Closed Population Models Research Articles

Lost in space and time: robust demography and enhanced resilience buffer adverse environmental effects in a highly isolated and sedentary pre-pleistocene landscape vertebrate

BackgroundFew animal populations have been studied under the framework of the OCBIL theory, which addresses the ecology and evolution of biodiversity on old climatically buffered infertile landscapes. Available genetic data challenge the low connectivity and high genetic differentiation predicted for isolated tepui-summit vertebrate communities, suggesting potential dispersal among summits. However, the OCBIL theory posits reduced dispersibility, enhanced resilience to habitat fragmentation and inbreeding due to small populations. We tested these hypotheses by conducting the first analytic evaluation of the spatial ecology and population biology of a tepui-summit vertebrate at multiple spatial scales.ResultsWe used harmonic radar tracking (100 individuals/448 points of contact) and capture-mark-recapture data (596 individuals captured/52 recaptured) to reveal the temporal niche, microhabitat use, population size, and dispersal abilities of the tepui-summit endemic toad Oreophrynella quelchii on Roraima-tepui. Abundance was determined using a closed population model incorporating sources of variation in capture probability. We tested the relative influence of biotic and abiotic variables on distances moved through model selection. Our data indicate that the population size of O. quelchii is remarkably large (ca. 12 million individuals), with strong seasonal demographic fluctuations. Ecology and observed limited spatial movements challenge the likelihood of active dispersal among tepui tops in this species. Our results are counter to those predicted by the available genetic data but support two hypotheses of the OCBIL theory: reduced dispersibility and enhanced resilience. However, they do not support the expectation of a small refugial population size.ConclusionWe postulate that the insular, hostile tepui-summit environment tends to produce robust demographic populations, likely to buffer stochastic adverse environmental effects, rather than diversity, as observed in much younger post-Pleistocene Neotropical landscapes. Our results draw attention to the value of faunal studies using an OCBIL framework to better understand the ecology and evolution of this unique biota worldwide.

First estimates of population size and home range of Caribbean reef and nurse sharks using photo-identification and BRUVS

The assessment of parameters population size and individual home range is important for effective conservation management of sharks. This study uses the novel application of photo identification (photo-ID) to BRUVS footage as a non-invasive alternative to tagging in order to generate individual capture histories. These were used in mark-recapture models to estimate effective population sizes and to determine home ranges. In the Cayman Islands a total of 499 shark sightings of six coastal shark species were recorded on BRUVS from 2015 - 2018, but re-sighting rates were only sufficient for the determination of population parameters for two species - Caribbean reef shark (Carcharhinus perezi) and nurse shark (Ginglymostoma cirratum). The calculated super-population sizes for Caribbean reef shark (180 ± 37 SE) and nurse shark (336 ± 61 SE) were greater than the estimates for each species based on a closed-population model (Caribbean reef shark: 128 ± 40 SE, nurse shark: 249 ± 48 SE), though both measures indicated that there were about twice as many nurse sharks (1.3 - 1.8 sharks/km2) as Caribbean reef sharks (0.7 – 1 shark/km2) within the study area. The demographic compositions included numerous immature individuals, indicating that breeding of both species takes place within the study area of 188 km2. Most recognizable individuals of both species showed linear home ranges of <20 km, but a few individuals were observed to have moved longer distances (Caribbean reef shark: 125.37 km, nurse shark: 156.07 km). The data indicate that the home ranges and long-distance movements of individual sharks observed within the islands’ marine protected areas (MPAs) often extend to areas beyond the MPA’s boundary, potentially exposing them to fishing activities. This study provides the first estimates of population size for Caribbean reef and nurse sharks in the Cayman Islands and the first estimate of a Caribbean reef shark population globally.

