Fine-scale biophysical interactions drive prey availability at a migratory stopover site for Phalaropus spp. in the Bay of Fundy, Canada

We examined the role of biophysical interactions in structuring the foraging habitat of phalaropes Phalaropus spp. at an important migratory stopover site in the Bay of Fundy. We sampled both biological and physical aspects of the environment and integrated these observations into generalized additive models (GAMs). Strong tidal currents interact with steep bathymetric gradients at the Brier Island ledges to enhance vertical mixing, creating dense surface aggregations of Calanus finmarchicus copepods at fine temporal and spatial scales. The resulting spatial variation in copepod density in near-surface waters creates a highly heterogeneous foraging environment for phalaropes, which are obligate surface feeders. Models of phalarope abundance over the ledges suggested that phalaropes forage on upwelled zooplankton aggregations as they drifted downstream. Our results highlight the importance of considering underlying physical processes when assessing hotspots of prey aggregations for marine species, particularly within highly dynamic systems such as the Bay of Fundy. This is particularly relevant to considerations of the conservation status of red-necked phalaropes Phalaropus lobatus, which have abandoned a long-time migratory stopover area previously used by more than one million birds during the mid-1980s. © Inter-Research 2013.

Duke Scholars

Author Andrew J Read Marine Science and Conservation