Relating Diets and Food Availability to Long-term Population Trends of Lesser Scaup Wintering on Lake Pontchartrain, Louisiana
Semester of Graduation
Master of Science (MS)
Renewable Natural Resources
Lake Pontchartrain provides wintering habitat for a continentally-significant proportion of lesser scaup (Aythya affinis). Mid-winter aerial surveys indicate dramatic variation in annual scaup abundance (0–1,194,907), though the mechanisms driving fluctuations have not been previously investigated. In response to natural and anthropogenic disturbances, species composition, abundance, and size structure of benthic invertebrate populations in Lake Pontchartrain exhibit drastic variability among years. Given that wintering scaup feed primarily on mollusks, environmental disturbances have the potential to influence scaup dynamics on the estuary by altering the benthic community. To diagnose trophic linkages and variation in scaup abundance, we collected ducks (n=60) and benthic samples (n=6) from the field to evaluate diet preferences, and then used this information to guide analyses using pre-existing long-term datasets on scaup and benthic populations. The most common prey species was the common rangia (Rangia cuneata), accounting for 43% of the total number of food items consumed and 60% of the aggregate dry weight ingested. Rangia was also highly preferred by scaup relative to availability. Medium-size classes (≥6 mm to≥11 mm tomm) of rangia appear to be particularly important, as they represented 71% of the total number and 91% of the aggregate dry weight of rangia consumed by scaup. Moreover, my long-term analyses revealed that scaup populations on Lake Pontchartrain were significantly influenced by the abundances of these medium-size classes. In agreement with prior studies, I found that rangia abundances were impacted by hurricanes; clam populations were greatly reduced in the same year as a hurricane, but significantly increased the following year. Scaup abundances also declined in the same year a hurricane occurred and increased the subsequent year. Thus, hurricanes appear to drive a bottom-up trophic cascade that ultimately affects scaup populations over multiple years on Lake Pontchartrain. My results provide valuable information on trophic linkages in an estuarine system that is particularly prone to increases in hurricane intensity predicted with climate change.
Stroud, Clay Michael, "Relating Diets and Food Availability to Long-term Population Trends of Lesser Scaup Wintering on Lake Pontchartrain, Louisiana" (2018). LSU Master's Theses. 4675.
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