Abstract. Great Salt Lake (Utah, USA) is one of the world's largest hypersaline lakes, supporting many of the western U.S.'s migratory waterbirds. This unique ecosystem is threatened, but it and other large hypersaline lakes are not well understood. The ecosystem consists of two weakly linked food webs: one phytoplankton-based, the other organic particle/benthic algae-based.Seventeen years of data on the phytoplankton-based food web are presented: abundances of nutrients (N and P), phytoplankton (Chlorophyta, Bacillariophyta, Cyanophyta), brine shrimp (Artemia franciscana), corixids (Trichocorixa verticalis), and Eared Grebes (Podiceps nigricollis). Abundances of less common species, as well as brine fly larvae (Ephydra cinerea and hians) from the organic particle/benthic algae-based food web are also presented. Abiotic parameters were monitored: lake elevation, temperature, salinity, PAR, light penetration, and DO. We use these data to test hypotheses about the phytoplankton-based food web and its weak linkage with the organic particle/benthic algae-based food web via structural equation modeling.Counter to common perceptions, the phytoplankton-based food web is not limited by high salinity, but principally through phytoplankton production, which is limited by N and grazing by brine shrimp. Annual N abundance is highly variable and depends on lake volume, complex mixing given thermo-and chemo-clines, and recycling by brine shrimp. Brine shrimp are food-limited, and predation by corixids and Eared Grebes does not depress their numbers. Eared Grebe numbers appear to be limited by brine shrimp abundance. Finally, there is little interaction of brine fly larvae with brine shrimp through competition, or with corixids or grebes through predation, indicating that the lake's two food webs are weakly connected.Results are used to examine some general concepts regarding food web structure and dynamics, as well as the lake's future given expected anthropogenic impacts.

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The Great Salt Lake (GSL) is an important region for millions of migratory waterbirds. However, high concentrations of some trace elements, including Hg and Se, have been detected within the GSL, and baseline ecotoxicological data are lacking for avian species in this system. We collected common goldeneye (Bucephala clangula), northern shoveler (Anas clypeata), and green-winged teal (A. crecca) from the GSL during the winters of 2004-2005 and 2005-2006 to evaluate sources of variation in liver trace element concentrations. Hg concentrations were among or exceeded the highest values reported in the published literature for common goldeneye, northern shoveler, and green-winged teal. Average Hg (total) concentrations of common goldeneye peaked in midwinter, whereas average Se concentrations peaked during late winter. During late winter, 100% and 88% of female goldeneye contained elevated concentrations of Hg [>or=1.0 microg/g wet weight (ww)] and Se (>or=3.0 microg/g ww), respectively, and 5% and 14% contained potentially harmful amounts of Hg (>or=30.0 microg/g ww) and Se (>10.0 microg/g ww), respectively. Similarly, 30% and 16% of male goldeneye contained potentially harmful concentrations of Hg and Se, respectively. Concentrations of Hg and Se were elevated in 100% and 79%, respectively, of northern shoveler samples (sexes combined) collected during February. We suggest that waterfowl contain biologically concerning amounts of Hg and Se during winter while on the GSL and further research is needed to evaluate the effect of these elements on GSL waterbirds.

