The Great Cape May Shorebird and Horseshoe Crab Spectacle

The Great Cape May Shorebird and Horseshoe Spectacle

by Dr. Lenore Tedesco

Originally published in

Cape May Magazine June 2014

The Great Cape May Shorebird and Horseshoe Spectacle Located between the Delaware Bay to the west and the Atlantic Ocean to the east, the Cape May Peninsula is situated in an area that hosts one of nature’s true wonders of the world.

By Lenore P. Tedesco for The Wetlands Institute

74 Cape May Magazine

June 2014

A Spectacle of Nature With an act of timing only Mother Nature can provide, each spring Horseshoe Crabs (Limulus polyphemus) climb onto the beaches of Delaware Bay to lay their eggs, while thousands of shorebirds time a stop on their northbound spring migration route to feed on these energy-packed eggs. Our shores host the largest concentration of spawning horseshoe crabs in their range, and the shorebird migration is one of the last great migrations on Earth.

What an amazing front-row view of these spectacular wildlife events we have right here in Cape May. The view has changed though, as those familiar with the sight can tell you. The beaches were once covered with spawning crabs an arm’s length deep; the sky was once filled with clouds of shorebirds. As amazing as the view still is, the recent changes are critical because the numbers we witness from the Cape May Peninsula and vicinity are the core of these populations. Change here matters a lot.

As many scientists do the hard work of understanding why populations are at historically low levels, it is important that we all take opportunities to improve the view through our actions.

An Intricate Relationship Known as “living fossils,� horseshoe crabs are the last survivors of a group of organisms that first appeared in the fossil record some 300 million years ago. These arthropods inhabit the sandy and muddy bottoms of shallow marine habitats and spend their entire lives in the water, except when they come ashore to mate.

Horseshoe crabs are of paramount importance to human health. Their blood contains a clotting agent, Limulus Amoebocyte Lysate (LAL), which provides a fast, reliable test for the presence of infectious bacteria in drugs, as well as prosthetic devices such as heart valves and hip replacements. The United States Food and Drug Administration requires virtually all medical devices and medications to be tested using LAL, and increased supplies will likely be needed in coming years to meet the growing demand.

Overharvesting of horseshoe crabs, coupled with loss of spawning habitat, has resulted in a precipitous decline (by as much as 90% since 1990) in the Delaware Bay crab

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population, and as a result the number of eggs available to migratory shorebirds. New Jersey has a moratorium on the taking of horseshoe crabs, and this may be helping.

However, the decline in horseshoe crab numbers has led to a dramatic decrease in migratory shorebird populations, whose long-distance annual migrations can be as far as 9,000 miles. For example, Red Knots (Calidris canutus rufa), which breed in the Canadian Arctic and primarily winter in Tierra del Fuego, have declined dramatically over the past twenty years. Previously estimated at 100,000-150,000 birds, the population now numbers 18,000-33,000. Red Knots are currently a candidate species for the Federal Endangered Species Program and are expected to be listed as threatened in the coming months. Some ornithologists fear Red Knots could become extinct in our lifetime.

When these shorebirds stop over at the Delaware Bay in the spring, they are here for one thing: fuel. Long-term research suggests that the availability of horseshoe crab This page: Spawning horseshoe crabs on Reeds Beach. Signs posted along beaches will alert visitors places to avoid during feeding and nesting times.

Horseshoe crab eggs which are vital to shorebirds. Opposite: Shorebirds feeding on horseshoe crab eggs.

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June 2014

eggs directly impacts the ability for Red Knots to gain the mass necessary to successfully reproduce in their Arctic nesting grounds. But not just any eggs will do, which is where the dense concentration of spawning crabs becomes relevant. Not only are huge numbers of eggs buried in the sand (nearly 80,000 a season by each spawning female), but with so many crabs using the same spawning beaches, the act of creating a new nest brings buried eggs to the surface, making eggs available for shorebirds to eat. To let the birds do what they’re here to do, uninterrupted, important spawning beaches are seasonally closed during peak shorebird migration (May 7 – June 7). Shorebirds cannot afford to waste time and energy avoiding disturbances, and these closures seem to be helping.

Conservation In Action

Since horseshoe crabs spawn along the high water line, an area typically associated with considerable wave action, many are overturned during spawning or become trapped behind bulkheads or other hazards. Usually, an overturned crab will use its tail to right itself. However, approximately 10% of the local population each year remain stranded and exposed on the beach, where they will either desiccate or be preyed upon. Both result in death. Simply turning stranded crabs over can help, but until recently this wasn’t possible on closed beaches.

To reduce this source of mortality for breeding crabs, which take ten years to sexually mature, a group of eight organizations have partnered with the New Jersey Division of Fish and Wildlife to create a program, reTURN the Favor, to rescue stranded horseshoe crabs on spawning beaches, including those closed during shorebird migration. The Wetlands Institute is taking a leading role in program organization and volunteer recruitment. In the 2013 inaugural season, over 150 reTURN the Favor volunteers saved nearly 5,000 crabs.

Program partners hope to double these efforts in 2014, and have adopted 16 beaches for rescue walks. Volunteers play an important role in collecting data on rescued crabs and stranding hazards, which will help guide conservation and beach restoration activities to benefit horseshoe crab and shorebird populations. 

reTURN the Favor Opportunities The Wetlands Institute is organizing rescue walks for horseshoe crabs on four Cape May County beaches this summer. Rescue walks last approximately one to two hours and cover approximately one to two miles of beach. Sign up to volunteer on reTURN the Favor walks on the program’s website returnthefavornj.org Horseshoe Crabmania Thursdays at The Wetlands Institute: Meet live horseshoe crabs, learn about our latest research, release a baby horseshoe crab raised at the Institute, and make cool crafts.

Thursday evening 5 pm, free with admission.

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