Date of Award:

12-2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Advisor/Chair:

Michael R. Conover

Abstract

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 isotope
and banding data.
I found that commercial harvest boats did not influence duck population numbers
or 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.

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