Recapture Surveys Research Articles

Habitat‐related differences in the adult longevity of two ecotypes of a specialized butterfly

AbstractThe life expectancy of adult butterflies is highly diverse. Substantial variation may be found among closely related species, and even on the intraspecific level, where it could be associated with sex, genetic differentiation, diet and weather conditions. We compared the demographic parameters of populations of the regionally endangered Boloria eunomia butterfly living in two different habitats. Across its boreal‐mountane distribution range in Europe, B. eunomia occurs in two ecotypes associated with wet meadows and raised bogs using distinct both larval and nectar plants. We carried out simultaneous studies of both ecotypes through mark–recapture surveys of two large populations in NE Poland, located close to each other. A total number of 1124 and 644 individuals were marked at the bog and meadow sites respectively, and 51 and 33% of them were recaptured at least once. The estimated adult population size of the bog population (about 3000) was twice as large as that of the meadow population, which however was characterized by more than three‐fold higher density. The emergence of imagoes was highly synchronized, and protandry was evident. The sex ratio was slightly male‐biased and the mean capture probability was significantly higher for males. More importantly, the estimated life span of males was considerably shorter than that of females at each site. Finally, both sexes of the ‘meadow’ ecotype lived significantly longer than those from the raised bog. The detected pattern can be related to distinct larval food plants and/or nectar resources, different pressures from predators, genetic variation and morphological differences affecting thermal properties. Further investigations would be useful to reveal if the shorter adult life span translates into reduced viability of bog populations and consequently whether they are potentially more threatened, at least in the southern margins of the distribution range in Central Europe.

Mass marking of juvenile Schizothorax wangchiachii (Fang) with alizarin red S and evaluation of stock enhancement in the Jinping area of the Yalong River.

Schizothorax wangchiachii is a key fish species in the stock enhancement program of the Yalong River hydropower project, China. Alizarin red S (ARS) was used to mark large numbers of juvenile S. wangchiachii in the Jinping Hatchery and later used to evaluate stock enhancement in the Jinping area of the Yalong River. In a small-scale pilot study, 7,000 juveniles of the 2014 cohort were successfully marked by immersion in ARS solution, and no mortality was recorded during the marking process. The ARS mark in the fish otoliths remained visible 20 months later. In the large-scale marking study, approximately 600,000 juveniles of the 2015 cohort were successfully marked. Mortalities of both marked and unmarked juveniles were very low and did not differ significantly. Total length, wet mass and condition factor did not differ significantly between unmarked and marked individuals after three months. On 24 July 2015, about 840,000 Jinping Hatchery-produced young S. wangchiachii, including 400,000 marked individuals, were released at two sites in the Jinping area. Recapture surveys showed that (1) marked and unmarked S. wangchiachii did not differ significantly in total length, wet mass and condition factor; (2) stocked individuals became an important part of recruitment of the 2015 cohort; (3) instantaneous growth rate of marked individuals tended to slightly increase; and (4) most stocked individuals were distributed along a 10–15 km stretch near the release sites. These results suggest that the ARS method is a cost-efficient way to mass mark juvenile S. wangchiachii and that releasing juveniles is an effective means of stock recruitment.

Lost but not forgotten: MHC genotypes predict overwinter survival despite depauperate MHC diversity in a declining frog

The amphibian disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has contributed to the decline of Chiricahua leopard frogs (Rana chiricahuensis), a federally threatened species native to the Southwestern United States. We characterized immunogenetic variability in R. chiricahuensis by sequencing an expressed Major Histocompatibility Complex (MHC) class IIβ gene across 13 natural populations in Arizona, USA, as well as 283 individuals that were captive reared from two egg masses. We recovered a total of five class IIβ MHC alleles compared to 84 alleles previously characterized in eight natural populations of the Arizona congener R. yavapaiensis, demonstrating reduced MHC diversity in R. chiricahuensis. One allele was fixed in five populations but none of the R. chiricahuensis alleles were closely related to R. yavapaiensis allele Q, which is significantly associated with chytridiomycosis resistance in laboratory trials. Nine of 13 R. chiricahuensis population localities were Bd positive, and bearing allele RachDRB*04 was the best genetic predictor of an individual being infected with Bd. A total of three class IIβ alleles were recovered from captive reared individuals, which were released to two natural population localities followed by recapture surveys to assess MHC-based survival over winter, the time when chytridiomycosis outbreaks are most severe. At one site, all released animals were fixed for a single allele and MHC-based survival could not be assessed. At the second site, fewer than half of the released but all of the recaptured individuals were homozygous for RachDRB*05, indicating that MHC genotype is important in determining Bd survival under natural field conditions. We conclude that the limited MHC variation in R. chiricahuensis is likely the consequence rather than the cause of natural selection favoring alleles that promote survival in the face of Bd. Our study highlights that preserving even low levels of functional genetic variation may be essential for population persistence, and that local disease adaptation may present as a reduction in genetic diversity. These finding also suggest that for populations that have declined due to a specific infectious pathogen, MHC-based genetically-informed reintroduction approaches may enhance species recovery efforts.

