Harvest Mortality Research Articles

Comparing winter distribution and harvest rates of transmitter‐marked and banded‐only mallards in western Tennessee

AbstractThe miniaturization of Global Positioning Systems (GPS) transmitters is providing insights into the ecology and management of migratory bird species at biologically‐relevant spatial scales. However, transmitters and their attachment methods could bias inferred behaviors, demographic rates, and resulting management decisions. We evaluated the effects of external harness‐style GPS transmitters by comparing direct harvest rates, winter dispersal distances, and subsequent harvest distributions of mallards (Anas platyrhynchos) equipped with GPS transmitters (n = 443) to a tarsal banded‐only control group (n = 1,123) captured in western Tennessee during winters 2019–2022. We found that transmitter‐marked mallards had similar harvest rates, winter dispersal distances, and harvest distributions as banded‐only mallards. Time between capture and harvest predicted dispersal distances but there was no effect of marker type. Specifically, the average time from capture to harvest was 30 (SE = 2) and 31 (SE = 3) days for banded‐only and transmitter‐marked mallards, respectively. Harvest rate () was only 2.2% greater for transmitter‐marked mallards compared to banded‐only mallards overall, but GPS transmitters affected harvest susceptibility of juveniles ( = 14.5%). Based on harvest rates and dispersal distances between transmitter‐marked and banded‐only cohorts, we suggest 7‐ to 10‐day data censoring periods may be warranted, especially for juveniles, as mallards acclimate to GPS transmitters. Overall, we concluded that modern harness‐style GPS transmitters provided reliable information of wintering mallard space use, movements, and harvest mortality and can be used to inform ecology and management of wintering mallards and other dabbling ducks. Future studies should evaluate effects of harness‐style GPS transmitters for other species and during different portions of dabbling ducks' life cycle, such as migration or nesting, when they may experience greater adverse effects.

Proximity among protected area networks promotes functional connectivity for wintering waterfowl

The equilibrium theorem provided a fundamental framework for understanding species’ distributions and movement in fragmented ecosystems. Wetland-dependent avian species are model organisms to test insular predictions within protected area networks because their mobility allows surveillance of isolated patches without landscape barriers. We hypothesized size and isolation would influence functional connectivity of sanctuaries by GPS-marked wintering mallards (Anas platyrhynchos) within a mesocosm protected sanctuary area network. We evaluated functional connectivity and sanctuary use, measured by movements between sanctuaries, using a multistate modeling framework. Proximity drove connectivity, underscoring that patch isolation—not size—influenced connectivity, even for an avian species with no ascertainable landscape resistance or barriers. We also found that sanctuary use increased overwintering survival by reducing harvest mortality. Our test of equilibrium theory predictions demonstrated that isolation of protected sanctuary areas supersedes their size in determining functional connectivity for mallards and access to these areas may have direct fitness consequences. Our findings could refine land acquisition, restoration, and management practices with equal or greater emphasis on adjacency in protected area network design, especially for wetland-dependent migratory gamebirds.

Harvest of transboundary grey wolves from Yellowstone National Park is largely additive

