Capture-recapture Approach Research Articles

Estimation ofMuscardinus avellanariuspopulation density by live-trapping

Common dormouse (Muscardinus avellanarius) density in Transylvanian Plain is investigated using live-traps. Estimated population size is 39 individuals. Results using non-spatial methods combined with ad hoc calculations of the effective trapping area overestimated common dormouse density, both when using the naive density estimation (27 ind./ha) and also when the “edge-effect” was accounted for by the addition of a boundary strip (16 ind./ha). Compared with published results using the same methods, our results are yet significantly higher. Spatially explicit capture-recapture approach yields lower density, of 13 ind./ha (maximum likelihood estimate), but still one of the highest densities reported for the species. Interspecific competition for traps was negligible at our study site.

Application of Spatial and Closed Capture-Recapture Models on Known Population of the Western Derby Eland (Taurotragus derbianus derbianus) in Senegal.

Camera trapping with capture-recapture analyses has provided estimates of the abundances of elusive species over the last two decades. Closed capture-recapture models (CR) based on the recognition of individuals and incorporating natural heterogeneity in capture probabilities are considered robust tools; however, closure assumption is often questionable and the use of an Mh jackknife estimator may fail in estimations of real abundance when the heterogeneity is high and data is sparse. A novel, spatially explicit capture-recapture (SECR) approach based on the location-specific capture histories of individuals overcomes the limitations of closed models. We applied both methods on a closed population of 16 critically endangered Western Derby elands in the fenced 1,060-ha Fathala reserve, Senegal. We analyzed the data from 30 cameras operating during a 66-day sampling period deployed in two densities in grid and line arrays. We captured and identified all 16 individuals in 962 trap-days. Abundances were estimated in the programs CAPTURE (models M0, Mh and Mh Chao) and R, package secr (basic Null and Finite mixture models), and compared with the true population size. We specified 66 days as a threshold in which SECR provides an accurate estimate in all trapping designs within the 7-times divergent density from 0.004 to 0.028 camera trap/ha. Both SECR models showed uniform tendency to overestimate abundance when sampling lasted shorter with no major differences between their outputs. Unlike the closed models, SECR performed well in the line patterns, which indicates promising potential for linear sampling of properly defined habitats of non-territorial and identifiable herbivores in dense wooded savanna conditions. The CR models provided reliable estimates in the grid and we confirmed the advantage of Mh Chao estimator over Mh jackknife when data appeared sparse. We also demonstrated the pooling of trapping occasions with an increase in the capture probabilities, avoiding violation of results.

Editorial

Editorial

The Capture-Recapture approach for population estimation in computer networks

The estimation of a large population’s size by means of sampling procedures is a key issue in many networking scenarios. Their application domains span from RFID systems to peer-to-peer networks; from traffic analysis to wireless sensor networks; from multicast networks to WLANs. The present contribution aims at illustrating and classifying in a coherent framework the main approaches proposed so far in the computer networks literature to deal with such a problem. In particular, starting from the methodologies proposed in ecological studies since the last century, this paper surveys their counterparts in the computer network domain, finding that many lessons can be gained from this insightful investigation. Capture-Recapture techniques are deeply analyzed to allow the reader to exactly understand their pros, cons, and applicability bounds. Finally, some open issues that deserve further investigations and could be relevant to afford estimation problems in next generation Internet are discussed for sake of completeness.

Estimating trends in the prevalence of problematic cocaine use (1999-2008)

ObjectiveTo examine trends in the prevalence of problematic cocaine use in a large city and describe the problems encountered when estimating these trends using capture-recapture techniques based on secondary data MethodsWe used clinical data on accident and emergency department episodes at four university hospitals in Barcelona (Spain) between 1999 and 2008 (3 capture periods per year). Users were categorized into two subgroups depending on concomitant heroin use (cocaine plus heroin, cocaine without heroin). ResultsThe mean age of users was 34 years and 25% were women (2008). The mean number of episodes per user differed between drug subgroups and over time. The estimated total number of cocaine users increased from 6,028 (95% confidence interval [95%CI]: 4,086-9,327) in 1999 to 22,640 (95%CI: 14,001-37,500) in 2006, but decreased thereafter. The prevalence of problematic use of cocaine plus heroin was stable throughout the study. Thus, trends in the prevalence of problematic cocaine use differed depending on concomitant heroin use. ConclusionOur results are consistent with those provided by health surveys and treatment registries. They also highlight the pitfalls of applying the capture-recapture approach to secondary data, and the need for a better understanding of how information is collected and changes over time.

