Les conséquences de la chasse au gros gibier chez deux omnivores opportunistes

La chasse peut entraîner plusieurs conséquences chez les populations animales exploitées, incluant la sélection de certains traits comportementaux et des changements de comportement induits par un paysage de la peur. Les activités de chasse peuvent être perçues comme une menace par les animaux qui ne sont pas ciblés et ces derniers modifient leur comportement de façon à moduler leur exposition au risque perçu. Les conséquences de la chasse ne se limitent donc pas qu’aux espèces ou groupes démographiques ciblés par les activités de chasse; cependant, peu d’études ont réellement tenté de documenter les effets de la chasse sur les espèces non ciblées et, plus particulièrement, chez les carnivores qui peuvent autant percevoir les chasseurs comme une menace qu’une source d’accès à la nourriture. En effet, une pratique courante chez les chasseurs est d’éviscérer le gibier sur le site d’abattage, ce qui augmente considérablement la quantité de biomasse disponible pour les charognards. Toutefois, consommer cette ressource pourrait être désavantageux sur le long terme. La chasse est une importante source d’émission de pollution puisque la majorité des chasseurs de gros gibier utilisent des munitions en plomb. Ces munitions se fragmentent après avoir atteint leur cible et incrustent des millions de fragments de plomb qui peuvent ensuite être ingérés par des charognards qui se nourrissent des restes d’abattage jetés par les chasseurs. En temps normal, il est avantageux d’adopter des comportements charognards, mais cela devient inadapté durant la période de chasse puisqu’une grande quantité de plomb se retrouve dans les restes d’abattage et que les charognards n’ont aucun moyen d’évaluer ce risque. L’objectif de ma thèse de doctorat était de documenter les conséquences de la chasse au gros gibier chez deux omnivores opportunistes. Mes travaux peuvent être divisés en deux grandes sections: une première sur les effets de la chasse sur le comportement de l’ours brun (Ursus arctos) Scandinave et une deuxième sur le lien entre la distribution des sites d’abattage de gros gibier et le risque d’exposition au plomb chez l’ours brun Scandinave en Suède et l’ours noir d’Amérique (Ursus americanus) au Québec. Les différents chapitres de cette thèse ont pu être réalisés grâce à des collaborations avec le Scandinavian Brown Bear Research Project (SBBRP) et le ministère des forêts, de la faune et des parcs du Québec. Le SBBRP réalise un suivi longitudinal de la population suédoise d’ours bruns depuis 1985 et plusieurs individus sont munis d’un collier GPS permettant de suivre leurs mouvements. Dans le chapitre 2, j’ai documenté la réponse des ours bruns face à la chasse à l’orignal (Alces alces) en Suède. J’ai montré que les ours évitent les sites d’abattage d’orignaux tant durant le jour que durant la nuit et qu’ils augmentent la sélection d’habitats moins favorables aux chasseurs durant les périodes de chasse à l’ours et à l’orignal. Cela suggère que les restes d’abattage n’ont pas un effet attractif chez les ours en Suède et que ces derniers ne font pas la différence entre les chasseurs d’ours et les chasseurs d’orignaux, puisqu’ils adoptent des tactiques d’anti-prédation similaires durant les deux périodes de chasse. Dans le chapitre 3, j’ai montré que la protection légale contre la récolte n’avait pas d’impact au niveau de la perception du risque chez les groupes protégés. Cela n'est pas surprenant en soi, mais mes résultats montrent que les femelles avec des jeunes dépendants se déplacent plus rapidement lorsqu’elles sont près des routes durant les heures légales de chasse. Cette réponse pourrait augmenter les coûts de locomotion chez les femelles avec des jeunes dépendants, et ce, malgré la protection dont elles bénéficient. Dans les chapitres 4 et 5, j’ai montré que les concentrations de plomb dans les tissus de deux espèces d’ours varient en fonction de la distribution des sites d’abattage. Ces résultats indiquent que les ours sont plus exposés au plomb dans les zones où il y a plus de chasse. Pour le moment, nous ne savons pas si les augmentations observées sont suffisantes pour induire des effets délétères chez les ours, mais les effets néfastes du plomb peuvent être observés à de très faibles concentrations. Il est donc possible que les chasseurs de gros gibier créent un piège évolutif pour les mammifères charognards comme c’est le cas pour les charognards aviaires. Dans le chapitre 5, j’ai aussi utilisé une fonction de sélection de ressources afin de prédire la distribution des sites d’abattage d’orignaux à l’intérieur de notre aire d’étude en Suède. Cette utilisation novatrice de la fonction de sélection de ressources pourrait être aisément répliquée dans d’autres systèmes d’étude et ainsi améliorer nos connaissances sur le lien entre la distribution des sites d’abattage et le risque d’exposition au plomb provenant des munitions chez les charognards. À travers les différents chapitres de cette thèse, j’ai montré que la chasse pouvait entraîner des conséquences variées chez les espèces ou les groupes démographiques qui ne sont pas convoités durant les activités de chasse. Les chasseurs peuvent induire des réponses anti-prédatrices chez plusieurs espèces; ces réponses peuvent être associées à des coûts nutritionnels ou une augmentation des dépenses énergétiques durant une période critique juste avant l’hiver. Les chasseurs sont aussi d’importants émetteurs de plomb dans l’environnement, ce qui pose un risque pour la santé des charognards qui se nourrissent des restes d’abattage jetés durant la période de chasse. L’exposition au plomb provenant de la chasse est un piège évolutif bien documenté chez les charognards aviaires et j’ai montré que les mammifères pouvaient aussi s’exposer au plomb de la même façon. Si des effets délétères de cette exposition venaient à être détectés chez les mammifères, le piège évolutif pourrait s’étendre à d’autres groupes de charognards

