The importance of survey design in distance sampling: field evaluation using domestic sheep

2011 ◽  
Vol 38 (3) ◽  
pp. 221 ◽  
Author(s):  
Tom A. Porteus ◽  
Suzanne M. Richardson ◽  
Jonathan C. Reynolds
Keyword(s):  
Population Size ◽  
Survey Design ◽  
Distance Sampling ◽  
Field Evaluation ◽  
Stage I ◽  
Stage Ii ◽  
Line Transect ◽  
Domestic Sheep ◽  
Management Decisions ◽  
Mobile Species

Context Sampling methods to estimate animal density require good survey design to ensure assumptions are met and sampling is representative of the survey area. Management decisions are often made based on these estimates. However, without knowledge of true population size it is not possible for wildlife biologists to evaluate how biased the estimates can be if survey design is compromised. Aims Our aims were to use distance sampling to estimate population size for domestic sheep free-ranging within large enclosed areas of hill country and, by comparing estimates against actual numbers, examine how bias and precision are impaired when survey design is compromised. Methods We used both line and point transect sampling to derive estimates of density for sheep on four farms in upland England. In Stage I we used limited effort and different transect types to compromise survey design. In Stage II we increased effort in an attempt to improve on the Stage I estimates. We also examined the influence of a walking observer on sheep behaviour to assess compliance with distance sampling assumptions and to improve the fit of models to the data. Key results Our results show that distance sampling can lead to biased and imprecise density estimates if survey design is poor, particularly when sampling high density and mobile species that respond to observer presence. In Stage I, walked line transects were least biased; point transects were most biased. Increased effort in Stage II reduced the bias in walked line transect estimates. For all estimates, the actual density was within the derived 95% confidence intervals, but some of these spanned a range of over 100 sheep per km2. Conclusions Using a population of known size, we showed that survey design is vitally important in achieving unbiased and precise density estimation using distance sampling. Adequate transect replication reduced the bias considerably within a compromised survey design. Implications Management decisions based on poorly designed surveys must be made with an appropriate understanding of estimate uncertainty. Failure to do this may lead to ineffective management.

scholarly journals The influence of animal mobility on the assumption of uniform distances in aerial line-transect surveys

2008 ◽  
Vol 35 (4) ◽  
pp. 275 ◽  
Author(s):  
Rachel M. Fewster ◽  
Colin Southwell ◽  
David L. Borchers ◽  
Stephen T. Buckland ◽  
Anthony R. Pople
Keyword(s):  
Survey Design ◽  
Distance Sampling ◽  
High Mobility ◽  
Line Transect ◽  
Transect Line ◽  
Aerial Surveys ◽  
Pack Ice ◽  
Capture Recapture ◽  
Distance Data ◽  
Crabeater Seals

Line-transect distance sampling is a widely used method for estimating animal density from aerial surveys. Analysis of line-transect distance data usually relies on a requirement that the statistical distribution of distances of animal groups from the transect line is uniform. We show that this requirement is satisfied by the survey design if all other assumptions of distance sampling hold, but it can be violated by consistent survey problems such as responsive movement of the animals towards or away from the observer. We hypothesise that problems with the uniform requirement are unlikely to be encountered for immobile taxa, but might become substantial for species of high mobility. We test evidence for non-uniformity using double-observer distance data from two aerial surveys of five species with a spectrum of mobility capabilities and tendencies. No clear evidence against uniformity was found for crabeater seals or emperor penguins on the pack-ice in East Antarctica, while minor non-uniformity consistent with responsive movement up to 30 m was found for Adelie penguins. Strong evidence of either non-uniformity or a failure of the capture–recapture validating method was found for eastern grey kangaroos and red kangaroos in Queensland.

Precision, accuracy and bias of walked line-transect distance sampling to estimate eastern grey kangaroo population size

2015 ◽  
Vol 42 (8) ◽  
pp. 633 ◽  
Author(s):  
Ruth Glass ◽  
David M. Forsyth ◽  
Graeme Coulson ◽  
Marco Festa-Bianchet
Keyword(s):  
Population Size ◽  
Distance Sampling ◽  
Accurate Method ◽  
Line Transect ◽  
Good Precision ◽  
Design Elements ◽  
Abundance Estimates ◽  
Grey Kangaroo ◽  
Eastern Australia ◽  
Free Ranging

