Hunting Mortality Research Articles

Effects of hunting on mating, relatedness, and genetic diversity in a puma population.

Hunting mortality can affect population abundance, demography, patterns of dispersal and philopatry, breeding, and genetic diversity. We investigated the effects of hunting on the reproduction and genetic diversity in a puma population in western Colorado, USA. We genotyped over 11,000 single nucleotide polymorphisms (SNPs), using double-digest, restriction site-associated DNA sequencing (ddRADseq) in 291 tissue samples collected as part of a study on the effects of hunting on puma population abundance and demography in Colorado from 2004 to 2014. The study was designed with a reference period (years 1-5), during which hunting was suspended, followed by a treatment period (years 6-10), in which hunting was reinstated. Our objectives were to examine the effects of hunting on: (1) paternity and male reproductive success; (2) the relatedness between pumas within the population, and (3) genetic diversity. We found that hunting reduced the average age of male breeders. The number of unique fathers siring litters increased each year without hunting and decreased each year during the hunting period. Mated pairs were generally unrelated during both time periods, and females were more closely related than males. Hunting was also associated with increased relatedness among males and decreased relatedness among females in the population. Finally, genetic diversity increased during the period without hunting and decreased each year when hunting was present. This study demonstrates the utility of merging demographic data with large-scale genomic datasets in order to better understand the consequences of management actions. Specifically, we believe that this study highlights the need for long-term experimental research in which hunting mortality is manipulated, including at least one non-harvested control population, as part of a broader adaptive, zone management scheme.

Prevalence of imbedded and ingested shot gun pellets in breeding sea ducks in the Baltic Sea—possible implications for future conservation efforts

Several sea duck species in Europe face dwindling population numbers with following increased conservation focus. Shot gun practices may put extra pressure on populations not only by direct hunting mortality but also crippling and lead poisoning from ingestion of pellets. In this study, we examined three sea duck species breeding in the Swedish Archipelago of the Baltic Sea by x-raying trapped incubating females to detect prevalence of imbedded and ingested shot gun pellets. The study was carried out during the 2021 and 2022 breeding seasons and designed to aid our understanding of the role of physical restraints of putative pellets to breeding performance at our study site. A total of 205 individual females of common eider (n = 113), velvet scoter (n = 57), and red-breasted merganser (n = 35) were x-rayed without finding any imbedded or ingested pellets. For this study, a combination of decreasing hunting pressure, remoteness of study site, improved hunters’ shooting performance along the flyway and depletion of crippling rates due to life-long negative effects of carrying imbedded pellets may explain our finding on non-detection. For common eider, specific interventions to reduce the negative impacts of shotgun practices have been reported successful, and our data suggest a continuing positive trend. Based on our findings, we advise future conservation efforts for the three species, breeding in this part of the flyway, to focus on other factors that may have negative impact on incubating female survival and reproduction.

Hunting-mediated predator facilitation and superadditive mortality in a European ungulate.

Predator‐prey theory predicts that in the presence of multiple types of predators using a common prey, predator facilitation may result as a consequence of contrasting prey defense mechanisms, where reducing the risk from one predator increases the risk from the other. While predator facilitation is well established in natural predator‐prey systems, little attention has been paid to situations where human hunters compete with natural predators for the same prey. Here, we investigate hunting‐mediated predator facilitation in a hunter‐predator‐prey system. We found that hunter avoidance by roe deer (Capreolus capreolus) exposed them to increase predation risk by Eurasian lynx (Lynx lynx). Lynx responded by increasing their activity and predation on deer, providing evidence that superadditive hunting mortality may be occurring through predator facilitation. Our results reveal a new pathway through which human hunters, in their role as top predators, may affect species interactions at lower trophic levels and thus drive ecosystem processes.

