Mark-recapture Models Research Articles

Genetic mark–recapture analysis reveals large annual variation in pre‐breeding sex ratio of greater sage‐grouse

Sex ratio, and the extent to which it varies over time, is an important factor in the demography, management, and conservation of wildlife populations. Greater sage‐grouse Centrocercus urophasianus populations in western North America are monitored using counts of males at leks in spring. Population estimates derived from lek‐count data typically assume a constant, female‐biased sex ratio, yet few rigorous, empirically derived estimates of sex ratio are available to test that assumption. We estimated pre‐breeding sex ratio of greater sage‐grouse in a peripheral, geographically isolated population in northwestern Colorado during two consecutive winters using closed‐population, robust‐design, multi‐state, genetic mark–recapture models in program MARK. Sex ratio varied markedly between years, with estimates of 3.29 (95% CI: 2.36–4.59) females per male in winter 2012–2013 and 1.54 (95% CI: 1.22–1.95) females per male in winter 2013–2014. Rather than assuming a constant sex ratio, biologists should consider the potential for large annual variation in sex ratio of greater sage‐grouse populations when estimating population size or trend from male lek‐count data.

Does coat colour influence survival? A test in a cyclic population of snowshoe hares.

Some mammal species inhabiting high-latitude biomes have evolved a seasonal moulting pattern that improves camouflage via white coats in winter and brown coats in summer. In many high-latitude and high-altitude areas, the duration and depth of snow cover has been substantially reduced in the last five decades. This reduction in depth and duration of snow cover may create a mismatch between coat colour and colour of the background environment, and potentially reduce the survival rate of species that depend on crypsis. We used long-term (1977-2020) field data and capture-mark-recapture models to test the hypothesis that whiteness of the coat influences winter apparent survival in a cyclic population of snowshoe hares (Lepus americanus) at Kluane, Yukon, Canada. Whiteness of the snowshoe hare coat in autumn declined during this study, and snowshoe hares with a greater proportion of whiteness in their coats in autumn survived better during winter. However, whiteness of the coat in spring did not affect subsequent summer survival. These results are consistent with the hypothesis that the timing of coat colour change in autumn can reduce overwinter survival. Because declines in cyclic snowshoe hare populations are strongly affected by low winter survival, the timing of coat colour change may adversely affect snowshoe hare population dynamics as climate change continues.

Population dynamics of killer whales (Orcinus orca) in the Crozet Archipelago, southern Indian Ocean: a mark-recapture study from 1977 to 2002

Population size and annual survival probabilities for the killer whales (Orcinus orca) inhabiting the inshore waters of Possession Island, Crozet Archipelago, southern Indian Ocean, were estimated through mark-recapture modelling. Capture histories were generated from a set of photographs taken under a photo-identification protocol and a set of photographs taken opportunistically, between 1964 and 2002. Photographs were selected according to their intrinsic quality and the degree of natural marking of individuals. Under those conditions, only well-marked individuals were considered as ‘marked’ from a capture-recapture perspective. The purpose of this double selection was to minimise identification errors and reduce the heterogeneity of capture probabilities. Abundance estimates were derived from the Mth sequential model for closed populations and adjusted for the proportion of well-marked individuals in the study population and for the number of photo-identified individuals. Under this framework, estimates of 98 (95% CI 70-156) individuals in 1988-89, and 37 (95% CI 32-62) individuals in 1998-2000 are proposed. After a weighted model averaging, the Cormack-Jolly-Seber models with the strongest support from the data produced low survival probability estimates, decreasing from 0.935 (95% CI 0.817-0.979) to 0.895 (95% CI 0.746-0.961) for males, and from 0.942 (95% CI 0.844-0.980) to 0.901 (95% CI 0.742-0.966) for females over the period 1977-2002. A Jolly-Seber model was used as a ‘second opinion’ model. It confirmed the worrying status of the population with a constant survival probability estimated at 0.89 (95% CI 0.84-0.93) and a constant rate of increase (applying to the well-marked fraction of the population) estimated at 0.94 (95% CI 0.90-0.99) for the period 1987-2000. This rate of increase is consistent with the abundance estimates presented here. Possible violations of the underlying model assumptions were investigated and it was concluded that the abundance estimates for the period 1988-89 and the CJS survival estimates should be the most reliable results. It is feared that the killer whales around Possession Island are in sharp decline, as may be true for the whole Crozet Archipelago. The effect of low prey stocks and lethal interactions with fisheries as the most likely causes of this decline are discussed.

