Mark-recapture Population Estimates Research Articles

Integration of mark-recapture and acoustic detections for unbiased population estimation in animal communities.

Abundance estimation methods that combine several types of data are becoming increasingly common because they yield more accurate and precise parameter estimates and predictions than are possible from a single data source. These beneficial effects result from increasing sample size (through data pooling) and complementarity between different data types. Here, we test whether integrating mark-recapture data with passive acoustic detections into a joint likelihood improves estimates of population size in a multi-guild community. We compared the integrated model to a mark-recapture-only model using simulated data first and then using a data set of mist-net captures and acoustic recordings from an Afrotropical agroforest bird community. The integrated model with simulated data improved accuracy and precision of estimated population size and detection parameters. When applied to field data, the integrated model was able to produce, for each bird guild, ecologically plausible estimates of population size and detection parameters, with more precision compared with the mark-recapture model. Overall, our results show that adding acoustic data to mark-recapture analyses improves estimates of population size. With the increasing availability of acoustic recording devices, this data collection technique could readily be added to routine field protocols, leading to a cost-efficient improvement of traditional mark-recapture population estimation.

Survival of Advanced‐Fingerlings of Florida Largemouth Bass Stocked in Small Florida Lakes

AbstractNumerous stocking evaluations of pellet‐reared advanced‐fingerling (80–120 mm TL) Largemouth Bass Micropterus salmoides have assessed the contribution of stocked fish to the wild population, but few studies have quantified longer‐term (1–2 years) survival. Hatchery researchers have developed spawning Florida Largemouth Bass Micropterus salmoides floridanus (hereafter, "Florida Bass") out of season (i.e., in fall), allowing for a similar‐sized product to be stocked earlier in the spring. Managers are interested in whether poststocking survival is improved by new culture techniques and whether survival can be affected by conditioning (acclimating to the natural environment) the fish before stocking. In this study, we stocked 11 small (<100 ha) lakes in central Florida with pellet‐reared advanced‐fingerling (mean 105 mm TL) Florida Bass that were spawned out of season, and we conducted mark–recapture population estimates at 1 and 2 years poststocking to assess survival. In the second year of the study, four lakes were stocked a second time with two treatments of Florida Bass (naïve and conditioned) to test for the effects of conditioning the fish on survival within the stocked lakes in 0.1‐ha predator‐limited enclosures for 7 d. At 1 year poststocking, survival ranged from 0.0% to 8.2% (values were <2.5% for all but one lake) and averaged 1.8%. At 2 years poststocking, survival ranged from 0.0% to 2.4% and averaged 0.9%. From the restocked lakes in year 2, we found no effect of conditioning (P = 0.57) on the number of stocked Florida Bass that were caught at 1 year poststocking, and survival ranged from 0.1% to 1.5% for the naïve treatment and 0.2% to 1.4% for the conditioned treatment. Despite improved culture techniques and the attempt to acclimate the stocked fish to the wild, survival averaged <2% at 1 year poststocking. Knowledge of projected Florida Bass survival can help managers make informed stocking decisions that are more likely to meet their desired outcome.

Swimming nets have positive effects on populations of the endangered White's seahorse Hippocampus whitei

Abstract Habitat degradation and destruction arising from rapidly increasing urbanization represents one of the most significant threats to biodiversity. Human populations are continuing to increase around coastal regions, and as marine habitats are displaced by artificial structures it is important to understand how marine species may be impacted by these changes in habitat availability. The endangered seahorse Hippocampus whitei has been observed inhabiting protective swimming nets in Sydney Harbour, Sydney, Australia, even in the presence of natural habitats. This study tested whether the presence of a swimming net results in increased seahorse numbers at sites around Sydney Harbour, or whether seahorses are attracted away from natural habitats. Density surveys and mark–recapture population estimates were done at sites with pre‐existing swimming nets and compared to control sites where only natural habitat was present. A manipulative experiment was conducted in which panels of swimming net material were installed at two sites in Sydney Harbour, with comparisons to control sites over a period of 14 months (April 2018 to June 2019) to test whether the installation of swimming nets would affect seahorses on surrounding natural habitat or increase site abundance. The pre‐existing and installed swimming nets were found to support greater densities of H. whitei as well as some increases in site‐scale abundance, with no effects on seahorse density on natural habitats. It is likely that increased seahorse production is occurring on the nets, with no evidence that seahorses are being attracted away from natural habitat; however, effects may vary across survey occasions and sites. Furthermore, swimming nets may serve as a useful replacement habitat in locations where natural habitat has become sparse or absent.