Annual survival and seasonal hunting mortality of midcontinent snow geese

ABSTRACTAnnual banding programs have allowed the estimation of key demographic parameters for many populations of harvested wildlife, yet they often provide little insight into vital rate variation among seasonally occupied habitats or among regions with differing hunting regulations. For lesser snow geese (Chen caerulescens caerulescens) in the midcontinent of North America, rapid growth in abundance and the consequent implementation of special conservation measures present a scenario where seasonal mortality estimates would be highly valuable. We evaluated variation in hunting mortality of adult and young geese among 3 seasons (autumn, winter, and spring) based on annual banding data from breeding colonies north and south of 60°N latitude, and seasonal hunting recoveries from the United States and Canada. Using band‐recovery models and data covering 1999 through 2015, we first estimated annual survival for geese of both age classes and breeding locations, and then subsequently used seasonal hunting recoveries to derive estimates of seasonal hunting mortality and annual non‐hunting mortality. Simulation models validated the accuracy of this approach. Hunting mortality in winter generally exceeded that during spring and autumn, but our estimates suggested that hunting mortality represented a small fraction of annual mortality for adult and young birds. Consistent with recent studies, our estimates pointed to a greater harvest effect for the smaller subarctic population breeding near southern Hudson Bay, Canada, than for the large arctic population breeding farther north. Although mean kill rates were higher for young than adult geese, natural mortality for young was high and temporally variable, implying that some hunting mortality experienced by young geese during their first year could be compensated by natural causes of death. Natural (non‐hunting) mortality and annual survival showed greater temporal variation than seasonal kill rates in adults and young geese, highlighting the importance of non‐harvest factors (e.g., climate, habitat, population density) to the dynamics of these populations. These novel estimates of seasonal kill rates and non‐hunting mortality contribute further support to the notion that internal dynamics of the lesser snow goose midcontinent population, including natural mortality and recruitment, currently influence population trajectory more than ongoing interventions through harvest management. © 2017 The Wildlife Society.

Effects of male targeted harvest regime on sexual segregation in mountain lion

Male targeted harvest regimes of carnivores are now widely accepted to result in increased sexually selected infanticide (SSI). Male targeted harvest regimes of males should therefore result in increased sexually segregated habitat use in infanticidal carnivores. We tested the effects of low and high levels of male hunting mortality and associated SSI on sexually segregated habitat use in mountain lions. The “no effect of hunting” hypothesis predicts that no sexual segregation would occur or that all female mountain lions would segregate from males because of sexual dimorphism. The “hunting effect” hypothesis predicts that females with kittens would segregate from younger immigrant males in the heavily hunted population during summer when kittens are vulnerable to SSI. We rejected the “no effect” hypothesis and accepted the “hunting effect” hypothesis for mountain lions. Females with kittens avoided immigrant males in the heavily hunted population during summer—others did not. This sexual segregation corresponded with females with kittens selecting for food-poor, high elevations in the heavily hunted population but not in the lightly hunted population. Avoidance of males and selection for high elevations resulted in prey switching by females with kittens from abundant primary prey in lower elevations to rare, sensitive and threatened secondary prey at higher elevations. It appears that remedial sport hunting of mountain lions to reduce predation on declining prey actually caused sexual segregation and increased predation on declining prey. We suggest that excess mortality of male carnivores could result in unanticipated cascade effects including sexual segregation and prey switching to declining prey.

A test of the compensatory mortality hypothesis in mountain lions: A management experiment in West‐Central Montana