Densities and Population Sizes of Clinch DaceChrosomussp. cf.sayloriin the Upper Clinch River Basin in Virginia

Estimates of abundance and density for the imperiled Clinch Dace (Chrosomus sp. cf. saylori) are needed across its range to indicate where populations exist and estimate their long-term viability. We generated estimates of population extent, measured in km of potentially occupied habitat, based on 206 site visits from four fish surveys since 1999 within the Clinch Dace's putative range. Next, we used mark–recapture surveys to estimate Clinch Dace densities in five occupied streams. A linear regression model generated from these data was used to transform single-pass count data into estimated abundance with 90% prediction intervals (PI) for Clinch Dace in sampled reaches. We combined estimates of individual population sizes to estimate global abundance. Finally, we examined the correlation between habitat variables and Clinch Dace abundance in occupied streams. Clinch Dace populations at low densities potentially occupy 31.5 km of the approximately 351 km of 2nd- and 3rd-order streams in northern Russell a...

Precipitation alters interactions in a grassland ecological community.

Climate change is transforming precipitation regimes world-wide. Changes in precipitation regimes are known to have powerful effects on plant productivity, but the consequences of these shifts for the dynamics of ecological communities are poorly understood. This knowledge gap hinders our ability to anticipate and mitigate the impacts of climate change on biodiversity. Precipitation may affect fauna through direct effects on physiology, behaviour or demography, through plant-mediated indirect effects, or by modifying interactions among species. In this paper, we examined the response of a semi-arid ecological community to a fivefold change in precipitation over 7years. We examined the effects of precipitation on the dynamics of a grassland ecosystem in central California from 2007 to 2013. We conducted vegetation surveys, pitfall trapping of invertebrates, visual surveys of lizards and capture-mark-recapture surveys of rodents on 30 plots each year. We used structural equationmodelling to evaluate the direct, indirect and modifying effects of precipitation on plants, ants, beetles, orthopterans, kangaroo rats, ground squirrels and lizards. We found pervasive effects of precipitation on the ecological community. Although precipitation increased plant biomass, direct effects on fauna were often stronger than plant-mediated effects. In addition, precipitation altered the sign or strength of consumer-resource and facilitative interactions among the faunal community such that negative or neutral interactions became positive or vice versa with increasing precipitation. These findings indicate that precipitation influences ecological communities in multiple ways beyond its recognized effects on primary productivity. Stochastic variation in precipitation may weaken the average strength of biotic interactions over time, thereby increasing ecosystem stability and resilience to climate change.

Population Trends, Survival, and Sampling Methodologies for a Population of Rana draytonii

Abstract Estimating population trends provides valuable information for resource managers, but monitoring programs face trade-offs between the quality and quantity of information gained and the number of sites surveyed. We compared the effectiveness of monitoring techniques for estimating population trends of Rana draytonii (California Red-legged Frog) at Point Reyes National Seashore, California, USA, over a 13-yr period. Our primary goals were to: 1) estimate trends for a focal pond at Point Reyes National Seashore, and 2) evaluate whether egg mass counts could reliably estimate an index of abundance relative to more-intensive capture–mark–recapture methods. Capture–mark–recapture (CMR) surveys of males indicated a stable population from 2005 to 2009, despite low annual apparent survival (26.3%). Egg mass counts from 2000 to 2012 indicated that despite some large fluctuations, the breeding female population was generally stable or increasing, with annual abundance varying between 26 and 130 individuals....