Quantitative and qualitative assessment of the bovine abortion surveillance system in France

Bovine abortion is the main clinical sign of bovine brucellosis, a disease of which France has been declared officially free since 2005. To ensure the early detection of any brucellosis outbreak, event-driven surveillance relies on the mandatory notification of bovine abortions and the brucellosis testing of aborting cows. However, the under-reporting of abortions appears frequent. Our objectives were to assess the aptitude of the bovine abortion surveillance system to detect each and every bovine abortion and to identify factors influencing the system's effectiveness. We evaluated five attributes defined by the U.S. Centers for Disease Control with a method suited to each attribute: (1) data quality was studied quantitatively and qualitatively, as this factor considerably influences data analysis and results; (2) sensitivity and representativeness were estimated using a unilist capture–recapture approach to quantify the surveillance system's effectiveness; (3) acceptability and simplicity were studied through qualitative interviews of actors in the field, given that the surveillance system relies heavily on abortion notifications by farmers and veterinarians. Our analysis showed that (1) data quality was generally satisfactory even though some errors might be due to actors’ lack of awareness of the need to collect accurate data; (2) from 2006 to 2011, the mean annual sensitivity – i.e. the proportion of farmers who reported at least one abortion out of all those who detected such events – was around 34%, but was significantly higher in dairy than beef cattle herds (highlighting a lack of representativeness); (3) overall, the system's low sensitivity was related to its low acceptability and lack of simplicity. This study showed that, in contrast to policy-makers, most farmers and veterinarians perceived the risk of a brucellosis outbreak as negligible. They did not consider sporadic abortions as a suspected case of brucellosis and usually reported abortions only to identify their cause rather than to reject brucellosis. The system proved too complex, especially for beef cattle farmers, as they may fail to detect aborting cows at pasture or have difficulties catching them for sampling. By investigating critical attributes, our evaluation highlighted the surveillance system's strengths and needed improvements. We believe our comprehensive approach can be used to assess other event-driven surveillance systems. In addition, some of our recommendations on increasing the effectiveness of event-driven brucellosis surveillance may be useful in improving the notification rate for suspected cases of other exotic diseases.

A comparison of death recording by health centres and civil registration in South Africans receiving antiretroviral treatment

IntroductionThere is uncertainty regarding the completeness of death recording by civil registration and by health centres in South Africa. This paper aims to compare death recording by the two systems, in cohorts of South African patients receiving antiretroviral treatment (ART).MethodsCompleteness of death recording was estimated using a capture–recapture approach. Six ART programmes linked their patient record systems to the vital registration system using civil identity document (ID) numbers and provided data comparing the outcomes recorded in patient files and in the vital registration. Patients were excluded if they had missing/invalid IDs or had transferred to other ART programmes.ResultsAfter exclusions, 91,548 patient records were included. Of deaths recorded in patients files after 2003, 94.0% (95% CI: 93.3–94.6%) were recorded by civil registration, with completeness being significantly higher in urban areas, older adults and females. Of deaths recorded by civil registration after 2003, only 35.0% (95% CI: 34.2–35.8%) were recorded in patient files, with this proportion dropping from 60% in 2004–2005 to 30% in 2010 and subsequent years. Recording of deaths in patient files was significantly higher in children and in locations within 50 km of the health centre. When the information from the two systems was combined, an estimated 96.2% of all deaths were recorded (93.5% in children and 96.2% in adults).ConclusionsSouth Africa's civil registration system has achieved a high level of completeness in the recording of mortality. However, the fraction of deaths recorded by health centres is low and information from patient records is insufficient by itself to evaluate levels and predictors of ART patient mortality. Previously documented improvements in ART mortality over time may be biased if based only on data from patient records.