Landscape of fear or landscape of food? Moose hunting triggers an antipredator response in brown bears

Hunters can affect the behavior of wildlife by inducing a landscape of fear, selecting individuals with specific traits, or altering resource availability across the landscape. Most research investigating the influence of hunting on wildlife resource selection has focused on target species and less attention has been devoted to nontarget species, such as scavengers that can be both attracted or repelled by hunting activities. We used resource selection functions to identify areas where hunters were most likely to kill moose (Alces alces) in southcentral Sweden during the fall. Then, we used step-selection functions to determine whether female brown bears (Ursus arctos) selected or avoided these areas and specific resources during the moose hunting season. We found that, during both day and nighttime, female brown bears avoided areas where hunters were more likely to kill moose. We found evidence that resource selection by brown bears varied substantially during the fall and that some behavioral changes were consistent with disturbance associated with moose hunters. Brown bears were more likely to select concealed locations in young (i.e., regenerating) and coniferous forests and areas further away from roads during the moose hunting season. Our results suggest that brown bears react to both spatial and temporal variations in apparent risk during the fall: moose hunters create a landscape of fear and trigger an antipredator response in a large carnivore even if bears are not specifically targeted during the moose hunting season. Such antipredator responses might lead to indirect habitat loss and lower foraging efficiency and the resulting consequences should be considered when planning hunting seasonsacceptedVersio

Lead exposure in brown bears is linked to environmental levels and the distribution of moose kills

Lead (Pb) is heterogeneously distributed in the environment and multiple sources like Pb ammunition and fossil fuel combustion can increase the risk of exposure in wildlife. Brown bears (Ursus arctos) in Sweden have higher blood Pb levels compared to bears from other populations, but the sources and routes of exposure are unknown. The objective of this study was to quantify the contribution of two potential sources of Pb exposure in female brown bears (n = 34 individuals; n = 61 samples). We used multiple linear regressions to determine the contribution of both environmental Pb levels estimated from plant roots and moose (Alces alces) kills to blood Pb concentrations in female brown bears. We found positive relationships between blood Pb concentrations in bears and both the distribution of moose kills by hunters and environmental Pb levels around capture locations. Our results suggest that the consumption of slaughter remains discarded by moose hunters is a likely significant pathway of Pb exposure and this exposure is additive to environmental Pb exposure in female brown bears in Sweden. We suggest that spatially explicit models, incorporating habitat selection analyses of harvest data, may prove useful in predicting Pb exposure in scavengers. Ursus arctos Pb Scavenger Slaughter remain Resource selection functionacceptedVersio

