Estimate Population Abundance Research Articles

Population size and demographic parameters of pantropical spotted dolphin (Stenella attenuata graffmani) (Cetartiodactyla: Delphinidae) in Golfo Dulce, Costa Rica

Introduction: The coastal form of pantropical spotted dolphins (Stenella attenuata graffmani) is commonly found along the Pacific coast of Costa Rica. Within Golfo Dulce, a fiord-like-embayment bordering the Osa Peninsula, pantropical spotted dolphins are sympatric with inshore bottlenose dolphins (Tursiops truncatus) and these marine predators provide an important source of revenue for local communities through boat-based tours.
 Objective: Here we estimated the population size and demographic parameters of the coastal pantropical spotted dolphins in Golfo Dulce.
 Methods: The study area was surveyed using non-random boat surveys. Upon encounter, dolphins were individually photo-identified using natural marks in their dorsal fins to estimate population abundance and survival using three emigration scenarios.
 Results: A total of 280 dolphins were photoidentified, 65 % of which were observed only once. A total of 30 models were produced, and only two were considered to be parsimonious. Both models explain seasonal apparent survival and its variation due to heterogeneity in capture-recapture probability, one under no emigration (ΔQAICc = 0.00) and the other under random emigration (ΔQAICc = 1.72). We deemed the latter to be a more realistic model as it better reflects our in-situ observations. Under this preferred model the population size of pantropical spotted dolphins in Golfo Dulce varied from 187.30 individuals (CI: 168.67 – 208.02, CV: 0.11) to 367.88 individuals (CI: 341.51 – 396.31, CV: 0.07), with no significant differences in abundance due to seasonality and very high apparent survival (S = 0.98, CI: 0.68 – 0.99, SE: 0.02).
 Conclusions: The number of identified dolphins and the proportion of individuals seen only once suggest the fluid movement of the population in and out of the gulf. However, the population size and demographic estimates are characterized by several identified individuals regularly recaptured inside the gulf. This group of dolphins appears to favor the inner basin as a critical foraging habitat. Given the increase of anthropogenic impacts within Golfo Dulce, future management and conservation efforts will require the recognition of an ecologically discrete population unit of coastal pantropical spotted dolphins within the gulf.

Abundance and population growth estimates for bare-nosed wombats.

Wildlife managers often rely on population estimates, but estimates can be challenging to obtain for geographically widespread species. Spotlight surveys provide abundance data for many species and, when conducted over wide spatial scales, have potential to provide population estimates of geographically widespread species. The bare-nosed wombat (Vombatus ursinus) has a broad geographical range and is subject to spotlight surveys. We used 19 years (2002-2020) of annual spotlight surveys to provide the first estimates of population abundance for two of the three extant bare-nosed wombat subspecies: V. u. ursinus on Flinders Island; and V. u. tasmaniensis on the Tasmanian mainland. Using distance sampling methods, we estimated annual rates of change and 2020 population sizes for both subspecies. Tasmanian mainland surveys included habitat data, which allowed us to also look for evidence of habitat associations for V. u. tasmaniensis. The average wombat density estimate was higher on Flinders Island (0.42 ha-1, 95% CI = 0.25-0.79) than on the Tasmanian mainland (0.11 ha-1, CI = 0.07-0.19) and both wombat subspecies increased over the 19-year survey period with an estimated annual growth rate of 2.90% (CI = -1.7 to 7.3) on Flinders Island and 1.20% (CI = -1.1 to 2.9) on mainland Tasmania. Habitat associations for V. u. tasmaniensis were weak, possibly owing to survey design; however, we detected regional variation in density for this subspecies. We estimated the population size of V. u. ursinus to be 71,826 (CI = 43,913-136,761) on Flinders Island, which when combined with a previously published estimate of 2599 (CI = 2254-2858) from Maria Island, where the subspecies was introduced, provides a total population estimate. We also estimated 840,665 (CI = 531,104-1,201,547) V. u. tasmaniensis on mainland Tasmania. These estimates may be conservative, owing to individual heterogeneity in when wombats emerge from burrows. Although these two subspecies are not currently threatened, our population estimates provide an important reference when assessing their population status in the future, and demonstrate how spotlight surveys can be valuable to inform management of geographically widespread species.