Examining disease prevalence for species of conservation concern using non‐invasive spatial capture–recapture techniques

Summary Non‐invasive techniques have long been used to estimate wildlife population abundance and density. However, recent technological breakthroughs have facilitated non‐invasive estimation of the proportion of animal populations with certain diseases. Giraffes Giraffa camelopardalis are increasingly becoming recognized as a species of conservation concern with decreasing population trajectories across their range in Africa. Diseases may be an important component impacting giraffe population declines, and the emerging ‘giraffe skin disease’ (GSD), characterized by the appearance of wrinkled skin and alopecic lesions on the limbs, neck and chest of infected giraffe, may hinder movement causing increased susceptibility to predation. We examined the prevalence of GSD in Tanzania's Ruaha National Park over a 4‐month period in 2015, using photographic capture–recapture surveys via road‐based transects. We divided the study area into five circuitous survey units, each approximately 100 km in length ( = 99·22 km, SD = 3·72), and surveyed for giraffes for 4 months. From these surveys, we developed a data base of spatially explicit giraffe photographs. We processed these photographs for individual identification and fitted spatial capture–recapture models to predict the spatial configuration of giraffe abundance and GSD prevalence within the study area. Our results indicated that >86% of the giraffe population showed signs of GSD and that the disease was more prevalent in the northern and north‐eastern portion of Ruaha National Park. Synthesis and applications. Our research shows that data from non‐invasive surveys can be used in spatial capture–recapture (SCR) models to estimate the proportion of a population affected by a visible disease. Researchers and conservationists can use SCR models to better examine the variation in parameters associated with these populations such as sex, age class, movement, and encounter rate, which may be linked to the prevalence of the disease, while incorporating broad spatial and temporal dimensions of the population in such areas. We discuss the implications of this research for conservation of threatened species with an emphasis on disease ecology and vulnerability to predations, and more broadly, for wildlife conservation.

Spatial Capture–Recapture Models

There has been a rapid growth in spatial capture–recapture (SCR) methods in the last decade. This paper provides an overview of existing SCR models and suggestions on how they might develop in future. The core of the paper is a likelihood framework that synthesises existing SCR models. This is used to illustrate similarities and differences between models. The key difference between conventional capture–recapture models and SCR models is that the latter include a spatial point process model for individuals’ locations and allow capture probability to depend on location. This extends the kinds of inferences that can be drawn from capture–recapture surveys, allowing them to address questions of a fundamentally spatial nature, relating to animal distribution, habitat preference, movement patterns, spatial connectivity of habitats and dependence of demographic parameters on spatial variables.

Overdispersion in the Estimation of Salmon Escapements by Mark–Recapture Surveys and Its Related Factors

AbstractThe Petersen method, a well-known mark–recapture method, is frequently used in the estimation of escapement of Pacific salmon Oncorhynchus spp. Robust estimates and associated variances can be obtained when the underlying assumptions of this method are met. However, in field surveys, it is often difficult to meet these assumptions because wild animals are often not randomly distributed. When the sampling variance of the estimator exceeds its binomial variance (resulting in overdispersion), the Petersen model underestimates variance. We assessed the occurrence of overdispersion in the mark–recapture data collected to estimate the escapements of Masu Salmon Oncorhynchus masou in a river in northern Japan in 1998 and 1999. The dispersion parameters estimated from 2-year data were 2.89 and 2.51 for males and 1.45 and 1.52 for females, indicating that overdispersion occurred in all cases. The magnitude of overdispersion for males exceeded that for females, probably related to differences in the postspa...

Horvitz–Thompson whale abundance estimation adjusting for uncertain recapture, temporal availability variation, and intermittent effort

A Horvitz–Thompson‐type estimator is introduced to estimate total abundance of the Bering–Chukchi–Beaufort Seas population of bowhead whales using combined visual and acoustic location data. The estimator divides sightings counts by three correction factors that are themselves estimated from various portions of the data. The first correction models how detection probabilities depend on covariates like offshore distance and visibility. The second correction adjusts for availability using the acoustic location data to estimate a time‐varying smooth function of the probability that animals pass within visual range of the observation stations. The third correction accounts for whales passing during periods when one or both sighting stations were temporarily closed down. We derive an asymptotically unbiased estimator of abundance incorporating all these components and a corresponding variance estimate. Correcting the count of 4011 observed whales yields a 2011 abundance estimate of 16,820 with a 95% confidence interval of (15,176, 18,643) and an estimated annual rate of population increase of 3.7% (2.9%, 4.6%). These results are indicative of very low conservation risk for this population under the current low levels of aboriginal hunting permitted by the International Whaling Commission. Although few other capture–recapture surveys will confront exactly the same set of challenges addressed here, many studies face one or more issues that could be resolved by adapting portions of our approach or relevant underlying concepts thereof. Moreover, the generic estimator we derive represents an improved way to handle random correction factors rather than assuming fixed values. Copyright © 2016 John Wiley & Sons, Ltd.