Estimating nest abundance while accounting for time‐to‐event processes and imperfect detection

Birds and their population dynamics are often used to understand and document anthropogenic effects on biodiversity. Nest success is a critical component of the breeding output of birds in different environments; but to obtain the complete picture of how bird populations respond to perturbations, we also need an estimate of nest abundance or density. The problem is that raw counts generally underestimate actual nest numbers because detection is imperfect and because some nests may fail or fledge before being subjected to detection efforts. Here we develop a state‐space superpopulation capture–recapture approach in which inference about detection probability is based on the age at first detection, as opposed to the sequence of re‐detections in standard capture–recapture models. We apply the method to ducks in which (1) the age of the nests and their initiation dates can be determined upon detection and (2) the duration of the different stages of the breeding cycle is a priori known. We fit three model variants with or without assumptions about the phenology of nest initiation dates, and use simulations to evaluate the performance of the approach in challenging situations. In an application to Blue‐winged Teal Anas discors breeding at study sites in North and South Dakota, USA, nesting stage (egg‐laying or incubation) markedly influenced nest survival and detection probabilities. Two individual covariates, one binary covariate (presence of grazing cattle at the nest site), and one continuous covariate (Robel index of vegetation), had only weak effects. We estimated that 5–10% of the total number of nests were available for detection but were missed by field crews. An additional 6–15% were never available for detection. These percentages are expected to be larger in less intense, more typical sampling designs. User‐friendly software nestAbund is provided to assist users in implementing the method.

Tiger density in a tropical lowland forest in the Eastern Himalayan Mountains.

Tropical evergreen forests in northeast India are a biological hot spot for conservation of flora and fauna. Little is known, however, about tiger abundance, which is a flagship species for tropical evergreen forests. Our objective was to document the capture rate and population density of tigers based on spatial explicit capture-recapture (SECR) approaches using camera trap data in an intensive study area (ISA) of 158 km2 in Pakke Tiger Reserve (PTR) during March to May 2006. The Reserve lies in the foothills of the Eastern Himalayan Mountains, northeast India. We monitored 38 camera traps in ISA for 70 days and documented 10 photo-captures of tigers (5 left and 5 right flanks) with an average trap success rate of 1.3 captures/100 trap days. The overall capture probability was 0.05. The tiger density estimated using a SECR model was 0.97 ± 0.23 individuals/100 km2. This is the first systematic sampling study in tropical semi evergreen forests of India, and information on capture rate and population density of tigers provides baseline data from which to determining changes in the future to assist conservation.

Estimating dispersal among numerous sites using capture-recapture data.

Dispersal affects processes as diverse as habitat selection, population growth, and gene flow. Inference about dispersal and its variation is thus crucial for assessing population and evolutionary dynamics. Two approaches are generally used to estimate dispersal in free-ranging animals. First, multisite capture-recapture models estimate movement rates among sites while accounting for survival and detection probabilities. This approach, however, is limited in the number of sites that can be considered. Second, diffusion models estimate movements within discrete habitat using a diffusion coefficient, resulting in a continuous processing of space. However, this approach has been rarely used because of its mathematical and implementation complexity. Here, we develop a multi-event capture-recapture approach that circumvents the issue of too many sites while being relatively simple to be implemented in existing software. Moreover, this new approach allows the quantifying of memory effects, whereby the decision of dispersing or not on a given year impacts the survival or dispersal likelihood of the following year. We illustrate our approach using a long-term data set on the breeding ecology of a declining passerine in southern Quebec, Canada, the Tree Swallow (Tachycineta bicolor).

Using double-observer aerial surveys to monitor nesting bald eagles in Alaska: Are all nests available for detection?

The abundance of nesting eagles is often identified as the parameter of primary interest for monitoring their populations. We compared the standard dual-frame estimator, which is recommended in the bald eagle post-delisting monitoring plan, with a Bayesian multistate capture-recapture approach to estimate the total number and number of active nests (nests with incubating adults) along the remote Kenai Fjords National Park coastline from 2009 to 2012. Two independent observers conducted aerial surveys of random transects during peak nest initiation in May. Both methods produced similar estimates of nest abundance, but the Bayesian multistate model allowed more flexibility to accommodate shifting management priorities. Estimates of the total number of nests and the number of active nests increased by approximately 49% between 2009 and 2012. This increase was much greater than expected based on feasible rates of nest loss and creation for our study area, indicating apparent estimator bias. Survey-specific conditions (e.g., aircraft height) that made some nests unavailable to both observers were the most likely cause of the bias. We recommend that bald eagle nest monitoring include 2 surveys during the early breeding season to reduce bias of annual capture-recapture estimators. Our results demonstrate that incomplete availability may be an important source of bias for many double-observer aerial wildlife surveys. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Selection based on the size of the black tie of the great tit may be reversed in urban habitats.

