Temporary Emigration Research Articles

L’emigrazione italiana verso i paesi europei negli anni ’60 e ’701

The article describes Italian emigration in the 1960s and 1970s. In this phase Italian emigration is characterized by a process of progressive professional specialization, by the prevalence of European destinations, by the effects of free circulation among EEC countries, and by the consequences of the 1973 oil crisis. In the 1960s there were still some elements common to the previous period, that of the immediate post-war period, such as temporary emigration and the presence of many unskilled workers. In the 1970s, new phenomena emerged, such as the large number of people returning home, the emergence of new professional figures, and the role of the regions in migration policies. The 60s and 70s represent a crucial period for Italian emigration, as they foreshadow some of the trends of the current scenario.

Integrating telemetry data at several scales with spatial capture–recapture to improve density estimates

AbstractAccurate population estimates are essential for monitoring and managing wildlife populations. Mark–recapture sampling methods have regularly been used to estimate population parameters for rare and cryptic species, including the federally listed Mojave desert tortoise (Gopherus agassizii); however, the methods employed are often plagued by violations of statistical assumptions, which have the potential to bias density estimates. By incorporating spatial information into conventional density estimation models, spatial capture–recapture (SCR) models can account for common assumption violations such as spatially heterogeneous detection probabilities and temporary emigration when animals leave plots during a survey. We conducted mark–recapture surveys at 10 1‐km2 plots in and adjacent to the Ivanpah Valley of California and Nevada from 2015 to 2019. Locality data were collected concurrently using radio‐telemetry and GPS data loggers. GPS data demonstrated that desert tortoises frequently exhibited temporary emigration outside a plot during the survey periods, thereby complicating standard approaches for closed‐model density estimation. We integrated mark–recapture survey data for subadults and adults at each plot with corresponding spatial capture locations and supplementary spatial data using a modified SCR model fitted in a Bayesian framework. We compared density estimates modeled with conventional non‐spatial methods, as well as three SCR models based on symmetrical usage areas described by various levels and types of supplementary spatial data. The conventional model consistently resulted in inflated estimates of density while the SCR models allowed us to generate spatially corrected estimates for a species where detectability and densities are low. However, we found that if not properly specified, the temporal scale of supplementary data may result in an unintended source of bias in parameter estimates. Integrating spatial data over a larger temporal scale than mark–recapture surveys were conducted resulted in higher detection probabilities and lower density estimates, due to an overestimation of space use. Our results not only demonstrate the importance of accounting for spatial information but also the value of understanding the potential for bias when integrating multiple data sets at different temporal resolutions. The methods presented can be used to enhance monitoring efforts for the Mojave desert tortoise and other species where mark–recapture methods are used.

Assessment and novel application ofN‐mixture models for aerial surveys of wildlife

AbstractAerial surveys are a critical tool for inference of wildlife populations, yet are limited by current available methods to account for imperfect detection without marking animals.N‐mixture models use count data from replicate surveys for estimation of wildlife abundance while accounting for imperfect detection. This statistical framework was recently developed but is rarely applied to aerial surveys of terrestrial wildlife. We applied anN‐mixture model incorporating temporary emigration to a novel aerial survey design to estimate the availability, detection probability, and abundance of an unmarked population of white‐tailed deer (Odocoileus virginianus) in Michigan, USA, using surveys in 2014 and 2016. We assessed the selection of the sample unit size for theN‐mixture model in a post hoc sensitivity analysis and compared all estimates to a hierarchical distance sampling (HDS) approach. Hierarchical distance sampling is an expansion of conventional distance sampling (CDS), a standard method applied to aerial survey designs for wildlife, where HDS allows for modeling spatial variation in abundance and detection probability using environmental covariates and can account for changing population demographics. We foundN‐mixture models produced similar parameter estimates to HDS with both models inferring a population increase between years, which was consistent with independently available estimates for this population (2014N‐mixture = 402 [CI: 303.8–515.27], and HDS = 391 [CI: 297.67–504.63]; 2016N‐mixture = 732 [CI: 572.89–924.22], and HDS = 708 [CI: 552.45–893.89]). Estimates from both models were sensitive to the sample unit size selected in an open population framework. We recommend using ecological (e.g., home range size) and statistical (e.g., sample size) considerations when selecting a sample unit size that reflects the movement ecology of a species and evaluating the sensitivity of parameters to sample unit size. In our study,N‐mixture models and HDS models afforded a practical field approach and analytical methodology that resulted in precise estimation in a population of unmarked deer over time. When used with aerial surveys in terrestrial systems where distance sampling methods may be difficult to implement,N‐mixture models can address observer error and estimate populations for conservation and management goals without marking individual animals.