Tony Whitaker: life and achievements of a pioneer New Zealand lizard ecologist

ABSTRACTTony Whitaker grew up in Pinehaven, north of Wellington, New Zealand. He soon became interested in natural history, with interests centred on lizard ecology. Newly developed nocturnal, mark–recapture and quadrat survey techniques enabled density and niche segregation studies, resulting in numerous scientific publications throughout his life. From 1966 to 1977 he worked as an ecologist at the Department of Scientific and Industrial Research (DSIR). His surveys of islands off northern New Zealand led to an important study of the impact of kiore (Polynesian rat; Rattus exulans) on lizard populations, showing that rat eradication was necessary for conservation. At DSIR he also researched birds and mammals. Later, Tony and his wife Viv established a farm near Motueka and began mainland studies of lizards, contracted to mining companies or the New Zealand Wildlife Service/Department of Conservation. Having built up a well-documented collection of New Zealand lizards (now at the Museum of New Zealand Te Papa Tongarewa), Tony then contributed to a bibliography, atlas and field guide. During the period when the taxonomy of lizards was revolutionised by the use of molecular techniques, Tony provided specimens, guidance and encouragement to many herpetologists. From 2000, his interests turned to the little-known and threatened lizards of New Caledonia, on which he contributed to 13 major papers. His life and work are here described under thematic, rather than strictly chronological, headings.

Spatiotemporal factors affecting detection of black bears during noninvasive capture–recapture surveys

Abstract Accounting for low and heterogeneous detection probabilities in large mammal capture–recapture sampling designs is a persistent challenge. Our objective was to improve understanding of ecological and biological factors driving detection using multiple data sources from an American black bear ( Ursus americanus ) DNA hair trap study in south-central Missouri. We used Global Positioning System telemetry and remote camera data to examine how a bear’s distance to traps, probability of space use, sex-specific behavior, and temporal sampling frame affect detection probability and number of hair samples collected at hair traps. Regression analysis suggested that bear distance to nearest hair trap was the best predictor of detection probability and indicated that detection probability at encounter was 0.15 and declined to < 0.05 at nearest distances > 330 m from hair traps. From remote camera data, number of hair samples increased with number of visits, but the proportion of hair samples from known visits declined 39% from early June to early August. Bears appeared attracted to lured hair traps from close distances and we recommend a hair trap density of 1 trap/2.6 km 2 with spatial coverage that encompasses potentially large male home ranges. We recommend sampling during the late spring and early summer molting period to increase hair deposition rates.

Who swarms with whom? Group dynamics of Myotis bats during autumn swarming

For many animal taxa, group-living is a strategy where the cohesion provided by groups confers fitness benefits to individuals. Bats are highly gregarious with many species living in groups with complex social structures. During the summer, many temperate species are sexually segregated among roosts where females have been found to exhibit dynamic social structures and males remain understudied. We studied the group dynamics of little brown and northern Myotis bats (Myotis lucifugus and Myotis septentrionalis) during autumn swarming, a period for which social interactions are largely unknown. Using capture–mark–recapture surveys, we characterized the occurrence and frequency of age and sex groups occurring at swarms. Within a night, young-of-the-year associated more often with other bats than did adult males and females. Further, they associated more often with other young-of-the-year than adults. We found no evidence to support the maternal guidance hypothesis predicting that there would be associations between mother–offspring pairs. Adult male and female bats associated less frequently with each other and were captured alone most often. When males were captured in groups, these groups were more likely to be composed of multiple males and in M. lucifugus, males had preferred male associates they grouped with over multiple nights. Groups formed during the autumn swarming season may represent cohort groups of young bats learning of the location of sites and groups of males that are potentially cooperating to secure more mating opportunities.

Estimating survival of rock lobsters from long-term tagging programmes: how survey number and interval influence estimates

Abstract A long-term tagging dataset on southern rock lobster (Jasus edwardsii) conducted at the Crayfish Point Scientific Reserve near Hobart, Tasmania, Australia, was used to determine how survey number and survey duration affected the precision of survival estimates of male and female lobsters to ensure sustainable exploitation of the population. Tagging surveys were undertaken twice yearly during 2000–2003 with unequal time-intervals between surveys and then once a year with equal time-intervals during 2004–2012 during the January–February period. The most parsimonious Cormack–Jolly–Seber model for estimating survival of lobsters was dependent on (i) timing of the tagging and recapture surveys, (ii) time between consecutive recapture surveys, and (iii) gender. The number of surveys required to provide a precise survival probability varied with gender and time between recapture surveys. For surveys where there was unequal time between recapture surveys, seven and five surveys were required for female and male lobsters, respectively, whereas only five surveys were required when annual surveys were undertaken. Thus, lobster tagging projects using annual surveys should ideally extend to at least 5 years, which is beyond the 3-year project duration common in marine science.