ABSTRACTMountain lions (Puma concolor) are widely hunted for recreation, population control, and to reduce conflict with humans, but much is still unknown regarding the effects of harvest on mountain lion population dynamics. Whether human hunting mortality on mountain lions is additive or compensatory is debated. Our primary objective was to investigate population effects of harvest on mountain lions. We addressed this objective with a management experiment of 3 years of intensive harvest followed by a 6‐year recovery period. In December 2000, after 3 years of hunting, approximately 66% of a single game management unit within the Blackfoot River watershed in Montana was closed to lion hunting, effectively creating a refuge representing approximately 12% (915 km2) of the total study area (7,908 km2). Hunting continued in the remainder of the study area, but harvest levels declined from approximately 9/1,000 km2in 2001 to 2/1,000 km2in 2006 as a result of the protected area and reduced quotas outside. We radiocollared 117 mountain lions from 1998 to 2006. We recorded known fates for 63 animals, and right‐censored the remainder. Although hunting directly reduced survival, parameters such as litter size, birth interval, maternity, age at dispersal, and age of first reproduction were not significantly affected. Sensitivity analysis showed that female survival and maternity were most influential on population growth. Life‐stage simulation analysis (LSA) demonstrated the effect of hunting on the population dynamics of mountain lions. In our non‐hunted population, reproduction (kitten survival and maternity) accounted for approximately 62% of the variation in growth rate, whereas adult female survival accounted for 30%. Hunting reversed this, increasing the reliance of population growth on adult female survival (45% of the variation in population growth), and away from reproduction (12%). Our research showed that harvest at the levels implemented in this study did not affect population productivity (i.e., maternity), but had an additive effect on mountain lion mortality, and therefore population growth. Through harvest, wildlife managers have the ability to control mountain lion populations. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Effects of male trophy hunting on female carnivore population growth and persistence

Carnivore populations are often managed based on the density dependent, compensatory mortality model, which suggests that trophy hunting of males causes an increase in female reproductive success, survival, and population growth. Our previous research on grizzly bears (Ursus acrtos) and cougars (Puma concolor) showed that increased mortality of males resulted in no net reduction in males due to increased immigration. Female reproduction and survival did not increase with male mortality. That research suggested that female demographics are additive to male mortality and might even be depensatory (inversely compensatory), whereby increased male immigration and infanticide may be associated with decreased female reproductive success, survival, and population growth. In this paper we test the compensatory, additive, and depensatory hypotheses by censoring female hunting deaths and plausible kitten infanticides from two independent cougar populations. The previously observed lack of compensatory demographics allowed us to censor deaths in this manner. The lightly hunted population (male hunting mortality=0.16) had a female population growth rate of 1.05. With female mortality from hunting removed the growth rate increased to 1.14. The heavily hunted population (male hunting mortality=0.35) had a female population growth rate of 0.78. With infanticide removed the growth rate increased to 0.89. With hunting mortality of females removed, the growth rate increased to 0.98. With both female mortalities and infanticide removed, the growth rate increased to 1.14. Light hunting of males (no net male immigration) decreased female population growth in an additive manner and heavy hunting of males (increased net male immigration) decreased female population growth in a depensatory manner. We reject the compensatory mortality hypothesis, and suggest that hunting of male carnivores has a negative additive or depensatory effect on female population growth depending on the intensity of male mortality. We recommend that hunting of polygnous carnivores not exceed their intrinsic growth rates to forestall excessive compensatory male immigration and infanticide. The Washington Department of Fish and Wildlife instituted a new “equilibrium” hunting management plan (hunting mortality<14%/year) for cougars in 2013 based on our findings and recommendations.

Long-term trends in reproductive and demographic parameters of female Northwest Atlantic hooded seals (Cystophora cristata): population responses to ecosystem change?

More than 2500 ovaries were collected from Northwest Atlantic hooded seals ( Cystophora cristata (Erxleben, 1777)) in the period 1956–2006 during moulting (data blocks: 1956–1960, 1970–1972, 1978), postmoulting (data blocks: 1990–1994, 1996–2006), and whelping (data blocks: 1967–1972, 1973–1976, 1979, 1983–1987, 1989–1995). Mean age at primiparity (MAP) was estimated as the mean age of females with a single corpus albicans or a corpus luteum from a postimplantation pregnancy. MAP was stable at 4.2–4.5 years during 1956–1978, increasing to 4.9–5.2 years in 1979 and to 6.1 years in 1989–1995 (later data insufficient). Patterns of corpus accumulation indicated occasional skipped pregnancies. This may have affected the accuracy of MAP estimates but not the main trends. Declining proportions of parae younger than 10 years after 1979 are consistent with effects of delayed maturation, reduced adult hunting mortality, and (or) increased juvenile mortality. From the 1990s, declining adult pregnancy rates are suggested by decreasing trends in proportions of older multiparae (8+) and other ovary-based proxies for pregnancy rates. Hooded seal abundance was largely stable from 1960 to the mid-1990s and changes in population parameters over this period are therefore more likely due to effects of ecosystem change on per-capita resource levels than population-mediated density dependence.