Abstract Large carnivores are globally threatened due to habitat fragmentation and loss, prey depletion and human exploitation. Human exploitation includes both legal and illegal hunting and trapping. Protected areas can create refugia from hunting and trapping; however, hunting can still threaten wide‐ranging large carnivores when they leave these areas. Large carnivore reintroductions to protected areas are often motivated to restore ecological processes, including wolf reintroduction to Yellowstone National Park (YNP). Determining if harvest is compensatory or additive is essential for informed conservation strategies, as it influences the overall impact on wolf populations and their ecosystems. If harvest was compensatory, then increasing harvest pressure outside YNP should not decrease overall survival for transboundary wolves. Alternatively, if increasing harvest was additive, then increasing harvest pressure outside YNP should decrease overall survival for transboundary wolves. We tested the effects of variable harvest pressure following delisting on the survival of YNP grey wolves (Canis lupus) from 1995 to 2022. We defined three harvest levels: no harvest, harvest with limited quotas and unlimited harvest. We used Cox‐proportional hazards models and cumulative incidence functions to estimate survival rates, factors affecting survival and cause‐specific mortality between these three harvest periods to test predictions of the additive mortality hypothesis. Most harvested wolves that primarily lived in YNP were killed adjacent to the park border. Cox‐proportional hazards models revealed that mortality was highest during years of unlimited harvest during winter outside YNP. Cause‐specific mortality analyses showed that natural mortality from other wolves and harvest were the two leading causes of death, but that harvest mortality had additive effects on wolf mortality. Wolf survival decreased with increased harvest mortality, while natural mortality remained relatively unchanged. Synthesis and applications. High rates of additive harvest mortality of wolves could negatively impact wolf survival in YNP. Harvest mortality of transboundary wolves is additive possibly due to source‐sink dynamics of uneven spatial susceptibility of wolves to harvest mortality across protected area borders, as well as effects of harvest on complex social dynamics of wolves in YNP. Transboundary management of large carnivores is challenging, yet cooperation between agencies is vital for wolf management in and around YNP. Our results support the use of small quota zones surrounding protected areas, that minimize transboundary mortality impacts on large carnivores living primarily inside protected areas.

Effects of lethal management on gray wolf pack persistence and reproduction in Wisconsin, USA.

Direct human-caused mortality accounts for about half of all large mammal mortality in North America. For social species like gray wolves (Canis lupus), the death of pack members can disrupt pack structure and cause pack dissolution, and mortality of breeding adults or wolves during reproduction and pup-rearing can decrease pup recruitment. We estimated minimum and maximum probability of wolf pack persistence in Wisconsin, USA, during biological years (15 April-14 April) 2011-2019 and evaluated the influence of pack size and legal harvest mortality on pack persistence during 2012-2014. Harvests comprised 75-161 mortalities within 194 monitored packs during 2012-2014, with 56-74% of packs having no wolves harvested each year. As an index of reproduction during 2013-2019, we also estimated the proportion of packs where pups responded to howl surveys. We evaluated the influence of pack size, legal harvest, and agency removal on reproduction during 2013-2015. Annual maximum pack persistence probability was uniformly high (0.95-1.00), and annual minimum pack persistence probability ranged from 0.86-0.98 with a possible decline during years of harvest. Reproduction was similar in years following harvest and agency removal (2013-2015, pup response = 0.27-0.40), and years without harvest or agency removal the year prior (2016-2019, pup response = 0.28-0.66). Pack size had a positive effect on pack persistence and reproduction. Total number of wolf mortalities and number of adult male and females removed did not influence pack persistence or reproduction. We suggest that low per-pack mortality, timing of harvest and agency removal, and harvest characteristics during 2012-2014 supported stable pack persistence and reproduction.

Not all sanctuaries are created equal: variation in protected area selection by wintering mallards