A decade of photo‐identification reveals contrasting abundance and trends of Type B killer whales in the coastal waters of the Antarctic Peninsula

AbstractThe Antarctic Peninsula (AP) is rapidly warming and empirical data on abundance trends of marine organisms are required to understand the impact of these physical changes, and interacting anthropogenic impacts, on the ecosystem. Recent estimates inferred increasing abundance of Type A killer whales at the top of this food chain, and here we provide new data on the abundance of Type B1 and B2 killer whales using photographic mark‐recaptures collected during austral summers from 2008/2009 to 2017/2018. Both ecotypes were regularly photographed around the AP coastline, particularly off the west side, and individuals of both showed site fidelity across years. B1s had a higher re‐identification rate (58% photographed in multiple years, range: 1–7 years) compared to B2s (31%, 1–4 years). We fit mark‐recapture models that allowed temporary emigration beyond the study area, to effectively monitor the size of wide‐ranging populations and documented contrasting trends for B1s and B2s. A smaller population size (~102) of B1s was estimated to use the area, with a declining trend in abundance (−4.7% per year) and reduced apparent survival in recent years. In contrast, a much larger population size (~740) of B2s was estimated to be generally stable in abundance and apparent survival over the past decade.

Population dynamics of sperm whales (Physeter macrocephalus) in Guadeloupe, French Caribbean: A mark‐recapture study from 2001 to 2013

AbstractSperm whales are present along the Caribbean islands in family groups of mature females, juveniles, and newborns. Their abundance and demographic rates remain poorly known. Using photo‐identification data, we estimated the abundance and annual survival of sperm whales in Guadeloupe from January to April 2001–2013. A total of 1,492 photographs of tail flukes were scored (ranging from 1 to 5) in terms of quality (Q) and marking (M) level. A total of 789 photographs were selected with Q ≥ 3 and M ≥ 3, corresponding to 109 individually identified adult females or immatures of both sexes. Capture histories were built and analyzed using the Pollock's robust design capture‐mark‐recapture model. The study consisted of 13 primary periods sequenced in 5–8 secondary periods. Mean annual survival rate of residents was 0.945, 95% CI [0.864, 0.979]. Abundance varied between years from 75 to 35 individuals. The geometric growth rate over the period 2001–2013 was 0.938, 95% CI [0.878, 0.997], suggesting a population decline of −6.2%/year. Sperm whales are moving between Guadeloupe and Dominica, with a high temporary emigration rate (0.163) and 50% of the individuals of Guadeloupe resighted in Dominica. These results highlight the fragility of the population and the necessity to consider it as one unit.

Abundance and demography of common bottlenose dolphins (Tursiops truncatus truncatus) in the Indian River Lagoon, Florida: A robust design capture-recapture analysis.

