How Do Density Fronts Interact with Zooplankton Distributions to Create Baleen Whale Prey-Fields in Roseway Basin?

Gennavieve Ruckdeschel, Dalhousie University, Oceanography, Halifax, NS, Canada, Tetjana Ross, Institute of Ocean Sciences, Sidney, BC, Canada and Kimberley Teresa Ann Davies, University of Victoria, Dept. of Geography, Victoria, BC, Canada
On the Scotian Shelf in the northwest Atlantic, Roseway Basin is a feeding ground for several species of large baleen whales, including the highly endangered North Atlantic right whale. In this habitat, aggregations of zooplankton must be present at concentrations high enough for baleen whales to obtain an energetic benefit. Regions of highly concentrated zooplankton are formed within the habitat through various biophysical interactions, such as fontal accumulation and retention. In Roseway Basin, humpback and fin whales prey on accumulated euphausiids, while right and sei whales forage for deep layers of Calanoid copepods. Right whales are found most often along the southeastern basin margin in Roseway, and this is also where density fronts occur and are associated with zooplankton patches that can form and disaggregate at tidal scales. The temporal persistence and biophysical mechanisms behind the observed interactions of zooplankton and frontal features have not been assessed. To understand how density fronts impact zooplankton distributions at the scale of feeding whales, we deployed Slocum gliders equipped with conductivity-temperature-depth sensors and echosounders in a series of cross-isobath transects along the sloped southeastern margin of Roseway Basin during August to November 2015. By looking for the presence of density fronts that are also regions of elevated acoustic backscatter (primarily from copepods and euphausiids) and quantifying their persistence over time, we aim to determine how these biophysical interactions create whale prey-fields.