AbstractPublic lands managed for wildlife frequently provide various forms of sanctuary to increase residency times and allow access to energetic and other habitat resources for waterfowl. The influence of sanctuary type and disturbance regime on resource use and fine‐scale movements of waterfowl has not been investigated extensively using currently available transmitter technologies. We examined mallard (Anas platyrhynchos) use of various types of waterfowl sanctuary and non‐sanctuary areas in the Mississippi Alluvial Valley region of eastern Arkansas, USA, during winters of 2019–2021. We deployed 105 global positioning system transmitters on mallards at 4 closed‐access spatial sanctuaries on or adjacent to Dale Bumpers White River National Wildlife Refuge. We used hourly transmitter locations to examine mallard use of public sanctuary areas, public hunt areas, and private lands using integrated step selection analysis. Public sanctuary areas provided varying levels of protected status, public hunt areas allowed for varying levels of hunting intensity by duck hunters, and private lands were open to waterfowl hunting and other forms of private uses but may or may not have been hunted at any specific frequency. Mallards selected spatial sanctuary and avoided public hunt areas, other sanctuary types, and private lands during the day. In contrast, mallards selected for private lands over spatial sanctuary at night. Mallards tended to avoid areas that allowed duck hunting or used them during the night when risk of harvest mortality was removed. After the hunting season closed, mallards began using areas that previously allowed duck hunting during the day, suggesting that risk was the primary factor influencing site use. Moreover, mallards were 1.6 times more likely to use public daily hunt areas and 2.1 times more likely to use private lands potentially open to hunting during the day than spatial sanctuary 2 weeks after the close of duck hunting season in February. Spatial sanctuaries appear more effective in influencing mallard use than temporal sanctuaries or inviolate sanctuaries, which are commonly used by state and federal agencies. Partial daily, daily, or activity‐specific (e.g., no hunting past noon, no hunting 3 days/week, no waterfowl hunting) closures to encourage mallard use of temporal sanctuaries do not appear to reduce the perceived harvest‐related risk to mallards enough for them to view these areas as accessible or significantly increase their use.

Prior choice and data requirements of Bayesian multivariate hierarchical models fit to tag-recovery data: The need for power analyses.

Recent empirical studies have quantified correlation between survival and recovery by estimating these parameters as correlated random effects with hierarchical Bayesian multivariate models fit to tag-recovery data. In these applications, increasingly negative correlation between survival and recovery has been interpreted as evidence for increasingly additive harvest mortality. The power of these hierarchal models to detect nonzero correlations has rarely been evaluated, and these few studies have not focused on tag-recovery data, which is a common data type. We assessed the power of multivariate hierarchical models to detect negative correlation between annual survival and recovery. Using three priors for multivariate normal distributions, we fit hierarchical effects models to a mallard (Anas platyrhychos) tag-recovery data set and to simulated data with sample sizes corresponding to different levels of monitoring intensity. We also demonstrate more robust summary statistics for tag-recovery data sets than total individuals tagged. Different priors led to substantially different estimates of correlation from the mallard data. Our power analysis of simulated data indicated most prior distribution and sample size combinations could not estimate strongly negative correlation with useful precision or accuracy. Many correlation estimates spanned the available parameter space (-1,1) and underestimated the magnitude of negative correlation. Only one prior combined with our most intensive monitoring scenario provided reliable results. Underestimating the magnitude of correlation coincided with overestimating the variability of annual survival, but not annual recovery. The inadequacy of prior distributions and sample size combinations previously assumed adequate for obtaining robust inference from tag-recovery data represents a concern in the application of Bayesian hierarchical models to tag-recovery data. Our analysis approach provides a means for examining prior influence and sample size on hierarchical models fit to capture-recapture data while emphasizing transferability of results between empirical and simulation studies.

Harvest Mortality of Mallards (Anas platyrhynchos) Banded at Lake St. Clair, CAN and Western Lake Erie, USA

Coastal marshes of Lake St. Clair, in southwest Ontario, CAN and Lake Erie, in northwest Ohio, USA are important migratory staging locations for waterfowl despite experiencing substantial wetland losses. Waterfowl habitat management at these locations focuses on providing food resources for Mallards (Anas platyrhynchos), a highly sought game species. We examined direct recovery rates of Mallards banded prior to the 2014, 2015, and 2016 hunting seasons as a measure of harvest mortality. We compared harvest mortality between the two locations, among years, among four sex and age cohorts, and as a function of body condition. We found that banding location for juvenile Mallards was an important variable predicting harvest mortality. The probability of being a direct recovery was 126% greater for juvenile females and 70% greater for juvenile males banded at Lake St. Clair compared to those banded in northwest Ohio. Average body condition was slightly less for juvenile male Mallards banded in northwest Ohio during 2016 compared to those banded in 2015 or those banded in LSC in 2014 or 2015. We did not detect any other significant differences related to body condition and location or location-year with respect to direct recovery rates. We hypothesize that harvest mortality of juvenile Mallards could be related to differences in harvest regulations, bird abundances, or hunter density between the two study sites, all of which may have different implications for those interested in managing Mallard populations in the lower Great Lakes region.

