Limulus Drawing
The Horseshoe Crab


Assessing the Population
Habitat Considerations
Present Condition of Habitats

Who Harvests Horseshoe Crabs?
Biological and Environmental Impacts
Socioeconomic Impacts

Assessing the Population

In order to accurately assess population trends in any group of animals, two things must happen: First, an accurate initial census (baseline) must be taken that counts (or estimates within an acceptable margin of error) the total number of individuals in a population. Second, the method by which the animals are counted after the baseline census must be consistent from location to location and from year to year. Unfortunately, in the case of horseshoe crabs, there is no accurate baseline data from previous years; in addition, governmental and environmental groups have employed different (i.e., inconsistent) censusing methods over the years. The end result is that, as of the year 2000, no one can say with certainty how many horseshoe crabs inhabit the Atlantic coast, or whether their numbers have gone up or down significantly in the past 10 or 20 years.

Assessing Annual Recruitment
The term "annual recruitment" refers to the number of juveniles that have been added to the population pool after a breeding season. Little is known about annual recruitment in horseshoe crabs. In addition, the number of larvae that survive to sexual maturity also remains unknown. Known factors about recruitment and mortality include the following: the maximum fecundity of the adults can be estimated (Shuster, 1982); most eggs that remain buried, and are not subject to shorebird predation, survive to hatching (Rudloe, 1979); and larval mortality from predation is substantial (Loveland et al., 1996). Because horseshoe crabs are slow maturing, long-lived, and repetitive spawners, current juvenile indexing techniques may have limited applicability. Additional information regarding larval and juvenile survival and mortality is essential to assessing annual recruitment. Furthermore, the total number of adult, sexually mature horseshoe crabs along the Atlantic Coast must be known to confidently estimate annual recruitment.

Assessing Spawning Stock Biomass
The spawning stock biomass (i.e., the total number of adult horseshoe crabs) for horseshoe crab populations along the Atlantic Coast is unknown due to a lack of information. The Peer Review Panel (PRP) of the Horseshoe Crab Technical Committee has identified collection of coast-wide spawning survey data as the highest research priority. Botton and Ropes (1987a) provided a conservative adult horseshoe crab estimate of 2.3 to 4.5 million individuals for the Atlantic Coast between New Jersey and Virginia, based on the National Marine Fisheries Service’s Northeast Fisheries Center trawl survey data. However, other trawl survey data from New Jersey indicate that a preponderance of horseshoe crabs occur inshore of the areas sampled by NMFS, which would mean that the NMFS survey missed the most densely-populated sectors. In addition, the type of equipment used by NMFS to conduct the survey may not have adequately sampled horseshoe crabs. Therefore, the estimate of abundance identified by Botton and Ropes (1987a) is considered extremely conservative.

Assessing Mortality
Horseshoe crab mortality has three components: natural mortality, mortality associated with commercial biomedical applications, and bait fishing mortality. Natural mortality includes beach strandings, predation, and other factors such as disease. Beach strandings may cause mortality in 10 percent of the adult horseshoe crab population in the Delaware Bay every year (Botton and Loveland, 1989). Stranding mortality may be higher than the reported 10 percent in areas where rip-rap and revetments entrap horseshoe crabs. In other areas, strandings may account for a much lower percentage (Rudloe, pers. comm., 1998). Shorebird predation on eggs may simply remove excess production (i.e., surface eggs). Adult horseshoe crabs provide a component of loggerhead turtle diets as evidenced by stomach content analyses. The percent of natural mortality attributable to other factors is unknown.

Of the estimated 200,000 to 250,000 horseshoe crabs bled by the biomedical industry each year, perhaps as many as 10 to 15 percent of the animals do not survive the bleeding procedure. This is a source of mortality not included in the statistics from the commercial fishing of horseshoe crabs (Rudloe, 1983; Thompson, 1998). Mortality due to the bleeding procedure may be lower (0 to 4 percent), depending on the individual biomedical facility (Swan, pers. comm., 1998). However, the mortality associated with collecting, shipping, and handling the animals remains unknown. Currently, the biomedical industry is estimated to account for the mortality of 20,000 to 37,500 horseshoe crabs per year (10 to 15 percent of the animals collected).