Natal colony influences age-specific movement patterns of the Yellow-legged gull (Larus michahellis)

BackgroundAs for other life history traits, variation occurs in movement patterns with important impacts on population demography and community interactions. Individuals can show variation in the extent of seasonal movement (or migration) or can change migratory routes among years. Internal factors, such as age or body condition, may strongly influence changes in movement patterns. Indeed, young individuals often tend to move across larger spatial scales compared to adults, but relatively few studies have investigated the proximate and ultimate factors driving such variation. This is particularly the case for seabirds in which the sub-adult period is long and difficult to follow. Here, we examine migration variation and the factors that affect it in a common Mediterranean seabird, the Yellow-legged gull (Larus michahellis).MethodsThe data include the encounter histories of 5158 birds marked as fledglings between 1999 and 2004 at 14 different colonies in southern France and resighted over 10 years. Using a multi-event mark-recapture modeling framework, we use these data to estimate the probability of movement and survival, taking into account recapture heterogeneity and age.ResultsIn accordance with previous studies, we find that young individuals have greater mobility than older individuals. However, the spatial extent of juvenile movements depends on natal colony location, with a strong difference in the proportion of sedentary individuals among colonies less than 50 km apart. Colony quality or local population dynamics may explain these differences. Indeed, young birds from colonies with strong juvenile survival probabilities (~ 0.75) appear to be more sedentary than those from colonies with low survival probabilities (~ 0.36).ConclusionsThis study shows the importance of studying individuals of different ages and from different colonies when trying to understand seabird movement strategies. Local breeding success and the availability of food resources may explain part of the among colony differences we observe and require explicit testing. We discuss our results with respect to the feedback loop that may occur between breeding success and mobility, and its potential implications for population demography and the dissemination of avian disease at different spatial scales.

Demographic response of a high-Arctic polar bear (Ursus maritimus) subpopulation to changes in sea ice and subsistence harvest

Climate change is a long-term threat to polar bears. However, sea-ice loss is hypothesized to provide transient benefits in high latitudes, where thick multiyear ice historically limited biological productivity and seal abundance. We used joint live-recapture and dead-recovery mark-recapture models to analyze data for one of the most northerly polar bear subpopulations, Kane Basin. The data consisted of 277 initial live captures and genetic identifications (1992-1997 = 150, 2012-2014 = 127), 89 recaptures or re-identifications (1992-1997 = 53, 2012-2014 = 36), and 24 harvest returns of research-marked bears during 1992-2014. We estimated mean annual abundance of 357 bears (95% CI: 221-493) for 2013-2014. This suggests a likely increase relative to our estimate of 224 (95% CI: 145-303) bears in the mid-1990s and relative to a previously published estimate of 164 (95% CI: 94-234) bears in the mid-1990s that used some of the same data. This is also supported by an apparent increase in the density of bears in eastern Kane Basin during 2012-2014. Estimates of total survival for females ≥3 yr old (mean ± SE: 0.95 ± 0.04) and their dependent offspring were similar to previous estimates from the 1990s, and estimates of unharvested survival for females ≥3 yr (0.96 ± 0.04) appear sufficient for positive population growth. Estimates of total survival were lower for males ≥3 yr (0.87 ± 0.06). We documented a reduction in mortality associated with subsistence harvest, likely attributable to implementation of a harvest quota by Greenland in 2006. Our findings, together with evidence for increased range sizes, improved body condition for all sex and age classes, and stable reproductive metrics, show that this small high-Arctic polar bear subpopulation remains productive and healthy. These benefits are likely temporary given predictions for continued climate change.