Eared Grebes (Podiceps nigricollis Brehm, 1831) use saline ecosystems throughout much of their life cycle, and greater than 90% of the North American population stage during fall at two hypersaline lakes. At one of these lakes, Great Salt Lake (GSL), Utah, a commercial harvest of brine shrimp (Artemia franciscana Kellogg, 1906) cysts occurs during fall and may impact Eared Grebe populations. We used photo surveys on the other hypersaline lake, Mono Lake, California, and on the GSL, as well as aerial counts on the GSL, to describe population fluctuations of Eared Grebes staging on these lakes. The long-term (1997-2012) Eared Grebe population was 1.4 million on the GSL and 1.0 million on Mono Lake. Populations changed on GSL and Mono Lake in synchrony, indicating population regulation is likely occurring at wintering, not staging, areas and is influenced by El Niño effects. Location of Eared Grebes on the GSL was influenced by brine shrimp densities and did not overlap with concentrations of commercial harvest boats. Spatial segregation of commercial harvesters and Eared Grebes reduces negative impacts of anthropogenic disturbance on Eared Grebes. Knowledge of population changes within and among staging areas will help managers monitor long-term abundances and reduce negative impacts between Eared Grebes and commercial harvesters. Résumé : Les grèbes à cou noir (Podiceps nigricollis Brehm, 1831) utilisent des écosystèmes salins pendant une bonne partie de leur cycle biologique, et plus de 90 % de la population nord-américaine utilise deux lacs hypersalins comme haltes migratoires à l'automne. À l'un de ces deux lacs, le Grand Lac salé (Utah; GSL), une récolte à des fins commerciales de kystes d'artémia (Artemia franciscana Kellogg, 1906) a lieu à l'automne et pourrait avoir un impact sur les populations de grèbes à cou noir. Nous avons utilisé des levés photographiques sur l'autre lac hypersalin, le lac Mono (Californie), et sur le GSL, et des décomptes aériens sur le GSL pour décrire les fluctuations des populations de grèbes à cou noir en halte migratoire à ces lacs. Les populations à long terme (1997-2012) de grèbes à cou noir étaient de 1,4 million et 1,0 million d'individus, respectivement, sur le GSL et le lac Mono. Les variations des populations sur le GSL et sur le lac Mono sont synchrones, ce qui indique que la régulation des populations s'opère vraisemblablement dans les aires d'hivernage plutôt qu'aux haltes migratoires, et qu'elle est influencée par les effets d'El Niño. La répartition des grèbes à cou noir sur le GSL était influencée par les densités d'artémias et ne recoupait pas les concentrations de bateaux s'adonnant à l'exploitation commerciale d'artémia. La ségrégation spatiale des exploitants et des grèbes à cou noir limite les impacts négatifs des perturbations humaines sur ces oiseaux. La connaissance des variations des populations dans les haltes migratoires et entre elles aidera les aménageurs à surveiller l'abondance à long terme des grèbes à cou noir et à réduire les impacts négatifs de l...

The value of saline lakes and associated wetlands as habitats in the xeric Great Basin is dependent on having water of sufficient quantity and quality to support wetland-dependent birds. To inform conservation and management of these habitats, models are needed to link birds and hydrological changes due to climate and human water use. We modeled seasonal relationships between counts for 35 migratory shorebird, waterfowl, and other waterbird species or taxonomic groups and hydrological metrics at Bear River Bay, a globally Important Bird Area at Utah's Great Salt Lake. We found that increased fall surface flows to the bay increased counts of 13 species, including American Avocets (Recurvirostra americana), American White Pelicans (Pelecanus erythrorhynchos), American Wigeons (Mareca americana), Northern Pintail (Anas acuta), Redheads (Aythya americana), and Ruddy Ducks (Oxyura jamaicensis). Increased spring surface flows increased counts of Forster's Terns (Sterna forsteri) and the sandpiper group, whereas intermediate spring flows produced peak counts for American White Pelicans. Thus, conservation or management actions that increase seasonal flows to Bear River Bay are expected to increase bay use by diverse members of the avian community. Counts for 11 species or taxonomic groups responded positively or negatively to the seasonal elevation of Great Salt Lake, and these responses are hypothesized to reflect the relative availability of habitats within the bay versus the lake as a whole. Our models provide tools that allow managers to understand how hydrological changes associated with climate change and human water use will affect birds in Bear River Bay. Addressing lake-wide and regional population implications of changing hydrological conditions at Bear River Bay, Great Salt Lake, and other locations across the Great Basin will require a regionally coordinated assessment of hydrology, habitat, and bird movements in response to changing habitat conditions.