Occurrence, abundance and some ecological aspects of the offshore bottlenose dolphin off Ecuador’s central coast

The presence of the offshore bottlenose dolphin (Tursiops truncatus) is poorly understood for most of the southeast Pacific Ocean. Its wide distribution, low density, and lack of understanding of its ecology make the species unpredictable to observe and difficult to study compared to the coastal ecotype. We assessed the occurrence of offshore bottlenose dolphins off the central coast of Ecuador (01°36’ S, 80°58’ W) using information taken from 2001 to 2022. Data were collected by two research groups based 80 km apart, one in Puerto López (north) and the other in Salinas (south). A total of 48 dolphin groups were documented, 22 at Puerto López and 26 at Salinas. In Puerto López, 163 dolphins were individually identified, of which 70 intra-annual sightings and 102 inter-annual sightings were found. Inter-annual resightings at Puerto López corresponded to 55 individuals (33.7%) recorded between two and 17 years (mean = 5.82 years, SD = 5.1). In Salinas, 58 dolphins were identified, without intra-annual resightings and only two inter-annual sightings. Only one individual was recorded in both areas. Two site fidelity indexes were calculated, Occurrence (Oi) and Permanence (Pi), resulting in 11 and 13.7 times higher respectively, in Puerto López. The abundance at Puerto López, 163 animals (95% CI, 120 - 203) in 2021-2022, was estimated with a closed population model. The prevalence of scars associated with previous encounters with fishing gear was 43.6%, commensal barnacle (Xenobalanus globicipitis) infestation 42.3%, predation 3.6%, and dermal nodules 0.61%. Our findings suggest both site fidelity and some degree of population structure, but additional monitoring and genetic studies are needed to clarify these aspects. Nevertheless, this study provides information on key aspects necessary for developing conservation strategies for offshore bottlenose dolphins.

First description of a remnant population of sterlet (Acipenser ruthenus, LINNAEUS 1758) in the eastern Austrian Danube

Sturgeon populations worldwide have collapsed due to various anthropogenic impacts but knowledge gaps in habitat requirements and population dynamics still exist. In the Austrian Danube, habitat loss and the blocking of migration routes due to the construction of a chain of ten hydropower plants (HPP) had left the sterlet (Acipenser ruthenus) as the only remaining sturgeon species, which is classified as “critically endangered”. Since available estimates for the Austrian Danube were based on expert judgement, this study aims to describe the population structure and to estimate the size of a remnant sterlet population in the free-flowing section east of Vienna based on monitoring data. Net fishing was conducted over four years in the tailwater of the HPP Freudenau and population estimates were generated using Capture-Mark-Recapture techniques. A total of 38 sterlets were captured: 27 females, 7 males and 4 with unknown sex. Females were on average larger and heavier (total length (TL) = 800 ± 62 mm; weight (W) = 3294 g ± 1324 g) than males (TL = 660 ± 73 mm; W = 1350 ± 358 g). The population size was estimated at 53 individuals (95 % CI = 43–80) by the POPAN and at 48 individuals (95 % CI = 42–63) by a closed population model. These first monitoring-based population estimates in a free-flowing section of the Austrian Danube provide a base for future population monitoring and the evaluation of ongoing restocking actions. Lacking evidence of natural reproduction and a small population size pose an urgent need to restore the migration corridor and to further improve habitat quality for sturgeons in the Danube and elsewhere.

An Age of Infection Kernel, an R Formula, and Further Results for Arino–Brauer A, B Matrix Epidemic Models with Varying Populations, Waning Immunity, and Disease and Vaccination Fatalities