Estimating abundance of Eastern Canada-West Greenland bowhead whales using genetic mark-recapture analyses

The Eastern Canada-West Greenland (EC-WG) bowhead whale (Balaena mysticetus) population is widely distributed across the eastern Canadian Arctic and across Baffin Bay to the western coast of Greenland. Their vast distribution makes obtaining population estimates via aerial surveys difficult, as coverage over their entire range is not possible. Genetic mark recapture analyses address this issue, as biopsy samples can be collected at various locales across the EC-WG bowhead whale population’s distribution and microsatellites can be analyzed to identify unique individuals. EC-WG bowhead whales were subject to intense commercial whaling pressure between the early 1700 s and early 1900 s, after which a moratorium on commercial whaling was put in place in 1915. We used available genetic samples from EC-WG bowhead whales in mark recapture models to estimate population abundance from 2012 to 2021 to gain insight on population dynamics ∼100 years post commercial whaling. The preferred model, using a Jolly-Seber structure, estimated the total abundance as 5173 individuals (CI: 3436–7788). Since the cessation of commercial whaling, the population has been thought to be rebounding, which is reflected by gradually increasing abundance estimates, from the low hundreds in the 1970 s and 1980 s, to ∼6000 in the early 2000 s, but our present estimate suggests population abundance may be plateauing well below the pre-commercial whaling carrying capacity estimate. This population estimate for EC-WG bowhead whales is required to update the population dynamics for conservation efforts.

Estimating Population Abundance Of Seahorse In Sebong Bay, Bintan Island

The decline in seahorse populations in the wild due to high fishing activity and habitat degradation prompted the inclusion of all seahorse species in Appendix II of CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) in 2002. By being included in Appendix II of CITES, data and information on the abundance of seahorse populations become crucial as the basis for determining the quota for fishing and trade. Estimating population abundance of seahorse requires knowledge of habitat area, which can be modeled using the MaxEnt (maximum entropty). In this study, an estimation of the abundance of seahorses was carried out in the waters of Sebong Bay, Bintan Island. MaxEnt modeling was implemented with data on seahorse presence locations and environmental parameter maps consisting of chlorophyll-a as primary productivity parameter, benthic habitat as habitat type parameter, and dissolved oxygen, salinity, and pH as physiological parameters. From this model, the value of the area of suitable habitat for seahorses is 54,6 ha, while the density of seahorse in this area is 60 ind/ha, so it can be determined that the abundance of seahorses in the Sebong Bay is 3.276 individuals. Therefore, seahorse population in Sebong Bay is critically endangered since it is below the number of individuals that required to prevent the loss of quantitative genetic variation in a species.

Processes driving individual variation in environmental DNA deposition rates in Daphnia magna

AbstractThe abundance of environmental DNA (eDNA) in water samples has been proposed as a sensitive, cost‐efficient, and non‐invasive alternative to infer population abundance and biomass, regardless of the acknowledgment that a number of biotic and abiotic factors can lead to substantially varying rates of eDNA deposition among organisms in a population. We tested how metabolic, nutritional, and life history processes shape intraspecific eDNA deposition rates in the freshwater invertebrate Daphnia magna. We extracted water samples from individual D. magna raised in glass vials under a 2 × 2 longitudinal factorial manipulation of temperature and food levels over their entire lifespan, and quantified eDNA daily deposition rates using digital droplet PCR (ddPCR). Analyzed using a hypothesis‐driven nested mixed‐effect modeling framework, we showed that per individual D. magna eDNA deposition rate varied by an order of magnitude over the course of each individual's lifespan due to multiple causes. We identified that large and pregnant D. magna had the highest eDNA deposition rates, particularly under warmer conditions with higher food levels, and thus, should be considered a prime target for field detections. We found that recently deceased individuals could potentially bias eDNA monitoring efforts by releasing a relatively higher amount of eDNA through decomposition. Our work supplies a more nuanced understanding of myriad factors that shape eDNA deposition, suggesting new and more useful ways to interpret eDNA monitoring data. We recommend that future work using eDNA to estimate population abundance or biomass should account for both energetic conditions and the reproductive cycle facing their target organism and prioritize sampling effort toward metabolically active individuals, especially when working with size‐structured populations that exhibit wide variation in body mass.