Context Distance sampling is widely used to estimate the size of wildlife populations, including kangaroos. However, the performance of distance-sampling abundance estimates has seldom been evaluated for wild mammal populations of known size. Aims We evaluated the precision, accuracy, bias and interval coverage of abundance estimates from walked line-transect sampling, a commonly used distance-sampling method, for a marked free-ranging population of eastern grey kangaroos (Macropus giganteus) at Yanakie Isthmus, Wilsons Promontory National Park, south-eastern Australia. Methods In each of two study periods (November 2012 and May 2013) we first determined the true size of the uniquely marked kangaroo population by conducting 10 intensive searches of the study area. We then conducted distance sampling along six systematically spaced line transects. We walked each transect four times in November 2012 and seven times in May 2013. Data were analysed using Program DISTANCE. Key results Our intensive searches revealed that 141 and 124 collared kangaroos were present in the study area in November 2012 and May 2013, respectively. When transects were walked four or more times (i.e. ≥400 observations), maximum precision (coefficient of variation; CV of ~13%) was achieved in both survey periods. Walking transects twice (i.e. ~200 observations) produced abundance estimates with CVs of <20% in each study period. The accuracy (root mean square error) of abundance estimates varied from 1 to 13 (November 2012) and from 3 to 28 (May 2013). Bias ranged from −9% to +23%, but stabilised at between −1% and −9% when transects were walked four or more times in each study period. The 95% confidence intervals for the abundance estimates always included the true population size. Conclusions Our results indicated that walked line-transect distance sampling is a precise and accurate method for estimating eastern grey kangaroo abundance. The small negative biases that occurred when sample sizes were large were likely to be due to some animals moving outside the study area. Implications Provided that the key design elements and assumptions are met, estimates of kangaroo abundance from walked line-transect distance sampling should have good precision (CV < 20%) and minimal (<10%) bias.

scholarly journals Aerial line transect survey to estimate abundance of marsh deer (Blastocerus dichotomus) (Illiger, 1815)

2005 ◽  
Vol 48 (5) ◽  
pp. 807-814 ◽  
Author(s):  
Artur Andriolo ◽  
Ubiratan Piovezan ◽  
Mateus José Rodrigues Paranhos da Costa ◽  
Jeff Laake ◽  
José Maurício Barbanti Duarte
Keyword(s):  
Population Size ◽  
River Basin ◽  
Distance Sampling ◽  
Aerial Survey ◽  
Line Transect ◽  
Sampling Methodology ◽  
Future Analysis ◽  
Line Transect Survey ◽  
Blastocerus Dichotomus ◽  
The Impact

The objective was to estimate abundance of marsh deer in the Paraná River basin of this work. The results provided information to support further analysis of the impact of the Porto Primavera flooding lake over population. Sixty-nine animals were recorded by aerial survey using distance sampling methodology. Animals were widely distributed throughout the study area. The uncorrected data resulted in a estimate density of 0.0035 ind/ha and a population size of 636 individuals. Correcting the g for the animals that could be missed the calculated abundance was 896 (CV=0.27) individuals. This methodology was applied with success to survey marsh deer. The result was important to evaluate the marsh deer status in the area, and for future analysis of the impact of the flooding dam.

scholarly journals Shifting trends: Detecting changes in cetacean population dynamics in shifting habitat

PLoS ONE ◽  
2021 ◽  
Vol 16 (5) ◽  
pp. e0251522
Author(s):  
Charlotte Boyd ◽  
André E. Punt
Keyword(s):  
Population Dynamics ◽  
Population Size ◽  
Wildlife Conservation ◽  
Population Change ◽  
Stock Assessment ◽  
Distance Sampling ◽  
Distribution Patterns ◽  
Population Trend ◽  
Mobile Species ◽  
Population Size Estimates

The ability to monitor population dynamics and detect major changes in population trend is essential for wildlife conservation and management. However, this is often challenging for cetaceans as surveys typically cover only a portion of a population’s range and conventional stock assessment methods cannot then distinguish whether apparent changes in abundance reflect real changes in population size or shifts in distribution. We developed and tested methods for estimating population size and trend and detecting changes in population trend in the context of shifting habitat by integrating additional data into distance-sampling analysis. Previous research has shown that incorporating habitat information can improve population size estimates for highly mobile species with dynamic spatial distributions. Here, using simulated datasets representative of a large whale population, we demonstrate that incorporating individual mark-recapture data can increase the accuracy and precision of trend estimation and the power to distinguish whether apparent changes in abundance reflect changes in population trend or distribution shifts. We recommend that similar simulation studies are conducted for specific cetacean populations to assess the potential for detecting changes in population dynamics given available data. This approach is especially important wherever population change may be confounded with long-term change in distribution patterns associated with regime shifts or climate change.