Common bottlenose dolphins (Tursiops truncatus truncatus) inhabiting the Indian River Lagoon (IRL) estuarine system along the east coast of Florida are impacted by anthropogenic activities and have had multiple unexplained mortality events. Given this, managers need precise estimates of demographic and abundance parameters. Mark-recapture photo-identification boat-based surveys following a Robust Design were used to estimate abundance, adult survival, and temporary emigration for the IRL estuarine system stock of bottlenose dolphins. Models allowed for temporary emigration and included a parameter (time since first capture) to assess evidence for transient individuals. Surveys (n = 135) were conducted along predetermined contour and transect lines throughout the entire IRL (2016–2017). The best fitting model allowed survival to differ for residents and transients and to vary by primary period, detection to vary by secondary session, and did not include temporary emigration. Dolphin abundance was estimated from 981 (95% CI: 882–1,090) in winter to 1,078 (95% CI: 968–1,201) in summer with a mean of 1,032 (95% CI: 969–1,098). Model averaged seasonal survival rate for marked residents was 0.85–1.00. Capture probability was 0.20 to 0.42 during secondary sessions and the transient rate was estimated as 0.06 to 0.07. This study is the first Robust Design mark-recapture survey to estimate abundance for IRL dolphins and provides population estimates to improve future survey design, as well as an example of data simulation to validate and optimize sampling design. Transients likely included individuals with home ranges extending north of the IRL requiring further assessment of stock delineation. Results were similar to prior abundance estimates from line-transect aerial surveys suggesting population stability over the last decade. These results will enable managers to evaluate the impact of fisheries-related takes and provide baseline demographic parameters for the IRL dolphin population which contends with anthropogenic impacts and repeated mortality events.

Subterranean movement inferred by temporary emigration in Barton Springs salamanders (Eurycea sosorum).

Movement behavior is an important aspect of animal ecology but is challenging to study in species that are unobservable for some portion of their lives, such as those inhabiting subterranean environments. Using four years of robust-design capture-recapture data, we examined the probability of movement into subterranean habitat by a population of endangered Barton Springs salamanders (Eurycea sosorum), a species that inhabits both surface and subterranean groundwater habitats. We tested the effects of environmental variables and body size on survival and temporary emigration, using the latter as a measure of subterranean habitat use. Based on 2,046 observations of 1,578 individuals, we found that temporary emigration was higher for larger salamanders, 79% of which temporarily emigrated into subterranean habitat between primary sampling intervals, on average. Body size was a better predictor of temporary emigration and survival compared to environmental covariates, although coefficients from lower ranked models suggested turbidity and dissolved oxygen may influence salamander movement between the surface and subsurface. Surface population dynamics are partly driven by movement below ground and therefore surface abundance estimates represent a fraction of the superpopulation. As such, while surface habitat management remains an important conservation strategy for this species, periodic declines in apparent surface abundance do not necessarily indicate declines of the superpopulation associated with the spring habitat.

The first estimate of interjurisdictional population dynamics for bonefish, Albula vulpes, a shared resource in the western Caribbean

Many tropical fisheries are data-poor and lack population demographic information needed for effective management and conservation. In this study we used mark-recapture of bonefish, Albula vulpes, an important species in catch-and-release recreational fisheries, to estimate capture probabilities. Moreover, for the first time we generated key demographic parameters including apparent survival, new entries and population size. We marked 9657 bonefish and recaptured 605 (6.3 % recapture rate) inside and outside protected areas in northern Belize and southern Mexico. We built 20 open population model types known as POPAN in program MARK. The model with a constant superpopulation and probability, and a time-dependent survival and capture probability was best supported by our data. A potentially stable superpopulation size of bonefish > 22 cm of approximately 197,350 individuals (SE = 16,010, lower bound = 168,382, upper bound = 231,302) inhabited a larger region beyond our sampled (40.8 km2 sample area). A combination of permanent and temporary immigration and emigration patterns resulted in seasonal variations in survival, capture probabilities, probability of entry of individuals and population size (or abundance). Approximately 188,000 adult bonefish migrate and congregate in near-shore pre-spawning aggregation sites of the Caribbean Sea near Belize and Mexico during the spawning season. Population stability is likely associated with bonefish protections enacted in 1977, protected areas, and conservation practices by fishing communities of Belize and Mexico. This highlights the importance of protected areas and interjurisdictional fisheries management and suggests the need for a paradigm shift in the Caribbean to include connectivity of habitats essential to all life stages for important fish species.