Lake Sturgeon population trends in the St. Clair–Detroit River system, 2001–2019

AbstractObjectiveThe Lake Sturgeon Acipenser fulvescens is listed as threatened or endangered in 15 states or provinces within the species' native range. Accordingly, investments in habitat and population restoration for this species have increased throughout the Great Lakes. To aid in the evaluation of restoration efficacy, robust population parameters are needed to inform management decisions. The St. Clair–Detroit River system (SCDRS) contains one of the largest self‐sustaining Lake Sturgeon populations in the Great Lakes; however, recent estimates of population abundance and growth parameters have not been assessed.MethodsOur study used baited setline and mark–recapture data collected between 2001 and 2019 to estimate whether the number of Lake Sturgeon captured varied annually and/or with water temperature and whether population abundance and the population growth rate (λ) varied among three subpopulations located in the SCDRS.ResultTrends in the number of Lake Sturgeon captured on setlines varied among subpopulations and by life stage. Annual trends in the number of Lake Sturgeon captured remained consistent over time in the upper St. Clair River, decreased for adults and increased for subadults in the lower St. Clair River, and increased in the Detroit River. With subpopulation abundances of 20,184 (95% confidence interval [CI] = 12,533–27,816) in the upper St. Clair River/southern Lake Huron, 6523 (95% CI = 5720–7327) in the lower St. Clair River, and 6416 (95% CI = 4065–8767) in the Detroit River, our study confirms that the SCDRS contains the largest Lake Sturgeon population with unimpeded access to the Great Lakes. The geometric mean λ for all subpopulations indicated stable populations and ranged from 1.00 to 1.16.ConclusionOur study provides an updated assessment of Lake Sturgeon population parameters that serve as a baseline to evaluate habitat restoration efforts and to inform management of the SCDRS recreational Lake Sturgeon fishery.

SNP Panel and Genomic Sex Identification in Atlantic Halibut (Hippoglossus hippoglossus).

The ability to identify sex is necessary in population biology for a proper understanding of the dynamics of a population. In Atlantic halibut, phenotypic sex identification is not possible due to the lack of significant external morphological differences. We developed an Illumina SNP panel for Atlantic halibut with 4000 SNPs spread evenly throughout the genome with a minor allele frequency MAF ≥ 0.4, except for N = 249 SNPs located in a sex-determining region on chromosome 12, N = 176 of these SNPs were selected to genetically identify male and female individuals using a DAPC analysis. The genomic identification of sex allows for non-lethal sex determination and validation of sex identification in the field. The SNP panel is a new genomic resource for Atlantic halibut that will make it possible to generate the genotypic data for the large number of individuals needed to estimate population abundance using genomics and the Close Kin Mark Recapture (CKMR) approach, an emerging component of fisheries management and stock monitoring.

Urban land cover and El Niño events negatively impact population viability of an endangered North American songbird

AbstractPopulation dynamics of migratory species are influenced by land use and climate patterns experienced across the full annual cycle. Identifying environmental factors influencing productivity, survival, and their relative contributions to abundance and population growth is critical for the recovery and management of at‐risk species in the face of continuing global change. The golden‐cheeked warbler (Setophaga chrysoparia) is an endangered passerine that breeds exclusively in the mixed Ashe juniper (Juniperus ashei)–oak (Quercus) woodlands of Central Texas, USA, and winters at high elevations in Central America. We evaluated the effects of precipitation, climate, and land cover on golden‐cheeked warbler productivity, adult male survival, and territory abundance using data from a long‐term monitoring site, the Balcones Canyonlands Preserve, in Austin, Texas. We jointly analyzed annual productivity, mark–recapture, and territory count data collected on 10 plots from 2011 to 2019 in an integrated population model. The number of young fledged per male territory was negatively related to percent urban land cover within 1 km of monitoring plots, and adult male survival was negatively related to a strong El Niño event. Estimates of population growth and abundance indicated a decline in abundance across our study period. We forecasted population viability 25 years into the future given increases in urban development and frequency of El Niño events. Quasi‐extinction probability increased from 0.17 under current urban land cover conditions and El Niño frequency to 0.41 under the scenario of a 10% increase in urban development around all plots and an increase in El Niño frequency. Productivity and adult survival were positively correlated with population growth, highlighting the need for conservation and management actions to maximize these vital rates on the breeding grounds and range‐wide.