Density-dependence produces spurious relationships among demographic parameters in a harvested species.

Harvest of wild organisms is an important component of human culture, economy, and recreation, but can also put species at risk of extinction. Decisions that guide successful management actions therefore rely on the ability of researchers to link changes in demographic processes to the anthropogenic actions or environmental changes that underlie variation in demographic parameters. Ecologists often use population models or maximum sustained yield curves to estimate the impacts of harvest on wildlife and fish populations. Applications of these models usually focus exclusively on the impact of harvest and often fail to consider adequately other potential, often collinear, mechanistic drivers of the observed relationships between harvest and demographic rates. In this study, we used an integrated population model and long-term data (1973-2016) to examine the relationships among hunting and natural mortality, the number of hunters, habitat conditions, and population size of blue-winged teal Spatula discors, an abundant North American dabbling duck with a relatively fast-paced life history strategy. Over the last two and a half decades of the study, teal abundance tripled, hunting mortality probability increased slightly ( ), and natural mortality probability increased substantially ( ) at greater population densities. We demonstrate strong density-dependent effects on natural mortality and fecundity as population density increased, indicative of compensatory harvest mortality and compensatory natality. Critically, an analysis that only assessed the relationship between survival and hunting mortality would spuriously indicate depensatory mortality due to multicollinearity between abundance, natural mortality and hunting mortality. Our findings demonstrate that models that only consider the direct effect of hunting on survival or natural mortality can fail to accurately assess the mechanistic impact of hunting on population dynamics due to multicollinearity among demographic drivers. This multicollinearity limits inference and may have strong impacts on applied management actions globally.

Trapping mortality accelerates the decline of the fisher, an endangered mesocarnivore, in British Columbia, Canada

Understanding the environmental, demographic, and anthropogenic factors driving the population dynamics of endangered species is critical to effective conservation. Habitat loss, fragmentation, and trapping all have been linked to declines in the endangered population of fishersPekania pennantiin central British Columbia (BC), Canada, hereafter referred to as the Columbian population. Although the commercial trapping season for fishers has recently been closed in central BC, the animals are still taken in traps legally set for other furbearer species, and with this continuing source of mortality, the sustainability of this vulnerable population remains unclear. We constructed population viability models in the program Vortex to evaluate the specific impacts that trapping mortality would have on Columbian fisher population persistence under different trapping scenarios. Our modeling predicted that current mortality sources, including deaths in traps set for other species, will cause the population to disappear within 11 yr. When fur harvest mortality was removed from our modeling, the Columbian population appeared unlikely to persist beyond 37 yr. Our analysis provides evidence that along with the continued trapping closure for fishers in central BC, it is likely necessary to modify trapping regulations and methods (including restricting the use of kill traps) for other furbearers within Columbian fisher range to sufficiently reduce mortality from bycatch and help to avoid extirpation of the population in the near future. Additionally, identifying areas where fishers are actively breeding and protecting these habitats from further disturbances will be needed to increase survival and reproductive rates to levels high enough to reverse population declines over the longer term.

Reservoir Fish Escapement in North America: A Historical Review and Future Directions