Fishing mortality is the number of horseshoe crabs that are removed from the population by human activities; this may include direct fishing mortality (i.e., intentional legal harvest) and non-harvest mortality (i.e., poaching and bycatch). The 1996 fishing mortality accounted for at least 2 million individuals throughout the Atlantic Coast, with at least 1.7 million individuals being taken between New Jersey and Virginia. These statistics are based on landings (catch) data provided by the individual states and the NMFS (1998). Reported commercial landings data show a substantial increase in harvest during the 1990s, which could be a result of both an increase in fishing effort and an increase in reporting.

The shrimp trawl fishery in the South Atlantic Bight may contribute to horseshoe crab mortality via bycatch (Thompson, 1998), but the amount of bycatch harvest remains unreported. Since the use of turtle excluder devices became mandatory in the shrimp trawl fishery, the amount of horseshoe crab bycatch has become very small (Cupka, pers. comm., 1998).

For details on the Atlantic States Marine Fisheries Commission (ASMFC) Horseshoe Crab Management Plan visit:
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Habitat Considerations

Description of Habitat
Essential habitat is defined as those waters and substrates necessary for horseshoe crab spawning, breeding, feeding, and growth to maturity. Horseshoe crabs use different habitats at different life stages. For example, protected beaches provide essential habitat for horseshoe crab spawning efforts, while nearshore shallow waters are essential nursery habitat.

Spawning Habitat
Spawning adults prefer sandy beach areas within bays and coves that are protected from wave energy. Beach habitat also must include porous, well-oxygenated sediments to provide a suitable environment for egg survival and development (Botton, et al., 1988). Optimal spawning areas are limited by the availability of suitable sandy beach habitat. However, spawning may occur along peat banks if sand is present in the upper intertidal regions and along the mouths of salt marsh creeks (Botton, 1995). Shuster (1996) states that spawning may occur along muddy tidal stream banks but not on peat banks because adults are sensitive to the hydrogen sulfide and anaerobic conditions found in the peat. Spawning habitat varies throughout the horseshoe crab range. In Massachusetts, New Jersey, and Delaware, beaches are typically coarse-grained and well-drained; in Florida, the beaches are typically fine-grained and poorly drained. These differences affect nest-site selection and nesting synchrony (Penn and Brockmann, 1994). Thompson (1998) found that preferentially selected spawning sites were located adjacent to large intertidal sand flat areas, which provide protection from wave energy and an abundance of food for juveniles. A Habitat Suitability Index model was developed for horseshoe crab spawning habitat within the Delaware Bay; however, this model is currently in draft form and has not undergone peer review, testing, or publication by the U.S. Fish and Wildlife Service (USFWS) (Brady and Schrading, 1996).

Nursery Habitat
The shoalwater and shallow water areas of bays such as the Delaware Bay and the Chesapeake Bay are essential nursery areas (Botton, 1995). Juveniles usually spend their first two years on intertidal sand flats (Rudloe, 1981). Thompson (1998) also found significant use of sand flats by juvenile horseshoe crabs in South Carolina. Salinity seems to play a role in determining which waters are suitable for juvenile development. Delaware Division of Fish and Wildlife's 16-foot bottom trawl survey data showed that over 99 percent of juvenile horseshoe crabs caught for the survey were found in waters where the salinity was greater than 5 parts per thousand (Michels, 1997). Juveniles were defined as those animals having a prosomal width of less than 160 mm.

Older juveniles will migrate out of the intertidal sand flats to deeper bay waters, where they will remain until they have developed into adults and are ready to reproduce.

Adult Habitat
Specific habitat requirements for adult horseshoe crabs are not known. Although the animals have been found at depths greater than 200 meters, Botton and Ropes (1987a) suggest that adults prefer depths of less than 30 meters. The National Marine Fisheries Service’s Northeast Fishery Center bottom trawl surveys collected 92 percent of their horseshoe crabs at these depths, even though 73 percent of the sampling effort was expended in depths greater than 27 meters. During the spawning season, adults typically inhabit bay areas adjacent to spawning beaches and feed on bivalves. In the fall, adults may remain in bay areas or migrate into the Atlantic Ocean to overwinter on the continental shelf.

Identification and Distribution of Essential Habitat
Beach areas, nearshore shallow waters, intertidal flats, and deep bay waters have all been identified as habitats that are essential to the success of the horseshoe crab as a species.