Detecting and analysing intraspecific genetic variation with eDNA: From population genetics to species abundance.

Advancements in environmental DNA (eDNA) approaches have allowed for rapid and efficient species detections in diverse environments. Although most eDNA research is focused on leveraging genetic diversity to identify taxa, some recent studies have explored the potential for these approaches to detect within-species genetic variation, allowing for population genetic assessments and abundance estimates from environmental samples. However, we currently lack a framework outlining the key considerations specific to generating, analysing and applying eDNA data for these two purposes. Here, we discuss how various genetic markers differ with regard to genetic information and detectability in environmental samples and how analysis of eDNA samples differs from common tissue-based analyses. We then outline how it may be possible to obtain species absolute abundance estimates from eDNA by detecting intraspecific genetic variation in mixtures of DNA under multiple scenarios. We also identify the major causes contributing to allele detection and frequency errors in eDNA data, discuss their consequences for population-level analyses and outline bioinformatic approaches to detect and remove erroneous sequences. This review summarizes the key advances required to harness the full potential of eDNA-based intraspecific genetic variation to inform population-level questions in ecology, evolutionary biology and conservation management.

Estimating Wolf Population Size and Dynamics by Field Monitoring and Demographic Models: Implications for Management and Conservation.

We estimated the current size and dynamics of the wolf population in Tuscany and investigated the trends and demographic drivers of population changes. Estimates were obtained by two different approaches: (i) mixed-technique field monitoring (from 2014 to 2016) that found the minimum observed pack number and estimated population size, and (ii) an individual-based model (run by Vortex software v. 10.3.8.0) with demographic inputs derived from a local intensive study area and historic data on population size. Field monitoring showed a minimum population size of 558 wolves (SE = 12.005) in 2016, with a density of 2.74 individuals/100 km2. The population model described an increasing trend with an average annual rate of increase λ = 1.075 (SE = 0.014), an estimated population size of about 882 individuals (SE = 9.397) in 2016, and a density of 4.29 wolves/100 km2. Previously published estimates of wolf population were as low as 56.2% compared to our field monitoring estimation and 34.6% in comparison to our model estimation. We conducted sensitivity tests to analyze the key parameters driving population changes based on juvenile and adult mortality rates, female breeding success, and litter size. Mortality rates played a major role in determining intrinsic growth rate changes, with adult mortality accounting for 62.5% of the total variance explained by the four parameters. Juvenile mortality was responsible for 35.8% of the variance, while female breeding success and litter size had weak or negligible effects. We concluded that reliable estimates of population abundance and a deeper understanding of the role of different demographic parameters in determining population dynamics are crucial to define and carry out appropriate conservation and management strategies to address human-wildlife conflicts.

A New Detection Function Model for Distance Sampling Based on the Burr XII Model

One of the most used techniques for determining animal abundance is distance sampling. The distance sampling framework depends on the idea of a detection function, and a number of options have been suggested. In this paper, we provide a new flexible parametric model based on the Burr XII distribution. To be more specific, we use the survival function of the Burr XII distribution for novel purposes in this context. The proposed model is appealing because it meets all of the requirements for a reliable detection function model, such as being monotonically decreasing and having a shoulder at the origin. It also has the features of having various asymmetric properties and a heavy right tail, which are rare properties in this setting. In the first part, we provide its key characteristics, such as shapes and moments. Then, the inferential aspect of the model is investigated. The maximum likelihood estimation method is used to estimate the parameters in a data-fitting scenario. The estimates of population abundance are derived and compared with some existing parametric estimates. A simulation is run to assess how well the resulting estimates perform in comparison to other widely applied estimates from the literature. The model is then tested using two real-world data sets. Based on the famous goodness-of-fit statistics, we show that it is preferable to some of the well-established models.