Rapid assessment of adult abundance and demographic connectivity from juvenile kin pairs in a critically endangered species

The viability of spatially structured populations depends on the abundance and connectivity between subpopulations of breeding adults. Yet, for many species, both are extremely difficult to assess. The speartooth shark is a critically endangered elasmobranch inhabiting tropical rivers with only three adults ever recorded in Australia. Close-kin mark-recapture models, informed by sibling pairs among 226 juveniles, were developed to estimate adult abundance and connectivity in two Australian river systems. Sixty-eight sibling pairs were found, and adult abundance was estimated at 892 for the Adelaide River and 1128 for the Alligator Rivers. We found strong evidence for female philopatry, with most females returning to the same river to pup. Adelaide River males appear largely philopatric, whereas Alligator Rivers males are highly connected to the Adelaide River. From only 4 years of sampling, our results demonstrate that juvenile-only kin pairs can inform simultaneous estimates of abundance and connectivity in a rare and threatened species.

Common dolphins (Delphinus delphis) in Israel: Unique dynamics of a critically endangered population

The most eastern population of common dolphins (Delphinus delphis) in the Mediterranean Sea inhabits the southern coastal waters of Israel. They are mainly observed in the shallow waters off Ashdod and Ashkelon, between the 15-30 m isobaths, with no reported observations north or west of this area. These dolphins were observed and studied year-round between 2016-2021 using boat-based surveys and photo identification methods. Common dolphins were encountered and photographed 43 times during the study period, resulting in 2,851 identifications of 25 distinctive mature individuals and 12 calves. Most individuals (62%) were sighted over multiple years, with high yearly and monthly sighting rates, indicating long-term site fidelity and residency. Closed population mark-recapture models estimated a total abundance of 25 (95% CI 24 – 37) individuals in 2016 that declined to only 15 (95% CI 15 – 15) individuals in 2021. Social network analysis described these remaining individuals as one closed and well-associated social unit. Survival probabilities for this population appeared lower than those of other delphinid populations. The decrease in their abundance, coupled with their apparent isolation level, qualifies the local population for a re-assessment of their conservation status. This study first describes the Israeli local population of common dolphins, their dynamics and an assessment of their status based on the IUCN Red List framework.

Population estimates of photo-identified individuals using a modified POPAN model reveal that Raja Ampat’s reef manta rays are thriving

The 6.7-million-hectare Raja Ampat archipelago is home to Indonesia’s largest reef manta ray (Mobula alfredi) population and a representative network of nine marine protected areas (MPAs). However, the population dynamics ofM. alfrediin the region are still largely unknown. Using our photo-identification database, we fitted modified POPAN mark-recapture models with transience and per capita recruitment parameters to estimate key demographic characteristics ofM. alfredifrom two of Raja Ampat’s largest MPAs: Dampier Strait and South East (SE) Misool. A total of 1,041 unique individuals were photo-identified over an 11-year period (2009–2019) from Dampier Strait (n = 515) and SE Misool (n = 536). In our models, apparent survival probabilities and per capita recruitment rates were strongly linked with El Niño–Southern Oscillation (ENSO) events. Our models also estimated high apparent survival probabilities and significant increases in (sub)population sizes in both MPAs over a decade. In Dampier Strait, the estimated population size increased significantly (p = 0.018) from 226 (95% CI: 161, 283) to 317 (280, 355) individuals. Likewise, the estimated population size in SE Misool increased significantly (p = 0.008) from 210 (137, 308) to 511 (393, 618) individuals. Regardless of variation in the percentage change in population size between years throughout the study, the estimated overall population change shows a compound growth of 3.9% (0.7, 8.6) per annum in Dampier Strait and 10.7% (4.3, 16.1) per annum in SE Misool. Despite the global decline in oceanic sharks and rays due to fishing pressure in the last five decades, our study demonstrates the positive impact of a suite of long-term conservation efforts, coupled with the influence of ENSO events, on increasingM. alfrediabundance in Raja Ampat MPAs. Our study also underscores the importance of long-term monitoring to evaluate the effectiveness of conservation management measures on manta ray populations. Our modification of the standard POPAN model by incorporating per capita recruitment and transience parameters represents an important advance in mark-recapture modelling that should prove useful when examining other manta ray populations and other highly migratory species that are likely to have a substantial percentage of transient individuals.