In this work, we first introduce a class of deterministic epidemic models with varying populations inspired by Arino et al. (2007), the parameterization of two matrices, demography, the waning of immunity, and vaccination parameters. Similar models have been focused on by Julien Arino, Fred Brauer, Odo Diekmann, and their coauthors, but mostly in the case of “closed populations” (models with varying populations have been studied in the past only in particular cases, due to the difficulty of this endeavor). Our Arino–Brauer models contain SIR–PH models of Riano (2020), which are characterized by the phase-type distribution (α→,A), modeling transitions in “disease/infectious compartments”. The A matrix is simply the Metzler/sub-generator matrix intervening in the linear system obtained by making all new infectious terms 0. The simplest way to define the probability row vector α→ is to restrict it to the case where there is only one susceptible class s, and when matrix B (given by the part of the new infection matrix, with respect to s) is of rank one, with B=bα→. For this case, the first result we obtained was an explicit formula (12) for the replacement number (not surprisingly, accounting for varying demography, waning immunity and vaccinations led to several nontrivial modifications of the Arino et al. (2007) formula). The analysis of (A,B) Arino–Brauer models is very challenging. As obtaining further general results seems very hard, we propose studying them at three levels: (A) the exact model, where only a few results are available—see Proposition 2; and (B) a “first approximation” (FA) of our model, which is related to the usually closed population model often studied in the literature. Notably, for this approximation, an associated renewal function is obtained in (7); this is related to the previous works of Breda, Diekmann, Graaf, Pugliese, Vermiglio, Champredon, Dushoff, and Earn. (C) Finally, we propose studying a second heuristic “intermediate approximation” (IA). Perhaps our main contribution is to draw attention to the importance of (A,B) Arino–Brauer models and that the FA approximation is not the only way to tackle them. As for the practical importance of our results, this is evident, once we observe that the (A,B) Arino–Brauer models include a large number of epidemic models (COVID, ILI, influenza, illnesses, etc.).

Abundance of Bering-Chukchi-Beaufort bowhead whales (Balaena mysticetus) in 2004 estimated from photo-identification data

Ice-based surveys near Point Barrow, Alaska, have been used to obtain most estimates of abundance for the Bering-Chukchi-Beaufort (B-C-B) stock of bowhead whales, but global warming has raised concerns that ice-based surveys may not be practical in the future. Aerial photographic surveys provide an alternative method for obtaining abundance estimates and may replace ice-based surveys. Aerial photographic surveys were conducted near Point Barrow during the spring migrations of bowhead whales in 2003 and 2004 and, in 2005, in the northern Bering Sea in spring and near Barrow in fall. The 2003 survey was the most complete photographic survey of the population conducted to date. These surveys provided photo-identification data for use in capture-recapture analyses. A screening procedure was used to define which whales captured in 2003, 2004 and/or 2005 were marked and could be reidentified if photographed on another occasion. An estimate of the number of marked whales was obtained using a closed population model for capture-recapture data. Several models were investigated, including models that accounted for heterogeneity in capture probabilities, but a simple model with no covariates produced the most precise estimate. To account for unmarked whales, the estimate of marked whales was divided by an estimate of the proportion of the bowhead population that was marked based on the 1989–2004 spring photographic surveys near Point Barrow. Abundance of the B-C-B bowhead population in 2004 (excluding calves) was estimated to be 12,631 with CV 0.2442, 95% bootstrap percentile confidence interval (7,900; 19,700) and 5% lower limit 8,400. These results were compared with results that used approximate variance expressions for the estimates of the number of marked whales, the proportion of the population that was marked and population abundance instead of using the bootstrap. The estimates of abundance in 2004 computed for comparison included one based on a modified Petersen estimate of the number of marked whales that omitted the 2005 data as well as the estimate of 12,631 described above. The comparison estimates also included estimates of abundance in 1985 computed from 1984–87 photographic survey data using the same methods. All the abundance estimates computed from photographic data were consistent with expectations based on independent abundance and trend estimates from the ice-based surveys conducted from 1978 to 2001.

Long‐term photo‐identification study of fin whales in the Pelagos Sanctuary (NW Mediterranean) as a baseline for targeted conservation and mitigation measures