Harvest, survival, and abundance of midcontinent lesser snow geese relative to population reduction efforts

We assessed the effectiveness of an extensive and unprecedented wildlife reduction effort directed at a wide-ranging migratory population of geese. Population reduction efforts that targeted several populations of light geese (greater snow geese (Chen caerulescens atlantica), lesser snow geese (C. c. caerulescens), and Ross's geese (C. rossii)) began in 1999 in central and eastern North America. Such efforts were motivated by a broad consensus that abundance of these geese was causing serious ecological damage to terrestrial and salt marsh ecosystems in central and eastern parts of the Canadian Arctic and subarctic regions along Hudson Bay. Starting in February 1999, special conservation measures (or, in the U.S., a conservation order) were added to the respective federal regulations that permitted hunters to take snow geese (in parts of Canada and the U.S.) and Ross's geese (in parts of the U.S.) during specified harvest periods outside of the hunting season. These measures were accompanied by increase or removal of daily kill and possession limits and by permissions to use previously prohibited equipment for hunting these species in certain regions of the continent. The intent was to reduce adult survival through increased hunting mortality, which was judged to be the most cost-effective approach to reversing population growth. Our principal goal was to assess the effectiveness of reduction efforts directed at the midcontinent population of lesser snow geese, which was thought to be the most serious threat to arctic and subarctic ecosystems of the 3 light goose populations. Our multiple objectives included the estimation and detection of change in the response measures of total annual harvest, harvest rate, survival rate, and abundance, using the 1998 hunting period (defined as 1 Aug 1998 to 31 Jul 1999) as a point of reference. We used information about hunter recoveries of leg- banded snow geese and estimates of regular-season harvest to estimate 1) conservation-order harvest and total annual harvest, 2) geographic and temporal distribution of recoveries by age class, 3) survival and recovery probability, and 4) abundance of snow geese each August using Lincoln's (1930) method. We also modeled population growth to infer the form of population response to management efforts. Toward that end, we also proposed a method of estimating conservation-order harvest and tested for differences in band-reporting rate between Canada and the United States. Overall, the balance of evidence favored the conclusion that the midcontinent population has continued to grow during the conservation order, although perhaps at a reduced rate. We suggest that annual rate of population growth ð^ lÞ, derived from estimates of annual population size in August, likely provides the most reliable inference about change in the midcontinent population. There was a decline in annual survival probability between these 2 periods from about 0.89 to about 0.83 among snow geese from the southern-nesting stratum (south of 608N latitude), thought to compose about 10% of the midcontinent population. However, we detected no change in the much larger northern-nesting stratum (north of 608N latitude), where annual survival remained at about 0.87 from 1989 to 2006. Thus, the conclusion that this population continued to increase during the conservation order was largely consistent with the finding that a weighted-survival probability for midcontinent snow geese essentially did not change between the period preceding (1989-1997) and during (1998-2006) the conservation order. Consistent with high survival rates were low harvest rates, which increased from 0.024 during 1989-1997 for northern geese to only 0.027 during 1998-2006 and from 0.031 to only 0.037 for southern geese. Despite the initial increase associated with the conservation order, harvest rates declined during the conservation order for geese from both strata. We suggest that the higher harvest rate evident for

