Winter Waterbird Ecology on the Great Salt Lake, Utah, and Interactions with Commercial Harvest of Brine Shrimp Cysts

Interactions among commercial fisheries and birds have been studied in open ocean ecosystems and at aquaculture facilities. On the Great Salt Lake (GSL), Utah, USA, a commercial harvest of brine shrimp (Artemia franciscana) eggs (i.e. cysts) occurs annually during fall and winter. Coinciding with commercial harvest is the use of the GSL by millions of waterbirds which has the potential to result in conflict among industry and birds. The objectives of my research were to examine fall and winter ecology of birds using the GSL and interactions with the brine shrimp cyst harvest. I examined the influence of temperature and food availability on the number and distribution of waterfowl and eared grebes (Podiceps nigricollis). I also assessed the diets of the same species to see how much cyst biomass is being consumed by birds compared to removal by commercial harvest. A mass die-off (i.e. downing) of migrating eared grebes occurred during my research, so I assessed differences among birds that died and those that did not to better explain this phenomenon. Finally, I assessed the breeding origin of northern shovelers (Anas clypeata) wintering on the GSL using stable isotopeand banding data.I found that commercial harvest boats did not influence duck population numbersor distribution; rather temperature and food availability most influenced abundance and distribution, though this influence varied by species. Compared to commercial harvest, northern shovelers, green-winged teal (Anas crecca), and eared grebes removed a small fraction of the total amount of cysts that were removed from the GSL. Waterfowl diets were mainly wetland plant seeds during fall and spring, but when freshwater marshes were frozen in winter, ducks ate mostly brine shrimp cysts and brine fly (Ephydra spp.) larvae. Eared grebes are highly associated with saltwater habitats and they consumed adult brine shrimp most of the fall. Eared grebes that perished during the downing had mercury and selenium concentrations above levels seen in pre- and post-downing birds and higher than observed concentration that impact bird species, providing a potential ultimate cause of death during snowstorms that accompany most downings. Stable isotope analysis indicated northern shovelers that winter on the GSL had breeding origins throughout the specie’s range, but most came from local or southern Prairie Pothole Region breeding populations

Stability of Noisy Metropolis-Hastings

Pseudo-marginal Markov chain Monte Carlo methods for sampling from intractable distributions have gained recent interest and have been theoretically studied in considerable depth. Their main appeal is that they are exact, in the sense that they target marginally the correct invariant distribution. However, the pseudo-marginal Markov chain can exhibit poor mixing and slow convergence towards its target. As an alternative, a subtly different Markov chain can be simulated, where better mixing is possible but the exactness property is sacrificed. This is the noisy algorithm, initially conceptualised as Monte Carlo within Metropolis (MCWM), which has also been studied but to a lesser extent. The present article provides a further characterisation of the noisy algorithm, with a focus on fundamental stability properties like positive recurrence and geometric ergodicity. Sufficient conditions for inheriting geometric ergodicity from a standard Metropolis-Hastings chain are given, as well as convergence of the invariant distribution towards the true target distribution

Morphology and thermal conductivity of model organic aerogels

The intersection volume of two independent 2-level cut Gaussian random fields is proposed to model the open-cell microstructure of organic aerogels. The experimentally measured X-ray scattering intensity, surface area and solid thermal conductivity of both polymeric and colloidal organic aerogels can be accounted for by the model.Comment: 5 pages. RevTex with 4 encapsulated figures. Higher resolution figures have been submitted for publication. To be published in Phys. Rev. E (Rapid Comm.). email, [email protected]

Nutrient Recycling by Eared Grebes in the Great Salt Lake

Nitrogen (N) and phosphorus (P) cycling in lakes can be impacted by numerous abiotic and biotic factors. Large animals, such as birds and mammals, may recycle nutrients within a system or bring them in from surrounding habitats or different landscapes. Eared Grebes (Podiceps nigricollis) congregate in large numbers in the fall on the Great Salt Lake (GSL), Utah, and may have an important role in recycling nutrients from macroinvertebrates back into the water column. We evaluated the role of Eared Grebes in N and P cycling within the GSL by estimating the magnitude of their nutrient recycling capacity. We estimated Eared Grebe population size on the GSL over 5 years at 300,000 to over 4,300,000 birds. We used a previously published food intake model to estimate monthly recycling of N (5 to 300 tonnes) and P (0.4 to 25 tonnes). The maximum estimates of N and P loading by Eared Grebes are about 25% of nutrient recycling in the GSL caused by turnover in the water column. Eared Grebes may speed up nutrient recycling, making nutrients available to primary producers sooner. The contribution of waterbirds to nutrient cycling is important for the entire N and P cycles within the GSL

Predators, Predator Removal, and Sage-Grouse: A Review

Populations of sage-grouse (Centrocercus urophasianus; i.e., sage-grouse) have been in a decline since the nineteenth century. We used our research, unpublished reports, and scientific literature to identify which predators kill greater sage-grouse and to assess whether lethal control of these predators benefited the species. We also asked state wildlife biologists and scientists if they had ever witnessed a predator kill sage-grouse. We identified 266 instances where the predator responsible for depredating nests or killing juvenile or adult sage-grouse could be ascertained. Most adult sage-grouse were killed by eagles (Accipitridae), owls (Strigiformes), or coyotes (Canis latrans), except where red foxes (Vuples vulpes) were abundant. Based on nest-cameras, most depredated eggs are taken by common ravens (Corvus corax), badgers (Taxidae taxus), or coyotes. There are too few studies to conclude that predator removal increases survival rates of juvenile or adult sage-grouse. No study has been conducted to determine if badger removal increases nest success of sage-grouse, and the only study on coyote removal produced ambiguous results. Several studies reported that more sage-grouse nests are successful (i.e., ≥1 eggs hatched) in areas where common ravens were removed or in areas where raven densities were lower than in other areas. Populations of sage-grouse have been in a decline for over a century, and predators are unlikely to have played a role in the decline during most of this period, but increasing numbers of ravens since the 1970s may have contributed to the declining sage-grouse populations in recent decades

A Hilbertian projection method for constrained level set-based topology optimisation

We present an extension of the projection method proposed by Challis et al ($\textit{Int J Solids Struct}$. Volume $\textbf{45}$(14-15) (2008) 4130-4146) for constrained level set-based topology optimisation that harnesses the Hilbertian velocity extension-regularisation framework. Our $\textit{Hilbertian projection method}$ chooses a normal velocity for the level set function as a linear combination of: 1) an orthogonal projection operator applied to the extended optimisation objective shape sensitivity; and 2) a weighted sum of orthogonal basis functions for the extended constraint shape sensitivities. This combination aims for the best possible first-order improvement of the optimisation objective in addition to first-order improvement of the constraints. Our formulation utilising basis orthogonalisation naturally handles linearly dependent constraint shape sensitivities. Furthermore, use of the Hilbertian extension-regularisation framework ensures that the resulting normal velocity is extended away from the boundary and enriched with additional regularity. Our approach is generally applicable to any topology optimisation problem to be solved in the level set framework. We consider several benchmark constrained microstructure optimisation problems and demonstrate that our method is effective with little-to-no parameter tuning. We also find that our method performs well when compared to a Hilbertian sequential linear programming method.Comment: 23 pages, 8 figure