Estimating abundance based on time‐to‐detection data

AbstractMany studies in ecology and management aim at quantifying absolute abundance based on counts at a set of surveyed sites. As time for data collection is typically limited, methods for reliable estimation of occupancy or abundance from low‐cost data are desirable. Time‐to‐detection (TTD) models have shown promise for the estimation of occupancy. However, they remain heavily underutilized, and restricted to inference about occupancy, rather than abundance.We developed a binomial N‐mixture model for species‐level TTD protocols that allows estimation of abundance with multiple‐ or single‐visit data. An extension of the multi‐visit version allows estimating availability per visit, given temporary emigration is random. We provide JAGS code and a new function (nmixTTD) in the R packageunmarkedfor fitting a variety of such models.Simulations showed accurate parameter estimation from single‐visit species‐level TTD data if individual detection probability is high (≥~0.7) and the number of visited sites is in the hundreds (≥~300). Additional visits improved the accuracy of estimates considerably. A comparison with the Royle‐Nichols‐ and the classic binomial N‐mixture‐model revealed that the performance of our model is between these two, but requires data that are less expensive and less error‐prone than count data required for binomial N‐mixture‐models. In a case study, we found similar results when analysing data with the Royle‐Nichols‐, the binomial N‐mixture‐model or the multi‐visit version of our TTD model. Analysing single‐visit data with our model yielded lower abundance and higher detectability estimates. Presumably these differences are due to temporary emigration, as the single‐visit method estimates the abundance of individuals available at one sampling occasion, whereas the multi‐visit methods refer to the superpopulation, that is, the number of individuals present over the study period.Our new TTD‐N‐mixture model shows promise because it enables estimation of abundance, corrected for imperfect detection, for single‐ and multiple‐visit data, based on data that are less expensive and that will be available in large quantities in the near future thanks to technical advances like autonomous recording units. The effects of unmodelled heterogeneity in detection rate and imperfect availability require further study.

Effects of snake fungal disease on short-term survival, behavior, and movement in free-ranging snakes.

Pathogenic fungi are increasingly associated with epidemics in wildlife populations. Snake fungal disease (SFD, also referred to as Ophidiomycosis) is an emerging threat to snakes, taxa that are elusive and difficult to sample. Thus, assessments of the effects of SFD on populations have rarely occurred. We used a field technique to enhance detection, Passive Integrated Transponder (PIT) telemetry, and a multi-state capture-mark-recapture model to assess SFD effects on short-term (within-season) survival, movement, and surface activity of two wild snake species, Regina septemvittata (Queensnake) and Nerodia sipedon (Common Watersnake). We were unable to detect an effect of disease state on short-term survival for either species. However, we estimated Bayesian posterior probabilities of >0.99 that R. septemvittata with SFD spent more time surface-active and were less likely to permanently emigrate from the study area. We also estimated probabilities of 0.98 and 0.87 that temporary immigration and temporary emigration rates, respectively, were lower in diseased R. septemvittata. We found evidence of elevated surface activity and lower temporary immigration rates in diseased N. sipedon, with estimated probabilities of 0.89, and found considerably less support for differences in permanent or temporary emigration rates. This study is the first to yield estimates for key demographic and behavioral parameters (survival, emigration, surface activity) of snakes in wild populations afflicted with SFD. Given the increase in surface activity of diseased snakes, future surveys of snake populations could benefit from exploring longer-term demographic consequences of SFD and recognize that disease prevalence in surface-active animals may exceed that of the population as a whole.

Bottlenose dolphins (Tursiops truncatus) in North Dalmatia, Croatia: Occurrence and demographic parameters

AbstractThe common bottlenose dolphin (Tursiops truncatus) population along the eastern Adriatic coast is believed to comprise discrete communities, yet many of them are unstudied. This study provides the first description of occurrence and demographic parameters for the community inhabiting waters of North Dalmatia. Dedicated boat‐based surveys conducted in summer months from 2013 to 2017 resulted in 13,896 km of research effort and 284 dolphin sightings from which 336 individuals were identified. Site‐fidelity analysis revealed that 52.1% of encountered marked adults occur in the area regularly or occasionally. No significant difference among years could be found for mean group sizes (5.73–7.46) and group encounter rates (1.159–1.942 groups/100 km). Pollock's Robust Design models estimated annually variable adult apparent survival (0.737–0.986) and constant temporary emigration rate of 0.172. The estimated abundance varied annually from 116 to 138 individuals and showed a negative slope, but a significant trend could not be confirmed. Age‐dependent models estimated first‐year calf survival at 0.875. These results provide a baseline for informed management of two Sites of Community Importance, and a benchmark for future monitoring in North Dalmatian waters, an area under significant anthropogenic pressure.