Spawning Atlantic cod (Gadus morhua L.) exposed to noise from seismic airguns do not abandon their spawning site

Abstract Seismic airgun surveys may disturb and displace fish at large ranges. If such displacement causes fish to abandon spawning grounds, reproductive success could be impacted. To investigate whether airgun sound causes cod (Gadus morhua L.) to leave their spawning grounds, acoustic telemetry arrays were deployed on two cod spawning grounds: a test and a reference site. From 2019 to 2021, 136 mature cod from the test site and 45 from the reference site were tagged with acoustic transmitters. Intermittent seismic shooting of two 40 in.3 airguns for 1 week during the spawning periods of 2020–2021 resulted in fluctuating sound exposure levels (SEL) at the test site, comparable to a full-scale industrial survey 5–>40 km away. Residency and survival of tagged cod were analysed with capture–mark–recapture models fitted to the detection and recapture data. Departure rate of the mature cod varied between spawning seasons but was similar between the test and reference sites. Neither survival nor departure significantly differed between seismic exposure and baseline periods. The results indicated that exposure to airguns at received SEL of up to ∼145 dB re 1 µPa2 s, comparable to a seismic survey occurring several kilometres away, did not displace tagged cod from spawning grounds.

Know what you don't know: Embracing state uncertainty in disease‐structured multistate models

Abstract Hidden Markov models (HMMs) are broadly applicable hierarchical models that derive their utility from separating state processes from observation processes yielding the data. Multistate models such as mark–recapture and dynamic multistate occupancy models are HMMs frequently used in ecology. In their early formulations, states, such as pathogen infection status, were assumed to be perfectly observed without ambiguity. However, state uncertainty is a pervasive feature of many ecological studies, and multievent models were developed to explicitly account for it. We developed a novel extended multievent mark–recapture model that incorporates state uncertainty at multiple levels of detection. Using a disease‐structured example, both false negative and false positive state assignment errors are modelled at two levels of state assignment—the pathogen sampling process and the diagnostic process that samples are subjected to. We additionally describe methods to jointly model infection intensity to integrate heterogeneity in ecological parameters, such as mortality and infection dynamics, and the pathogen detection processes. We provide code to simulate and analyse datasets with various underlying ecological processes and fit our model to a mark–recapture dataset of Mixophyes fleayi (Fleay's barred frog) infected with the amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd). In our case study, we found evidence for various state assignment errors: the sampling protocol performed poorly in detecting Bd, pathogen detection was highly dependent on infection intensity and false positives were non‐negligible. Incorporating state uncertainty yielded significantly higher estimates of infection prevalence and 4–5 times lower rates of infection state transitions compared to those obtained from a traditional multistate model. Our results highlight that incorporating state assignment errors improves inference on the ecological process, especially when sensitivity and specificity of the state assignment processes are low. The general model structure can be applied to other HMMs, providing a foundation for modelling state uncertainty in related models. For disease‐structured multistate models, we recommend conducting robust design surveys and collecting samples during each capture event to facilitate incorporating pathogen detection errors.

Assessing Size‐Dependent Population‐Level Effects of Largemouth Bass Tournament Mortality

AbstractAs black bass Micropterus spp. tournaments continue to grow in popularity, so too must evaluations on the population‐level effects of live‐release angling events. Although factors influencing the tournament mortality of individuals are well studied, assessments at the population level are lacking. We evaluated differences in tournament capture probability and survival of two size‐classes of Largemouth Bass M. salmoides (medium: 381–457 mm; large: >457 mm) using a multistate mark–recapture model. Changes in estimated capture and survival rates of medium and large bass were then simulated to assess potential effects on population size structure. Tournament capture probabilities for medium bass were approximately three times higher than those for large bass, and tournament capture probabilities for both size‐classes increased with air temperature. Medium bass also experienced higher survival rates than large bass after tournaments, and survival rates of both groups declined with increasing water temperature. Our simulations indicated that both increases in tournament capture probability and reductions in posttournament survival of large bass resulted in some reductions in population size structure. However, increases in tournament capture probability or reductions in tournament survival of medium bass or medium and large bass alone had little to no effect. Our results suggest that under the observed tournament conditions, tournaments have little effect on bass population size structure, but size structure could be reduced with higher capture probabilities and lower posttournament survival; this information is useful for managing the fishery effects of tournament angling. Our modeling approach also provides a framework for understanding population‐level effects of tournaments on other populations under alternative conditions.

