Movement and foraging behaviours of surf scoters wintering in habitats modified by shellfish aquaculture.

I investigated movement patterns and foraging effort of surf scoters wintering in two sites with shellfish aquaculture, one with clam and the other with mussel prey. Scoters at the clam site exhibited very little movement and high site fidelity, whereas scoters in the mussel habitats exhibited much larger movements. These habitat-specific movement patterns were likely related to temporal patterns of prey availability; clams remained relatively stable while mussels declined dramatically, depleted by scoters. Mussels occurring on aquaculture structures were novel prey favoured by foraging sea ducks because they occurred in higher densities with less defensive morphology than intertidal mussels. Surf scoters did not respond to depletion of these mussels by intensifying foraging efforts but rather moved to alternate feeding areas. Though shellfish aquaculture has modified habitats in coastal British Columbia, these changes have not compromised scoter foraging opportunities and, in some cases, have improved the availability and quality of prey.