Climate-Related Hazards and Internal Migration Empirical Evidence for Rural Vietnam

In this paper we employ commune-level data from Vietnam to study whether three types of natural disasters have an impact on emigration figures. We thereby distinguish between temporary and permanent emigration and also differentiate between the effects of recently occurring disaster events and changes in medium-term disaster trends. We find that episodic droughts and flood events tend to cause emigration from the affected communes. While droughts primarily cause temporary migration, flood events tend to induce permanent moves out of the affected regions. Whenever drought or flood events are perceived to have become more severe over the last decade, we also find systematically higher emigration from the affected communes. Episodic typhoons or worsening typhoon trends remain without any significant effect in both the short- and the long-run.

Full-annual demography and seasonal cycles in a resident vertebrate.

Wildlife demography is typically studied at a single point in time within a year when species, often during the reproductive season, are more active and therefore easier to find. However, this provides only a low-resolution glimpse into demographic temporal patterns over time and may hamper a more complete understanding of the population dynamics of a species over the full annual cycle. The full annual cycle is often influenced by environmental seasonality, which induces a cyclic behavior in many species. However, cycles have rarely been explicitly included in models for demographic parameters, and most information on full annual cycle demography is restricted to migratory species. Here we used a high-resolution capture-recapture study of a resident tropical lizard to assess the full intra-annual demography and within-year periodicity in survival, temporary emigration and recapture probabilities. We found important variation over the annual cycle and up to 92% of the total monthly variation explained by cycles. Fine-scale demographic studies and assessments on the importance of cycles within parameters may be a powerful way to achieve a better understanding of population persistence over time.

Sea turtle populations are overestimated worldwide from remigration intervals: correction for bias

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 41:141-151 (2020) - DOI: https://doi.org/10.3354/esr01019 Sea turtle populations are overestimated worldwide from remigration intervals: correction for bias Paolo Casale1,*, Simona A. Ceriani2,3 1Department of Biology, University of Pisa, Via A. Volta 6, 56126 Pisa, Italy 2Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission, Saint Petersburg, FL, USA 3Department of Biology, University of Central Florida, Orlando, FL, USA *Corresponding author: paolo.casale1@gmail.com ABSTRACT: Estimating population abundance is key for species of conservation concern. This is particularly challenging for marine animals, like sea turtles, with ocean-scale distribution and migratory nature. However, sea turtles lay clutches on land where they can be easily counted; thus, clutch number has always been the most common index of population abundance. A female typically lays >1 clutch per year and does not reproduce every year. Therefore, 2 conversion factors are needed to convert the number of egg clutches to the number of adult females: the number of clutches laid by a female in a nesting season and the fraction of adult females reproducing in a season, which is linked to the breeding periodicity. The effects of breeding periodicity, probability of detection and annual survival probability on the derived adult female abundance were investigated by simulating a virtual population of adult females over a 15 yr beach monitoring period. The results indicate that current methods may greatly overestimate the abundance of sea turtle populations, especially in situations with a low detection probability, including temporary emigration. The factors involved and ways to minimize biases and errors are discussed, including a method which is easy to implement using existing datasets. A careful reassessment of current estimates of sea turtle abundance derived from nest counts and capture-mark-recapture data would be appropriate, and the potential error associated with such estimates should be considered when they are used in conservation status assessments. KEY WORDS: Sea turtle · Remigration interval · Abundance · Breeding proportion · Mortality · Detection · Simulation Full text in pdf format Supplementary material PreviousNextCite this article as: Casale P, Ceriani SA (2020) Sea turtle populations are overestimated worldwide from remigration intervals: correction for bias. Endang Species Res 41:141-151. https://doi.org/10.3354/esr01019 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 41. Online publication date: January 30, 2020 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2020 Inter-Research.

