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Introduction: Terrestrial species in riverine ecosystems face unique constraints leading to diverging patterns of population structure, connectivity, and disease dynamics. Desert bighorn sheep (Ovis canadensis nelsoni) in Grand Canyon National Park, a large native population in the southwestern USA, offer a unique opportunity to evaluate population patterns and processes in a remote riverine system with ongoing anthropogenic impacts. We integrated non-invasive, invasive, and citizen-science methods to address questions on abundance, distribution, disease status, genetic structure, and habitat fragmentation. Methods: We compiled bighorn sightings collected during river trips by park staff, commercial guides, and private citizens from 2000-2018 and captured bighorn in 2010-2016 to deploy GPS collars and test for disease. From 2011-2015, we noninvasively collected fecal samples and genotyped them at 9-16 microsatellite loci for individual identification and genetic structure. We used assignment tests to evaluate genetic structure and identify subpopulations, then estimated gene flow and recent migration to evaluate fragmentation. We used spatial capturerecapture to estimate annual population size, distribution, and trends after accounting for spatial variation in detection with a resource selection function model. Results and discussion: From 2010-2018, 3,176 sightings of bighorn were reported, with sightings of 56-145 bighorn annually on formal surveys. From 2012-2016, bighorn exhibiting signs of respiratory disease were observed along the river throughout the park. Of 25 captured individuals, 56% were infected by Mycoplasma ovipneumoniae, a key respiratory pathogen, and 81% were recently exposed. Pellet sampling for population estimation from 2011-2015 yielded 1,250 genotypes and 453 individuals. We detected 6 genetic clusters that exhibited mild to moderate genetic structure (FST 0.022-0.126). The river, distance, and likely topography restricted recent gene flow, but we detected cross-river movements in one section via genetic recaptures, no subpopulation appeared completely isolated, and genetic diversity was among the highest reported. Recolonization of one large stretch of currently empty habitat appears limited by the constrained topology of this system. Annual population estimates ranged 536-552 (95% CrI range 451-647), lamb:ewe ratios varied, and no significant population decline was detected. We provide a multi-method sampling framework useful for sampling other wildlife in remote riverine systems. [ABSTRACT FROM AUTHOR]

Bighorn sheep (Ovis canadensis) are herbivorous ungulates that live in forage-poor areas of the American west. The trace minerals that herbivores derive from forage are important for immune function. Therefore, identifying trace minerals that affect immune function in bighorn sheep could provide important insights into disease susceptibility and population health in threatened populations. We sought to determine whether trace mineral composition in blood or plasma correlates to survival and determine whether immunologic parameters correlate with any trace minerals that affect survival. We used data collected from 2016 to 2018 as part of a large study on bighorn sheep in southeastern Oregon and northern Nevada, US. We measured the survival of 135 bighorn sheep during the 8-mo monitoring period, including general metrics of immune function and trace mineral levels. We found that animals with higher selenium had improved survival over the monitoring period, with higher peripheral blood mononuclear cell activity (lymphocytes and monocytes) and lower bacterial killing ability in an in vitro assay. This suggests that bighorn sheep may have altered immune function when selenium levels are low, making them more likely to die during the 8-mo monitoring period. Future work should consider whether habitat management strategies that increase selenium intake might improve disease resistance and survival in bighorn sheep in selenium-poor areas. [ABSTRACT FROM AUTHOR]

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