Abstract Historical abundance estimates are important for establishing baselines from which trends can be determined using more recent data. Long‐term studies based on photo‐identification were merged and used to estimate population size, survival rate and sex ratio (biopsy sampling) of fin whales in the North‐western Mediterranean. Merging four existing photo‐id catalogues yielded a Mediterranean catalogue with 507 individually identified fin whales. Ninety‐five (18.7%) individuals were resighted at least once during the study period (1990–2007): 71 whales were resighted in different years, 24 within the same season and 13 both in the same season and in different years. The number of resightings within‐season ranged from one to four, over periods from 1 to 90 days. Capture histories from these individuals were used in the capture–recapture analyses. Estimates of the animals present in the area each year between 1991 and 1995 through different modelling approaches were consistent: 900–1,000 from a POPAN open population model; 1,200 from a multi‐sample closed population model; and 900–1,100 from simple two‐sample closed population models for pairs of consecutive years, all with heavily overlapping 95% confidence intervals. The estimated apparent survival rate of 0.916 (95% CI = 0.773–0.972) was lower than expected, which may be linked to temporary or permanent emigration, or mortality possibly owing to ship strikes. Conservation and mitigation measures such as Important Marine Mammal Areas and Particularly Sensitive Sea Areas are presented and discussed.

Integrated animal movement and spatial capture-recapture models: Simulation, implementation, and inference.

Over the last decade, spatial capture-recapture (SCR) models have become widespread for estimating demographic parameters in ecological studies. However, the underlying assumptions about animal movement and space use are often not realistic. This is a missed opportunity because interesting ecological questions related to animal space use, habitat selection, and behavior cannot be addressed with most SCR models, despite the fact that the data collected in SCR studies - individual animals observed at specific locations and times - can provide a rich source of information about these processes and how they relate to demographic rates. We developed SCR models that integrated more complex movement processes that are typically inferred from telemetry data, including a simple random walk, correlated random walk (i.e., short-term directional persistence), and habitat-driven Langevin diffusion. We demonstrated how to formulate, simulate from, and fit these models with standard SCR data using data-augmented Bayesian analysis methods. We evaluated their performance through a simulation study, in which we varied the detection, movement, and resource selection parameters. We also examined different numbers of sampling occasions and assessed performance gains when including auxiliary location data collected from telemetered individuals. Across all scenarios, the integrated SCR movement models performed well in terms of abundance, detection, and movement parameter estimation. We found little difference in bias for the simple random walk model when reducing the number of sampling occasions from T = 25 to T = 15. We found some bias in movement parameter estimates under several of the correlated random walk scenarios, but incorporating auxiliary location data improved parameter estimates and significantly improved mixing during model fitting. The Langevin movement model was able to recover resource selection parameters from standard SCR data, which is particularly appealing because it explicitly links the individual-level movement process with habitat selection and population density. We focused on closed population models, but the movement models developed here can be extended to open SCR models. The movement process models could also be easily extended to accommodate additional "building blocks" of random walks, such as central tendency (e.g., territoriality) or multiple movement behavior states, thereby providing a flexible and coherent framework for linking animal movement behavior to population dynamics, density, and distribution.

Analysis of Methods to Estimate Abundance of River Cooters, Pseudemys concinna: An Example from the Santa Fe River, Florida

A multitude of different statistical models are commonly used to monitor trends in wildlife populations. Most are used to estimate abundance or survival (or both), and these estimates are then examined over time to infer trends in a population. The choice of which model to use is influenced by the key research question of interest and the types of data available. The accuracy and precision of any estimate from a population model are determined by whether the data meet the model assumptions. We assessed the performance of both closed and open capture–recapture models for determining trends in abundance and survival of River Cooters, Pseudemys concinna, in the Santa Fe River, Florida from 2009–2019. We fit three closed models to estimate abundance, one open model to estimate survival, and two robust design models to estimate both abundance and survival. We then used simulation to generate three datasets that represented different sampling designs, including one that mimics our field data, to assess model performance and compare tradeoffs in sampling design. We recommend using the robust design framework when possible as this design and model estimation returned accurate and precise estimates of abundance and survival. This model estimated survival ranging from 0.69–0.95 and capture probability from 0.21–0.25. This design requires consistent sampling of at least three events per year during a closed period, repeated over at least five years, to estimate survival between years. In situations where samples could not be repeated across years, closed population models are likely the most reliable framework in terms of model precision and accuracy. Overall, sampling designs that allow for repeated sampling and align the biology of the study species and the assumptions of the statistical model are likely the most informative approaches for sampling River Cooters and similar species.

