Change-in-ratio density estimator for feral pigs is less biased than closed mark - recapture estimates

2008 ◽  
Vol 35 (7) ◽  
pp. 695 ◽  
Author(s):  
Laura B. Hanson ◽  
James B. Grand ◽  
Michael S. Mitchell ◽  
D. Buck Jolley ◽  
Bill D. Sparklin ◽  
...  
Keyword(s):  
Estimation Method ◽  
Density Estimator ◽  
Density Estimates ◽  
Mark Recapture ◽  
Closed Population ◽  
Feral Pigs ◽  
Open Population ◽  
Detection Probabilities ◽  
Models Comparison

Closed-population capture–mark–recapture (CMR) methods can produce biased density estimates for species with low or heterogeneous detection probabilities. In an attempt to address such biases, we developed a density-estimation method based on the change in ratio (CIR) of survival between two populations where survival, calculated using an open-population CMR model, is known to differ. We used our method to estimate density for a feral pig (Sus scrofa) population on Fort Benning, Georgia, USA. To assess its validity, we compared it to an estimate of the minimum density of pigs known to be alive and two estimates based on closed-population CMR models. Comparison of the density estimates revealed that the CIR estimator produced a density estimate with low precision that was reasonable with respect to minimum known density. By contrast, density point estimates using the closed-population CMR models were less than the minimum known density, consistent with biases created by low and heterogeneous capture probabilities for species like feral pigs that may occur in low density or are difficult to capture. Our CIR density estimator may be useful for tracking broad-scale, long-term changes in species, such as large cats, for which closed CMR models are unlikely to work.

scholarly journals Evaluation of Long-Term Mark-Recapture Data for Estimating Abundance of Juvenile Fall-Run Chinook Salmon on the Stanislaus River from 1996 to 2017

2019 ◽  
Vol 17 (1) ◽  
Author(s):  
Tyler Pilger ◽  
Matthew Peterson ◽  
Dana Lee ◽  
Andrea Fuller ◽  
Doug Demko
Keyword(s):  
Chinook Salmon ◽  
Oncorhynchus Tshawytscha ◽  
Estimation Method ◽  
Central Valley ◽  
Mark Recapture ◽  
Important Species ◽  
Trap Efficiency ◽  
Monitoring Programs ◽  
Abundance Estimates

Conservation and management of culturally and economically important species rely on monitoring programs to provide accurate and robust estimates of population size. Rotary screw traps (RSTs) are often used to monitor populations of anadromous fish, including fall-run Chinook Salmon (Oncorhynchus tshawytscha) in California’s Central Valley. Abundance estimates from RST data depend on estimating a trap's efficiency via mark-recapture releases. Because efficiency estimates are highly variable and influenced by many factors, abundance estimates can be highly uncertain. An additional complication is the multiple accepted methods for how to apply a limited number of trap efficiency estimates, each from discrete time-periods, to a population’s downstream migration, which can span months. Yet, few studies have evaluated these different methods, particularly with long-term monitoring programs. We used 21 years of mark-recapture data and RST catch of juvenile fall-run Chinook Salmon on the Stanislaus River, California, to investigate factors associated with trap efficiency variability across years and mark-recapture releases. We compared annual abundance estimates across five methods that differed in treatment of trap efficiency (stratified versus modeled) and statistical approach (frequentist versus Bayesian) to assess the variability of estimates across methods, and to evaluate whether method affected trends in estimated abundance. Consistent with short-term studies, we observed negative associations between estimated trap efficiency and river discharge as well as fish size. Abundance estimates were robust across all methods, frequently having overlapping confidence intervals. Abundance trends, for the number of increases and decreases from year to year, did not differ across methods. Estimated juvenile abundances were significantly related to adult escapement counts, and the relationship did not depend on estimation method. Understanding the sources of uncertainty related to abundance estimates is necessary to ensure that high-quality estimates are used in life cycle and stock-recruitment modeling.

scholarly journals Population status, structure and distribution of the greater one-horned rhinoceros Rhinoceros unicornis in Nepal

