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20
Incorporating covariates into standard line transect analyses
 Biometrics
, 2003
"... Summary. An implicit assumption of standard line transect methodology is that detection probabilities depend solely on the perpendicular distance of detected objects to the transect line. Heterogeneity in detection probabilities is commonly minimized using stratification,but this may be precluded by ..."
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Cited by 38 (7 self)
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Summary. An implicit assumption of standard line transect methodology is that detection probabilities depend solely on the perpendicular distance of detected objects to the transect line. Heterogeneity in detection probabilities is commonly minimized using stratification,but this may be precluded by small sample sizes. We develop a general methodology which allows the effects of multiple covariates to be directly incorporated into the estimation procedure using a conditional likelihood approach. Small sample size properties of estimators are examined via simulations. As an example the method is applied to eastern tropical Pacific dolphin sightings data.
Estimating animal abundance: review III
 Statistical Science
, 1999
"... The literature describing methods for estimating animal abundance and related parameters continues to grow. This paper reviews recent developments in the subject over the past seven years and updates two previous reviews. ..."
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Cited by 23 (0 self)
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The literature describing methods for estimating animal abundance and related parameters continues to grow. This paper reviews recent developments in the subject over the past seven years and updates two previous reviews.
Zigzag Survey Designs in Line Transect
"... Zigzag survey lines are frequently used in shipboard and aerial line transect surveys of animal populations. Analysis proceeds assuming that coverage probability through the survey region is uniform. We show that the two types of zigzag design that are in wide use do not generally have this property ..."
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Cited by 11 (4 self)
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Zigzag survey lines are frequently used in shipboard and aerial line transect surveys of animal populations. Analysis proceeds assuming that coverage probability through the survey region is uniform. We show that the two types of zigzag design that are in wide use do not generally have this property, and explore the degree of bias in abundance estimates that can be anticipated. We construct a zigzag design for convex survey regions that has even coverage probability with respect to distance along a design axis. We also provide HorvitzThompson estimators that allow coverage probability to vary by location through
Distance sampling: a discussion document produced for the Department of Conservation
 SCIENCE & RESEARCH INTERNAL REPORT 175. DEPARTMENT OF CONSERVATION
, 2000
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Predicting and correcting bias caused by measurement error in line transect sampling using multiplicative error models
 Biometrics
, 2004
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INCORPORATING MEASUREMENT ERROR AND DENSITY GRADIENTS IN DISTANCE SAMPLING SURVEYS
, 2007
"... Distance sampling is one of the most commonly used methods for estimating density and abundance. Conventional methods are based on the distances of detected animals from the center of point transects or the center line of line transects. These distances are used to model a detection function: the pr ..."
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Cited by 3 (1 self)
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Distance sampling is one of the most commonly used methods for estimating density and abundance. Conventional methods are based on the distances of detected animals from the center of point transects or the center line of line transects. These distances are used to model a detection function: the probability of detecting an animal, given its distance from the line or point. The probability of detecting an animal in the covered area is given by the mean value of the detection function with respect to the available distances to be detected. Given this probability, a HorvitzThompsonlike estimator of abundance for the covered area follows, hence using a modelbased framework. Inferences for the wider survey region are justified using the survey design. Conventional distance sampling methods are based on a set of assumptions. In this thesis I present results that extend distance sampling on two fronts. Firstly, estimators are derived for situations in which there is measurement error in the distances. These estimators use information about the measurement error in two ways: (1) a biased estimator based on the contaminated distances is multiplied by an appropriate correction factor, which is a function of the errors (P DF approach), and
Line Transect Methods for Plant Surveys
"... SUMMARY. Interest in surveys for monitoring plant abundance is increasing, due in part to the need to quantify the rate of loss of biodiversity. Line transect sampling offers an efficient way to monitor many species. However, the method does not work well in some circumstances, for example on small ..."
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Cited by 3 (1 self)
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SUMMARY. Interest in surveys for monitoring plant abundance is increasing, due in part to the need to quantify the rate of loss of biodiversity. Line transect sampling offers an efficient way to monitor many species. However, the method does not work well in some circumstances, for example on small survey plots, when the plant species has a strongly aggregated distribution, or when plants that are on the line are not easily detected. We develop a crossed design, together with methods that exploit the additional information from such a design, to address these problems. The methods are illustrated using data on a colony of cowslips.
DoubleObserver Line Transect Methods: Levels of Independence
"... Doubleobserver line transect methods are becoming increasingly widespread, especially for the estimation of marine mammal abundance from aerial and shipboard surveys when detection of animals on the line is uncertain. The resulting data supplement conventional distance sampling data with twosample ..."
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Doubleobserver line transect methods are becoming increasingly widespread, especially for the estimation of marine mammal abundance from aerial and shipboard surveys when detection of animals on the line is uncertain. The resulting data supplement conventional distance sampling data with twosample markrecapture data. Like conventional markrecapture data, these have inherent problems for estimating abundance in the presence of heterogeneity. Unlike conventional markrecapture methods, line transect methods use knowledge of the distribution of a covariate which affects detection probability (namely distance from the transect line) in inference. This knowledge can be used to diagnose unmodelled heterogeneity in the markrecapture component of the data. By modelling the covariance in detection probabilities with distance, we show how the estimation problem can be formulated in terms of different levels of independence. At one extreme, full independence is assumed, as in the Petersen estimator (which does not use distance data); at the other extreme, independence only occurs in the limit as detection probability tends to one. Between the two extremes, there is a range of models, including those currently in common use, which have intermediate levels of independence. We show how this framework can be used to provide more reliable analysis of doubleobserver line transect data. We test the methods by 1 simulation, and by analysis of a dataset for which true abundance is known. We illustrate the approach through analysis of minke whale sightings data from the North Sea and adjacent waters.
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"... The estimation of the detection function and g(0) for shortbeaked common dolphins (Delphinus delphis), using doubleplatform data collected during the NASS95 Faroese survey ..."
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The estimation of the detection function and g(0) for shortbeaked common dolphins (Delphinus delphis), using doubleplatform data collected during the NASS95 Faroese survey
1 Point transect sampling with traps or lures 2 3 4 5 6 7 8
"... 1. The ability to monitor abundance of animal populations is becoming increasingly important, in light of growing concerns over the loss of biodiversity through anthropogenic changes. A widelyused tool for such monitoring is distance sampling, in which distances of detected animals from a line or p ..."
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1. The ability to monitor abundance of animal populations is becoming increasingly important, in light of growing concerns over the loss of biodiversity through anthropogenic changes. A widelyused tool for such monitoring is distance sampling, in which distances of detected animals from a line or point are modelled, to estimate detectability and hence abundance. Nevertheless, many species still prove problematic to survey. We develop two extensions to point transect sampling that potentially allow abundance to be estimated of a number of species from diverse taxa for which good survey methods have not previously been available. 2. For each method, the primary survey comprises a random sample of points, or more usually a systematic grid of points, through the region of interest. Animals are lured to a point, or trapped at a point, and the number of animals observed at each point is recorded. A separate study is conducted on a subset of animals, to record whether they