Estimating Population Abundance of Atlantic Bottlenose Dolphins (Tursiops truncatus) in the Coastal Waters of Palm Beach County, Southeastern Florida

Atlantic bottlenose dolphins (Tursiops truncatus)are frequently observed in the coastal waters of Palm Beach County, Florida. In this study, mark-recapture surveys using photo-identification techniques were used to estimate population abundance of Atlantic bottlenose dolphins in this area for the first time. Surveys were conducted for 11 years, between 2005 and 2016, during which 384 individuals were identified and catalogued from distinctive nicks and notches on their dorsal fins. Each marked individual was documented an average of 2.4 times (range 1 to 19). Low resighting rates and a constant rate of encounter with previously unmarked individuals suggest that the population is open, comprising both residents and transients. The Jolly-Seber method was used to estimate population abundance. Estimates of abundance varied greatly in time with an overall average of 264 individuals and a 95% confidence interval of 162 to 366 (SE = 51.3), indicating a variable population size. As threats in the region continue to rise, such as overfishing, toxic algae blooms, and environmental pollutants, this understudied population may be vulnerable to decline. A better understanding of the population dynamics could facilitate more effective conservation action.

Round Goby Detection in Lakes Huron and Michigan—An Evaluation of eDNA and Fish Catches

Aquatic surveys for fish in large water bodies (e.g., Laurentian Great Lakes of North America) often require a flexible approach using multiple methods, surveying different depths, and sampling across seasons, especially when the target species is elusive in its natural habitat. The round goby (Neogobius melanostomus) is an invasive, bottom-dwelling fish inhabiting rocky areas of all five Great Lakes. While trawl surveys are typically used for abundance assessments, angling has been demonstrated as a means of supplementing surveys with additional data. Yet, round goby abundance and distribution is still not well described. Recently, with considerable success, scientists have explored sampling environmental DNA (eDNA) to complement traditional monitoring techniques for population abundance estimates, early detection of invasive species, and spawning or migration events. Therefore, we collected eDNA from water samples alongside bottom trawls and hook and line angling in Lakes Huron and Michigan to detect round goby. eDNA samples were analyzed by both droplet digital PCR (ddPCR) and quantitative PCR (qPCR) to maximize the likelihood of detection. Overall, round goby was captured in 23% of the trawls, but the eDNA based methods detected round goby in 74% and 66% of samples by ddPCR and qPCR, respectively, mostly in samples collected at <30 m depths, and mostly in the fall. More studies comparing eDNA based methods to traditional monitoring, especially trawls in large open waters, may contribute to a better understanding of using eDNA in population assessments.

Scat DNA as a non-invasive method for estimating the abundance of the vulnerable mala (Lagorchestes hirsutus)

