The number of mating horseshoe crabs on the beach peaks at the night of full moon and at the time of high tide. The huge number of horseshoe crab eggs attracts many birds to converge for this annual feast. This month's full moon is on the 9th, and in June it will be on the 7th. Activity is likely to be at its peak in the latter part of May approaching the June full moon.
Horseshoe crabs are "living fossils" and have remained basically the same for 300 million years. The females (which are generally larger than males) carry tens of thousands of eggs which they deposit in the sand for males to fertilize.
Three beaches that people visit to watch horseshoe crabs and birds are Pickering Beach on the Delaware side, Reeds Beach on the New Jersey side and Plum Island in Sandy Hook, New Jersey. The locations and directions to these three beaches are:
Pickering Beach is at 19 S. Sandpiper Road, about 5 miles south east of Dover. A narrow public access path is near the intersection of S. Sandpiper Dr and Pickering Beach Rd.
Reeds Beach is in Cape May, NJ which offers many birding opportunities. Parking for watching migratory shorebirds and horseshoe crabs is at the end of N. Beach Avenue. There are two observation areas - from the designated beach area at the lot, and from the left side of a cement dike which offers a closer view of mating horseshoe crabs and feeding shorebirds. The left ocean-side of the dike is place to watch horseshoe crabs and shorebirds.
Plum Island is part of Sandy Hook Gateway National Recreation Area in New Jersey. The NJ Audubon Society is a good source of information on their Sandy Hook activities.
For more about horseshoe crab viewing locations on the East Coast, see www.ocean.udel.edu/horseshoecrab/
The spring migration of many species of shorebirds coincides with the arrival of the horseshoe crabs in Delaware Bay. Bird counts of migratory shorebirds show disturbing decreases in numbers, and those who study the migrations see a correlation shorebird population declines and horseshoe crab over-harvesting.
Horseshoe crabs have survived 300 million years of a changing planet, but may not survive human interference. Loss of habitat is a concern, but the use of the crabs as bait is more of a threat.
Between 1960 and 1980, scientists estimated the number of horseshoe crabs in the Delaware Bay to be relatively constant at 2-4 million horseshoe crabs. In 1990, 900,000 adults were counted in the annual horseshoe crab census coordinated by the University of Delaware Sea Grant Marine Advisory Service. Only 400,000 were counted in the 1999 census. From 1999 through 2002, the spawning population appears to have stabilized, remaining around 400,000 adults on the peak-night census.