Oryx ◽  
2013 ◽  
Vol 47 (3) ◽  
pp. 352-360 ◽  
Author(s):  
Naresh Subedi ◽  
Shant Raj Jnawali ◽  
Maheshwar Dhakal ◽  
Narendra M.B. Pradhan ◽  
Babu Ram Lamichhane ◽  
...  
Keyword(s):  
National Park ◽  
Null Model ◽  
Closed Population ◽  
Rhinoceros Unicornis ◽  
Detection Probabilities ◽  
Potential Habitats ◽  
Chitwan National Park ◽  
Wildlife Reserve ◽  
Abundance And Distribution

AbstractWe assessed the abundance and distribution of the greater one-horned or Indian rhinoceros Rhinoceros unicornis in all its potential habitats in Nepal, using block counts. In April 2011 5,497 km were searched in 3,548 elephant-hours over 23 days. The validity of the block count was assessed by comparing it with counts obtained from long-term monitoring using photographic identification of individual rhinoceroses (ID-based), and estimates obtained by closed population sighting–mark–resighting in the 214 km2 of Chitwan National Park. A total of 534 rhinoceroses were found during the census, with 503 in Chitwan National Park (density 1 km−2), 24 in Bardia National Park (0.28 km−2) and seven in Suklaphanta Wildlife Reserve (0.1 km−2). In Chitwan 66% were adults, 12% subadults and 22% calves, with a female : male ratio of 1.24. The population estimate from sighting–mark–resighting was 72 (95% CI 71–78). The model with different detection probabilities for males and females had better support than the null model. In the Sauraha area of Chitwan estimates of the population obtained by block count (77) and ID-based monitoring (72) were within the 95% confidence interval of the estimate from sighting–mark–resighting. We recommend a country-wide block count for rhinoceroses every 3 years and annual ID-based monitoring in a sighting–mark–resighting framework within selected subpopulations. The sighting–mark–resighting technique provides the statistical rigour required for population estimates of the rhinoceros in Nepal and elsewhere.

scholarly journals Demography and population structure of Northeastern mediterranean monk seal population

2020 ◽  
Author(s):  
MERVE KURT ◽  
ALI CEMAL GÜCÜ
Keyword(s):  
Population Size ◽  
Camera Traps ◽  
The Body ◽  
Closed Population ◽  
Open Population ◽  
Seal Population ◽  
Conservation Actions ◽  
Term Monitoring ◽  
Natural Marks

The Northeastern Mediterranean coasts that border southern Turkey host one of the last strongholds for the survival of the endangered Mediterranean monk seal (Monachus monachus, 1779). The seal colonies inhabiting south coast of Turkey have been studied since 1994 through various short-term research projects focusing on distinct small populations that were thought to be isolated. In this study, the entire extent of the area was monitored approximately for 3 years (between 2015 and 2018) with camera traps places in 20 caves known to be actively used by the seals. A total of 7014 images taken throughout the study period, along with 25,100 images taken previously, were used to identify the seals inhabiting the area.  In total, 37 individuals were identified based on the natural marks on the body. Based on photo-identified seals, a mark-recapture method was applied to estimate the total population size within the Northeastern Mediterranean. The overall population size was found to be 46 (SE=7.7) in the case of closed population and 53(SE=34.8) in the case of open population during the study period.  The range of identified seals was almost six times larger than previously documented in the same area, reaching distances up to 245 km. The population estimate indicated a decrease in population size compared to previous studies.  Finally, the study emphasises the importance of long-term monitoring studies elucidating changes in the demographic parameters in relation to threats posed, rather than cut-paste measurement suggestions which are not applicable in reality, while structuring the conservation actions targeting survival of this highly endangered species.

