Horseshoe Crabs Annual Census on the Delaware Bay Beaches

Horseshoe Crabs Inundate the Delaware Bay Shoreline

Delaware Bay beaches come alive with activity in mid-May as migrating shorebirds fly in from Central and South America, horseshoe crabs swim ashore to lay their eggs, and census takers count the number of crabs finding mates. The shorebirds refuel by feasting on the eggs that are half-buried in the sand and then continue their flight northward. The remaining eggs that are covered by sand will mature and hatch after a month or more of development, in relatively calm water when the moon is full. Waves sweep the half inch long crabs into shallow water where they stay for nearly a week until they are ready to molt. The young crabs then live in the nearby intertidal flats for the first two years of life. 

During the full and new moons of late May and early June over a million horseshoe crabs appear on the beaches of the Delaware Bay. Most of them favor the beaches mid-way up the Delaware Bay, such as Pickering Beach, which often has the highest densities of horseshoe crabs in the Delaware Bay, according to the U.S. Geological Survey's horseshoe crab census. Researchers counted an average of 27 horseshoe crabs per square meter at Pickering Beach during the peak of spawning season. Other beaches with large populations of horseshoe crabs are Mahon Beach, Kitts Hummock Beach, Fowlers Beach, Bowers Beach, Big Stone Beach, Slaughter Beach, and Prime Hook Beach. The highlighted beaches have been reviewed in my earlier blogs, and the other beaches will be reviewed in upcoming blogs.  

Since 1990 the University of Delaware Sea Grant College Program sponsors a horseshoe crab census to estimate the population on Delaware beaches. The data from these annual crab counts provide a valuable management tool for long-term monitoring of the Delaware Bay horseshoe crab population. You can volunteer for the Annual Horseshoe Crab census by contacting Dr. Bill Hall (Delaware) at (302) 645-4253 or by e-mail at bhall@udel.edu. An excellent source of information about the Delaware horseshoe crab population is the University of Delaware's College of Earth, Ocean, and Environment's website at http://www.ceoe.udel.edu/horseshoecrab.