A standard approach to model how selection shapes phenotypic traits is the analysis of capture–recapture data relating trait variation to survival. Divergent selection, however, has never been analyzed by the capture–recapture approach. Most reported examples of differences between urban and nonurban animals reflect behavioral plasticity rather than divergent selection. The aim of this paper was to use a capture–recapture approach to test the hypothesis that divergent selection can also drive local adaptation in urban habitats. We focused on the size of the black breast stripe (i.e., tie width) of the great tit (Parus major), a sexual ornament used in mate choice. Urban great tits display smaller tie sizes than forest birds. Because tie size is mostly genetically determined, it could potentially respond to selection. We analyzed capture/recapture data of male great tits in Barcelona city (N = 171) and in a nearby (7 km) forest (N = 324) from 1992 to 2008 using MARK. When modelling recapture rate, we found it to be strongly influenced by tie width, so that both for urban and forest habitats, birds with smaller ties were more trap-shy and more cautious than their larger tied counterparts. When modelling survival, we found that survival prospects in forest great tits increased the larger their tie width (i.e., directional positive selection), but the reverse was found for urban birds, with individuals displaying smaller ties showing higher survival (i.e., directional negative selection). As melanin-based tie size seems to be related to personality, and both are heritable, results may be explained by cautious personalities being favored in urban environments. More importantly, our results show that divergent selection can be an important mechanism in local adaptation to urban habitats and that capture–recapture is a powerful tool to test it.

Fine-Scale Genetic Structure and Cryptic Associations Reveal Evidence of Kin-Based Sociality in the African Forest Elephant

Spatial patterns of relatedness within animal populations are important in the evolution of mating and social systems, and have the potential to reveal information on species that are difficult to observe in the wild. This study examines the fine-scale genetic structure and connectivity of groups within African forest elephants, Loxodonta cyclotis, which are often difficult to observe due to forest habitat. We tested the hypothesis that genetic similarity will decline with increasing geographic distance, as we expect kin to be in closer proximity, using spatial autocorrelation analyses and Tau Kr tests. Associations between individuals were investigated through a non-invasive genetic capture-recapture approach using network models, and were predicted to be more extensive than the small groups found in observational studies, similar to fission-fusion sociality found in African savanna (Loxodonta africana) and Asian (Elephas maximus) species. Dung samples were collected in Lopé National Park, Gabon in 2008 and 2010 and genotyped at 10 microsatellite loci, genetically sexed, and sequenced at the mitochondrial DNA control region. We conducted analyses on samples collected at three different temporal scales: a day, within six-day sampling sessions, and within each year. Spatial autocorrelation and Tau Kr tests revealed genetic structure, but results were weak and inconsistent between sampling sessions. Positive spatial autocorrelation was found in distance classes of 0–5 km, and was strongest for the single day session. Despite weak genetic structure, individuals within groups were significantly more related to each other than to individuals between groups. Social networks revealed some components to have large, extensive groups of up to 22 individuals, and most groups were composed of individuals of the same matriline. Although fine-scale population genetic structure was weak, forest elephants are typically found in groups consisting of kin and based on matrilines, with some individuals having more associates than observed from group sizes alone.

Inferences about population dynamics from count data using multistate models: a comparison to capture–recapture approaches

Wildlife populations consist of individuals that contribute disproportionately to growth and viability. Understanding a population's spatial and temporal dynamics requires estimates of abundance and demographic rates that account for this heterogeneity. Estimating these quantities can be difficult, requiring years of intensive data collection. Often, this is accomplished through the capture and recapture of individual animals, which is generally only feasible at a limited number of locations. In contrast, N-mixture models allow for the estimation of abundance, and spatial variation in abundance, from count data alone. We extend recently developed multistate, open population N-mixture models, which can additionally estimate demographic rates based on an organism's life history characteristics. In our extension, we develop an approach to account for the case where not all individuals can be assigned to a state during sampling. Using only state-specific count data, we show how our model can be used to estimate local population abundance, as well as density-dependent recruitment rates and state-specific survival. We apply our model to a population of black-throated blue warblers (Setophaga caerulescens) that have been surveyed for 25 years on their breeding grounds at the Hubbard Brook Experimental Forest in New Hampshire, USA. The intensive data collection efforts allow us to compare our estimates to estimates derived from capture–recapture data. Our model performed well in estimating population abundance and density-dependent rates of annual recruitment/immigration. Estimates of local carrying capacity and per capita recruitment of yearlings were consistent with those published in other studies. However, our model moderately underestimated annual survival probability of yearling and adult females and severely underestimates survival probabilities for both of these male stages. The most accurate and precise estimates will necessarily require some amount of intensive data collection efforts (such as capture–recapture). Integrated population models that combine data from both intensive and extensive sources are likely to be the most efficient approach for estimating demographic rates at large spatial and temporal scales.