Survival and harvest‐related mortality of white‐tailed deer in massachusetts

AbstractWe monitored 142 radiocollared adult (≥1.0 yr old) white‐tailed deer (Odocoileus virginianus) in 3 study areas of Massachusetts, USA, to estimate annual survival and mortality due to legal hunting. We then applied these rates to deer harvest information to estimate deer population trends over time, and compared these to trends derived solely from harvest data estimates. Estimated adult female survival rates were similar (0.82–0.86), and uniformly high, across 3 management zones in Massachusetts that differed in landscape composition, human density, and harvest regulations. Legal hunting accounted for 16–29% of all adult female mortality. Estimated adult male survival rates varied from 0.55 to 0.79, and legal hunting accounted for 40–75% of all mortality. Use of composite hunting mortality rates produced realistic estimates for adult deer populations in 2 zones, but not for the third, where estimation was hindered by regulatory restrictions on antlerless deer harvest. In addition, the population estimates we calculated were generally higher than those derived from population reconstruction, likely due to relatively low harvest pressure. Legal harvest may not be the dominant form of deer mortality in developed landscapes; thus, estimates of populations or trends that rely solely on harvest data will likely be underestimates. © 2011 The Wildlife Society.

Culling Versus Density Effects in Management of a Deer Population

Abstract: Wildlife managers often manipulate hunting regulations to control deer populations. However, few empirical studies have examined the level of hunting effort (hunter‐days) required to limit population growth and demographic effects through harvesting of females. Moreover, the relative importance of density effects on population growth has not been quantified. We reconstructed a sika deer [Cervus nippon] population over a period of 12 years (1990–2001) using age‐ and sex‐specific harvest data. Using cohort analysis, we analyzed population dynamics, focusing on 1) the relationship between hunting effort and hunting‐induced mortality rate, 2) relative contributions of hunting mortality and recruitment of yearlings to annual changes in population growth rate, and 3) annual variation in recruitment rate. Population size increased until 1998 and declined thereafter. The population growth rate changed more in response to annual changes in recruitment rate than hunting mortality rate. Temporal variation in recruitment rate was not controlled by birth rate alone; direct density dependence, intensities of hunting mortality for fawns, and for females (≥2 yr of age), which accounted for the fawn survival rate, were required as factors to explain temporal variation. Density effects on the recruitment rate were not strong enough to regulate the population within the study period; high hunting mortality, with intensive female harvesting, was necessary to prevent population growth. Hunting effort was a good predictor of the hunting mortality rate, and female harvest had a negative effect on the recruitment rate through fawn survival. We suggest that &gt;3,500 hunter‐days and prioritization of female harvesting are required to prevent increases in this deer population.

Does hunting regulate cougar populations? A test of the compensatory mortality hypothesis

Many wildlife species are managed based on the compensatory mortality hypothesis, which predicts that harvest mortality (especially adult male mortality) will trigger density-dependent responses in reproduction, survival, and population growth caused via reduced competition for resources. We tested the compensatory mortality hypothesis on two cougar (Puma concolor) populations in Washington, USA (one heavily hunted and one lightly hunted). We estimated population growth, density, survival, and reproduction to determine the effects of hunting on cougar population demography based on data collected from 2002 to 2007. In the heavily hunted population, the total hunting mortality rate (mean +/- SD) was 0.24 +/- 0.05 (0.35 +/- 0.08 for males, 0.16 +/- 0.05 for females). In the lightly hunted population, the total hunting mortality rate was 0.11 +/- 0.04 (0.16 +/- 0.06 for males, 0.07 +/- 0.05 for females). The compensatory mortality hypothesis predicts that higher mortality will result in higher maternity, kitten survival, reproductive success, and lower natural mortality. We found no differences in rates of maternity or natural mortality between study areas, and kitten survival was lower in the heavily hunted population. We rejected the compensatory mortality hypothesis because vital rates did not compensate for hunting mortality. Heavy harvest corresponded with increased immigration, reduced kitten survival, reduced female population growth, and a younger overall age structure. Light harvest corresponded with increased emigration, higher kitten survival, increased female population growth, and an older overall age structure. Managers should not assume the existence of compensatory mortality when developing harvest prescriptions for cougars.

