An experiment to examine how Red Knots Calidris canutus rufa and other shorebirds respond to oyster culture at Reed’s Beach, Delaware Bay, New Jersey

We examined how Red Knots Calidris canutus and other shorebirds responded to experimental oyster racks at Reed’s Beach, New Jersey, USA. Our goal was to investigate ways that human activities (e.g. oyster culture) and migrant shorebirds can co-exist without negatively impacting each other. The expansion of oyster culture just offshore from beaches where shorebirds feed on Horseshoe Crabu Limulus polyphems eggs could have positive benefits or negative effects on shorebird foraging. In collaboration with a local oysterman, oyster racks were constructed 25 m offshore from Reed’s Beach South, one of the primary shorebird foraging sites, and regular surveys were carried out throughout the Delaware Bay shorebird stopover period in May 2013.

We found that oyster racks (whether the beach had racks or was a reference site), tidal stage, people, and interactions amongst these variables, significantly affected shorebird numbers. Specifically, (1) oyster racks and tidal stage (alone and as interactions) had the greatest effect on presence and abundance of shorebirds and gulls, except for Red Knots, (2) Red Knots were most affected by people, followed by tide, (3) more shorebirds were present at high tide than at other tide times, (4) numbers were highest on the beach near the oyster racks, largely reflecting those of Semipalmated Sandpipers Calidris pusilla, (5) fewer shorebirds of any species were present when workers were present, compared to when beach-users were present, and (6) virtually no Red Knots and Ruddy Turnstones Arenaria interpres were present when workers or beach-users were present on the beach next to the oyster racks. The number of shorebirds feeding was highest when no people were present, intermediate when beach-users were present, and lowest when workers were present. These preliminary results suggest that Red Knots are more sensitive to oyster culture activities than other shorebird species. Therefore we suggest that regulators and managers should incorporate this sensitivity in their management and rule-making.