AbstractDownstream escapement of fishes from reservoirs via release structures can represent a loss to populations that is comparable to natural and harvest mortality. Consequently, quantifying and managing fish escapement constitute a critical component of sustainable reservoir fish management. We reviewed existing literature to assess the state of knowledge of reservoir fish escapement and found 57 unique papers published from 1942 through 2021. Early studies sought to evaluate escapement by directly capturing fish below release structures. More recently, advances in technology have enabled more detailed studies on factors influencing escapement and the influence it has on regulating reservoir fisheries. Evaluations have occurred throughout North America, assessing escapement of 49 species through a number of different outlet structures. Annual escapement estimates ranged from 0% to 100%, and escapement tended to be higher from spillways and surface release outlets compared to other outlets. Further, smaller‐bodied individuals tended to escape at higher rates than larger fish and escapement was generally positively related to reservoir discharge metrics. Sixteen papers assessed benefits of physical and nonphysical barriers for reducing reservoir fish escapement and determined that the barriers were effective for retaining fish in reservoirs. We conclude by describing management options to address escapement as well as three pressing research needs that will broaden the existing knowledge base regarding fish escapement. In light of predicted changes in precipitation events and subsequent adaptations to reservoir management, quantifying and mitigating fish escapement will be a critical component of sustainable reservoir fish management in the future.

Quantifying anthropogenic wolf mortality in relation to hunting regulations and landscape attributes across North America.

Understanding the types and magnitude of human‐caused mortality is essential for maintaining viable large carnivore populations. We used a database of cause‐specific mortality to examine how hunting regulations and landscape configurations influenced human‐caused mortality of North American gray wolves (Canis lupus). Our dataset included 21 studies that monitored the fates of 3564 wolves and reported 1442 mortalities. Human‐caused mortality accounted for 61% of mortality overall, with 23% due to illegal harvest, 16% due to legal harvest, and 12% the result of management removal. The overall proportion of anthropogenic wolf mortality was lowest in areas with an open hunting season compared to areas with a closed hunting season or mixed hunting regulations, suggesting that harvest mortality was neither fully additive nor compensatory. Proportion of mortality from management removal was reduced in areas with an open hunting season, suggesting that legal harvest may reduce human‐wolf conflicts or alternatively that areas with legal harvest have less potential for management removals (e.g., less livestock depredation). Proportion of natural habitat was negatively correlated with the proportion of anthropogenic and illegal harvest mortality. Additionally, the proportion of mortality due to illegal harvest increased with greater natural habitat fragmentation. The observed association between large patches of natural habitat and reductions in several sources of anthropogenic wolf mortality reiterate the importance of habitat preservation to maintain wolf populations. Furthermore, effective management of wolf populations via implementation of harvest may reduce conflict with humans. Effective wolf conservation will depend on holistic strategies that integrate ecological and socioeconomic factors to facilitate their long‐term coexistence with humans.

Recruitment exceeds mortality in subtropical secondary forest after conventional selective logging

Studies on the dynamics of managed forests are essential for planning and executing management strategies. Timber harvesting can modify recruitment rates, mortality, gain and loss of basal area of the remaining stand. In secondary forests, especially in the Atlantic Forest, these studies are still scarce. Our study hypothesis is that the management intervention stimulates the growth of the remaining trees, overcoming the reduction of the growth of the damaged trees and the harvest mortality. We investigated the dynamics of the remaining trees and recruits (in number of individuals and basal area), with DBH ≥ 5 cm, by ecological group of the species, and the damage to the remaining adult individuals. We measured eleven permanent plots with 1.600m² each, before and four years after being harvested in a secondary forest in southern Brazil. We found that the different harvesting intensities significantly influence the forest dynamics, special the annual recruitment rates, while basal area gain/loss showed a weaker relationship to logging intensity. However, the mortality rates are similar in control plots and managed plots. We also observed that in the managed plots, the recruitment rate (5.3 ± 1.9% year-¹) exceeded mortality (2.3 ± 1.2% year-¹). Among ecological groups, we found less recruitment of climax species than of secondary species. In general, the proportion of damage of remaining trees decreased over time. We conclude that the management has modified the forest dynamics, indicating that planning, including adequate cutting limits and low impact harvesting methods are essential for achieving the sustainability of forest management.