Of all these habitats, the beaches are the most critical (Shuster, 1994). Optimal spawning beaches may be a limiting reproductive factor for the horseshoe crab population. Based on geomorphology of the beaches, Botton, et al. (1992) estimated that only 10 percent of the New Jersey shore adjacent to Delaware Bay provides optimal horseshoe crab spawning habitat. The densest concentrations of horseshoe crabs in New Jersey occur on small, sandy beaches surrounded by salt marshes or bulkheaded areas (Loveland et al., 1996).

Prime spawning habitat is widely distributed throughout Maryland's Chesapeake and coastal bays and includes some tributaries. Horseshoe crabs are restricted to areas where the salinity exceeds seven parts per thousand (Maryland Department of Natural Resources, 1998). In the Chesapeake Bay, spawning habitat generally extends to the mouth of the Chester River but can occur farther north during years of above-normal salinity levels. Prime spawning beaches within the Delaware Bay consist of sand beaches between the Maurice River and the Cape May Canal in New Jersey and between Bowers Beach and Lewes in Delaware (Shuster, 1994).
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Present Condition of Habitats

Based on estimates from the 1980s, the United States has approximately 100,400 acres of marine intertidal shoreline (Frayer, 1991). However, this estimate includes marine intertidal habitat on the Pacific Coast and does not necessarily represent potential horseshoe crab spawning habitat. The southeastern United States (from North Carolina to Florida), has only 49,100 acres of marine intertidal habitat, according to an estimate from the 1980s (Hefner, et al., 1994). These values represent the maximum potential spawning habitat for horseshoe crabs. Actual spawning habitat used by horseshoe crabs is considerably less due to other selection criteria that the horseshoe crab has (see Natural History – put in a link). For example, Botton, et al. (1988) conducted beach surveys on approximately 80 kilometers of beach along the New Jersey side of the Delaware Bay. Only 10.6 percent (8.5 kilometers) provided optimal spawning habitat and only 21.1 percent (17.0 kilometers) provided suitable spawning habitat.

Studies conducted by Botton, et al. (1988), showed that only 31.7 percent of marine intertidal habitat surveyed provided optimal or suitable spawning habitat for horseshoe crabs. Viable spawning habitat throughout the Atlantic coast is probably only a fraction of total marine intertidal areas.

Loss and Degradation
Habitat degradation is likely an important component of the population dynamics of horseshoe crabs. Groins and bulkheads may adversely impact horseshoe crab spawning habitat. Bulkheads may block access to intertidal spawning beaches, while groins and seawalls intensify local shoreline erosion and prevent natural beach migration. An estimated 10 percent of the New Jersey shoreline adjacent to the Delaware Bay has been severely disturbed by shoreline protection structures (Botton, et al., 1988). Rip-rap and revetments also adversely impact horseshoe crabs by minimizing potential spawning sites and by entrapping and stranding the animals. A contributing factor in the decline of horseshoe crabs in the Delaware Bay between 1871 and 1981 may be the increased number of jetties and residential development (Shuster and Botton, 1985).

Shoreline erosion, combined with shoreline development, results in the loss of potentially suitable spawning beaches. Beach migration is a coastwide phenomenon, where beaches move landward associated with erosional events such as storms, wind, tidal action etc. However, hard structures (e.g., bulkheads, seawalls, revetments) associated with beach "development" interfere with the natural beach migration and cause habitat loss. Beaches along the New Jersey shore of the Delaware Bay have generally eroded at varying rates ranging from one to twelve feet per year for the last 100 years (U.S. Army Corps of Engineers, 1997). Erosion rates of one to twenty-six feet per year (averaging three to five feet per year) and the existence of hard structures limiting beach migration have resulted in a decline in Delaware beaches (U.S. Army Corps of Engineers, 1991). McCormick and McCormick (1998) report that the annual rate of erosion in the Chesapeake Bay averages one foot per year.

Eroded shoreline areas with high concentrations of silt or peat are less suitable for horseshoe crab reproduction because the anaerobic conditions reduce egg survivability. Erosion affects spawning by influencing the beach characteristics that are most important in site selection, such as beach topography, sediment texture, and geochemistry (Botton et al., 1988).