Population Dynamics Reveal a Core Community of the Common Bottlenose Dolphin (Tursiops truncatus) in Open Waters of the South-Western Gulf of Mexico

The presence of transient and temporary individuals in capture-mark-recapture studies may violate the assumption on equal catchability, and thus yield biased estimates. We investigated the effects of residency patterns on population parameters of bottlenose dolphins inhabiting the coastal waters off the Alvarado Lagoon System (ALS), Veracruz, Mexico. We hypothesized that this population is open but there exists a “core community” that behaves as a closed population. Between 2006 and 2010, we conducted 75 photo-identification surveys and recorded 263 dolphin group encounters, in which 231 dolphins were identified. Individuals present during only one season, classified as transients (n= 85), were excluded from the study, and a standardized residency index (IH4) was computed for each dolphin that remained in the sample (n= 146). We used the K-means clustering method to split the sample into groups based on individual (seasonal, annual) IH4values. These clusters were named as regular residents (RR,n= 55), occasional residents (OR,n= 45), and occasional visitors (OV,n= 46). The cumulative frequency of newly identified individuals displayed an asymptotic trend for the whole sample and all clusters, indicating that most of the individuals present in the study area during the study period were identified. The assumption of demographic closure was tested to define the core community, and was rejected for the whole sample and the OV cluster (p< 0.001 in both cases), indicating that the population is open. The closure assumption was not rejected for RR and OR clusters (χ2= 6.88, DF = 13,p= 0.91, and χ2= 17.8, DF = 16,p= 0.33, respectively), indicating that these clusters were demographically closed over the 5-year period. Thus, we defined this aggregation of individuals as the “core community”. The closed population model Mthindicated that the total abundance of this core community was 123 individuals (95% CI: 114–133). Our results provide quantitative evidence of the existence of a core community in open waters of the Gulf of Mexico, and points toward residency pattern as a main driver of population dynamics. These results highlight the importance of considering residency patterns when dealing with heterogeneity in the sample of a highly mobile species.

Avian response to prolonged drought in drylands: The case of two dove species in Brazil's semi-arid region

In view of the scenario of global warming, understanding how individuals disperse and populations fluctuate in response to climatic extremes is becoming increasingly important. Thereby, we used a capture-mark-recapture approach on Columbina minuta and Columbina picui in two Caatinga physiognomies (shrubby-woodland and savanna) during and following a prolonged drought in northeastern Brazil. We evaluated three hypotheses: density is higher in the savanna, doves are more abundant during the rainy season, and doves are able to undertake regional movements in response to drought. We used Huggins closed population models to estimate detection rates and population size. The results revealed low capture and recapture rates, greater abundance in the savanna, a higher density of C. minuta in both study areas, and a higher density of both species in the rainy season. We also observed that the prolonged drought has negatively impacted on doves density. The recovery of banded individuals at other sites indicates that nomadism may be the principal strategy adopted by doves to endure periods of drought. Our findings show that conservation units in the Caatinga are important to conservation of granivorous birds and contribute to understanding the birds' strategies to face seasonality and severely dry periods in semiarid areas.

Estimating Population Abundance of Burying Beetles Using Photo-Identification and Mark-Recapture Methods.

Successful conservation and management of protected wildlife populations require reliable population abundance data. Traditional capture-mark-recapture methods can be costly, time-consuming, and invasive. Photographic mark-recapture (PMR) is a cost-effective, minimally invasive way to study population dynamics in species with distinct markings or color patterns. We tested the feasibility and the application of PMR using the software Hotspotter to identify Nicrophorus spp. from digital images of naturally occurring spot patterns on their elytra. We conducted a laboratory study evaluating the identification success of Hotspotter on Nicrophorus americanus (Olivier, 1790) and Nicrophorus orbicollis (Say, 1825) before implementation of a mark-recapture study in situ. We compared the performance of Hotspotter using both 'high-quality' and 'low-quality' photographs. For high-quality photographs, Hotspotter had a false rejection rate of 2.7-3.0% for laboratory-reared individuals and 3.9% for wild-caught individuals. For low-quality photographs, the false rejection rate was much higher, 48.8-53.3% for laboratory-reared individuals and 28.3% for wild-caught individuals. We subsequently analyzed encounter histories of wild-caught individuals with closed population models in Program MARK to estimate population abundance. In our study, we demonstrated the utility of using PMR in estimating population abundance for Nicrophorus spp. based on elytral spot patterns.