A Likelihood Method for Estimating Pacific Salmon Escapement based on Fence Counts and Mark–Recapture Data

1994 ◽  
Vol 51 (3) ◽  
pp. 552-566 ◽  
Author(s):  
M. Labelle
Keyword(s):  
Pacific Salmon ◽  
Estimation Method ◽  
Population Models ◽  
Small Sample ◽  
Field Conditions ◽  
Likelihood Method ◽  
Ancillary Data ◽  
Mark Recapture ◽  
Open Population ◽  
Natural Streams

Pacific salmon escapements in natural streams are often determined by conducting fence counts in conjunction with mark–recapture operations. Typical field conditions are characterized by protracted floods, undetected immigration, variation in sampling rates, mortality during the census periods, small sample sizes, and few successive recaptures. Closed population models tend to overestimate escapement under such conditions, and traditional open population models cannot always be relied on due to the lack of sufficient data. A likelihood-based estimation method was specifically designed for such conditions. A distinguishing feature of this model is that individual recapture histories are not required for parameter estimation. The model is also structured to incorporate ancillary data in the estimation process to improve the precision and accuracy of the estimates. The model is described in detail, and suggestions are made to facilitate its application. Constructed data sets resembling those obtained under field conditions were used to evaluate the performance of the model. The estimates generated with simulated data and actual field data were compared with those based on visual foot surveys and other mark–recapture models.

scholarly journals Adaptive Estimation of Spatial Clutter Measurement Density Using Clutter Measurement Probability for Enhanced Multi-Target Tracking

Sensors ◽  
2019 ◽  
Vol 20 (1) ◽  
pp. 114
Author(s):  
Seung Hyo Park ◽  
Sa Yong Chong ◽  
Hyung June Kim ◽  
Taek Lyul Song
Keyword(s):  
Monte Carlo Simulation ◽  
Target Tracking ◽  
Density Estimation ◽  
Adaptive Estimation ◽  
Estimation Method ◽  
Radar Data ◽  
Tracking Performance ◽  
Density Estimator ◽  
Density Estimates ◽  
Multi Target Tracking

The point detections obtained from radars or sonars in surveillance environments include clutter measurements, as well as target measurements. Target tracking with these data requires data association, which distinguishes the detections from targets and clutter. Various algorithms have been proposed for clutter measurement density estimation to achieve accurate and robust target tracking with the point detections. Among them, the spatial clutter measurement density estimator (SCMDE) computes the sparsity of clutter measurement, which is the reciprocal of the clutter measurement density. The SCMDE considers all adjacent measurements only as clutter, so the estimated clutter measurement density is biased for multi-target tracking applications, which may result in degraded target tracking performance. Through the study in this paper, a major source of tracking performance degradation with the existing SCMDE for multi-target tracking is analyzed, and the use of the clutter measurement probability is proposed as a remedy. It is also found that the expansion of the volume of the hyper-sphere for each sparsity order reduces the bias of clutter measurement density estimates. Based on the analysis, we propose a new adaptive clutter measurement density estimation method called SCMDE for multi-target tracking (MTT-SCMDE). The proposed method is applied to multi-target tracking, and the improvement of multi-target tracking performance is shown by a series of Monte Carlo simulation runs and a real radar data test. The clutter measurement density estimation performance and target tracking performance are also analyzed for various sparsity orders.

Theory and application of mark - recapture and related techniques to aerial surveys of wildlife

2008 ◽  
Vol 35 (4) ◽  
pp. 268 ◽  
Author(s):  
Richard Barker
Keyword(s):  
Conditional Independence ◽  
Survey Design ◽  
Imperfect Detection ◽  
Mark Recapture ◽  
Closed Population ◽  
Aerial Surveys ◽  
Detection Probabilities ◽  
Complete Independence ◽  
Multiple Observer ◽  
Observer Studies

The key difficulty in assessing animal numbers from the air is that not all animals are seen by the observers. Methods for estimating detection probabilities, or accounting for imperfect detection, are reviewed including double surveys, use of sightability models, mark–resight, and mark–recapture. The assumptions needed for each method are considered as well as issues concerning survey design. For closed-population mark–recapture modelling particular attention is given to multiple observer studies. An emphasis is that an assumption of complete independence in double-observer studies is rarely justifiable and that independent observers will generally only satisfy an assumption of conditional independence and not complete independence.

scholarly journals A comparison of mark - recapture distance-sampling methods applied to aerial surveys of eastern grey kangaroos