Current Threats
The rate at which coastal wetlands and beach areas are lost is directly related to human population density (Gosselink and Baumann, 1980). Impacts on beaches from development and related infrastructures (e.g., bulkheads, groins, revetments, and seawalls) continue to degrade essential horseshoe crab habitat. In general, erosion and shoreline protection structures (e.g., bulkheads, seawalls, revetments constructed to minimize erosion impacts) compromise the integrity of essential habitat by interfering with natural beach migration.

Jetties, however, may benefit horseshoe crab spawning activities by reducing the amount of wave action sustained by a particular beach (Maryland Department of Natural Resources, unpublished data, 1998). Beach nourishment projects, such as dune restoration and low-impact dredging, that protect developed areas and their associated infrastructure may provide habitat for horseshoe crab spawning. However, if beach nourishment projects do not keep pace with erosion in developed areas, potential horseshoe crab spawning beaches may be reduced. Ultimately, the long-term and short-term benefits and potential adverse impacts from beach nourishment projects on horseshoe crabs must be assessed.

Channel dredging and overboard spoil disposal are common throughout the Atlantic coast, but currently have unknown effects on the environment and horseshoe crab habitat. Changes in salinity as a result of dredging projects could alter horseshoe crab distribution. Additionally, dredging associated with whelk and other fisheries may damage the horseshoe crab’s benthic realm; however, the significance of this impact also remains unknown.

Global warming and the subsequent rise in sea level could adversely affect horseshoe crab spawning activities. Sea level is predicted to rise above current levels by approximately one-half to one meter by the year 2100 (Oerlemans 1989; Titus et al., 1991). Land subsidence along the Atlantic Coast adds to the effect of sea level rise, resulting in an increase greater than the global average (Hull and Titus, 1986).

Pollution has the potential to adversely impact the horseshoe crab population or its habitat. Currently, no data exist suggesting unusual sensitivity by horseshoe crabs to urban or agricultural contaminants (e.g., pesticides and herbicides) (Botton, 1995). However, mosquito control agencies in New Jersey and Delaware have recently expanded their use of the mosquito larvicide methoprene, an insect growth regulator (IGR) that mimics juvenile growth hormones. IGR insecticides have been found to adversely affect crustaceans when the animals attempt to molt, according to laboratory experiments at levels of exposure higher than field applications (Kas'yanov and Costlow, 1984). However, due to the low concentrations of IGR’s applied in the field, the low potential for bioaccumulation, its short half life, and a low probability of direct exposure to horseshoe crabs, it is unlikely that IGR’s would have any measurable adverse impact on horseshoe crabs (Meredith, pers. comm., 1998). Additional information needs to be collected to determine if there is any impact on horseshoe crabs from actual or simulated operational use under normal field conditions of mosquito larvicides applied in coastal marshes.

Horseshoe crabs are relatively tolerant of petroleum hydrocarbons, but their tolerance decreases with increasing temperature. Nelson (pers. comm., 1997) reports that high-density #6 oil resulted in adult horseshoe crab mortality in New Hampshire. However, this mortality was probably due to mechanical impairment of the horseshoe crab’s book gills by the oil and not from systemic toxicity caused by absorption of the product. Exposure to oil and chlorinated hydrocarbons resulted in delayed molting and elevated oxygen consumption in horseshoe crab eggs and juveniles (Laughlin and Neff, 1977). Maghini (1996) found trace metal and organochlorine concentrations to be relatively low in shorebird, horseshoe crab, and substrate samples from Delaware beaches and concluded that existing concentrations were of low toxicological concern. Red tide events may result in significant mortality, particularly to juveniles inhabiting intertidal areas and tidal flats (Rudloe, pers. comm., 1998).

In the Delaware Bay, Burger (1997) identified low levels of mercury (27 to 93 parts per billion) in horseshoe crab eggs between 1993 and 1995 and low cadmium levels in 1993 and 1995 (17 ppb and 24 ppb, respectively). However, relatively higher levels of cadmium were found in 1994 (310 ppb). Lead (558 to 87 ppb), chromium (5,059 to 250 ppb), and manganese (18,371 to 7,118 ppb) levels in eggs generally decreased from 1993 to 1995 in the Delaware Bay, while selenium levels (1,965 to 3,472 ppb) increased in those years (Burger, 1997). Burger (1997) concluded that the additional stress on horseshoe crab eggs from the presence of heavy metals could lower reproductive success.