Use of genetic mark-recapture to estimate breeding site fidelity and philopatry in a threatened sea duck population, Alaska-breeding Steller’s eiders

The Steller’s eider Polysticta stelleri is a sea duck that breeds in Arctic tundra regions of Russia and Alaska (USA). The Alaska-breeding population is listed as ‘threatened’ under the US Endangered Species Act because of a perceived contraction of the breeding range in North America. Understanding demography of the listed population is critical for evaluating measures that can lead to increased abundance and thus, long-term viability. Specifically, estimates of return rates to breeding areas by adult females and natal areas by juvenile females are needed for planning effective recovery actions. We used a suite of polymorphic loci to genotype individuals and generated genetic profiles of nesting females and female offspring from nest materials collected between 1995 and 2016 in a ~170 km2 study area near Utqiagvik, Alaska. We analyzed capture histories of genetically identified individuals to estimate breeding site fidelity, temporary emigration, and philopatry. From a sample of 365 nests, we found that breeding site fidelity of adult females was high (0.91 ± 0.07 SE), and temporary emigration was also high (0.77 ± 0.06) and annually variable (range 0.34-0.97). From egg shell remains of 124 hatched females, we observed 9 recaptures as nesting adults, suggesting that philopatry was also high (range 0.6-1.0). Given the relatively high rates of adult female breeding site fidelity and female philopatry that we estimated, management actions that reduce mortality of adult females and increase annual productivity are likely to help maintain the population of a few hundred breeding Steller’s eiders on the Arctic Coastal Plain of Alaska.

Population stability in an unmanaged population of the green and golden bell frog in northern New South Wales, Australia

Population monitoring is required to guide conservation programs. We conducted a capture–mark–recapture study of a population of the vulnerable green and golden bell frog (Litoria aurea) at the northern end of its range. Frogs were captured and marked over three breeding seasons (2015/16, 2016/17, 2017/18) in a large coastal lagoon. We aimed to: (1) produce annual estimates of population size to describe population trajectory, and (2) investigate monthly variation in abundance, capture probability, and temporary emigration to understand how these factors change at a finer temporal scale. Frog abundance varied across the three annual breeding seasons: 60–280 adult males, 120–190 adult females, and 90–420 subadults. We infer that the population is stable because adult abundance estimates were higher after 2015/16. Because our study sampled only half the available breeding habitat, the overall population may number 350–850 adults. Our modelling revealed >40 males but <20 females were detected in the sample area in our monthly samples. Estimates of temporary emigration were high (males: 0.54; females: 0.79), suggesting behaviour that made frogs unavailable for capture between months. Our results suggest that monitoring at greater than annual intervals should be adequate to monitor the future trend of this population.

Миграционные установки аспирантов: к вопросу об «утечке мозгов»

The article presents results of the inquiry that involved 803 postgraduate students of research organizations involved in the preparation of postgraduate students in the field of education sciences. The inquiry helps to investigate the specificity of plans of postgraduate students to work abroad and to move abroad for permanent residence. It also helps to reveal and describe the impacts of various socio-demographic and socio-stratification factors. In addition, there was made a comparison of the attitudes of postgraduate students and scientific researchers to temporary or permanent migration. The data is processed using mathematical statistics methods. The results of the study indicate that the migration attitudes of graduate students are determined by the influence of a number of socio-demographic (gender, age, presence and structure of the family) and socio-stratification (financial status, educational status of parents) factors. A comparison of the opinions of graduate students and scientific researchers shows that migration attitudes towards both temporary migration and emigration abroad are more widespread among postgraduate students than among scientific researchers.

Demography of the salt marsh harvest mouse (Reithrodontomys raviventris halicoetes) and associated rodents in tidal and managed wetlands.