Difference in factors explaining growth rate variability inEuropean eel subpopulations: the possible role of habitat carrying capacity

AbstractAs a key parameter in the management of fish populations, individual growth rate (GR) variations were examined in theEuropean eel (Anguilla anguilla; > 150 mm) using extensive mark–recapture surveys in the lotic habitats of two small rivers of westernFrance: theFrémur, supposed to be saturated, and at the same latitude, theOir with densities fivefold lower than those of theFrémur. In both systems, generalised linear models were used to test whether spatiotemporal factors such as dominant habitat type or local density affectGRvariability. In the presumed unsaturated system, theOir,GRvariability is mainly explained by a set of habitat suitability drivers (density, dominant habitat type). In theFrémur,GRs appear independent of differences in habitat density or productivity. Below saturation, an increase in density will decrease theGRthrough intraspecific competition. At saturation, intraspecific competition reaches such high levels that regardless of eel density and productivity, the resources available by individual are similar throughout the system. In these circumstances, the effect of density on growth was presumed undetectable. Despite these contrasted results, meanGRs observed in both catchments were closed (~20 mm·year−1). This is an unexpected result asGRis expected to be higher in unsaturated systems. This similarity could be explained by the difference between the two systems in terms of: (i) sex ratio (the Frémur is dominated by male, whereas the female is dominant in theOir), (ii) habitat type distribution or (iii) possible interspecific competition (important salmonid populations in theOir).

Using infrared cameras and skunk lure to monitor swift fox (Vulpes velox)

Abstract State agencies and managers seek more efficient and cost-effective survey methods to monitor wildlife populations in an attempt to maintain biologically defensible results amid continued budgetary constraints. We employed a noninvasive approach using infrared cameras and a skunk-based lure on 52 grids to estimate detection and occupancy rates of swift foxes (Vulpes velox) in eastern Colorado. We used eight camera stations within 31-km2 grids, monitored each grid for five consecutive nights, and collected 331 swift fox detections from August–October 2011. We documented 78 more swift fox detections on 25% more grids using remote cameras with skunk lure while deploying 60% fewer survey stations per grid than previous mark–recapture surveys. Our estimates showed improvements in precision and accuracy for detecting swift foxes and estimating occupancy across eastern Colorado. Using infrared cameras and a skunk-based lure proved to be an efficient and effective technique for monitoring swift foxes on a...

Evaluating the Accuracy and Precision of Multiple Abundance Estimators Using State‐Space Models: A Case Study for a Threatened Population of Chinook Salmon in Johnson Creek, Idaho

AbstractOver the last century, Chinook Salmon Oncorhynchus tshawytscha populations in the Pacific Northwest have experienced dramatic declines, leading to many of them being listed as threatened under the Endangered Species Act. The abundance of these threatened populations relative to the thresholds for delisting remains the primary metric for assessing recovery, yet determining the true population abundances from multiple survey types with unknown levels of accuracy and precision remains difficult. The abundance of the spring–summer Chinook Salmon population in Johnson Creek, Idaho, has been measured using a mark–recapture survey and three different redd count surveys (RCSs) that vary temporally and spatially. Using a state‐space model, we determined the accuracy and precision of each survey type by decoupling the observation error of the survey from the process error describing the annual variability in the true population abundance. We then extended the results of the model to determine the risk of managers’ incorrectly delisting the population (a type I error) or incorrectly keeping it listed (a type II error). Finally, we show that salmon managers with data‐limited populations (primarily those with only single‐pass index RCSs) might use the results of our risk analysis to determine whether expanding survey efforts to minimize management risks is appropriate when they are confronted with dwindling financial resources. For example, we determined that although both the multiple‐pass extended RCS (CV = 0.06) and mark–recapture surveys (CV = 0.14) provide unbiased estimates of salmon abundance in Johnson Creek, the mark–recapture study can have annual costs that are 30–100 times greater. Managers may determine that directing research funds toward acquiring information unique to weir‐based mark–recapture surveys (i.e., migration timing, good genetics samples, etc.) may not be justified for all populations.Received October 7, 2013; accepted March 5, 2014