Distribution, Habitat, and Population Size of Island Night Lizards on San Nicolas Island, California

The Island Night Lizard (Xantusia riversiana) was removed from the federal list of threatened species in May 2014. This strongly differentiated species is endemic to 3 of the southern California Channel Islands—San Clemente, San Nicolas, and Santa Barbara. Suitable habitat for Island Night Lizards is extensive on San Clemente Island, and the species is abundant there. Habitat is limited and fragmented, however, on San Nicolas Island and small Santa Barbara Island. Bringing together extensive field surveys and mark-recapture sampling, we synthesize available data for Island Night Lizards on San Nicolas Island and calculate population and density estimates for the species in major habitats on the island. Island Night Lizards are widely distributed across most of the eastern half of San Nicolas Island. In contrast, they are nearly absent over the western third of the island except for isolated populations in boulder beach habitats. We combined mark-recapture population estimates with comprehensive measurements of the extent of cactus, boxthorn, and other habitat types on the island to arrive at a more accurate assessment of the status of Island Night Lizards on San Nicolas Island. High densities of Island Night Lizards on the island are found in small areas of cholla cactus (Cylindropuntia prolifera; mean of 4100 lizards/ha), boulder beach habitat (mean of 3400 lizards/ha), and prickly pear cactus (Opuntia spp.; mean of 1700 lizards/ha); low numbers are found in more extensive mixed-shrub habitat (mean of 250 lizards/ha). The U.S. Fish and Wildlife Service requires a post-delisting program for “monitoring the overall health of the Island Night Lizard” to assure the continued long-term viability of the species in its restricted distribution. The information on population size and habitat presented here will inform and guide conservation and management efforts by the U.S. Navy on San Nicolas Island over the coming years.

The effect of wildfire on population dynamics for two native small mammal species in a coastal heathland in Queensland, Australia

The influences of wildfire through population dynamics and life history for two species of small mammals in a south-east Queensland heathland on Bribie Island are presented. Trapping results provided information on breeding, immigration and movement of Melomys burtoni (Grassland melomys) and Rattus lutreolus (Swamp rat). We first investigated and optimized the design of trapping methodology for producing mark-recapture population estimates to compare two adjacent populations, one of which was subjected to an extensive wildfire during the two year study. We consider how well rodents survive wildfire and whether the immediate impacts of fire or altered habitat have the greatest impact on each species. We found the R. lutreolus population was far more influenced by the fire than the M. burtoni population both immediately after the fire and over 18 months of vegetation recovery.

An assessment of the efficacy of rub stations for detection and abundance surveys of Canada lynx (Lynx canadensis)

Barbed and scented rub pads that rely on a cheek-rubbing behavioural response are a standard survey design that has been used extensively across the range of Canada lynx (Lynx canadensis Kerr, 1792). However, there have not been any published studies evaluating the effectiveness of rub stations for detecting lynx by comparing other simultaneous survey methods. We used a combination of paired rub stations and remote cameras at 41 sites to compare detection probabilities between the two methods and conduct a mark–recapture population estimate of Canada lynx using rub stations to further interpret our findings. The detection probability calculated using cameras approached 1.0 for most of the winter season (mean = 0.88), whereas it remained less than 0.52 for hair rub stations (mean = 0.27). The low and variable detection probability using hair snags, high detection probability using cameras, and the potential gender or individual bias in rubbing behaviour based on our mark–recapture analysis suggest that rub stations are not the most efficient survey method available for Canada lynx. Until additional research incorporating spatial scale, seasonal timing, gender bias, and survey design is conducted, we urge caution in the use of hair stations that rely on the cheek-rubbing behaviour of Canada lynx.

Comparison of Visual Survey and Mark–Recapture Population Estimates of a Benthic Fish in Hawaii