Estimating the population size of a threatened arboreal marsupial: use of distance sampling to dispense with ad hoc survey techniques

2010 ◽  
Vol 37 (6) ◽  
pp. 512 ◽  
Author(s):  
Paul J. de Tores ◽  
Sue Elscot
Keyword(s):  
Land Use ◽  
Population Size ◽  
Ad Hoc ◽  
Conservation Status ◽  
Distance Sampling ◽  
Potential Effect ◽  
Decision Makers ◽  
Biological Information ◽  
Line Transect ◽  
Land Use Decisions

Context. Long-term land-use decisions potentially affecting the conservation status of rare fauna are often based on a dearth of relevant biological information and population estimates are regularly derived from ad hoc methodologies. This can significantly affect the outcomes from development assessment and approval processes. Aim. Our aims were to apply distance-sampling techniques to derive robust, quantitative estimates of the population size of a threatened arboreal marsupial, the western ringtail possum (Pseudocheirus occidentalis Thomas, 1888), demonstrate the advantages of this approach and, in doing so, provide conservation managers, decision makers and consultants with a reliable framework for surveying the species. Methods. We used line-transect sampling to derive estimates of density and abundance for P. occidentalis at two sites in south-western Western Australia where estimates were previously derived through ad hoc techniques. Key results. Our findings support the assertion that previous surveys of P. occidentalis populations have underestimated the population size to a varying extent at both of our survey sites. Land-use and development-application decisions have previously been based on similar surveys. Conclusions. Distance sampling, if applied routinely when surveying P. occidentalis, will reduce the uncertainty associated with derived estimates of abundance. Implications. Appropriate use of distance-sampling methods will enable managers and decision makers to assess more quantitatively the potential effect from, and place appropriate approval conditions on, proposals that modify or destroy P. occidentalis habitat. The use of the program Distance will enable such decisions to be based on robust, repeatable estimates of population size, with quantified confidence limits and variance estimates.

scholarly journals How many fish? Comparison of two underwater visual sampling methods for monitoring fish communities

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5066 ◽  
Author(s):  
Zoi Thanopoulou ◽  
Maria Sini ◽  
Konstantinos Vatikiotis ◽  
Christos Katsoupis ◽  
Panayiotis G. Dimitrakopoulos ◽  
...  
Keyword(s):  
Species Richness ◽  
Large Scale ◽  
Sampling Methods ◽  
Survey Design ◽  
Distance Sampling ◽  
Fish Communities ◽  
High Mobility ◽  
Line Transect ◽  
Rocky Reef ◽  
Line Transects

Background Underwater visual surveys (UVSs) for monitoring fish communities are preferred over fishing surveys in certain habitats, such as rocky or coral reefs and seagrass beds and are the standard monitoring tool in many cases, especially in protected areas. However, despite their wide application there are potential biases, mainly due to imperfect detectability and the behavioral responses of fish to the observers. Methods The performance of two methods of UVSs were compared to test whether they give similar results in terms of fish population density, occupancy, species richness, and community composition. Distance sampling (line transects) and plot sampling (strip transects) were conducted at 31 rocky reef sites in the Aegean Sea (Greece) using SCUBA diving. Results Line transects generated significantly higher values of occupancy, species richness, and total fish density compared to strip transects. For most species, density estimates differed significantly between the two sampling methods. For secretive species and species avoiding the observers, the line transect method yielded higher estimates, as it accounted for imperfect detectability and utilized a larger survey area compared to the strip transect method. On the other hand, large-scale spatial patterns of species composition were similar for both methods. Discussion Overall, both methods presented a number of advantages and limitations, which should be considered in survey design. Line transects appear to be more suitable for surveying secretive species, while strip transects should be preferred at high fish densities and for species of high mobility.

scholarly journals Line transect estimates of humpback whale abundance and distribution on their wintering grounds in the coastal waters of Gabon

2020 ◽  
pp. 153-160 ◽  
Author(s):  
Samantha Strindberg ◽  
Peter J. Ersts ◽  
Tim Collins ◽  
Guy-Philippe Sounguet ◽  
Howard C. Rosenbaum
Keyword(s):  
Coastal Waters ◽  
Survey Design ◽  
Distance Sampling ◽  
Research Programme ◽  
Humpback Whale ◽  
Aerial Survey ◽  
Hydrocarbon Exploration ◽  
Humpback Whales ◽  
Equatorial Guinea ◽  
Line Transect

