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Bio-physical coupling of seabirds with a dynamic river plume

Released: 2016
Phillips, EM, JK Horne, JE Zamon, J Adams. 2016. Bio-physical coupling of seabirds with a dynamic river plume. 2016 Ocean Sciences Meeting, New Orleans, LA. 21 – 26 February 2016 [Poster Presentation]

Freshwater plumes and plume density fronts, typically formed at the mouths of large rivers flowing into the ocean, are important regions of bio-physical coupling. On the west coast of North America, discharge from the Columbia River into the northern California Current creates a large, dynamic plume and multiple plume fronts. These nutrient-rich productive waters fuel primary and secondary production, which supports a wide variety of small pelagic prey fish species, large populations of Pacific salmon, seabirds, and marine mammals. To determine the influence of the Columbia River plume on marine predators, we analyzed at-sea seabird counts, in situ environmental data measurements, surface trawl catch densities of prey fish, and acoustic backscatter measurements collected from research vessels in May and June 2010-2012. Concurrent distribution patterns and residence times of satellite-tagged sooty shearwaters (Puffinus griseus) and common murres (Uria aalge) were compared to counts from ship surveys. We found that both seabird species occur in plume waters disproportionate to the surveyed area, concentrating in the river plume when river flow and plume volume decreases. Murres, which are central-place foragers, were consistently within 20 km of the geographic mean center of the river plume.  In contrast, shearwaters consistently occurred ~100 km to the north of the plume center, where high densities of prey fish occur. Acoustically detected prey also occurred in higher densities in the plume when volume decreased, while surface catches of prey in the plume did not vary with changing plume conditions. Geographic indices of colocation (GIC) were low between murres and prey species caught in surface trawls, whereas GICs were >0.5 between shearwaters and prey species including juvenile Chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon. We conclude that the river plume is an identifiable and predictable physical feature that foraging seabirds track to maximize prey encounter rates, with potential impacts on anadromous salmonid species.

This product is associated with the following project:
Seabird Vulnerability Assessment for Renewable Energy Projects

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