Differential survival in the presence of spatially structured ptarmigan harvest suggests additive mortality

AbstractThe effects of hunting on wildlife populations vary dramatically, depending on the timing and magnitude of harvest, and population‐specific states and vital rates. We examined the hypothesis that spatially and seasonally concentrated harvest decreases annual survival probabilities of willow ptarmigan (Lagopus lagopus). We estimated survival of radio‐marked willow ptarmigan at 2 categories of sites: those where ptarmigan were easily accessible and heavily hunted and those that were remote and received little or no hunting pressure in Alaska, USA. We predicted that seasonal survival estimates during the willow ptarmigan hunting season would be lower in access corridors than at remote sites and that this would result in lower annual survival unless subsequent seasonal compensatory mortality occurred. Consistent with our prediction, annual survival was higher at remote sites (adult males: 0.50, 95% credible interval [CrI] = 0.42–0.57; adult females: 0.36, 95% CrI = 0.26–0.46; juveniles: 0.39, 95% CrI = 0.29–0.50) than at accessible sites (adult males: 0.36, 95% CrI = 0.26–0.46; adult females: 0.23, 95% CrI = 0.12–0.32; juveniles: 0.25, 95% CrI = 0.13–0.37) for all demographic groups. Concentrated harvest occurred in accessible sites during the hunting season (Aug–Mar). During the post‐breeding season (Aug–Nov), when willow ptarmigan were near their breeding sites and the hunting season was open, survival was higher for those from remote sites than for those from accessible sites when accounting for demographic group (adult male, adult female, juvenile). In contrast, during winter (Dec–Mar), when willow ptarmigan had moved away from breeding territories and were no longer segregated into remote and accessible sites, survival estimates did not differ between those from remote breeding territories and those from accessible breeding territories. This pattern of differential survival indicates an association between concentrated hunting at accessible sites and reduced survival, and it suggests an additive component of harvest mortality. In addition, the timing of these survival patterns relative to seasonal movements suggests that early season harvest (prior to seasonal movements away from breeding territories) may have a greater impact on local breeders in accessible areas than later harvest.

Comparative influence of anthropogenic landscape pressures on cause-specific mortality of mammals

The Human Influence Index (HII) quantifies anthropogenic landscape pressures by combining eight measures of human influence: human population density, built environments, crop lands, pasture lands, lights, roads, railways and navigable waterways. The comparative influence of the HII components on cause-specific mammal mortality remains unexplored. Using a database of North American mammal cause-specific mortality, we compared the influence of these components on proportion of mammal mortality resulting from harvest, vehicle collision, predation, and overall anthropogenic mortality. Our dataset consisted of 487 studies that monitored the fates of 48,551 individuals across 70 species with 17,837 mortalities of known cause. For both adults and juveniles, human population density best explained proportion of mortality from anthropogenic causes and showed a positive relationship. Human population density also provided best model fit for adult harvest mortality at low HII values. Lights, built environments, and human population density explained similar variation in adult vehicle mortality, whereas human population density provided best fit for vehicle mortality of juveniles. Predation was negatively associated with human population density and provided best model fit for both age classes. Our work indicates that the effectiveness of conservation programs for North American mammals could be enhanced by reducing the negative consequences of human population density.

Model of two competing populations in two habitats with migration: Application to optimal marine protected area size

The standard model of a single population fragmented into two patches connected by migration, was first introduced in the 1970s by Freedman and Waltman, since generating long-term research interest, though its full analysis for arbitrary values of migration rate has only been completed relatively recently. Here, we present a model of two competing species in a two-patch habitat with migrations between patches. We derive equilibrium solutions of this model for three cases of migration rate resulting in isolated, well-mixed and semi-isolated habitats. We evaluate the full range of effects of habitat, life-history and migration parameters on population sizes. Finally, we add harvesting mortality and define conditions under which introduction of a no-harvesting (protected) area may lead to increased maximum sustainable yield. The results have applications in mixed fishery management and the design of wildlife protection zones, including marine protected areas (MPAs).