Abundance of East coast Australian humpback whales (Megaptera novaeangliae) in 2005 estimated using multi-point sampling and capture-recapture analysis

The humpback whales (Megaptera novaeangliae) that migrate along the east coast of Australia were hunted to near extinction during the lastcentury. This remnant population is part of Breeding Stock E. Previous abundance estimates for the east Australian portion of Breeding Stock Ehave been based mainly on land-based counts. Here we present a capture-recapture abundance estimate for this population using photo-identificationdata. These data were collected at three locations on the migration route (Byron Bay – northern migration, Hervey Bay and Ballina – southernmigration) in order to estimate the population of humpback whales that migrated along the east coast of Australia in 2005. The capture-recapturedata were analysed using a variety of closed population models with a model-averaged estimate of 7,041 (95% CI 4,075–10,008) whales.

A Simulation Study on Increasing Capture Periods in Bayesian Closed Population Capture-Recapture Models with Heterogeneity

Capture-Recapture models are useful in estimating unknown population sizes. A common modeling challenge for closed population models involves modeling unequal animal catchability in each capture period, referred to as animal heterogeneity. Inference about population size N is dependent on the assumed distribution of animal capture probabilities in the population, and that different models can fit a data set equally well but provide contradictory inferences about N. Three common Bayesian Capture-Recapture heterogeneity models are studied with simulated data to study the prevalence of contradictory inferences is in different population sizes with relatively low capture probabilities, specifically at different numbers of capture periods in the study.

Competencia interespecífica y demografía de pequeños mamíferos en hábitats lineales

Fil: Serafini, Vanesa Natalia. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas Fisicoquimicas y Naturales. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente; Argentina

A spatial open-population capture-recapture model.

A spatial open-population capture-recapture model is described that extends both the non-spatial open-population model of Schwarz and Arnason and the spatially explicit closed-population model of Borchers and Efford. The superpopulation of animals available for detection at some time during a study is conceived as a two-dimensional Poisson point process. Individual probabilities of birth and death follow the conventional open-population model. Movement between sampling times may be modeled with a dispersal kernel using a recursive Markovian algorithm. Observations arise from distance-dependent sampling at an array of detectors. As in the closed-population spatial model, the observed data likelihood relies on integration over the unknown animal locations; maximization of this likelihood yields estimates of the birth, death, movement, and detection parameters. The models were fitted to data from a live-trapping study of brushtail possums (Trichosurus vulpecula) in New Zealand. Simulations confirmed that spatial modeling can greatly reduce the bias of capture-recapture survival estimates and that there is a degree of robustness to misspecification of the dispersal kernel. An R package is available that includes various extensions.

Population dynamics of an endangered forest bird using mark–recapture models based on DNA-tagging