AbstractVisual surveys are conducted to rapidly estimate population densities of stream fishes, often without calibration against more established or more widely used methods to determine precision and accuracy or to correct for potential biases. We compared population density estimates from a visual survey (VS) point quadrat method widely used in Hawaii with estimates from “in hand” individual and batch mark–recapture (BMR) methods. Visual survey sampling and individual mark–recapture (IMR) sampling were conducted in three watersheds that represent gradients of land use and prevalence of nonnative poeciliid fishes on the Island of Hawaii. Focusing on adult O‘opu Nākea Awaous stamineus, VSs were conducted prior to IMR events to allow direct comparisons of results independent of location and time. Density estimates of O‘opu Nākea from VS and IMR samplings were strongly correlated, although VS estimates were generally higher and underrepresented exceptionally large fish. Batch mark–recapture estimates of O‘opu Nākea densities were conducted for comparison with VSs at 13 sites across the archipelago. Estimates of VSs were not significantly different from BMR estimates. Estimates of VSs also exhibited less variance than did BMR estimates across sites. General linear models showed that the relationship between VS and IMR estimates varied significantly among watersheds but not seasons and that land use was associated with a greater mismatch between VS and BMR estimates of population density. These findings indicate that visual surveys using a point quadrat method are an efficient and accurate approach for estimating the abundance of small benthic fishes, such as O‘opu Nākea, in wadeable streams and that obtaining absolute densities or size distributions from VS methods would benefit from a calibration with IMR not BMR estimates.Received July 15, 2015; accepted February 23, 2016 Published online June 29, 2016

A noninvasive method to detect Mexican wolves and estimate abundance

Monitoring wolf abundance is important for recovery efforts of Mexican wolves (Canis lupus baileyi) in the Blue Range Wolf Recovery Area in Arizona and New Mexico, USA. Although radiotelemetry has been a reliable method, collaring and tracking wolves in an expanding population will be prohibitively expensive and alternative methods to estimate abundance will become necessary. We applied 10 canid microsatellite loci to 235 Mexican wolf samples, 48 coyote (C. latrans) samples, and 14 domestic dog (C. lupus familiaris) samples to identify alleles that provide reliable separation of these species. We then evaluated an approach for prescreening, noninvasively collected DNA obtained from fecal samples to identify Mexican wolves. We generated complete genotypes for only those samples identified as probable Mexican wolves. We used these genotypes to estimate mark–recapture population estimates of Mexican wolves and compared these to known numbers of wolves in the study area. We collected fecal samples during 3 sampling periods in 2007–2008 and used Huggins-type mark–recapture models to estimate Mexican wolf abundance. We were able to generate abundance estimates with 95% confidence for 2 of 3 sampling periods. We estimated abundance to be 10 (95% CI = 6–34) during one sampling period when the known abundance was 10 and we estimated abundance to be 9 (95% CI = 6–30) during the other sampling period when the known abundance was 10. The application of this noninvasive method to estimate Mexican wolf abundance provides an alternative monitoring tool that could be useful for long-term monitoring of this and other recovering populations. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Elytron-Branding as a Permanent Marking Technique forNicrophorusFabricius (Coleoptera: Silphidae)

Abstract Mark-recapture population estimates require the use of permanent marks that do not alter the survival or behavior of marked individuals. A number of marks have been developed to monitor populations of the federally endangered American burying beetle, Nicrophorus americanus Olivier. Surveys that employ marks are needed to determine population size and monitor population trends, which are required information to support recovery of this insect. However, studies have revealed problems with mark retention or damage to tested individuals associated with permanent marks. Currently used permanent marking techniques involve making a hole or removing a wedge from an ABB elytron. In this study, we tested the efficacy of elytron branding using a surgical cauterizer. The cauterizer was used to ablate one of the orange maculations on the elytron of four species of Nicrophorus Fabricius. We found that the marking technique was rapid compared with other techniques, permanent, and easily interpreted. American bu...

Photo-ID as a tool for studying and monitoring the endangered Saimaa ringed seal

Photo-identification (photo-ID) with camera traps was examined as a non-invasive method for studying and monitoring the endangered Saimaa ringed seal Phoca hispida saimensis. An average of 51 game cameras were set up at shoreline haul-out sites in central Lake Saimaa during the moulting seasons in each of the years from 2010 to 2014. Individuals were identified from their lifelong unique lateral fur patterns. A total of 220 000 digital images of seals were obtained from these game cameras and from digital cameras during this period, allowing 164 indi- viduals to be identified, 43% of which were re-sighted in successive years. In the majority of game camera images, both sides of the seal were shown, and it was possible to determine the sex of the seal. The average distance between sightings of individual seals in different years was 1.6 km, suggesting that Saimaa ringed seals exhibit a high degree of moulting site fidelity. In addition, the results support suggestions of natal site fidelity. We propose that photo-ID sampling based on camera traps, and larger-scale photographic survey of the seals, should be implemented as a pop- ulation monitoring tool of the Saimaa ringed seal. Further application of the photo-ID technique may facilitate mark-recapture population and survival rate estimates for this threatened seal spe- cies and provide significant insights into its life history and social behaviour.