Population responses to harvest depend on harvest intensity, demographics, and mate replacement in sandhill cranes

Recent examinations of hunting’s impact on populations of long-lived species illustrate the rarity of strong compensatory responses. The extent to which sandhill crane populations exhibit compensatory, partially compensatory, or additive responses to harvest mortality is poorly known. To examine how sandhill crane harvests might impact resident, breeding crane populations, we simulated harvests of a well-studied population of individually marked birds at varying harvest intensities and degrees of selectivity within the social structure of territorial and non-territorial cranes. Simulations occurred in a demographically-explicit stochastic population model developed from a previous long-term (2000–2014) study of a sandhill crane population at carrying capacity in southcentral Wisconsin, USA. Non-selective harvest models that did not account for reproductive lags after territorial birds replaced lost mates produced additive responses and resulted in declining populations when ≥ 7% of the population was harvested annually. When models of non-selective harvest incorporated reproductive lags, this threshold was reduced to ≥ 5%. Harvesting at or above 5% harvest intensities continuously decreased population size over a 100-year period. In all models of selective harvests, when only non-territorial birds were harvested, all populations returned to equilibrium. Population responses to harvest are sensitive to the number of territorial birds harvested, and this sensitivity increases when accounting for lags in reproduction stemming from mortality-induced mate replacement. If possible, limiting harvest of territorial birds from any one specific population would help maintain stability of populations when implementing a hunt. This study provides evidence for harvest impacts at a localized scale, and it represents an important first step toward better understanding the potential impacts of hunting on population responses at a regional scale, especially where resident, territorial birds might be harvested.

Demographic consequences of harvesting: a case study from a small and isolated moose population

Harvesting can have a substantial impact on population dynamics and individual performance in wild populations. While the direct consequences of harvest on individual survival and population growth rate are often apparent, harvesting can also have indirect and more subtle demographic consequences. Disentangling these consequences, however, requires in-depth knowledge of individual life histories of both females and males in the population. Here, we summarise demographic research on a population where such data exist: the Vega moose population in northern Norway. In this population, vital rates vary considerably among both females and males, and harvesting increases this variation by generating positive covariation between reproductive performance and survival. The skewed age and sex structure, which is typical of many harvested populations, also has demographic consequences: it reduces the ratio of effective to total population size and influences variation in vital rates in males and females. The moose harvest at Vega is structured by age- and sex-specific quotas, but it is not intentionally selective regarding size or other phenotypic characteristics. Still, harvest selection for earlier birth rates and larger calves was apparent, likely due to habitat-performance relationships and habitat-specific harvest mortality. Together, the bulk of research on this population shows that harvesting impacts population demography through many different pathways, with some being more subtle than others. These complex pathways influence the demographic variance and affect stochastic processes such as population growth, genetic drift, and rates of evolutionary change, and they must therefore be acknowledged in management plans to achieve sustainable harvesting.

Towards a future without stocking: harvest and river regulation determine long-term population viability of migratory salmonids

Freshwater species are particularly vulnerable to emerging threats linked to climate change because they are often already heavily impacted by habitat destruction, pollution, and exploitation. For many harvested populations of freshwater fish, these combined impacts have been mitigated for decades through stocking with captive-bred individuals. However, stocking may lead to loss of genetic variation, which may be crucial for adaptation under climate change. Exploration of sustainable alternatives is therefore paramount. We used a female-based integral projection model (IPM) to assess the consequences of terminating a long-term stocking programme for a population of landlocked, migratory brown trout Salmo trutta, and to evaluate relative effectiveness of alternative management strategies involving harvest regulations and river habitat improvement. The IPM classified individuals by body size, life history stage, and location relative to a hydropower dam, and was parameterised with 50 yr of individual-based data, supplemented with literature values. Model simulations indicated a strong population decline of 22-29% per year without stocking, much of which was attributed to high harvest mortality. Consequently, drastic reductions in fishing pressure were predicted to be necessary to ensure population viability without stocking. Mitigation measures reducing mortality associated with the hydropower dam or restoring spawning areas could further contribute to population viability when combined with changes in harvest regulations. Our results thus emphasise that large changes in management strategies, such as termination of long-term stocking programmes, require a thorough assessment of potential consequences and alternative mitigation strategies using data and models, or, at the very least, a precautionary approach under consideration of on-going climate change.