Density of threatened ocelotLeopardus pardalisin the Sierra Abra-Tanchipa Biosphere Reserve, San Luis Potosí, Mexico

AbstractThere is little information on the population status of the ocelotLeopardus pardalisin Mexico. In the Sierra Abra-Tanchipa Biosphere Reserve, in San Luis Potosí, ocelots are affected by habitat loss and fragmentation as a result of increased agricultural development. We used photographic identification in camera-trapping capture–recapture surveys to determine population abundance and density during the dry season and subsequent early and late humid seasons during April 2011–March 2012. We recorded 80 photographs of 15 individuals (10 males, one female, and four of undetermined sex) in 7,786 camera-days. Abundance was estimated using a closed capture heterogeneity model, yielding an estimated population of 9 ± SE 3 in the dry season and 21 ± SE 8 and 15 ± SE 5 during the subsequent early and late humid seasons, respectively. Spatially explicit density estimates were 0.04 and 0.03–0.18 individuals per km2for the dry and humid seasons, respectively, and were similar (P > 0.612) among seasons. Peaks in ocelot activity occurred during 20.00–04.00. We conclude that the ocelots of the Sierra Abra-Tanchipa Reserve have a low population density and may face geographical and biological isolation as a result of habitat conversion. Continued monitoring and improved understanding of the movements and habitat preferences of ocelots are necessary to ensure their continued persistence, and connectivity between this population and others in north-east Mexico.

Continuous‐time spatially explicit capture–recapture models, with an application to a jaguar camera‐trap survey

SummaryMany capture–recapture surveys of wildlife populations operate in continuous time, but detections are typically aggregated into occasions for analysis, even when exact detection times are available. This discards information and introduces subjectivity, in the form of decisions about occasion definition.We develop a spatiotemporal Poisson process model for spatially explicit capture–recapture (SECR) surveys that operate continuously and record exact detection times. We show that, except in some special cases (including the case in which detection probability does not change within occasion), temporally aggregated data do not provide sufficient statistics for density and related parameters, and that when detection probability is constant over time, our continuous‐time (CT) model is equivalent to an existing model based on detection frequencies. We use the model to estimate jaguar density from a camera‐trap survey and conduct a simulation study to investigate the properties of a CT estimator and discrete‐occasion estimators with various levels of temporal aggregation. This includes investigation of the effect on the estimators of spatiotemporal correlation induced by animal movement.The CT estimator is found to be unbiased and more precise than discrete‐occasion estimators based on binary capture data (rather than detection frequencies) when there is no spatiotemporal correlation. It is also found to be only slightly biased when there is correlation induced by animal movement, and to be more robust to inadequate detector spacing, while discrete‐occasion estimators with binary data can be sensitive to occasion length, particularly in the presence of inadequate detector spacing.Our model includes as a special case a discrete‐occasion estimator based on detection frequencies, and at the same time lays a foundation for the development of more sophisticated CT models and estimators. It allows modelling within‐occasion changes in detectability, readily accommodates variation in detector effort, removes subjectivity associated with user‐defined occasions and fully utilizes CT data. We identify a need for developing CT methods that incorporate spatiotemporal dependence in detections and see potential for CT models being combined with telemetry‐based animal movement models to provide a richer inference framework.

Evaluating monitoring methods to guide adaptive management of a threatened amphibian (Litoria aurea).

Prompt detection of declines in abundance or distribution of populations is critical when managing threatened species that have high population turnover. Population monitoring programs provide the tools necessary to identify and detect decreases in abundance that will threaten the persistence of key populations and should occur in an adaptive management framework which designs monitoring to maximize detection and minimize effort. We monitored a population of Litoria aurea at Sydney Olympic Park over 5 years using mark–recapture, capture encounter, noncapture encounter, auditory, tadpole trapping, and dip-net surveys. The methods differed in the cost, time, and ability to detect changes in the population. Only capture encounter surveys were able to simultaneously detect a decline in the occupancy, relative abundance, and recruitment of frogs during the surveys. The relative abundance of L. aurea during encounter surveys correlated with the population size obtained from mark–recapture surveys, and the methods were therefore useful for detecting a change in the population. Tadpole trapping and auditory surveys did not predict overall abundance and were therefore not useful in detecting declines. Monitoring regimes should determine optimal survey times to identify periods where populations have the highest detectability. Once this has been achieved, capture encounter surveys provide a cost-effective method of effectively monitoring trends in occupancy, changes in relative abundance, and detecting recruitment in populations.