Source populations in carnivore management: cougar demography and emigration in a lightly hunted population

AbstractWildlife agencies typically attempt to manage carnivore numbers in localized game management units through hunting, and do not always consider the potential influences of immigration and emigration on the outcome of those hunting practices. However, such a closed population structure may not be an appropriate model for management of carnivore populations where immigration and emigration are important population parameters. The closed population hypothesis predicts that high hunting mortality will reduce numbers and densities of carnivores and that low hunting mortality will increase numbers and densities. By contrast, the open population hypothesis predicts that high hunting mortality may not reduce carnivore densities because of compensatory immigration, and low hunting mortality may not result in more carnivores because of compensatory emigration. Previous research supported the open population hypothesis with high immigration rates in a heavily hunted (hunting mortality rate=0.24) cougar population in northern Washington. We test the open population hypothesis and high emigration rates in a lightly hunted (hunting mortality rate=0.11) cougar population in central Washington by monitoring demography from 2002 to 2007. We used a dual sex survival/fecundity Leslie matrix to estimate closed population growth and annual census counts to estimate open population growth. The observed open population growth rate of 0.98 was lower than the closed survival/fecundity growth rates of 1.13 (deterministic) and 1.10 (stochastic), and suggests a 12–15% annual emigration rate. Our data support the open population hypothesis for lightly hunted populations of carnivores. Low hunting mortality did not result in increased numbers and densities of cougars, as commonly believed because of compensatory emigration.

Red fox population decrease in hungary: Competition or carrying capacity limitation?

In the last two decades the Hungarian red fox (Vulpes vulpes) population (POP) has grown significantly. The growing trend was broken in 2002. We tested two hypotheses: (1) the POP falling due to a fox POP size that is above the carrying capacity (CC) that initiates internal control mechanisms (H1); or (2) a fall in the POP due to competition from the expanding golden jackal POP (H2). Data was collected in one of three ways: (1) voluntary questionnaire survey from Game Management Units regarding estimated (EST) fox POP size; (2) country and countywide hunting (HUNT) bag data from the National Wildlife Database; and (3) POP dynamics (DYN) data obtained from 1,352 dissected fox carcasses. For H1, the pop density was calculated from the EST fox POP size, the hunt mortality (MORT) was calculated from the hunt bag data, and the natural mortality was calculated from the difference between the following year’s EST POP size and the average litter size and stock of the current year. For H2 we examined data from three counties (Baranya, Bacs-Kiskun, Somogy) where a considerable breeding golden jackal POP exists. The county data have been compared with each other and with data for the whole of Hungary. The average POP DYN parameters have increased significantly from 1998 to 2002. In 2002, density was 9.47 sp/1,000 hectares, HUNT MORT was 8.2 sp/1,000 hectares, litter size was 7.1 sp, the reproductive (REP) rate for bitches was 55.14%, and the overall reproductive rate was 22.04 sp/1,000 hectares (the natural MORT rate was 15.36). In 2002, the natural mortality rate was nearly two times the HUNT bag rate. The Bacs-Kiskun county data parallels the average country’s data. Some differences in Baranya county’s data were noticeable when compared to the country’s data POP DYN parameters were of larger magnitude. In 2002 the POP density was 19.23 sp/1,000 hectares, the HUNT MORT was 9.8 sp/1,000 hectares, the REP rate was 44.77 sp/1,000 hectares, and the natural MORT rate was 42.96 in Baranya county. H1 seems to be supported by our results. POP size was above carrying capacity and internal control mechanisms were at work. The rodent POP decline in 2003 may have assisted in Dogs and other canines in the wild 63

Disentangling Natural From Hunting Mortality in an Intensively Hunted Wild Boar Population

Abstract We assessed age-specific natural mortality (i.e., excluding hunting mortality) and hunting mortality of 1,175 male and 1,076 female wild boar (Sus scrofa) from Châteauvillain-Arc en Barrois (eastern France), using a 22-year dataset (1982–2004) and mark–recapture–recovery methods. Overall yearly mortality was >50% for all sex and age-classes. Low survival was mostly due to high hunting mortality; a wild boar had a >40% of chance of being harvested annually, and this risk was as high as 70% for adult males. Natural mortality rates of wild boar were similar for males and females (approx. 0.15). These rates were comparable to rates typical of male ungulates but high for female ungulates. Wild boar survival did not vary across sex and age-classes. Despite high hunting mortality, we did not detect evidence of compensatory mortality. Whereas natural mortality for males was constant over time, female mortality varied annually, independent of fluctuations in mast availability. Female wild boar survival pa...

