Environmental gradients and prey availability relative to glacial features in Kittlitz's murrelet foraging habitat

Abstract

"The goal of this study was to characterize Kittlitz's murrelet (Brachyramphus brevirostris) foraging habitat relative to prey availability and oceanography in Kenai Fjords National Park, a glacial-marine system. I conducted oceanographic, hydroacoustic, trawl, beach seine, and marine bird surveys monthly from June-August in 2007 and 2008. High sediment load from glacial river runoff shaped the marine ecosystem, and this appeared critically important to Kittlitz's murrelets at sea. Submerged moraines influenced inner fjord habitat that was characterized by cool, fresh, stratified, and silt-laden waters. This silty glacial runoff limited light availability to chlorophyll near tidewater glaciers, but zooplankton abundance was enhanced in the surface waters, perhaps due to the absence of a photic cue for vertical migration. Zooplankton community structure was influenced by glacial features and varied along an increasing temperature gradient over the summer. Acoustic measurements suggested that low density aggregations of fish and zooplankton were available in the surface waters near glacial river outflows where murrelets typically forage. Dense fish aggregations moved into the fjords by August. Kittlitz's murrelets were more likely to occur in areas with higher acoustic biomass near glaciers, making these birds more susceptible to climate change than the congeneric marbled murrelet (B. marmoratus), which was most associated with shallow, ice-free areas"--Leaf iii