Color marked sanderling and ruddy turnstone at Delaware Bay - Photo Credit: n/a

Color marked red knot and horeshoe crabs in Delaware Bay. The marked red knot was marked in Argentina. - Photo Credit: n/a

Delaware Bay Estuary Project provided equipment and technical expertise to the state of Delaware for monitoring shorebird use of Delaware Bay during the Spring and fall stopovers.  Target species include red knot, ruddy turnstone, semipalmated sandpiper, and sanderling.

Background:  Delaware Bay hosts the largest spawning population of horseshoe crabs in the world and the second largest population of migrating shorebirds in North America. Delaware Bay is designated within the Western Hemisphere Shorebird Reserve Network as having the highest reserve status. In addition to providing the principal food source for migratory birds in Delaware Bay, research indicates horseshoe crabs may comprise the main diet of juvenile loggerhead turtles.

The Delaware Bay is a critical migratory stopover for Western Hemispheric populations of migratory shorebirds, including red knot (Calidris canutus rufa), ruddy turnstone (Arenaria interpres), sanderling (Calidris alba), and semipalmated sandpiper (Calidris pusilla). These migrants depend on the eggs of spawning horseshoe crabs for a major portion of their diets (50 to 90 percent) each spring before migrating from the Delaware Bay beaches to Artic nesting grounds.

Migratory shorebirds on the Delaware Bay beaches declined in the late 1990s and early 200s. Since 2003 the population has been stable based on winter surveys in South America and Aerial Peak Counts in Delaware Bay. The local threats that have been identified include reduced food availability, human disturbance, predation, loss of sandy beaches and suitable roost sites, and risk of oil and hazardous materials spills. The high harvest of horseshoe crabs leading up until the late 1990s has reduced the crab population and may have led to declines in migratory shorebirds including red knot, sanderling, semipalmated sandpiper, and ruddy turnstone.

The issue of meeting the energetic requirements of migratory Shorebirds has driven the controversy over management of horseshoe crab (Limulus polyphemus) populations in the mid-Atlantic region and particularly in Delaware Bay. The ASMFC Horsehoe Crab Fishery Management Plan has multiple goals: 1) sustaining horseshoe crab population levels, 2) providing critical food resources for other species (migratory shorebirds in particular), 3) allowing harvest for bait, and 4) providing continued use for LAL production, which is required for testing the safety of medical supplies World-wide. Even more problematic is the fact that the migratory shorebird populations are dependent on horseshoe crab eggs that are surplus to the needs of the horseshoe crab population. 

Work on the Strategic Habitat Conservation (SHC) and Structured Decision Making effort to aid management decision making relies on critical monitoring programs.  These programs serve as the basis for status and trend analysis of key biological indicators, such as weight gain at Delaware Bay, stopover duration, and population survival.