Informing Management of Atlantic Bluefin Tuna Using Telemetry Data

Sustainable management of exploited marine fish and wildlife populations requires knowledge about their productivity. Survival from natural causes of mortality is a key component of population productivity, but is notoriously difficult to estimate. We evaluate the potential for acoustic telemetry as a long-term monitoring tool to estimate rates of natural mortality. We present a Bayesian multistate mark-recapture model for telemetry data collected over a decade from 188 Atlantic bluefin tuna (Thunnus thynnus) and apply it to estimate the rate of natural mortality using only acoustic tag detections for all animals, or using acoustic tag detections for 96 single-tagged tuna plus acoustic tag detections combined with estimated positions from pop-up satellite archival tags for 92 double-tagged animals. We support the model for bluefin tuna with a simulation study to quantify bias in estimates of population dynamics parameters and investigate the effect of auxiliary information from satellite tagging on mortality rate estimates for different acoustic tag detection probability scenarios.We obtained posterior estimates of the instantaneous annual natural mortality (survival) rate across a decade of tagging for Atlantic bluefin tuna of 0.17 yr-1 (0.84 yr-1) both using only acoustic tagging data, and using a combination of acoustic and satellite tagging data. Use of a prior implying a higher rate of fishing mortality yielded an instantaneous annual natural mortality (survival) estimate of 0.10 yr-1 (0.90 yr-1), with combined acoustic and satellite tag data. Results from the simulation study indicate that the use of satellite tags can improve the precision and accuracy of estimates of detection probabilities, area-specific movement probabilities and mortality rates, where the extent of the improvement depends on true underlying acoustic tag detection probabilities. Our work demonstrates that long-term acoustic tagging data sets have strong potential for monitoring of highly migratory marine fish and wildlife populations, providing information on a number of key parameters, including survival and movement rates. However, improved information on tag reporting rates or fishing mortality is needed to better separate natural and fisheries mortality for Atlantic bluefin tuna.

Length of stay and departure strategies of Semipalmated Sandpipers (Calidris pusilla) during post-breeding migration in the upper Bay of Fundy, Canada

The Bay of Fundy, Canada is a critical staging area for Semipalmated Sandpipers (Calidris pusilla) during post-breeding migration. Recent range-wide population declines and changes in diet and migratory timing in the Bay of Fundy prompted a re-examination of staging ecology, including length of stay (last estimated in 1981), which is used in calculating migratory population estimates. We used radio-telemetry and the Motus Wildlife Tracking System to estimate individual length of stay and departure conditions for 159 Semipalmated Sandpipers in 2013 and 2014. Using tracking data we compared two estimation methods, minimum length of stay and mark-recapture modelling. Using minimum length of stay, the mean length of stay was approximately 21 days, an increase from the previous estimate of 15 days. Mark-recapture models suggested a much longer staging period that is inconsistent with other data. Sandpipers captured early in the staging period stayed longer on average than those captured later. Departures from the staging area were correlated with north-westerly winds, moderate to high wind speeds and low but rising atmospheric pressures. We suggest that Semipalmated Sandpipers in the Bay of Fundy are not operating on a time-selected migration schedule and instead wait for favourable weather conditions to depart, which occur more often later in the migratory period. Population trends in the Bay of Fundy should be re-evaluated in light of the increased length of stay.

Estimating density of ocelots in the Atlantic Forest using spatial and closed capture–recapture models

