The Distribution and Abundance of Aquatic of Macrophytes Between Nearshore and Farshore Transects at the Harriman State Park of Idaho Trumpeter Swan Wintering Ground, 1988-2015

• Main Author: Freeman, Jessica L.
• Format: Text
• Language: English
• Published: Digital Commons@WOU 2018
• Subjects: Spring River; Zannichellia palustris
• Online Access: https://digitalcommons.wou.edu/honors_theses/182; https://digitalcommons.wou.edu/cgi/viewcontent.cgi?article=1181&context=honors_theses

Trumpeter Swans, Cygnus buccinator, are native to North America and the largest waterfowl species in the world. This study was designed to determine the abundance and distribution of aquatic macrophytes in one of the most important wintering grounds that serve as a winter food resource of Trumpeter Swans: Harriman State Park of Idaho. Within five sampled river sections, I sampled 20 transects, and approximately 320 point intercept frames. Total percent cover for nearshore transects among all four years was 72.57%, whereas total percent cover for farshore transects among all four years was 74.58 %. The top three species composing this coverage remains the same between both nearshore and farshore transects; Zannichellia palustris, Elodea canadensis, and Potamogeton pectinatus (stuckenia spp.). I found significant differences in species composition and total vegetative cover between nearshore and farshore transects. Species composition differences included bare ground, Potamogeton pectinatus (stuckenia spp.), Rannunculus aquatilis, and Zannichellia palustris. Bare ground was significantly higher within nearshore transects, as was Zannichellia palustris. Contradictorily, I found significantly greater cover in the farshore transects for Potamogeton pectinatus (stuckenia spp.) and Rannunculus aquatilis. Species composition between sections and years differed over time. In 2012, I found greater bare ground coverage in section D compared to 1988, 2011, and 2015. This may be due to increased spring river discharges carrying and depositing greater sediment loads into the section. These results allow for important implications to be made regarding food availability for swans during the winter months when the top layer of the river freezes from the shore to the thalweg. Favored swan foods like Zannichellia palustris may be unavailable when ice-covered, whereas Elodea canadensis, Rannunculus aquatilis and Potamogeton pectinatus (stuckenia spp.) may be available during the early winter, even as reduced river discharges increase river icing across the entire river channel.