High concentrations of lead (Pb) in blood and milk of free-ranging brown bears (Ursus arctos) in Scandinavia

Exposure to lead (Pb) is a global health problem for both humans and wildlife. Despite a dramatic decline in human Pb exposure following restrictions of leaded gasoline and industry and thereby an overall reduction of Pb entering the environment, Pb exposure continues to be a problem for wildlife species. Literature on scavenging terrestrial mammals, including interactions between Pb exposure and life history, is however limited. We quantified Pb concentration in 153 blood samples from 110 free-ranging Scandinavian brown bears (Ursus arctos), 1-25 years old, using inductively coupled plasma sector field mass spectrometry. We used generalized linear models to test effects of age, body mass, reproduction status and spatial distribution on the blood Pb concentrations of 56 female bears. We sampled 28 females together with 56 dependent cubs and paired their blood Pb concentrations. From 20 lactating females, we measured the Pb concentration in milk. The mean blood Pb concentration was 96.6 mu g/L (range: 38.7-220.5 mu g/L). Both the mean and range are well above established threshold concentrations for developmental neurotoxicity (12 mu g/L), increased systolic blood pressure (36 mu g/L) and prevalence of kidney disease in humans (15 mu g/L). Lactating females had higher Pb blood concentrations compared to younger, non-lactating females. Blood Pb concentrations of dependent cubs were correlated with their mother's blood Pb concentration, which in turn was correlated with the Pb concentration in the milk. Life-long Pb exposure in Scandinavian brown bears may have adverse effects both on individual and population levels. The high blood Pb concentrations found in brown bears contrast the general reduction in environmental Pb contamination over the past decades in Scandinavia and more research is needed to identify the sources and pathways of Pb exposure in the brown bears

High concentrations of lead (Pb) in blood and milk of free-ranging brown bears (Ursus arctos) in Scandinavia

Exposure to lead (Pb) is a global health problem for both humans and wildlife. Despite a dramatic decline in human Pb exposure following restrictions of leaded gasoline and industry and thereby an overall reduction of Pb entering the environment, Pb exposure continues to be a problem for wildlife species. Literature on scavenging terrestrial mammals, including interactions between Pb exposure and life history, is however limited. We quantified Pb concentration in 153 blood samples from 110 free-ranging Scandinavian brown bears (Ursus arctos), 1–25 years old, using inductively coupled plasma sector field mass spectrometry. We used generalized linear models to test effects of age, body mass, reproduction status and spatial distribution on the blood Pb concentrations of 56 female bears. We sampled 28 females together with 56 dependent cubs and paired their blood Pb concentrations. From 20 lactating females, we measured the Pb concentration in milk. The mean blood Pb concentration was 96.6 μg/L (range: 38.7.0–220.5 μg/L). Both the mean and range are well above established threshold concentrations for developmental neurotoxicity (12 μg/L), increased systolic blood pressure (36 μg/L) and prevalence of kidney disease in humans (15 μg/L). Lactating females had higher Pb blood concentrations compared to younger, non-lactating females. Blood Pb concentrations of dependent cubs were correlated with their mother's blood Pb concentration, which in turn was correlated with the Pb concentration in the milk. Life-long Pb exposure in Scandinavian brown bears may have adverse effects both on individual and population levels. The high blood Pb concentrations found in brown bears contrast the general reduction in environmental Pb contamination over the past decades in Scandinavia and more research is needed to identify the sources and pathways of Pb exposure in the brown bears. Lead, Blood, Milk, Ursus arctos, Carnivor