Improved Models for Predicting Walleye Abundance and Setting Safe Harvest Quotas in Northern Wisconsin Lakes

AbstractIn Wisconsin, the management of Walleyes Sander vitreus relies on a set of log‐linear regressions to predict Walleye abundance and to set safe harvest. The regression models predict mean Walleye abundance from lake area, but they ignore variability among years; they also predict equal Walleye populations in lakes with the same size and recruitment source. We evaluated three alternative models in terms of predictive accuracy and the risk of overharvest. We used 899 mark–recapture population estimates (collected between 1953 and 2013) from 219 lakes to develop and evaluate (1) a log‐linear mixed‐effects model that used all individual observations and estimated adult Walleye abundance from lake area and lake‐specific deviations from the overall intercept; (2) a mixed‐effects model that builds on model 1 by adding a linear fixed effect of sampling year; and (3) a mixed‐effects model that builds on model 1 by adding a random year effect. Walleye abundance was positively correlated with lake area in all models and was negatively correlated with sampling year (when included). Alternative models improved predictive accuracy by 17–22% over the current regression model. Restricting data to those collected during the most recent 20 years improved model responsiveness to new data and reduced the value of including a linear time trend. When all data were used for model construction, the relative risk of overharvest was lowest under the mixed‐effects model with a linear time trend; when the most recent 20 years of data were used, the risk was lowest under the mixed‐effects model with a random year effect. Accounting for variability among years would allow harvest to track changing Walleye populations and would allow management to be more adaptive. We recommend using the mixed‐effects model with a random year effect and restricting the data inputs to the most recent 20 years.Received May 20, 2015; accepted September 17, 2015

Distribution and Abundance of Alvord Chub in Oregon and Nevada

Abstract Alvord Chub are small minnows endemic to the Alvord Basin, a endorheic desert basin in southeastern Oregon and northwestern Nevada. Comprehensive distribution surveys were last conducted 30 y ago. Recent, limited surveys raised concern that the range and abundance of Alvord Chub may have contracted. We conducted a comprehensive survey at historically occupied locations in 2013 and obtained mark-recapture population estimates. Despite 2 y of below average precipitation, Alvord Chub were present at the majority of historically occupied drainages, were abundant at many locations, but were restricted in distribution in several drainages. Additionally, we documented current threats, which included water withdrawals, nonnative fishes, grazing, habitat fragmentation, and desiccation. Based on our observations, we suggest a number of management recommendations.

An evaluation of multiple-pass seining to monitor blackstripe topminnow Fundulus notatus (Rafinesque, 1820) in the Sydenham River (Ontario, Canada)

Summary Multiple-pass (i.e. removal) sampling and mark-recapture experiments were undertaken in the Sydenham River (Ontario, Canada) to assess the effectiveness of seining to detect and estimate the local abundance of blackstripe topminnow, Fundulus notatus (Rafinesque, 1820) as well as to compare catch characteristics from closed and open (with and without block nets) sample units. Probability of species detection using three-pass seining was estimated to be 0.58 in closed units, and 0.51 in open units. To be 95% confident of occupancy status, a minimum of five repeat surveys is required. A decline in catch occurred in only half of the sample units, population size estimates were often imprecise, and attempts to generate mark-recapture population estimates were unsuccessful. Mean capture probabilities were 0.48 in closed units and 0.65 in open units, when depletion occurred. For blackstripe topminnow and other fishes encountered, there were no significant differences between closed and open units in the frequency of depletion or capture probability. Compared to single-pass surveys, monitoring programs that employ three seine hauls are more likely to detect the presence of the blackstripe topminnow and any decline in local abundance.

Mark–recapture and playback surveys reveal a steep decline of European Storm Petrels Hydrobates pelagicus at the largest colony in western Scotland

None of the indices of population change for seabirds in the northeast Atlantic have included European Storm Petrel Hydrobates pelagicus, because their cryptic breeding behaviour makes monitoring difficult. The aim of this paper is to present the results of a long-term project to monitor this species on Priest Island, one of the largest breeding colonies in Scotland. Mark–recapture and playback-response methods both showed a steep decline in the population size between 2001 and 2012. The population estimate at the main study site used for mark–recapture was 8,472 birds ± 1,466 (standard error) in 2001 and has declined by about 460 birds per year to 3,854 ± 437 in 2012. The adult annual survival rate was high in 2001/02 and 2002/03 but has since fluctuated between 0.73 and 0.83; these survival estimates are lower than those for the whole of Britain & Ireland estimated from ring recoveries (0.86 from 1967 to 1996, and above 0.9 since 2007/08). Recaptures of birds at three sites at varying distances from the main site used for this study indicated that only birds at the nearest site (c 90 m away) could be considered to be part of the same breeding population. Thus, the minimum distance between study sites for mark–recapture population estimates should be in excess of 100 m. The decline in population revealed by this study may be due to insufficient recruitment resulting from poor productivity, low survival to breeding age, or emigration, and emphasises the importance of future studies to monitor productivity.