Abstract Monitoring variation in population features such as abundance and density is essential for evaluating and implementing conservation actions. Camera trapping can be important for assessing population status and trends and is increasingly used to generate density estimates through capture–recapture models. Moreover, success in using this technique can vary seasonally given shifting animal distributions and camera encounter rates. Notwithstanding these potential advantages, a gap still exists in our understanding of the performance of such models for estimating density of cryptic Neotropical terrestrial carnivores with low encounter rate probability with cameras. In addition, scanty information is available on how sampling design can affect the accuracy and precision of density estimates for Neotropical carnivores. We evaluate the performance of spatially explicit versus nonspatial capture–mark–recapture models for estimating densities and population size of ocelots (Leopardus pardalis) within an Atlantic Forest fragment in Brazil. We conducted two spatially concurrent surveys, a random camera-trap deployment covering the entire study area and a systematic camera-trap deployment in a small portion of the study area, where trails and unpaved roads were located. We obtained 244 photographs of ocelots in the Rio Doce State Park from April 2016 to November 2017, using 54-double camera stations spaced approximately 1.5 km apart (random placement) totaling 4,320 trap-nights and 15-double camera stations spaced from 0.3–10 km apart (systematic placement) totaling 1,200 trap-nights. Using the random placement design, ocelot density estimates were similar during the dry season, 14.0 individuals/km2 (± 5.6 SE, 6.6–30.0, 95% CI) and 13.78 individuals/km2 (± 4.25 SE, 5.4–22.1, 95% CI) from spatially explicit capture–recapture and nonspatial models, respectively. Using the systematic placement design spatially explicit models had smaller and less precise ocelot density estimates than nonspatial models during the dry season. Ocelot density was 12.4 individuals/100 km2 (± 5.0 SE, 5.8–26.7, 95% CI) and 19.9 individuals/km2 (± 5.2 SE, 9.7–30.1, 95% CI) from spatially explicit and nonspatial models, respectively. During the rainy season, we found the opposite pattern. Using the systematic placement design, spatial-explicit models had higher and less precise estimates than nonspatial models. Ocelot density was 24.6 individuals/100 km2 (± 13.9 SE, 8.7–69.4, 95% CI) and 11.89 individuals/km2 (± 3.93 SE, 4.19–19.59, 95% CI) from spatially explicit and nonspatial models, respectively. During the rainy season, we could not compare models using the random placement design due to limited number of recaptures to run nonspatial models. In addition, a single recapture yielded an imprecise population density estimate using spatial models (high SE and large 95% CIs), thus precluding any comparison between nonspatial and spatially explicit models. We demonstrate relative differences and similarities between the performance of spatially explicit and nonspatial capture–mark–recapture models for estimating density and population size of ocelots and highlight that both types of capture–recapture models differ in their estimation depending on the sampling design. We highlight that performance of camera surveys is contingent on placement design and that researchers need to be strategic in camera distribution according to study objectives and logistics. This point is especially relevant for cryptic or endangered species occurring at low densities and having low detection probability using traditional sampling methods.

Deep learning algorithm outperforms experienced human observer at detection of blue whale D‐calls: a double‐observer analysis

AbstractAn automated algorithm for passive acoustic detection of blue whale D‐calls was developed based on established deep learning methods for image recognition via the DenseNet architecture. The detector was trained on annotated acoustic recordings from the Antarctic, and performance of the detector was assessed by calculating precision and recall using a separate independent dataset also from the Antarctic. Detections from both the human analyst and automated detector were then inspected by an independent judge to identify any calls missed by either approach and to adjudicate whether the apparent false‐positive detections from the automated approach were actually true positives. A final performance assessment was conducted using double‐observer methods (via a closed‐population Huggins mark–recapture model) to assess the probability of detection of calls by both the human analyst and automated detector, based on the assumption of false‐positive‐free adjudicated detections. According to our double‐observer analysis, the automated detector showed superior performance with higher recall and fewer false positives than the original human analyst, and with performance similar to existing top automated detectors. To understand the performance of both detectors we inspected the time‐series and signal‐to‐noise ratio (SNR) of detections for the test dataset, and found that most of the advantages from the automated detector occurred at low and medium SNR.

Pulsed resources and the resource‐prediction strategy: a field‐test using a 36‐year study of small mammals

Pulsed resource environments are known for their marked variations in resource availability over space and time. Animals living in such environments usually increase reproduction after resources become available. Some small mammal populations, however, may use environmental cues that precede large crops of seeds (e.g. pollen, flowers, unripe seeds) to ‘predict' mast‐seeding events and reproduce in advance. In other words, these populations exhibit a resource‐prediction strategy based on future fitness prospects. Habitat selection might play a key role in the resource‐prediction strategy, but our understanding of habitat selection in pulsed resource environments is extremely limited. We used a 36‐year dataset on small mammal trapping and seed availability collected in Maine (USA) to test if American red squirrels Tamiasciurus hudsonicus, eastern chipmunks Tamias striatus, white‐footed mice Peromyscus leucopus and southern red‐backed voles Myodes gapperi select habitats based on upcoming resources and examine the consequences to individual fitness. Small mammal trapping was conducted in summer before seeds were available, thus trapping occurred when only the cues of an upcoming mast event were available. Using home‐range estimations and capture data, we performed resource selection analyses to assess if individuals select habitat to maximize future resource acquisitions. Using capture–mark–recapture models, we also estimated individual survival (a proxy for fitness). Our results do not support habitat selection as a mechanism underlying the resource‐prediction hypothesis, indicating that individuals do not select habitats based on the upcoming seed availability. Nevertheless, we found that white‐footed mice with home ranges in areas characterized by a greater quantity of white oak acorns have up to a 15% higher survival rate. Our empirical study advances the understanding of predator response to pulsed resources by not supporting a key mechanism thought to underpin the anticipatory responses that have been observed in many ecosystems worldwide.

