oregon

As part of the U.S. Geological Survey's National Water-Quality Assessment Program, fish were collected from 24 selected stream sites in the Willamette Basin during 1993-1995 to determine the composition of the fish assemblages and their relation to the chemical and physical environment. Variance in fish relative abundance was greater among all sites than among spatially distinct reaches within a site (spatial variation) or among multiple sampled years at a site (temporal variation). Therefore, data from a single reach in an individual year was considered to be a reliable estimator of the fish assemblage structure at a site when the data were normalized by percent relative abundance. Multivariate classification and ordination were used to examine patterns in environmental variables and fish relative abundance over differing spatial scales (among versus within ecoregions). Across all ecoregions (all sites), fish assemblages were primarily structured along environmental gradients of water temperature and stream gradient (coldwater, high-gradient forested sites versus warmwater, low-gradient Willamette Valley sites); this pattern superseded patterns that were ecoregion specific. Water temperature, dissolved oxygen, and physical habitat (e.g., riparian canopy and percent riffles) were associated with patterns of fish assemblages across all ecoregions; however, pesticide and total phosphorus concentrations were more important than physical habitat within the Willamette Valley ecoregion. Consideration of stream site stratification (e.g., stream size, ecoregion, and stream gradient), identification of fish to species level (particularly the sculpin family), and detailed measurement of habitat, diurnal dissolved oxygen, and water temperature were critical in evaluating the composition of fish assemblages in relation to land use. In general, these low-gradient valley streams typical of other agricultural regions had poor riparian systems and showed increases in water temperature, nutrients, and fine grain sediments that were associated with degradation in the native fish assemblages. There was an association of high abundances of introduced species and high percent external abnormalities in medium-sized river sites of mixed land use and high abundances of tolerant species in small streams of predominantly agricultural land use.

Oregon↗

USGS2003

Assessing the efficacy of single-pass backpack electrofishing to characterize fish community structure

Two-pass backpack electrofishing data collected as part of the U.S. Geological Survey's National Water-Quality Assessment Program were analyzed to assess the efficacy of single-pass backpack electrofishing. A two-capture removal model was used to estimate, within 10 river basins across the United States, proportional fish species richness from one-pass electrofishing and probabilities of detection for individual fish species. Mean estimated species richness from first-pass sampling (p s1 ) ranged from 80.7% to 100% of estimated total species richness for each river basin, based on at least seven samples per basin. However, p s1 values for individual sites ranged from 40% to 100% of estimated total species richness. Additional species unique to the second pass were collected in 50.3% of the samples. Of these, cyprinids and centrarchids were collected most frequently. Proportional fish species richness estimated for the first pass increased significantly with decreasing stream width for 1 of the 10 river basins. When used to calculate probabilities of detection of individual fish species, the removal model failed 48% of the time because the number of individuals of a species was greater in the second pass than in the first pass. Single-pass backpack electrofishing data alone may make it difficult to determine whether characterized fish community structure data are real or spurious. The two-pass removal model can be used to assess the effectiveness of sampling species richness with a single electrofishing pass. However, the two-pass removal model may have limited utility to determine probabilities of detection of individual species and, thus, limit the ability to assess the effectiveness of single-pass sampling to characterize species relative abundances. Multiple-pass (at least three passes) backpack electrofishing at a large number of sites may not be cost-effective as part of a standardized sampling protocol for large-geographic-scale studies. However, multiple-pass electrofishing at some sites may be necessary to better evaluate the adequacy of single-pass electrofishing and to help make meaningful interpretations of fish community structure.

Transactions of the American Fisheries Society↗

USGS2005

Temporal and spatial variation in relative abundance and length structure of salmonids in reservoirs: Implications for monitoring

Spatial and temporal variations in salmonid catch per unit effort (C/f) may affect monitoring efforts in lakes and reservoirs. This study evaluated the spatial and temporal variation in gill-net C/f and length structure of captured salmonids in nearshore (???7.6-m bottom depth) and offshore (>7.6-m bottom depth) areas of two Wyoming reservoirs. Floating experimental gill nets were set as nearshore and offshore pairs at 24 locations in both reservoirs during each of four sampling periods (spring, early summer, late summer, and fall). Salmonid C/f was significantly higher in nearshore areas than in offshore areas during all periods in one reservoir and during all periods except spring in the other reservoir. Mean C/f of rainbow trout Oncorhynchus mykiss was not significantly different between nearshore and offshore areas when water temperatures were 10-13??C in both reservoirs. Length structure of salmonids differed significantly between nearshore and offshore locations and among periods in both reservoirs. These patterns should be considered in both the design and analysis phases of monitoring efforts that use floating experimental gill nets and other sampling gears. ?? Copyright by the American Fisheries Society 2005.

North American Journal of Fisheries Management↗