Assessing noninvasive hair and fecal sampling for monitoring the distribution and abundance of river otter

AbstractMonitoring the distribution and abundance of populations is an important component of efforts to meet management or conservation goals. Although the objectives for such studies are easy to define, cost‐effective, precise, and accurate estimates are often elusive. We tested the efficacy and compared the cost‐effectiveness of methods for estimating the number and recording the distribution of river otter (Lontra canadensis). We genotyped otter hair sampled using two noninvasive instruments and compared those results with a hypothetical study design based on DNA extracted from fecal matter. Patterns of distribution generated from DNA collected at latrine sites were then compared to observations of otter collected using VHF radiotelemetry. We achieved a high probability of genotyping river otter with a small number of hairs (i.e., 59.0 % probability of producing a genotype with 1 guard hair and >5 under hair samples) collected using wire body snares and knaplock hair snags. Body snares were more effective at collecting otter hair, but there was relatively little additional cost to using both sampling instruments. Genotyped hair resulted in a high multi‐year recapture rate (61.9 %). Hair collection and genotyping was the most cost‐effective method for monitoring populations of river otter ($168.50 US/datum) followed by radiotelemetry ($264.50 US/datum), and the extraction of DNA from fecal matter ($266.00 US/datum). However, the noninvasive techniques did not represent the full distribution and fine‐scale movements of otter, as observed using radiotelemetry. There has been much recent reporting of the efficacy of fecal matter as a source of DNA for conducting mark–recapture population estimates for mesocarnivores. Our data suggested that collecting DNA in hair may be a more cost‐effective and efficient approach.

Population Densities of the Threatened Blackside Dace, Chrosomus cumberlandensis, in Kentucky and Tennessee

Chrosomus cumberlandensis (Blackside Dace) is a rare cyprinid fish restricted to small tributaries in the upper Cumberland River drainage in southeastern Kentucky and northeastern Tennessee. One hundred and nineteen 200-m reaches within 55 streams were sampled during June–August 2003, 2005, and 2006 via AC and pulsed-DC singlepass backpack electrofishing, thereby representing the most comprehensive quantitative survey conducted for this species to date. Dace were found to inhabit 43 of 55 streams and 78 of 119 reaches, although in two-thirds of the reaches the species was either not detected or was present in low numbers (i.e., catch rates ≤10 dace per 200 m). For the 78 reaches where the dace was detected, single-pass electrofishing catch rates ranged from 1 to 151 (mean ± SD = 27 ± 34) dace per 200 m. Petersen mark-recapture population estimates conducted on 16 reaches within 12 streams were used to build a regression model to calibrate single-pass electrofishing catch for the remaining 62 reaches inhabited by dace. Population estimates for the 78 reaches harboring Blackside Dace averaged 90 ± 121 dace per 200 m, and associated densities averaged 14.1 ± 19.4 dace per 100 m2. Electrofishing sampling efficiency for Blackside Dace was 0.30 as revealed through our mark-recapture efforts. The small population sizes documented in many streams coupled with restricted distributions and relatively limited mobility may render many populations susceptible to local extinction due to stochastic events, poor recruitment, or additional habitat degradation.

Comparison of Two Life History Strategies after Impoundment of a Historically Anadromous Stock of Columbia River Redband Trout