High concentrations of lead (Pb) in blood and milk of free-ranging brown bears (Ursus arctos) in Scandinavia

Exposure to lead (Pb) is a global health problem for both humans and wildlife. Despite a dramatic decline in human Pb exposure following restrictions of leaded gasoline and industry and thereby an overall reduction of Pb entering the environment, Pb exposure continues to be a problem for wildlife species. Literature on scavenging terrestrial mammals, including interactions between Pb exposure and life history, is however limited. We quantified Pb concentration in 153 blood samples from 110 free-ranging Scandinavian brown bears (Ursus arctos), 1–25 years old, using inductively coupled plasma sector field mass spectrometry. We used generalized linear models to test effects of age, body mass, reproduction status and spatial distribution on the blood Pb concentrations of 56 female bears. We sampled 28 females together with 56 dependent cubs and paired their blood Pb concentrations. From 20 lactating females, we measured the Pb concentration in milk. The mean blood Pb concentration was 96.6 μg/L (range: 38.7–220.5 μg/L). Both the mean and range are well above established threshold concentrations for developmental neurotoxicity (12 μg/L), increased systolic blood pressure (36 μg/L) and prevalence of kidney disease in humans (15 μg/L). Lactating females had higher Pb blood concentrations compared to younger, non-lactating females. Blood Pb concentrations of dependent cubs were correlated with their mother's blood Pb concentration, which in turn was correlated with the Pb concentration in the milk. Life-long Pb exposure in Scandinavian brown bears may have adverse effects both on individual and population levels. The high blood Pb concentrations found in brown bears contrast the general reduction in environmental Pb contamination over the past decades in Scandinavia and more research is needed to identify the sources and pathways of Pb exposure in the brown bears

Toxic elements in arctic and sub-arctic brown bears: Blood concentrations of As, Cd, Hg and Pb in relation to diet, age, and human footprint

Contamination with arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) is a global concern impairing resilience of organisms and ecosystems. Proximity to emission sources increases exposure risk but remoteness does not alleviate it. These toxic elements are transported in atmospheric and oceanic pathways and accumulate in organisms. Mercury accumulates in higher trophic levels. Brown bears (Ursus arctos), which often live in remote areas, are long-lived omnivores, feeding on salmon (Oncorhynchus spp.) and berries (Vaccinium spp.), resources also consumed by humans. We measured blood concentrations of As, Cd, Hg and Pb in bears (n = 72) four years and older in Scandinavia and three national parks in Alaska, USA (Lake Clark, Katmai and Gates of the Arctic) using high-resolution, inductively-coupled plasma sector field mass spectrometry. Age and sex of the bears, as well as the typical population level diet was associated with blood element concentrations using generalized linear regression models. Alaskan bears consuming salmon had higher Hg blood concentrations compared to Scandinavian bears feeding on berries, ants (Formica spp.) and moose (Alces). Cadmium and Pb blood concentrations were higher in Scandinavian bears than in Alaskan bears. Bears using marine food sources, in addition to salmon in Katmai, had higher As blood concentrations than bears in Scandinavia. Blood concentrations of Cd and Pb, as well as for As in female bears increased with age. Arsenic in males and Hg concentrations decreased with age. We detected elevated levels of toxic elements in bears from landscapes that are among the most pristine on the planet. Sources are unknown but anthropogenic emissions are most likely involved. All study areas face upcoming change: Increasing tourism and mining in Alaska and more intensive forestry in Scandinavia, combined with global climate change in both regions. Baseline contaminant concentrations as presented here are important knowledge in our changing world.Validerad;2023;Nivå 2;2023-05-10 (joosat);Funder: Research Council of Norway; Inland Norway University of Applied Sciences; Norwegian Environment Agency (grant number 19047048); National Park ServiceLicens fulltext: CC BY License</p