Survival and cause-specific mortality of harvested willow ptarmigan (Lagopus lagopus) in central Norway.

Survival is a key demographic component that often varies as a result of human activities such as recreational harvest. Detailed understanding of seasonal variation in mortality patterns and the role of various risk factors is thus crucial for understanding the link between environmental variation and wildlife population dynamics and to design sustainable harvest management systems. Here, we report from a detailed seasonal and cause‐specific decomposition of mortality risks in willow ptarmigan (Lagopus lagopus) in central Norway. The analyses are based on radio‐collared (n = 188) birds that were monitored across all seasons, and we used time‐to‐event models for competing risks to estimate mortality patterns. Overall, annual survival was estimated at 0.43 (SE: 0.04), with no distinct difference among years (2015/16 to 2018/19) or between sexes. Analysis of mortality risk factors revealed that on the annual basis, the risk of harvest mortality was lower than the risk of dying from natural causes. However, during the autumn harvest season (September–November), survival was low and the dominating cause of mortality was harvest. During winter (December–March) and spring seasons (April–May), survival was in general high and did not vary between males and females. However, during the spring season, juveniles (i.e., birds born last year) of both sexes had lower survival than adults, potentially because they are more prone to predation. During the summer season (June–August), females experienced a higher hazard than males, underlining the greater parental investment of females during egg production, incubation, and chick rearing compared to males. Our analyses provide unique insight into demographic and seasonal patterns in willow ptarmigan mortality risks in a harvested population and revealed a complex interplay across seasons, risk factors, and demographic classes. Such insight is valuable when designing sustainable management plans in a world undergoing massive environmental perturbations.

White‐Tailed Deer Population Dynamics Following Louisiana Black Bear Recovery

ABSTRACTChanging predator communities have been implicated in reduced survival of white‐tailed deer (Odocoileus virginianus) fawns. Few studies, however, have used field‐based age‐specific estimates for survival and fecundity to assess the relative importance of low fawn survival on population growth and harvest potential. We studied white‐tailed deer population dynamics on Tensas River National Wildlife Refuge (TRNWR) in Louisiana, USA, where the predator community included bobcats (Lynx rufus), coyotes (Canis latrans), and a restored population of Louisiana black bear (Ursus americanus luteolus). During 2013–2015, we radio‐collared and monitored 70 adult (≥2.5 yrs) and 21 yearling (1.5‐yr‐old) female deer. Annual survival averaged 0.815 (95% CI = 0.734–0.904) for adults and 0.857 (95% CI = 0.720–1.00) for yearlings. We combined these estimates with concurrently collected fawn survival estimates (0.27; 95% CI = 0.185–0.398) to model population trajectories and elasticities. We used estimates of nonhunting survival (annual survival estimated excluding harvest mortality) to project population growth (λ) relative to 4 levels of harvest (0, 10%, 20%, 30%). Finally, we investigated effects of reduced fawn survival on population growth under current management and with elimination of female harvest. Despite substantial fawn predation, the deer population on TRNWR was increasing (λ = 1.06) and could sustain additional female harvest; however, the population was expected to decline at 20% (λ = 0.98) and 30% (λ = 0.94) female harvest. With no female harvest, the population was projected to increase with observed (λ = 1.15) and reduced fawn survival (λ = 1.02), but the population could not sustain current female harvest (10%) if fawn survival declined (λ = 0.90). For all scenarios, adult female survival was the most elastic parameter. Given the importance of adult female survival, the relative predictability in response of adult survival to harvest management, and the difficulty in altering fawn survival, reducing female harvest is likely the most efficient approach to compensate for low fawn survival. On highly productive sites such as ours, reduction, but not necessarily elimination, of harvest can mitigate effects of low fawn survival on population growth. © 2020 The Wildlife Society.