AbstractIn this study we collected information on abundance, age structure, migration, and exploitation to characterize the population demographics and reproductive characteristics of a historically anadromous Columbia River Redband Trout Oncorhynchus mykiss gairdneri population now isolated in a southwestern Idaho reservoir and limited to resident and adfluvial life histories. We estimated there were 3,905 adfluvial individuals in Mann Creek Reservoir in October 2008 based on a mark–recapture population estimate. The adfluvial population sex ratio of 2.78 females per male captured at a weir, peak spawn timing near the peak of the hydrograph (late April), age at spawning (4–6 years), and growth patterns (slow growth in the stream followed by rapid growth in the reservoir) were all characteristic of an anadromous population. Resident fish abundance was not estimated, but the fish were characterized by relatively slow growth, earlier sexual maturity, and a reverse sex ratio (0.23 females per male) compared with the adfluvial fish. The two life histories (resident and adfluvial) and their differential use by the sexes are consistent with life history theory, which suggests female salmonids maximize fitness by increasing body size and fecundity while males attempt to maximize survival at the expense of growth. The migratory fish in this drainage that could have historically exercised an anadromous life history appear to be exercising the next‐best option, an adfluvial life history, which has relatively similar costs and benefits to the anadromous form as distinct from the stream‐resident form. Future studies should evaluate other similar native populations isolated in reservoir systems because these populations could play a role in recovery of endangered steelhead (anadromous Rainbow Trout) populations in the western USA.

Culture of Plains Topminnow in a Pond Constructed for Species Conservation

AbstractThe plains topminnow Fundulus sciadicus appears to be experiencing reductions in geographic range and local abundance, which has led to regional protection throughout its native range. Conservation of this species may require introductions to reestablish populations at known historic locations. Therefore, a pond was constructed during September 2007 to house a refuge population of plains topminnow in Nebraska. A total of 123 plains topminnow were stocked into the pond in two stocking events during 2008. Plains topminnow populations were sampled throughout 2008 and mark–recapture population estimates were conducted after reproductive events during 2009 and 2010 resulting in estimates of 9,844 ± 1,698 (mean ± SD) and 3,974 ± 452 plains topminnow, respectively. Mean fish weight was used as an estimate of pond biomass, which was 28.4 kg/ha in 2009 and 44.9 kg/ha in 2010. Reproduction was first observed in 2008 and in each following year, and a strong year‐class was produced in 2009, which suggested there were factors that limited reproduction in the other 2 years. Extensive culture may be an effective way to rear plains topminnow and related species. However, more research is needed to determine factors that affect year‐class strength and production.

Validation of mark-recapture population estimates for invasive common carp, Cyprinus carpio, in Lake Crescent, Tasmania

Summary A mark-recapture study based on the Petersen method was implemented in 1998 to estimate the abundance of the invasive common carp, Cyprinus carpio L., in Lake Crescent, Tasmania. Multiple gear types were employed to minimise capture bias, with multiple capture and recapture events providing an opportunity to compute and compare Petersen and Schnabel estimates. A single Petersen estimate on recapture data and two Schnabel estimates – one each on mark (forward-Schnabel estimate) and recapture (reverse-Schnabel estimate) data – were conducted. An independent long-term double tag study facilitated estimation of the annual natural mortality. Subsequent fish-down of the population suggests that, in all likelihood, the carp have been eradicated from the lake, providing an unprecedented opportunity to verify the forward population estimates carried out in 1998. Results suggest that all three estimates were close to the true population size, with the reverse-Schnabel estimate being the most accurate and within 1% of the true population in this relatively large lake (2365 ha). Greater accuracy of the reverse-Schnabel approach can be attributed to either minimised fish behavioural (i.e. gear susceptibility or avoidance) or computational bias associated with the forward- Schnabel and Petersen approaches, respectively. While the original estimates served as a guide in eradication of carp from the lake, the ultimate validation provides a reliable framework for abundance estimation of this invasive fish in relatively large water bodies elsewhere.

Testing the effectiveness of capture mark recapture population estimation techniques using a computer simulation with known population size

Estimation of small mammal population sizes is important for monitoring ecosystem condition and for conservation. Here, we test the accuracy of standard methods of population size estimation using Capture-Mark-Recapture (CMR) on a simulated population of agents. The use of a computer simulation allows complete control of population sizes and behaviors, thereby avoiding assumptions that may be violated in real populations. We find that the recommended protocol for CMR sampling, using uniformly distributed traps, consistently overestimates population sizes by as much as 100% when studies are conducted over only two trapping periods. More than 20 trapping periods are required before this method, or that of placing traps randomly, gives an accurate estimation of population size (i.e., within a 95% confidence limit of the actual value). Non-random sampling, by placing traps on runways used by small mammals, produces the most accurate, and least variable, estimates of population. However, we show that around 10 trapping periods are still required to produce an accurate population estimate using this method. Given that most real populations do not comply with the ‘ideal’ assumptions made by CMR, we suggest that population estimates based on CMR may be fundamentally flawed, and recommend that protocols for CMR population estimation methods may need revising.