Context Population-monitoring programs often use direct (e.g. live capture or spotlighting) or indirect (e.g. scats sightings) observations to estimate population abundance. Such methods, however, are often inadequate for rare, elusive, or cryptic species due to the difficulty in achieving sufficient encounters or detection rates. The mala (Lagorchestes hirsutus), a small native Australian macropod, listed as Vulnerable by the IUCN, is difficult to capture, susceptible to capture myopathy, and not easily sighted in their dense habitat; consequently, the population size cannot always be estimated. The use of molecular markers to identify individual genotypes from non-invasively collected samples is increasingly being used in wildlife conservation and may be an alternative approach for mala. Aim The aim of this study was to evaluate the efficacy of non-invasive scat DNA sampling to estimate the population abundance of mala. Methods A panel of microsatellite markers was developed for the identification of individual mala via profiling of their scats. Scats were systematically collected from a wild mala population located in an 1100-ha fenced reserve in Western Australia. Individual genotypes were determined using the microsatellite markers, and the abundance of mala was estimated using the genotypes with spatially explicit capture–recapture (SECR) and mark–resight analyses. Key results The genetic markers proved variable and with sufficient exclusionary power to confidently identify unique individuals (mean locus genotyping error rate: 3.1%). Individual genetic identification from scat sampling, when used with traditional mark–recapture/resight analytical models, provides feasible estimates of population abundance. This is the first reliable abundance estimate of this mala population, suggesting a >70% increase in population size since the initial reintroduction of 64 individuals in 2011–13. Conclusions Given the inherent difficulties in surveying mala, this approach would be valuable to ensure effective monitoring of the few remaining fenced and island mala populations to prevent further decline of this vulnerable species. Implications This is the first study to identify species-specific microsatellite markers for mala and use genetic-capture sampling with scat DNA to estimate the abundance of a mala population. The study provides an evaluation of a valuable species monitoring technique that can be applied to other rare, elusive, or cryptic threatened species.

Comparing fecal DNA capture‐recapture to mark‐resight for estimating abundance of mule deer on winter ranges

AbstractMonitoring big game populations is necessary for making well‐informed management decisions. In the eastern Sierra Nevada in California, USA, mule deer (Odocoileus hemionus) herds have been monitored using traditional mark‐resight methods on winter ranges since the 1990s. Although mark‐resight methods work well for estimating abundance, animal capture for marking is expensive, invasive, and risky. We were motivated to evaluate fecal DNA‐based capture‐recapture for estimating abundance on winter ranges based on the effectiveness of this new technique in other populations in California. This method has been successful for estimating abundance when animals are concentrated around a required resource or pellets are collected from game trails, but it has not been evaluated using randomly selected transects on winter ranges where traditional methods work well. We compared precision (CV) and cost of fecal DNA capture‐recapture surveys to aerial mark‐resight surveys for estimating population abundance. In the Round Valley and Goodale study areas in the eastern Sierra Nevada, we conducted annual aerial mark‐resight surveys and collected fecal pellet samples in Round Valley during winter 2020. We genotyped fecal DNA from pellets to identify unique individuals and sex. Population abundance estimates from aerial mark‐resight surveys were more precise in Round Valley (CV = 6.6%) compared to abundance estimates from fecal DNA capture‐recapture (CV = 20.4%). But based on simulations from Round Valley data, to obtain the same CV (CV = 10%), fecal DNA capture‐recapture was about 63% less expensive than aerial mark‐resight using very high frequency collars and 70% less expensive than aerial mark‐resight using global positioning system collars. In contrast, fecal DNA capture‐recapture did not succeed in the Goodale study area because of weather and logistical constraints. Determining which method is best depends on the situation, but fecal DNA capture‐recapture provides another tool for estimating population size on winter range. We conclude that fecal DNA capture‐recapture is a cost‐effective alternative for estimating abundance of ungulates on winter ranges when weather is not limiting and when researchers can survey an adequate proportion of the study area and collect an adequate number of samples.

How Many Reindeer? UAV Surveys as an Alternative to Helicopter or Ground Surveys for Estimating Population Abundance in Open Landscapes

Conservation of wildlife depends on precise and unbiased knowledge on the abundance and distribution of species. It is challenging to choose appropriate methods to obtain a sufficiently high detectability and spatial coverage matching the species characteristics and spatiotemporal use of the landscape. In remote regions, such as in the Arctic, monitoring efforts are often resource-intensive and there is a need for cheap and precise alternative methods. Here, we compare an uncrewed aerial vehicle (UAV; quadcopter) pilot survey of the non-gregarious Svalbard reindeer to traditional population abundance surveys from ground and helicopter to investigate whether UAVs can be an efficient alternative technology. We found that the UAV survey underestimated reindeer abundance compared to the traditional abundance surveys when used at management relevant spatial scales. Observer variation in reindeer detection on UAV imagery was influenced by the RGB greenness index and mean blue channel. In future studies, we suggest testing long-range fixed-wing UAVs to increase the sample size of reindeer and area coverage and incorporate detection probability in animal density models from UAV imagery. In addition, we encourage focus on more efficient post-processing techniques, including automatic animal object identification with machine learning and analytical methods that account for uncertainties.