Because the Delaware estuary is a major petrochemical center on the East Coast (Sharp, 1988) with an associated high level of tanker traffic, oil spills can and do occur. A large spill during the horseshoe crab spawning season could threaten populations in the Delaware Bay. In addition, mercury, lead, zinc, and cadmium may be of concern in some coastal estuaries and rivers, such as the Cohansey (New Jersey) and Saint Jones (Delaware) Rivers (Sharp, 1988). Delaware Division of Fish and Wildlife's 16-foot trawl survey data indicate that the area off the Saint Jones River is a major nursery area for horseshoe crabs.
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Who Harvests Horseshoe Crabs?

Description of the Fishery
The fishing effort for horseshoe crabs is generally concentrated within the mid-Atlantic area, specifically New Jersey, Delaware, Maryland, Virginia, and adjacent federal waters. Because no known recreational fishery for horseshoe crabs exists, fishing mortality of horseshoe crabs is predominantly from the commercial fisheries, including the bait fishery and the biomedical fishery.

Current Fishery Regulations
Current fishing regulations vary dramatically among the Atlantic coastal states . Generally, fishing regulations for horseshoe crabs are minimal to nonexistent in comparison with other fisheries. However, several states (New Hampshire, New Jersey, Delaware, Maryland, and Virginia) have recently initiated or proposed more restrictive harvest regulations. South Carolina has prohibited harvest except for the biomedical industry since 1991.

The Commercial Fishery
Between the 1850s and the 1920s, over one million horseshoe crabs were harvested annually for fertilizer and livestock feed (Shuster, 1982; Shuster and Botton, 1985). Reported harvests in the 1870s were 4 million horseshoe crabs annually, and 1.5 to 1.8 million horseshoe crabs annually between 1880s and 1920s (Finn et al., 1991). Shuster (1960) reports that in the late 1920s and early 1930s, four to five million crabs were harvested annually along the Atlantic coast. Shuster (1960) reports that over one million crabs were harvested each year during the 1940s and 500,000 to 250,000 horseshoe crabs were harvested annually in the 1950s. By the 1960s, only 42,000 horseshoe crabs were reported to be harvested annually (Finn et al., 1991). Early harvest records are suspect due to under-reporting. The period of time between 1950 and 1960 is considered the nadir of horseshoe crab abundance. The substantial commercial-scale harvesting of horseshoe crabs ceased in the 1960s (Shuster, 1996).

The Bait Fishery
Currently, horseshoe crabs are commercially harvested for use as American eel, conch (or whelk), and catfish bait along certain regions of the Atlantic coast. The horseshoe crab fishery is unique in that crabs can be easily harvested with minimal expense during their spawning season. The eel fishery is highly dependent on sustained populations of horseshoe crabs and prefers to use female horseshoe crabs with eggs. The conch fishery also is dependent on horseshoe crabs, but it uses both male and female horseshoe crabs.

Landings Data
Commercial data detailing the number or tonnage of horseshoe crabs caught ("landings" data) are collected by the National Marine Fisheries Service (NMFS) by state, year, and equipment type. Commercial landings data may include harvest totals for both the bait and biomedical fisheries. However, the NMFS data are relatively incomplete and disjointed. For example, for certain years that the NMFS reported no landings in some states, state biologists reported that landings did occur (Michels, pers. comm., 1997). In addition, the NMFS reported Maryland's harvest at 232,000 pounds in 1994 and 117,000 pounds in 1995. Based on state landings records, actual Maryland harvest was approximately one million pounds during these each of these years (O'Connell, pers. comm., 1998).

The NMFS depends on central dealers for much of its landings data, but in many cases, horseshoe crabs are harvested and used directly by eel, catfish, or whelk fishers, or arrangements are made for harvesters to sell directly to such fisheries without going through dealers. These private sales are not reported, resulting in an underestimation by the NMFS of the total catch. Based on the NMFS data, commercial harvest for the northeastern Atlantic coast has ranged between 10,000 pounds in 1969 to over five million pounds in 1996 (NMFS, 1998). Since 1988, commercial landings have averaged 1,436,808 pounds annually.