Should hunting mortality mimic the patterns of natural mortality?

With growing concerns about the impact of selective harvesting on natural populations, researchers encourage managers to implement harvest regimes that avoid or minimize the potential for demographic and evolutionary side effects. A seemingly intuitive recommendation is to implement harvest regimes that mimic natural mortality patterns. Using stochastic simulations based on a model of risk as a logistic function of a normally distributed biological trait variable, we evaluate the validity of this recommendation when the objective is to minimize the altering effect of harvest on the immediate post-mortality distribution of the trait. We show that, in the absence of compensatory mortality, harvest mimicking natural mortality leads to amplification of the biasing effect expected after natural mortality, whereas an unbiased harvest does not alter the post-mortality trait distribution that would be expected in the absence of harvest. Although our approach focuses only on a subset of many possible objectives for harvest management, it illustrates that a single strategy, such as hunting mimicking natural mortality, may be insufficient to address the complexities of different management objectives with potentially conflicting solutions.

Pintail and Mallard Survival in California Relative to Habitat, Abundance, and Hunting

ABSTRACT The influence of habitat, waterfowl abundance, and hunting on winter survival of waterfowl is not well understood. We studied late August‐March survival of 163 after‐hatch‐year (AHY) and 128 hatch‐year (HY) female mallards (Anas platyrhynchos) radiotagged in Sacramento Valley (SACV) and 885 AHY female northern pintails (A. acuta) radiotagged throughout the Central Valley of California, USA, relative to flooded habitat (HAB), January abundance of each species (JMAL or JPIN), hunter‐days (HDY), and a hunting pressure index (HPI) that combined these variables. From EARLY (1987–1994) to LATE (1998–2000), HAB increased 39%, JPIN increased 45%, JMAL increased 53%, HDY increased 21%, duck‐hunting season increased from 59 days to 100 days, and the female daily bag limit doubled to 2 for mallards but remained 1 for pintails. Survival (± SE) was greater during LATE versus EARLY for pintails radiotagged in each region (SACV: 93.2 ± 2.1% vs. 87.6 ± 3.0%; Suisun Marsh: 86.6 ± 3.2% vs. 77.0 ± 3.7%; San Joaquin Valley: 86.6 ± 3.1% vs. 76.9 ± 4.1%) but not for SACV mallards (AHY: 70.6 ± 7.2% to 74.4 ± 7.7% vs. 80.1 ± 7.2% to 82.8 ± 5.6%; HY: 48.7 ± 9.1% [1999–2000 only] vs. 63.5 ± 8.8% to 67.6 ± 8.0%). Most pintail (72%) and mallard (91%) deaths were from hunting, and lower HPI and higher JPIN or JMAL were associated with reduced mortality. Increased HAB was associated with reduced winter mortality for pintails but not for SACV mallards. Pintail survival rates that we measured were within the range reported for other North American wintering areas, and during LATE were higher than most, even though our study duration was 68–110 days longer. Winter survival rates of SACV mallards were also within the reported range. However, with higher bag limits and longer seasons, mallard survival during LATE was lower than in most other wintering areas, especially during 1999–2000, when high winds on opening weekend resulted in high hunting mortality. Habitat conservation and favorable agriculture practices helped create a Central Valley wintering environment where natural mortality of mallards and pintails was low and survival varied with hunting mortality. We recommend regulations and habitat management that continue to minimize natural mortality while allowing sustainable harvest at a level that helps maintain strong incentive for management of Central Valley waterfowl habitats, including the large portion that is privately owned.