Populations of vertebrates are built of individuals of different sex, age class or stage, which often affect distinctly the population dynamics. Such intrapopulation partitioning of vital rates needs to be identified to develop efficient conservation actions. Using DNA extracted from feces and feathers we combined DNA-tagging and mark–recapture analyses to evaluate sex-specific population dynamics of an endangered population of capercaillie (Tetrao urogallus; Phasianidae). We built encounter histories for 120 individuals in the mating seasons of 2009–2011, in a study area of about 424 km2. Minimum number of individuals per mating season and estimates of population size ranged 56–67 and 76–115, respectively. Estimates of population size were consistently lower in multiple-season, open-population models than in single-season closed-population models. The super-population in the study area was 149 individuals for the whole study period. Sex-ratio was notably male-biased. Probability of recapture p ranged 0.62–0.70, and was similar for males and females. Female apparent survival φ was lower than expected, and much lower than male apparent survival. It includes however movements in and out of the sampled population, thus comparison with previously reported values based on conventional tagging should be cautious. Females showed higher turnover, indicated by higher probability β of entering the sampled population, and higher number of entries from the super-population, Bgross. Realized population growth rate ʎ was > 1 for both females and males. The combination of non-intrusive DNA-tagging and the analytical framework of mark–recapture models provided inferences on population dynamics that would have been hardly feasible with conventional methods. Male-biased sex ratios, higher female turnover and seemingly low female apparent survival were our key findings. While the whole population needs continuous monitoring, we believe that adult females deserve priority attention in evaluation and design of conservation actions.

On the estimation of population sizes in capture–recapture experiments

This work considers a nested mark–recapture experiment with two levels of sampling: within each primary sampling period of an open population model, there are secondary capture occasions to estimate the size of the population at that primary period. This scheme is known as Pollock’s robust design. Two sources of information are then available to estimate the population size for a primary period: the within and the between primary period data. This work proves that the population size estimators derived from these two sources are asymptotically independent for a large class of closed population models. In this context, the robust design maximum likelihood estimator of population size is shown to be asymptotically equivalent to a weighted sum of the estimators for the open population Jolly–Seber model (Jolly, 1965; Seber, 1965) and for the closed population model. This article shows that the weighted estimator is more efficient than the moment estimator of Kendall et al. (1995). A closed form expression for the efficiency associated with this estimator is given and evaluated in a Monte Carlo study and in a numerical example about the estimation of the size of dolphin populations discussed by Santostasi et al. (2016).

Open population maximum likelihood spatial capture-recapture.

Open population capture-recapture models are widely used to estimate population demographics and abundance over time. Bayesian methods exist to incorporate open population modeling with spatial capture-recapture (SCR), allowing for estimation of the effective area sampled and population density. Here, open population SCR is formulated as a hidden Markov model (HMM), allowing inference by maximum likelihood for both Cormack-Jolly-Seber and Jolly-Seber models, with and without activity center movement. The method is applied to a 12-year survey of male jaguars (Panthera onca) in the Cockscomb Basin Wildlife Sanctuary, Belize, to estimate survival probability and population abundance over time. For this application, inference is shown to be biased when assuming activity centers are fixed over time, while including a model for activity center movement provides negligible bias and nominal confidence interval coverage, as demonstrated by a simulation study. The HMM approach is compared with Bayesian data augmentation and closed population models for this application. The method is substantially more computationally efficient than the Bayesian approach and provides a lower root-mean-square error in predicting population density compared to closed population models.

Estimating the population size of the endangered white-clawed crayfish Austropotamobius pallipes using mark-recapture at three Special Areas of Conservation (SACS)

The white-clawed crayfish, Austropotamobius pallipes, is the sole native freshwater crayfish species found in Ireland, with Irish populations being considered the most substantial and important in Europe. At present, the size of the majority of Irish crayfish populations is unknown. Recent outbreaks of the crayfish plague Aphanomyces astaci in Ireland amplify the need to acquire accurate population estimates. The Schnabel estimator and closed population model, the Mth model, were employed in this study to estimate the adult A. pallipes population sizes from three specific sites. All adult individuals captured using both hand-search and baited trap methods were marked by ablation and released back into the sampling area in close proximity to suitable refuges. Both methods provided similar population estimates, although the Mth model appears to be the most precise. The estimated adult crayfish population size using the Mth model method was 214 individuals at the River Abbert, 1392 at the River Manulla, 18,153 at Lough Owel Site 1 and 27,325 at Lough Owel Site 2. A significant relationship was found between baited trap CPUE and population estimate, indicating that with further research a CPUE value could be used to generate a rough estimate of population size. Mark-recapture data and population estimate results indicate abundant populations of A. pallipes are present at each site.