The Horseshoe Crab -- Putting Science To Work To Help "Man's Best Friend"

"Horseshoe crabs are critical to the welfare of migrating shorebirds that stop along the Delaware Bay each spring to fuel up for the flight north to Arctic nesting grounds. Some of these birds double and even triple their weight by feasting on horseshoe crab eggs," Hall says.

"Yet the horseshoe crab is just as important to humans as it is to wildlife," he notes. "This animal's blood contains a unique clotting agent that the pharmaceutical industry uses to test intravenous drugs for bacteria. No IV drug reaches your hospital pharmacy without its horseshoe crab test. So if you or someone you love has ever been hospitalized, you owe a lot to the horseshoe crab."

"Delaware Bay is the world's population center for horseshoe crabs, but during the past few years, we've noted a significant downturn in the animal's population, from 1.2 million spawning females down to about 400,000," Hall says. Hall helps organize a regional census of the Delaware Bay's spawning horseshoe crab population. Now in its tenth year, volunteers from Delaware and New Jersey conduct the census on selected bay beaches each May and June. This year, the census will be expanded to additional beaches along both sides of the bay with support from the Atlantic States Marine Fisheries Commission.

The peak census activity will take place this weekend (May 28-June 1). Hall says three beaches just southeast of Dover, Delaware are likely to draw the most crabs, but overall eight beaches on both the Delaware and New Jersey shorelines will be patrolled.

The best Delaware beaches for viewing the animal survey are Kittshummock, Pickering and Bowers Beach, both north and south. Hall says the prime times to see the animals come ashore will be the late evening tide, around 9 p.m. on Sunday. Counts will also be taken on Friday and again on Tuesday. Hall himself will focus on Bowers Beach on Sunday.

"Scientists believe the decline is due to overfishing of the crab for eel and conch bait and to the loss of the sandy beaches it needs for spawning," he notes. "The census is designed to help resource managers and scientists gain a better understanding of the horseshoe crab's status and what we can do to guard our 'golden goose.' "

Developing an Artificial Bait to Reduce Fishing Pressure On the Horseshoe Crab

In Sea Grant research at the University of Delaware, marine biologist Nancy Targett has been working to minimize fishing pressure on the horseshoe crab through biochemistry. She has made significant progress toward identifying the stimulant in female horseshoe crabs that makes them such an irresistible bait for eels and whelks. With this information, she wants to develop an artificial bait that will attract eels and whelks just as well as female horseshoe crabs do.

Targett and her graduate students are in the home stretch in chemically characterizing the attractant. The next step will be to incorporate the compound into a variety of artificial bait types and test their effectiveness. Several commercial fishermen in Delaware have contacted Targett, offering to test the baits when they are ready.

"The fishing industry is very supportive of this effort," Targett says. "With their help, our goal is to develop an artificial horseshoe crab bait that will work as well as the traditional one. The result should be a win-win situation for the fishermen as well as the horseshoe crab, resulting in more horseshoe crabs for spawning and sustainable uses in medicine."

Horseshoe Crab Facts

Although called a "crab," the horseshoe crab is actually closely related to spiders and scorpions. It is also one of the Earth's oldest creatures, having appeared here 100 million years before the dinosaurs. Scientists have learned a lot about the human eye by studying the horseshoe crab's large compound eyes. The horseshoe crab also has numerous smaller eyes called photoreceptors on its top shell and along its tail. Sensitive to light, they help synchronize the crab's internal clock with daily cycles of light and darkness.

The horseshoe crab's sword-like tail, called the telson, isn't poisonous as some people believe. When the crab has been overturned, it simply uses its tail as a lever to flip itself to an upright position.