Presented by Kevin M. Ringelman - Email: kringelman@agcenter.lsu.edu
The estuaries of Louisiana overwinter a continentally-significant proportion of Lesser Scaup (Aythya affinis; colloquially, bluebills), a species of conservation concern since population declines began in the 1980s. Thirty-eight years of aerial waterfowl surveys of Lake Pontchartrainan oligohaline estuarine lagoon in southeast Louisianashow that scaup abundance fluctuates between 0 and 1,194,907 birds, though the mechanisms driving this variation are unknown. Previous studies have shown that scaup feed primarily on mollusks, so changes in the benthic prey community have the potential to strongly influence scaup dynamics on the Lake. Benthic communities are in turn shaped by both natural and anthropogenic disturbances (e.g., hurricanes and spillway openings), potentially creating a lagged bottom-up trophic cascade that ultimately affects scaup abundance. Here, we evaluated diet of scaup collected from Lake Pontchartrain and found that scaup consumed almost entirely mollusks, especially selecting medium-sized (616 mm) common rangia clams (Rangia cuneata). Scaup also selected dark false mussels (Mytilopsis leucophaeata) and dwarf surf clams (Mulinia lateralis) relative to their availability. Having established important diet items for scaup, we then used 22 years of paired benthic invertebrate and aerial waterfowl survey data to diagnose their covariation in relation to environmental disturbance. We found scaup abundance increased with the abundance of medium-sized rangia and dwarf surf clams. Those prey species declined in years when the Lake was hit by a hurricane, but medium-sized Rangia rebounded strongly the year after, likely because storm surge salinity induces spawning. Using long-term aerial survey data for scaup, we indeed found strong scaup declines on the Lake in years when a hurricane made landfall, but scaup abundance increased the following year, presumably responding to large numbers of medium-sized rangia. Our multi-part analysis makes a strong case for a hurricane-driven bottom-up trophic cascade that affects scaup abundance on Lake Pontchartrain.Q.4-01: Bluebills and bayou bivalves: hurricane-driven trophic cascades affect wintering abundance of Lesser Scaup in Louisiana
Clay M. Stroud, School of Renewable Natural Resources, Louisiana State University AgCenter, Baton Rouge, LA
Claire E. Caputo, Department of Biological Sciences, University of New Orleans, New Orleans, LA
Michael A. Poirrier, Department of Biological Sciences, University of New Orleans, New Orleans, LA
Larry A. Reynolds, Louisiana Department of Wildlife and Fisheries, Baton Rouge, LA
Kevin M. Ringelman, School of Renewable Natural Resources, Louisiana State University AgCenter, Baton Rouge, LA
Claire E. Caputo, Department of Biological Sciences, University of New Orleans, New Orleans, LA
Michael A. Poirrier, Department of Biological Sciences, University of New Orleans, New Orleans, LA
Larry A. Reynolds, Louisiana Department of Wildlife and Fisheries, Baton Rouge, LA
Kevin M. Ringelman, School of Renewable Natural Resources, Louisiana State University AgCenter, Baton Rouge, LA