Saturday, May 18, 2013

Viewing the Horseshoe Crab Natural Phenomena on Delaware Bay


Three beaches that people in our area visit to watch horseshoe crabs and birds are Pickering Beach on the Delaware side, Reeds Beach on the New Jersey side and Plum Island on Sandy Hook, New Jersey. (Location information below.)

I love these "living fossils" that have remained basically the same for 450 million years and have tried to write regularly about them here. The females (which are generally larger than males) carry tens of thousands of eggs which they deposit in the sand for males to fertilize.

The number of mating horseshoe crabs on the beach peaks in the Delaware Bay during the evening and full moon tides in May and June. The huge number of horseshoe crab eggs attracts many birds to converge for this annual feast. This month's full moon is on May 24 and the next is June 23.

horseshoe crabs, Sandy Hook - photos by Brian Richards
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 there is a correlation between shorebird population declines and horseshoe crab decline. For the crabs, 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. Those numbers fell closer to 1 million in the late 1990s through 2005. Since a moratorium was put in crab harvesting in NJ and to a lesser extent in Delaware, the number seems to have settled at around 2 million, according to The Wetlands Institute.

Adult horseshoe crabs winter in water 20 to 60 feet deep on the continental shelf.  As the water temperature and daylight increases, adults migrate toward sandy beaches for spawning.

The females dig a shallow hole and deposit their eggs in clumps within the intertidal zone.

For viewing the birds and crabs, Reeds Beach in Cape May, NJ 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.

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.

For more about horseshoe crab viewing locations on the East Coast, see www.ocean.udel.edu/horseshoecrab/


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