2008 ◽  
Vol 35 (4) ◽  
pp. 320 ◽  
Author(s):  
Rachel M. Fewster ◽  
Anthony R. Pople
Keyword(s):  
Goodness Of Fit ◽  
Distance Sampling ◽  
Density Estimates ◽  
Mark Recapture ◽  
Transect Line ◽  
Aerial Surveys ◽  
Commercial Harvest ◽  
Coefficients Of Variation ◽  
Detection Probabilities ◽  
Full Independence

Aerial surveys of kangaroos (Macropus spp.) in Queensland are used to make economically important judgements on the levels of viable commercial harvest. Previous analysis methods for aerial kangaroo surveys have used both mark–recapture methodologies and conventional distance-sampling analyses. Conventional distance sampling has the disadvantage that detection is assumed to be perfect on the transect line, while mark–recapture methods are notoriously sensitive to problems with unmodelled heterogeneity in capture probabilities. We introduce three methodologies for combining together mark–recapture and distance-sampling data, aimed at exploiting the strengths of both methodologies and overcoming the weaknesses. Of these methods, two are based on the assumption of full independence between observers in the mark–recapture component, and this appears to introduce more bias in density estimation than it resolves through allowing uncertain trackline detection. Both of these methods give lower density estimates than conventional distance sampling, indicating a clear failure of the independence assumption. The third method, termed point independence, appears to perform very well, giving credible density estimates and good properties in terms of goodness-of-fit and percentage coefficient of variation. Estimated densities of eastern grey kangaroos range from 21 to 36 individuals km–2, with estimated coefficients of variation between 11% and 14% and estimated trackline detection probabilities primarily between 0.7 and 0.9.

scholarly journals Arenavirus infection correlates with lower survival of its natural rodent host in a long-term capture-mark-recapture study

2018 ◽  
Vol 11 (1) ◽  
Author(s):  
Joachim Mariën ◽  
Vincent Sluydts ◽  
Benny Borremans ◽  
Sophie Gryseels ◽  
Bram Vanden Broecke ◽  
...  
Keyword(s):  
Rodent Host ◽  
Mark Recapture ◽  
Lower Survival

scholarly journals Challenges and opportunities for monitoring wild Nile crocodiles with scute mark-recapture photography

Koedoe ◽  
2018 ◽  
Vol 60 (1) ◽  
Author(s):  
Bernard W.T. Coetzee ◽  
Sam M. Ferreira ◽  
Kristine Maciejewski
Keyword(s):  
Conservation Status ◽  
Field Conditions ◽  
High Turnover ◽  
Mark Recapture ◽  
Non Invasive ◽  
Open Population ◽  
Challenges And Opportunities ◽  
In Captivity ◽  
In The Wild

The global conservation status of Nile crocodiles (Crocodylus niloticus) was last assessed in 1996. The species presents particular difficulty in monitoring because it can be cryptic, require expertise to handle, and caudal tail tags and transmitters are often lost. Some studies advocate mark-recapture techniques based on photograph identification of the unique scute markings of crocodile tails as a non-invasive means of monitoring their populations. Researchers developed this method with crocodiles in captivity. In this study, we test the technique under field conditions by monitoring crocodiles from 2015 to 2017 in the Sunset Dam in the Kruger National Park. Using a Cormack-Jolly-Seber open population model, we found that the dam may host 15–30 individuals, but that there is a high turnover of individuals and much uncertainty in model outputs. The dam’s population thus has high rates of immigration and emigration. The method proved challenging under field conditions, as there was bias in identifying scute markings consistently. The efficient use of the method requires an exceptional quality of photographic equipment. Animal crypsis, however, remains an issue. In this study, we discuss how to improve the mark-recapture photography methodology, especially to adapt the technique for citizen science initiatives.Conservation implications: Using scute mark-recapture photography presents challenges under field conditions. These challenges require innovative, practical and analytical solutions to successfully use the technique before monitoring programmes, aimed at ensuring the persistence of crocodiles in the wild, can be implemented.

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