Time-Dependent Instantaneous Mortality Rates from Multiple Tagging Experiments with Exact Times of Release and Recovery

Instantaneous natural mortality rates and a nonparametric hunting mortality function are estimated from a multiple-year tagging experiment with arbitrary, time-dependent fishing or hunting mortality. Our theory allows animals to be tagged over a range of times in each year, and to take time to mix into the population. Animals are recovered by hunting or fishing, and death events from natural causes occur but are not observed. We combine a long-standing approach based on yearly totals, described by Brownie et al. (1985, Statistical Inference from Band Recovery Data: A Handbook, Second edition, United States Fish and Wildlife Service, Washington, Resource Publication, 156), with an exact-time-of-recovery approach originated by Hearn, Sandland and Hampton (1987, Journal du Conseil International pour l'Exploration de la Mer, 43, 107-117), who modeled times at liberty without regard to time of tagging. Our model allows for exact times of release and recovery, incomplete reporting of recoveries, and potential tag shedding. We apply our methods to data on the heavily exploited southern bluefin tuna (Thunnus maccoyii).

Effects of exceptional conservation measures on survival and seasonal hunting mortality in greater snow geese

Summary Large‐scale conservation measures aimed at reducing the abundance of a wild population offer a unique opportunity to study the impacts of human exploitation on demographic parameters. We examined the effects of a spring conservation harvest and liberalized autumn/winter regulations introduced recently to control the rapid population growth of greater snow geese Anser caerulescens atlantica. We predicted that these changes in regulations affected survival and recovery probabilities, as well as kill rates. This was evaluated by analysing data on geese shot by hunters before and after implementation of these measures. Annual survival and recovery probabilities were estimated using likelihood‐based ring recovery models, and we developed a new, flexible seasonal model to determine the specific effects of regulation changes made during different hunting seasons. We used harvest survey data to estimate ring‐reporting rate, and thus to convert recovery rates into kill rates. Adult recovery and kill rates increased considerably with the implementation of the new measures in 1998–99. The addition of the spring harvest in Québec and the liberalized winter regulations in the USA had the largest impacts, whereas autumn regulation changes in Québec apparently had little effect. Juvenile recovery and kill rates also showed a moderate increase, but were highly variable. We observed a decline in mean annual adult survival rate, from 83·0% to 72·5%, although the implementation of conservation measures did not fully explain temporal variation in adult survival; juvenile survival showed no change. Adult survival was negatively related to harvest rate in adults but not in juveniles. Synthesis and applications. We demonstrate that the spring conservation harvest led to a decrease in adult survival and an increase in hunting mortality, and probably contributed to the decline in abundance observed since its implementation. However, regulations during the traditional autumn and winter hunting seasons could also be manipulated for future population control once the spring conservation harvest is discontinued. Our approach for evaluating hunting mortality on a seasonal basis should be useful in the management of other migratory populations that move through several jurisdictions.

Interactions between land use, habitat use, and population increase in greater snow geese: what are the consequences for natural wetlands?

AbstractThe North American greater snow goose population has increased dramatically during the last 40 years. We evaluated whether refuge creation, changes in land use on the wintering and staging grounds, and climate warming have contributed to this expansion by affecting the distribution, habitat use, body condition, and migration phenology of birds. We also reviewed the effects of the increasing population on marshes on the wintering grounds, along the migratory routes and on the tundra in summer. Refuges established before 1970 may have contributed to the initial demographic increase. The most important change, however, was the switch from a diet entirely based on marsh plants in spring and winter (rhizomes ofScirpus/Spartina) to one dominated by crops (corn/young grass shoots) during the 1970s and 1980s. Geese now winter further north along the US Atlantic coast, leading to reduced hunting mortality. Their migratory routes now include portions of southwestern Québec where corn production has increased exponentially. Since the mid‐1960s, average temperatures have increased by 1–2.4°C throughout the geographic range of geese, which may have contributed to the northward shift in wintering range and an earlier migration in spring. Access to spilled corn in spring improved fat reserves upon departure for the Arctic and may have contributed to a high fecundity. The population increase has led to intense grazing of natural wetlands used by geese although these habitats are still largely undamaged. The foraging in fields allowed the population to exceed limits imposed by natural marshes in winter and spring, but also prevented permanent damage because of their overgrazing.