There have been few recent estimates of abundance for humpback whales (Megaptera novaeangliae) in the eastern South Atlantic Ocean. The firstdistance sampling survey of the coastal waters of Gabon was conducted in 2002. The difficult logistics of covering a large survey region withlimited time, effort and refuelling opportunities required a line transect survey design that carefully balanced the theoretical demands of distancesampling with these constraints. Inshore/offshore zigzag transects were conducted to a distance of up to approximately 50 n.miles from the coastof Gabon corresponding to the 1,000m depth contour, from the border with Equatorial Guinea to a point south of Mayumba, near the Congo borderrepresenting 1,488 n.miles of survey effort. Seventy-nine different groups of humpback whales were observed throughout the survey area comprisinga northern (Equatorial Guinea to Cap Lopez) and southern (Cap Lopez to Gamba) survey stratum. Relatively large numbers of whales wereencountered throughout the southern stratum; encounter rates and densities were considerably lower in the northern stratum. The initial abundanceestimate from a distance sampling analysis suggests that more than 1,200 humpback whales were present in Gabon’s coastal waters during thesurvey period. This estimate does not account for either availability or perception bias. In addition, this instantaneous snapshot of the number ofwhales occupying Gabon’s coastal waters is likely to correspond to only a portion of the population that uses these waters over time. However, theabundance estimate derived from the aerial survey are consistent with those based on photographic and genetic capture-recapture techniques. Acontinuing research programme in this area will help refine estimates of humpback whale abundance and using genetic and photographic data alsoestablish the relationships between this and other populations. This is important given the potential overlap of humpback whales in large numbersthroughout this region and the current extent and continued expansion of hydrocarbon exploration and extraction activities throughout the Gulf ofGuinea.

Identification of biomarkers and functional modules from genomic data in stage-wise breast cancer

2020 ◽  
Vol 15 ◽  
Author(s):  
Athira K ◽  
Vrinda C ◽  
Sunil Kumar P V ◽  
Gopakumar G
Keyword(s):  
Breast Cancer ◽  
Expression Patterns ◽  
Differential Expression Analysis ◽  
Predictive Biomarkers ◽  
Stage I ◽  
Stage Ii ◽  
Stage Iii ◽  
Functional Modules ◽  
Incidence And Mortality ◽  
Multiple Stages

Background: Breast cancer is the most common cancer in women across the world, with high incidence and mortality rates. Being a heterogeneous disease, gene expression profiling based analysis plays a significant role in understanding breast cancer. Since expression patterns of patients belonging to the same stage of breast cancer vary considerably, an integrated stage-wise analysis involving multiple samples is expected to give more comprehensive results and understanding of breast cancer. Objective: The objective of this study is to detect functionally significant modules from gene co-expression network of cancerous tissues and to extract prognostic genes related to multiple stages of breast cancer. Methods: To achieve this, a multiplex framework is modelled to map the multiple stages of breast cancer, which is followed by a modularity optimization method to identify functional modules from it. These functional modules are found to enrich many Gene Ontology terms significantly that are associated with cancer. Result and Discussion: predictive biomarkers are identified based on differential expression analysis of multiple stages of breast cancer. Conclusion: Our analysis identified 13 stage-I specific genes, 12 stage-II specific genes, and 42 stage-III specific genes that are significantly regulated and could be promising targets of breast cancer therapy. That apart, we could identify 29, 18 and 26 lncRNAs specific to stage I, stage II and stage III respectively.

Cardiac transthyretin wild-type amyloidosis (ATTRwt): a prospective study of 400 patients followed at the Italian referral center

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
P Milani ◽  
L Obici ◽  
R Mussinelli ◽  
M Basset ◽  
G Manfrinato ◽  
...  
Keyword(s):  
Natural History ◽  
Median Survival ◽  
Troponin I ◽  
Stage I ◽  
Stage Ii ◽  
Stage Iii ◽  
Wild Type ◽  
Staging Systems ◽  
Significant Difference ◽  
History Of