The total average horseshoe crab catch for the Atlantic Coast, assuming an adult horseshoe crab weighs four pounds, has increased from 476,515 animals in 1993 to 1,288,408 in 1996 (NMFS, 1998). This increase is similar to increases reported by Michels (unpublished data, 1997) for the Delaware Bay harvest, which ranged from 330,333 horseshoe crabs in 1993 to 896,540 in 1996. However, Michels (unpublished data, 1997) did not include the Maryland harvest, which can be substantial.

The Horseshoe Crab Technical Committee's Stock Assessment Subcommittee (SAS) and Peer Review Panel (PRP) concluded that commercial landings data show a substantial increase in reported harvest during the 1990s (see below for statistics by state). This growth is primarily a result of the increase in demand for American eel and whelk; horseshoe crabs are used as bait in these fisheries (Michels, unpublished data, 1997; NMFS, 1998; Thompson, 1998). This increase could also be, in part, a function of increased harvest reporting efficiency and the institution of mandatory reporting.

NMFS data compiled by Delaware Division of Fish and Wildlife (1997) identified that among the northeastern and mid-Atlantic states, Maryland, New Jersey, and Delaware harvest the majority of horseshoe crabs (36, 31, and 14 percent of the total annual catch, respectively). Estimates in Delaware, Maryland, New Jersey, New York, and Rhode Island indicate a rapid increase in the growth of the horseshoe crab fishery (Michels, unpublished data, 1997; NMFS, 1998; Thompson, 1998). Massachusetts, North Carolina, and Virginia indicate declines in current harvest compared with harvest in the late 1970s and early 1980s (NMFS, 1998), and little to no harvesting of horseshoe crabs was reported in Maine, New Hampshire, or Connecticut (Botton and Ropes, 1987b). The Chesapeake Bay in Maryland and Virginia likely has a substantial harvest, but without quantitative studies, the catch remains under-reported.

Maryland landings
Maryland has been responsible for 23 to 78 percent of the total annual commercial catch of horseshoe crabs from the northeastern Atlantic coast since 1980 (NMFS, 1998). Maryland averaged 357,000 pounds a year between 1981 and 1991 from a small, directed ocean fishery and from bycatch from the clam fishery. Since 1992, harvest has increased significantly in Maryland with 2.6 million pounds landed in 1996. Offshore trawlers collect the majority of these horseshoe crabs, and more than 95 percent of the harvest occurs between July and November. In 1996, nearly all of Maryland's harvest was from offshore waters; 52 percent of the total harvest was from state waters (one to three miles offshore), and 44 percent was from federal waters (more than three miles off shore). Only three percent was collected from coastal bays, and less than one percent was from the Chesapeake Bay (O'Connell, pers. comm., 1998).

New Jersey Landings
New Jersey reported an increase in horseshoe crab harvests from approximately 250,000 animals in 1993 to over 600,800 in 1996. However, due to an alarming drop in the number of adult crabs seen spawning on the beaches, a moratorium was placed on their collection for 1998 only. Currently, New Jersey allows a minimal harvest and has tight restrictions on the conditions under which a permit for harvest is issued.

Delaware Landings
The Delaware Division of Fish and Wildlife (1997) reported a six-fold increase in landings between 1990 (under 250,000 pounds) and 1997 (over 1,500,000 pounds). However, prior to 1991 little or no reporting occurred within the Delaware Bay. Thus, the increase in horseshoe crab harvest during the 1990s may be partially related to the institution of mandatory harvest reporting. In addition, the Delaware Division of Fish and Wildlife (1997) reports that more collection permits have been issued; the number of permittees increased from 18 in 1991 to 131 in 1997.

In 1997, the majority (85 percent) of horseshoe crabs in Delaware were landed by hand-harvest, while dredge harvest made up approximately 15 percent (Delaware Division of Fish and Wildlife, 1997). Between 1991 and 1996, the majority of the horseshoe crabs were landed by hand-harvest (63 percent) compared to dredging (37 percent) (Delaware Division of Fish and Wildlife, 1997). This increase in harvest mirrored the increase in the number of hand-collection permits issued (Delaware Division of Fish and Wildlife, 1997).