Known unknowns in an imperfect world: incorporating uncertainty in recruitment estimates using multi-event capture-recapture models.

Studying the demography of wild animals remains challenging as several of the critical parts of their life history may be difficult to observe in the field. In particular, determining with certainty when an individual breeds for the first time is not always obvious. This can be problematic because uncertainty about the transition from a prebreeder to a breeder state – recruitment – leads to uncertainty in vital rate estimates and in turn in population projection models. To avoid this issue, the common practice is to discard imperfect data from the analyses. However, this practice can generate a bias in vital rate estimates if uncertainty is related to a specific component of the population and reduces the sample size of the dataset and consequently the statistical power to detect effects of biological interest. Here, we compared the demographic parameters assessed from a standard multistate capture–recapture approach to the estimates obtained from the newly developed multi-event framework that specifically accounts for uncertainty in state assessment. Using a comprehensive longitudinal dataset on southern elephant seals, we demonstrated that the multi-event model enabled us to use all the data collected (6639 capture–recapture histories vs. 4179 with the multistate model) by accounting for uncertainty in breeding states, thereby increasing the precision and accuracy of the demographic parameter estimates. The multi-event model allowed us to incorporate imperfect data into demographic analyses. The gain in precision obtained has important implications in the conservation and management of species because limiting uncertainty around vital rates will permit predicting population viability with greater accuracy.

Combining camera-trapping and noninvasive genetic data in a spatial capture–recapture framework improves density estimates for the jaguar

Abundance and density are key pieces of information for questions related to ecology and conservation. These quantities, however, are difficult to obtain for rare and elusive species, where even intensive sampling effort can yield sparse data. Here, we combine data from camera-trapping and noninvasive genetic sampling (scat surveys) of a jaguar population in the Caatinga of northeastern Brazil, where the species is threatened and little studied. We analyze data of both survey types separately and jointly in the framework of spatial capture–recapture. Density estimates were 1.45 (±0.46) for the camera-trap data alone, 2.03 (±0.77) for the genetic data alone, and 1.57 (±0.43) and 2.45 (±0.70) for the two methods, respectively, in the joint analysis. Density and other parameters were estimated more precisely in the joint model. Particularly the differences in movement between males and females were estimated much more precisely when combining both data sources, especially compared to the genetic data set alone. When compared to a previous non-spatial capture–recapture approach, present density estimates were more precise, demonstrating the superior statistical performance of spatial over non-spatial capture recapture models. The ability to combine different surveys into a single analysis with shared parameter allows for more precise population estimates, while at the same time enabling researchers to employ complementary survey techniques in the study of little known species.

Habitat-dependent population recovery in the Dartford Warbler Sylvia undata following a severe winter episode

Capsule After a population crash following a long period of winter freezing and snow blanketing the ground, Dartford Warblers underwent a population recovery, positive in heathlands but non-existent in nearby early-growth forest. Aims To estimate the impact of a severe winter episode on the population size of Dartford Warblers in two habitats, heathland and early-growth forest. Methods We analysed data collected on 124 point counts in three successive years, 1 year before and 2 years after the cold spell. We first estimated trends in detected numbers in the two habitats. Second, we used distance sampling and capture–recapture approaches to estimate global population sizes corrected for detection probability, verifying that the observed trends were not biased by detection probability. Results Warbler populations crashed after the severe winter in 2008–9, while numbers increased in spring 2010 only on heathlands, not in early-growth forests. Variation in detection probability alone could not explain this difference. Conclusion After the severe winter episode, Dartford Warblers showed a short-term population recovery only in heathland.