Abstract Background Cardiac wild type transthyretin (ATTRwt) amyloidosis, formerly known as senile systemic amyloidosis, is an increasingly recognized, progressive, and fatal cardiomyopathy. Two biomarkers staging systems were proposed based on NT-proBNP (in both cases) and troponin or estimated glomerular filtration rate, that are able to predict survival in this population. The availability of novel effective treatments requires large studies to describe the natural history of the disease in different populations. Objective To describe the natural history of the disease in a large, prospective, national series. Methods Starting in 2007, we protocolized data collection in all the patients diagnosed at our center (n=400 up to 7/2019). Results The referrals to our center increased over time: 5 cases (1%) between 2007–2009, 33 (9%) in 2010–2012, 90 (22%) in 2013–2015 and 272 (68%) in 2016–2019. Median age was 76 years [interquartile range (IQR): 71–80 years] and 372 patients (93%) were males. One hundred and seventy-three (43%) had atrial fibrillation, 63 (15%) had a history of ischemic cardiomyopathy and 64 (15%) underwent pacemaker or ICD implantation. NYHA class was I in 58 subjects (16%), II in 225 (63%) and III in 74 (21%). Median NT-proBNP was 3064 ng/L (IQR: 1817–5579 ng/L), troponin I 0.096 ng/mL (IQR: 0.063–0.158 ng/mL), eGFR 62 mL/min (IQR: 50–78 mL/min). Median IVS was 17 mm (IQR: 15–19 mm), PW 16 mm (IQR: 14–18 mm) and EF 53% (IQR: 45–57%). One-hundred and forty-eight subjects (37%) had a concomitant monoclonal component in serum and/or urine and/or an abnormal free light chain ratio. In these patients, the diagnosis was confirmed by immunoelectron microscopy or mass spectrometry. In 252 (63%) the diagnosis was based on bone scintigraphy. DNA analysis for amyloidogenic mutations in transthyretin and apolipoprotein A-I genes was negative in all subjects. The median survival of the whole cohort was 59 months. The Mayo Clinic staging based on NT-proBNP (cutoff: 3000 ng/L) and troponin I (cutoff: 0.1 ng/mL) discriminated 3 different groups [stage I: 131 (35%), stage II: 123 (32%) and stage III: 127 (33%)] with different survival between stage I and II (median 86 vs. 81 months, P=0.04) and between stage II and III (median 81 vs. 62 months, P&lt;0.001). The UK staging system (NT-proBNP 3000 ng/L and eGFR 45 mL/min), discriminated three groups [stage I: 170 (45%), stage II: 165 (43%) and stage III: 45 (12%)] with a significant difference in survival: between stage I and stage II (86 vs. 52 months, P&lt;0.001) and between stage II and stage III (median survival 52 vs. 33 months, P=0.045). Conclusions This is one of the largest series of patients with cardiac ATTRwt reported so far. Referrals and diagnoses increased exponentially in recent years, One-third of patients has a concomitant monoclonal gammopathy and needed tissue typing. Both the current staging systems offered good discrimination of staging and were validated in our independent cohort. Funding Acknowledgement Type of funding source: None

scholarly journals Getting the Most From Surveys: How Method Selection and Method Modification Impact Butterfly Survey Data

2021 ◽  
Author(s):  
Katherine C Kral-O’Brien ◽  
Adrienne K Antonsen ◽  
Torre J Hovick ◽  
Ryan F Limb ◽  
Jason P Harmon
Keyword(s):  
Species Richness ◽  
New Species ◽  
Count Data ◽  
Distance Sampling ◽  
Line Transect ◽  
Similar Species ◽  
Method Selection ◽  
M 10 ◽  
Sampling Procedures

Abstract Many methods are used to survey butterfly populations, with line transect and area surveys being prominent. Observers are typically limited to search within 5 or 10 m from the line, while observers are unrestricted in larger specified search regions in area surveys. Although methods differ slightly, the selection is often based on producing defendable data for conservation, maximizing data quality, and minimizing effort. To guide method selection, we compared butterfly surveys using 1) line versus area methods and 2) varying width transects (5 m, 10 m, or unrestricted) using count data from surveys in North Dakota from 2015 to 2018. Between line and area surveys, we detected more individuals with area surveys, even when accounting for effort. However, both methods accumulated new species at similar rates. When comparing transect methodology, we detected nearly 60% more individuals and nine more species when transect width increased from 5 m to unrestricted, despite similar effort across methodology. Overall, we found line surveys slightly less efficient at detecting individuals, but they collected similar species richness to area surveys when accounting for effort. Additionally, line surveys allow the use of unrestricted-width transects with distance sampling procedures, which were more effective at detecting species and individuals while providing a means to correct count data over the same transect length. Methods that reduce effort and accurately depict communities are especially important for conservation when long-term datasets are unavailable.

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