NATURALIST'S 



NOTEBOOK 



HUMANITY'S LUCKY HORSESHOE 



Humans also have acquired a dependence 

 on this enduring organism, although one of a 

 more economic nature. 



Modern commercial harvest of horseshoe 

 crabs as bait supports a $2 million conch fishery 

 and a $6 million American eel fishery. 



"In Delaware Bay alone, watermen derive 

 20 to 50 percent of their total fishing income 

 from conch or eel harvests," write University of 

 Delaware marine biologist Nancy Targett and 

 former graduate student Kirsrin Ferrari. 



The horseshoe crab also is a valuable 

 resource to biomedical companies because its 

 blood contains a clotting agent, Limulus 

 ameobocyte lysate (LAL), which reacts to 

 bacteria. LAL can be produced by extracting 

 the blood from live horseshoe crabs, and is used 

 to detect microbial pathogens in human blood, 

 injectable drugs, intravenous fluids and other 

 medical devices and supplies. The extraction 

 procedure generally does not harm the 

 horseshoe crabs. 



HORSESHOE CRABS IN PERIL? 



They have survived through millions of 

 years of global change, predation and even an 

 asteroid blast. So why are so many horseshoe 



crab monitoring programs sprouting along the 

 Atlantic? 



"Since horseshoe crabs are used for the 

 production of LAL, there has been more interest 

 in their abundance," explains Whitney Kurz, 

 coastal training program coordinator for the N. C. 

 National Estuarine Research Reserve, who 

 organizes a census in North Carolina. 



Also, the Atlantic States Marine Fisheries 

 Commission (ASMFC) has enacted the Interstate 

 Fishery Management Plan for the Horseshoe 

 Crab. Fifteen Atlantic states, including North 

 Carolina, must abide by the plan, which aims to 

 "determine horseshoe crab population densities 

 and spawning locations," says Kurz. 



One volunteer-driven census of breeding 

 horseshoe crabs, conducted in the Delaware Bay 

 area since 1990, was recently modified to meet 

 ASMFC standards. 



Delaware Sea Grant organized the first 

 census, and now, every spring, volunteers 

 continue their count on nine key beaches in 

 Delaware and nine in New Jersey. The recent 

 census was designed through the cooperation of 

 the U.S. Geologic Survey, U.S. Fish and Wildlife 

 Service, several universities and state 

 management agencies and a biomedical 

 company. 



Hall, who helps organize the annual 

 Delaware census, describes the spawning 

 population structure of the horseshoe crabs as 

 having "bottomed out" because it has remained 

 relatively stable over the past three years. 

 He compares this trend to the initial decline 

 beginning in the early 1990s, which "noted 

 a significant downturn in the animal's 

 population, from 1.2 million spawning 

 females down to about 250,000." 



There are many theories as to the causes 

 of the decline, such as loss of spawning habitat 

 and global change. But, overfishing is believed 

 to be the primary cause of the rapid decrease in 

 horseshoe crab spawning populations. And, 

 since commercial fishing is a factor that is 

 within immediate human control, research 

 continues to analyze the negative effects of 

 horseshoe crab harvesting. 



For instance, current research may 

 convert the economic and ecological problem 

 of the harvesting of horseshoe crabs into a win/ 

 win situation. 



Targett is working on a Sea Grant-funded 

 project to create artificial bait by zeroing in on 

 the compound that attracts eels and conch to 

 prey on horseshoe crabs. One of Targett's main 

 objectives is to "take some of the pressure off 

 of the horseshoe crab population." 



The bait is created by using an attractant 

 derived from the horseshoe crabs eggs, and is 

 currently undergoing preliminary field trials. 

 Targett hopes to eventually "develop a source 

 of the attractant that is independent of the 

 horseshoe crab." □ 



TOUCH AND ADMIRE/ 

 LEARN AND APPRECIATE 



Volunteer for horseshoe crab surveys in 

 North Carolina by contacting Whitney Kurz at 

 252/728-2170 or whitney_kurz@ncnerr.org. 



Delaware Sea Grant is developing a 

 regional horseshoe crab website. Look for it 

 later this year at www.ocean.udel.edu/seagranL 



For more information also check "Tlie 

 Bridge, " Sea Grant's marine education site, at 

 www.vims.edu/bridge. 



COASTWATCH 29 