Suisun Marsh (Solano County, California) is the largest contiguous marsh remaining on the West Coast of the United States, and makes up approximately 10% of the wetlands remaining in the San Francisco Estuary. Suisun Marsh has been safeguarded from development through the operation of over 100 privately owned waterfowl hunting clubs, which manage for diked waterfowl habitat. However, this management—and the subsequent loss of tidal influence—has been considered harmful for some species, including the endangered salt marsh harvest mouse (SMHM; Reithrodontomys raviventris). To determine the value of tidal wetlands relative to those managed for waterfowl, we performed periodic surveys for rodents in managed and tidal wetlands over 5 years, and used capture-mark-recapture analyses to estimate demographic parameters and abundance for the three most common rodents—the northern SMHM (R. r. halicoetes), the western harvest mouse (a sympatric native species; R. megalotis, WHM), and the house mouse (a sympatric invasive species; Mus musculus). Wetland type had no effect on detection, temporary emigration, or survival for any of these species. However, fecundity and population growth for all three species were affected by an interaction of season and wetland type, although none of these parameters was consistently superior in either habitat type. Estimated abundance of SMHM and Mus was similar in both wetland types, whereas WHM were more abundant in managed wetlands. Salt marsh harvest mice also showed no affinity for any microhabitat characteristics associated with tidal wetlands. Managed wetlands in Suisun Marsh support SMHM and Mus equally, and abundances of WHM were greater than in tidal wetlands, suggesting managed wetlands may be superior in terms of supporting native rodents. As climate change and sea level rise are predicted to threaten coastal marshes, these results suggest the recovery strategy for SMHM could incorporate managed wetlands.

Power to detect trends in abundance within a distance sampling framework

Abstract Ensuring that inferences from biological monitoring are reliable requires a level of sampling effort that is commensurate with programmatic objectives and reflects attributes of target populations. Consensus guidelines have emerged to guide allocation of sampling effort for programmes designed to detect trends in occupancy but not for abundance, despite its prevalence as a target parameter. We evaluated the influence of population attributes (density, availability, detection probability and magnitude of trend) and sampling design features (number of sites, number of repeat surveys, and survey‐year interval) on a Bayesian analogue of statistical power to detect declines in abundance estimated using distance sampling methods. For a range of values common to terrestrial vertebrates, we simulated spatially and temporally replicated populations from which we generated survey data. We then analysed each dataset with a hierarchical open‐population model that allowed for temporary emigration to estimate power for periods of 5–20 years. For a given amount of sampling effort, power to detect trends was highest when effort was allocated to maximizing the number of sites by decreasing the number of repeat surveys within a year and increasing the interval between survey years. For example, to have an 80% chance of detecting a 3% annual decline required 40% longer when 67 sites were surveyed three times per year compared to 600 sites surveyed once every three years despite both allocations requiring 4,000 surveys over 20 years. Notably, these patterns were independent of density or detectability of the target species, which contrasts with occupancy studies where optimal allocation shifts from surveying more sites to more repeat surveys when detectability is low or occupancy is high. Synthesis and applications. Our findings provide guidance for allocating resources efficiently for distance sampling studies focused on terrestrial vertebrates. By comparing the approximate density and detectability of target populations to those we considered, monitoring programmes can balance the amount of survey effort allocated to sites, surveys per site, and annual revisits to help ensure sufficient power to meet objectives effectively and efficiently. These decisions are increasingly important as budgets for conservation decrease and consequences of inaction continue to increase.

Using mark-recapture methods to estimate population size and survival of pyjama sharks Poroderma africanum in Mossel Bay, South Africa

The pyjama shark Poroderma africanum (family Scyliorhinidae) is endemic to coastal waters of South Africa but its population characteristics are poorly known. This study aims to estimate baseline demographic parameters for P. africanum in Mossel Bay. We applied mark-recapture methods following Pollock’s robust design (PRD) and Cormack–Jolly–Seber (CJS) models, using five-year tag-recapture data and one-year acoustic-telemetry data, respectively. Estimates of abundance, survival, capture probabilities and temporary emigration were obtained using these models. The PRD model indicated random temporary emigration (0.955 period–1 [95% CI 0.755–0.993]), constant survival, and season-varying capture and recapture probabilities with a negative behavioural response to first capture (β = −5.34 [−6.89 to −3.80]). Abundance estimates ranged from 11 (10.01–13.21) to 53 (52.05–56.82) sharks in Mossel Bay. The CJS model indicated constant survival (0.271 y–1 [95% CI 0.0–0.75]) and sex-independent probabilities of being captured at least once annually (1.0 y–1 for both sexes). This study provides the first demographic information for the management of this population. Further studies should utilise larger sample sizes and more complex models, and investigate specific management options.