Virginia Landings
In Virginia, the horseshoe crab harvest averaged 190,000 pounds annually between 1980 and 1988. With a ban on trawling in state waters since 1989, horseshoe crab landings have decreased considerably, with an annual average of 22,000 pounds (Butowski, 1994); a peak of 86,294 pounds occurred in 1996 (NMFS, 1998). Demand for horseshoe crabs remains high because the demand for whelk has increased significantly; whelk landings in Virginia have increased from 75,000 pounds in 1994 to 750,000 pounds in 1995 (Petrocci, 1997).

New York Landings
Between 1996 and 1997, 406,554 horseshoe crabs were harvested for bait (NMFS,1998); in 1998, 352,462 were harvested (NMFS).

Rhode Island Landings
Although Rhode Island has been identified, along with Delaware, Maryland, and Virginia, as a "primary harvest" state, Rhode Island reported only 184 animals taken for bait between 96-97 (NMFS,1998 ). Rhode Island did not submit a harvest report to NMFS in 1998.

Dollar Value of the Bait Fishery
The reported dockside value of horseshoe crabs from the northeastern Atlantic coast has jumped from $289 (1967) to $1,541,260 (1996). Fishery statistics for the period from 1970 through 1997 indicate a variable value. As previously mentioned, fishery statistics probably underestimate the catch of horseshoe crabs because the sale of crabs for bait is often arranged between private individuals and is therefore unreported in NMFS landings statistics (Botton and Ropes 1987b).

Biomedical Fishery
In the biomedical industry, horseshoe crabs have been used in eye research, the manufacture of surgical sutures, and the development of wound dressings for burn victims. But perhaps most important is the use of a component of the horseshoe crab’s blood called Limulus Amebocyte Lysate (LAL), which is indispensable for the detection of bacterial endotoxins in drugs and intravenous devices (Hall, 1992). To manufacture LAL, the companies catch adult horseshoe crabs, collect a portion (1/3) of their blood, and then release them alive.

In 1989, the FDA reported that 130,000 horseshoe crabs were used in the biomedical industry. The current estimate of medical usage is between 200,000 and 250,000 horseshoe crabs per year on the Atlantic Coast (Swan, pers. comm., 1998; McCormick, pers. comm., 1998). The FDA mandates conservation by requiring the return of horseshoe crabs to the environment. Most labs return bled crabs to their habitat within 72 hours of capture, but may or may not release crabs at the collection site (Botton, 1995). Approximately 10 percent of the crabs do not survive the bleeding procedure, which comprises a source of mortality that is not included in the commercial catch statistics (Rudloe, 1983). Based on a tagging and controlled mortality study, Thompson (1998) reported similar post-processing mortality of horseshoe crabs (10 to 15 percent). Mortality due to the bleeding procedure may be lower (0 to 4 percent), depending on the biomedical facility (Swan, pers. comm., 1998), but the mortality associated with collection, shipping, and handling remains unknown. This mortality is minimal compared to that from the commercial bait fishery.

In South Carolina, live horseshoe crabs may be taken only for use in LAL production, and the animals are returned to their natural habitat after the procedure. Landings in South Carolina by hand-harvest and by trawl have increased since the late 1980s. The annual reported harvest in South Carolina has increased over 300 percent since reporting requirements were established in 1991 (Thompson, 1998). Presumably, this increase in harvest was driven by the biomedical industry's demand for more horseshoe crab products.

Horseshoe crabs are also used to make chitin filament for suturing (Hall, 1992). Since the mid-1950s, medical researchers have known that chitin-coated suture material reduces healing time by 35-50 percent. Currently, horseshoe crabs are harvested on a limited basis to manufacture chitin-coated suture material and chitin wound dressings (Hall, 1992).
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Biological And Environmental Impacts

If harvesting is not carefully managed, the risk of adversely affecting the horseshoe crab population becomes a certainty. Several factors that contribute to this risk includeHorseshoe crabs mature slowly, requiring nine to eleven years to attain sexual maturity (Shuster and Botton, 1985). Some bait harvesters prefer gravid females (those carrying eggs). Horseshoe crabs congregate inshore seasonally to spawn, which makes them especially vulnerable to exploitation.
Changes in abundance (increases or decreases) are not readily recognizable because they occur over a period of years (Shuster, 1996).