Abundance, spatial distribution and threats to Indo-Pacific bottlenose dolphins (Tursiops aduncus) in an Important Marine Mammal Area in Tanzania

Abundance estimates of cetaceans in the western Indian Ocean are rare, but important, as many cetacean populations are under threat, especially those in coastal habitats. This study aimed to generate first estimates of abundance for Indo-Pacific bottlenose dolphins (Tursiops aduncus), assessed as Near Threatened on the IUCN Red List, in an area identified by the Marine Mammal Protected Area Task Force as an ‘Important Marine Mammal Area’. Two study sites were surveyed along the east and west coastlines of the Pemba Channel, Tanzania. In west Pemba, between 2014 and 2016 four boat-based visual surveys conducted a total of 2467 km of survey effort sighting a total of 16 groups of T. aduncus. Abundance was estimated using mark-recapture models of photo-identified individuals as 83 animals (CV 7.8%, 95% CI 72-97) in the 1084km2 study area. In the Tanga study area in 2016 two boat-based visual surveys covered 1254 km of effort during which 15 groups of T. aduncus were sighted, resulting in a photo-ID based mark-recapture abundance estimate of 196 (CV 8.9%, 95% CI 165-233) individuals in the 1562 km2 study site. Group encounter rate for this species in Tanga was double that recorded in the Pemba study site. A total of 23% of identified dolphins bore the scars of interactions with fishing gear.

Lake Sturgeon (Acipenser fulvescens) in Goulais Bay, Lake Superior: Cohort strength determinants and population viability

Lake Sturgeon (Acipenser fulvescens) is a species of conservation concern throughout North America, and healthy populations are rare. Earlier sampling efforts identified the Goulais Bay population in Lake Superior as a potentially healthy population after three years of sampling. With seven additional years of sampling, we updated the earlier analysis and developed a matrix population model to conduct a population viability analysis (PVA). We identified a non-linear relationship between cohort strength and May river discharge rate which was incorporated into the population model to evaluate the influence of future discharge scenarios on population persistence. Population size was estimated, with an open-population mark-recapture model, at approximately 5,200 juvenile Lake Sturgeon. This estimate equates to approximately 440 mature females and 625 mature males in the population. A population of this size has a probability of extinction of 4 % and 18 % over 250 and 1000 years under status quo conditions. If the May river discharge were to decrease in the future, which may represent the most likely scenario under future climate conditions, our model predicts an increased risk of population extirpation. This indicates that increased management actions may be required to ensure this population remains resilient.

Estimating survival probabilities of Cambridge Bay Arctic char using acoustic telemetry data and Bayesian multistate capture–recapture models

Arctic fishes are threatened by climatic change and other anthropogenic stressors, yet information on how such changes impact survival remains scarce. Acoustic telemetry has become valuable for studying aspects of fish ecology, including survival, which is invaluable in understanding potential responses to changing conditions. In Cambridge Bay, NU, we have been using acoustic telemetry to study movements and habitat use of the culturally and commercially important Arctic char ( Salvelinus alpinus). Here, we combine acoustic telemetry data and Bayesian multistate mark–recapture models to study the survival of Arctic char from 2014 to 2018 in the region in freshwater and marine/estuarine habitats. We found that survival probabilities were high (>0.87) and models considering two environments (freshwater and marine) perform better than those considering three (including estuarine habitats). Furthermore, the survival in fresh water was higher than survival in marine/estuary environments. Overall, the results of this study further our understanding of important demographic parameters (i.e., survival) for Arctic char in the region, which will be useful in refining fishery management plans for the largest commercial fishery for this species in Canada.

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

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