Enhancing UAV images to improve the observation of submerged whales using a water column correction method

Enhancing <scp>UAV</scp> images to improve the observation of submerged whales using a water column correction method

Index‐based large carnivore population density and abundance estimates for the Ruaha‐Rungwa conservation complex in Tanzania

Index‐based large carnivore population density and abundance estimates for the <scp>Ruaha‐Rungwa</scp> conservation complex in Tanzania

Development of modelling and mapping methods to predict spatial distributions and abundance of estuarine and coastal fish species life‐stages in Florida

AbstractSuitability modelling and mapping methods were developed to predict spatial distributions and population abundance of fish and macroinvertebrate species in Florida estuaries and coastal zones. Habitats were mapped in Pensacola Bay, Tampa Bay, and Charlotte Harbor using data from fisheries‐independent monitoring. Starting in 1997, suitability functions from habitat suitability index models were linked to habitat grids to create seasonal maps for early‐juvenile, juvenile, and adult life‐stages. After 2003, habitat suitability models (HSM) were linked to seasonal habitat grids to create seasonal maps validated by reciprocal transfer of suitability functions between estuaries. A quantitative method was used with five factor models and models with fewer environmental factors for four species in 2005 and for 11 species by life‐stages in 2009. In 2006, suitability functions transferred from Charlotte Harbor were linked with habitat grids for Rookery Bay and Fakahatchee Bay and HSM maps produced for three time periods to test transferability to estuaries lacking long‐term monitoring. Analyses in 2012 demonstrated that HSM maps for Tampa Bay derived independently from earlier suitability functions were almost identical to HSM maps created using recent suitability functions. Salinity was the most significant environmental variable for predicting abundance in models for species life‐stages in the Peace River and Charlotte Harbor, although nutrient concentrations from upriver may have influenced species’ abundances associated with low (&lt;5 psu) to moderate (5–10 psu) salinities. Population abundance estimates for Charlotte Harbor were derived from seasonal HSM maps created in 2019 and 2021. The 2021 paper compared changes in seasonal population numbers between Baseline and Minimum Flows associated with projected water withdrawals from the Peace River. Electronic logbooks were developed in 2001 and 2004 to collect data on shrimp fishing vessels and HSM maps for the West Florida Shelf created for 16 months in 2004–2005. Methodologies evolved as enabling technology became available.

Evaluation of the distance sampling technique to monitor gregarious species: A simulation exercise

AbstractWildlife count data are used to provide estimates of population abundance. To quantify changes in the size of populations, it is necessary to determine the precision of abundance estimates. Ground or aerial survey methods are often intended to be a census and thus do not provide estimates of precision. One solution is to switch approaches to a different sampling and estimation procedure, such as distance sampling. Using an example of the long‐term waterfowl censuses in the Camargue, a major wintering area in southern France, we used simulation to quantify the precision and cost effectiveness of transitioning to a distance sampling approach. Based on abundance and distribution data for 14 species of waterbirds (Anatidae and coot [Fulica atra]) in the Camargue, we evaluated 5 distance sampling scenarios with parallel line transects corresponding to 5 different sampling intensities. Our results suggested that, if the objective of counts is to estimate the abundance of all waterfowl together, switching from pseudo‐total to distance sampling counts would be realistic on both statistical and financial grounds. The most advantageous scenario would correspond to a sampling effort with transect lines spaced 1,000 m apart, which would allow a coefficient of variation of 0.20 for total waterfowl abundance with a 27% increase in flight costs compared to the current method. Heterogeneity in the size of detected bird groups contributed to the variability in our results, however, adjusting sampling effort from 1,750 m spaced transect to 760 m allowed reduced variation by 55%. We recommend proceeding to test flights which would allow some site‐specific parameters to be refined before changing methods. However, the distance sampling method as simulated here would prove impractical to evaluate the abundance and distribution of one species alone.