Population data indicate that after harvesting ceases, horseshoe crabs do not rebound for approximately one decade, which corresponds to the time required for horseshoe crabs to reach sexual maturity (Shuster, 1994).

A decline in the number of horseshoe crabs will impact other species, particularly shorebirds and sea turtles. Shorebirds primarily feed on horseshoe crab eggs exposed on the surface, but sufficient surface eggs are available only if horseshoe crabs are spawning at high densities. Therefore, adequate spawning densities must be maintained to ensure availability of horseshoe crab eggs for shorebirds. Sea turtles feed on adult horseshoe crabs, but their diet depends on relative abundance of the prey species.

Identifying and maintaining optimal sustainable yield for the commercial fishery is critical. Appropriate coast-wide management of the horseshoe crab population would ensure the long-term viability of the population for continued harvest and would provide necessary quantities of adults and eggs for fish and wildlife resources.
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Socioeconomic Impacts

Horseshoe crabs are the primary bait for the American eel and conch fisheries in many mid-Atlantic States. In Maryland, the estimated value of the horseshoe crab fishery in 1996 for 10 horseshoe crab harvesters was $398,596 (Maryland Department of Natural Resources, 1998). Also in 1996, one Maryland seafood dealer, supplying horseshoe crabs to 20 American eel and 25 conch harvesters, estimated that the value of horseshoe crabs for these fisheries was $151,200. Horseshoe crab prices vary and are reported to be between $0.65 to $0.75 per animal (Maryland Department of Natural Resources, 1998).

In 1997, American eel and conch harvesters in Delaware used an average of 4,714 and 20,502 horseshoe crabs per season per harvester, respectively. In New Jersey, American eel and conch harvesters used an average of 4,005 and 22,654 horseshoe crabs per season per harvester, respectively (Munson, 1998). Many conch and American eel harvesters in New Jersey and Delaware harvest their own bait, supplying 18 to 65 percent of their bait needs (Munson, 1998). While only nine percent of the fishing income (of respondents in the Delaware Bay Watermen's study) is attributable to the direct sale of horseshoe crabs, an average of 58 percent of the eel and conch fishing income depends on using horseshoe crabs as bait (Munson, 1998). American eel harvesters in the Delaware Bay area report that approximately 21 percent of their total fishing income is attributable to eeling, while conch harvesters report that an average of 53 percent of their total fishing income depends on the conch fishery (Munson, 1998). In 1996, the commercial harvest of horseshoe crabs was estimated to be a $1.5 million industry.

Horseshoe crabs are vital to medical research and the pharmaceutical products industry. The worldwide market for LAL is currently estimated to be approximately $50 million per year. This estimate is based on bleeding 250,000 horseshoe crabs per year, generating approximately $200 in revenue per crab for the biomedical industry. The biomedical industry either directly collects horseshoe crabs on spawning beaches or purchases horseshoe crabs for as much as $3.00 per crab. The biomedical industry pays approximately $375,000 per year for horseshoe crabs based on an estimate of 250,000 horseshoe crabs harvested at an average price of $1.50 per crab.

Eco-tourism is critical to the economies of many states, including New Jersey and Delaware, and it depends on the abundance and health of the ecosystems within the region. In 1988, over 90,000 "birders" spent $5.5 million in Cape May, New Jersey (Kerlinger and Weidner, 1991) to watch the interaction between spawning horseshoe crabs and migrating shorebirds. In 1996, approximately 606,000 people in New Jersey and Delaware took trips away from their residence (travelling more than one mile) for the primary purpose of watching wildlife. Of these people, 409,000 individuals specifically stated that they were watching shorebirds (U.S. Bureau of Census and USFWS, 1998).

In 1996, New Jersey and Delaware wildlife watchers spent between nine and 12 days per year (on average) away from home (travelling more than one mile) watching wildlife (U.S. Bureau of Census and USFWS, 1998). In New Jersey and Delaware, total expenditures, including food, lodging, transportation, and equipment in 1996 for the primary purpose of wildlife watching was $639,992,000 (USFWS, 1998). The type of wildlife watched was not identified in this survey. The 1996 regional economic impact resulting from expenditures by wildlife watchers in New Jersey and Delaware was the creation of 15,127 jobs and the generation of a total household income of $399 million (USFWS, 1998).
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