Assessing the mandatory bovine abortion notification system in France using unilist capture-recapture approach.

The mandatory bovine abortion notification system in France aims to detect as soon as possible any resurgence of bovine brucellosis. However, under-reporting seems to be a major limitation of this system. We used a unilist capture-recapture approach to assess the sensitivity, i.e. the proportion of farmers who reported at least one abortion among those who detected such events, and representativeness of the system during 2006–2011. We implemented a zero-inflated Poisson model to estimate the proportion of farmers who detected at least one abortion, and among them, the proportion of farmers not reporting. We also applied a hurdle model to evaluate the effect of factors influencing the notification process. We found that the overall surveillance sensitivity was about 34%, and was higher in beef than dairy cattle farms. The observed increase in the proportion of notifying farmers from 2007 to 2009 resulted from an increase in the surveillance sensitivity in 2007/2008 and an increase in the proportion of farmers who detected at least one abortion in 2008/2009. These patterns suggest a raise in farmers’ awareness in 2007/2008 when the Bluetongue Virus (BTV) was detected in France, followed by an increase in the number of abortions in 2008/2009 as BTV spread across the country. Our study indicated a lack of sensitivity of the mandatory bovine abortion notification system, raising concerns about the ability to detect brucellosis outbreaks early. With the increasing need to survey the zoonotic Rift Valley Fever and Q fever diseases that may also cause bovine abortions, our approach is of primary interest for animal health stakeholders to develop information programs to increase abortion notifications. Our framework combining hurdle and ZIP models may also be applied to estimate the completeness of other clinical surveillance systems.

Threatened predator on the equator: multi-point abundance estimates of the tiger Panthera tigris in central Sumatra

AbstractInformation on spatial and temporal variation in abundance is crucial for effective management of wildlife. Yet abundance estimates for the Critically Endangered Sumatran tiger Panthera tigris sumatrae are lacking from Riau, the province historically believed to hold the largest percentage of this subspecies. Recently, this area has had one of the highest global rates of deforestation. Using camera traps we investigated tiger abundance across peatland, flat lowland, and hilly lowland forest types in the province, and over time, in the newly established Tesso Nilo National Park, central Sumatra. We estimated densities using spatially explicit capture–recapture, calculated with DENSITY, and traditional capture–recapture models, calculated with CAPTURE. With spatially explicit capture–recapture the lowest tiger density (0.34 ± SE 0.24 per 100 km2) was estimated in the hilly lowland forest of Rimbang Baling and the highest (0.87 ± SE 0.33 per 100 km2) in the flat lowland forest of the Park. Repeated surveys in the Park documented densities of 0.63 ± SE 0.28 in 2005 to 0.87 ± SE 0.33 per 100 km2 in 2008. Compared to traditional capture–recapture the spatially explicit capture–recapture approach resulted in estimates 50% lower. Estimates of tiger density from this study were lower than most previous estimates in other parts of Sumatra. High levels of human activity in the area appear to limit tigers. The results of this study, which covered areas and habitat types not previously surveyed, are important for overall population estimates across the island, provide insight into the response of carnivores to habitat loss, and are relevant to the interventions needed to save the tiger.

Efficacy of novel sampling approaches for surveying specialised recreational fisheries

Advances in fishing technologies have increased the efficiency and diversification of recreational fisheries. This poses challenges for surveying specialised or ‘hard-to-reach’ recreational fishers (e.g. sport fishers) that may take the majority of the recreational catch for some species, but are too rare within the general population to be sampled cost-effectively using existing methods. We trialled two new methods—time-location sampling (TLS) and online diaries—for surveying specialised recreational longtail tuna (Thunnus tonggol) fishers. Results were compared with a concurrent traditional access point survey (APS). Online diaries were inexpensive but unsuitable for collecting representative data due to avidity, volunteerism, and differential recruitment bias. APS yielded high resolution data on catch, effort and size composition but was expensive and ineffective for sampling all components of the fishery. In contrast, TLS conducted at fishing tackle stores was cost-effective for accessing the breadth of fisher types due to the need for all fishers to purchase or to inspect fishing-related products at some point. Given the frequent absence of complete list frames for recreational fisheries, we suggest undertaking multiple TLS surveys to collect catch rate data and to simultaneously estimate population size using capture-recapture approaches in order to estimate the total recreational catch of species of interest.