Frank Germano, Alison Leschen

Interstate Plan Development
At its annual meeting in October 1997, the Atlantic States Marine Fisheries Commission (ASMFC) voted to develop an interstate fishery management plan for horseshoe crab (Limulus polyphemus). The Commission was concerned that horseshoe crab populations were poorly understood and that increased exploitation by fishermen and other user groups may be having an adverse impact on crab stocks, particularly in Delaware Bay. Horseshoe crabs are the preferred bait for the conch and eel pot fisheries. The biomedical industry bleeds crabs to extract a reagent in the crab's blood, Limulus Amoebocyte Lysate, or LAL, used to detect bacterial endotoxins.

On October 22, 1998, ASMFC approved and adopted the Interstate Fishery Management Plan for Horseshoe Crab (FMP). The plan required regulations to conserve and protect the horseshoe crab resource to ensure its continued role in the ecology of coastal ecosystems, while providing for its continued use over time. The FMP also required monitoring programs which included monthly reporting by harvesters of all crabs landed for bait and biomedical use by sex and harvest location.

Addendum I of the FMP, approved on February 9, 2000, required states to establish a cap on bait landings at 25% below reference period landings by May 1, 2000. Reference period landings were based upon reported landings between 1995 and 1997. States like Massachusetts which did not have mandatory reporting prior to 1998 were allowed to use 1998 or 1999 harvest data. Massachusetts 1998 landings were based upon anecdotal information from bait dealers and were not used as reference period landings. In 1999, MarineFisheries required crab harvesters to submit monthly catch reports, but we believe 1999 landings (545,715) were inflated in an effort to obtain high quota. MarineFisheries reduced this number and submitted a 1999 harvest figure of 440,503 horseshoe crabs to ASMFC that was then used to establish the Massachusetts annual quota was established at 330,377 crabs.

Horseshoe Crab Management in MA
MarineFisheries currently issues two types of horseshoe crab harvest permits, bait and biomedical. The bait permit allows the harvester to take crabs for bait or to sell to one of two New Bedford dealers, Dockside Fisheries or Haggerty Fisheries (formerly Coldwater Crab). The dealer may sell crabs for bait to another dealer or to the sole biomedical company, Associates of Cape Cod (ACC). Crabs sold to the biomedical company are returned to the dealer after being bled and are resold as bait. The biomedical harvest permit allows harvest for biomedical use only with the understanding that the harvester will return crabs to the place of harvest after crabs are bled. Crabs can not be sold to other bait dealers or used as bait when harvested under the authority of a biomedical harvest permit.

Horseshoe crabs harvested with a biomedical permit are not counted towards the quota because the crabs are returned to the water and bled crabs have a low bleeding mortality rate (~10-15%). Studies conducted by ACC indicate that horseshoe crab's blood cell count returns to normal levels in about two to three months after being returned to the water, allowing them to be harvested year after year. Theoretically, crabs could be bled several times a year, but ACC bleeds individual crabs only once per year.

Horseshoe Crab Bait Fishery
Horseshoe crabs are the preferred bait used by pot fishermen targeting whelk (Busycon canaliculatum) and eel (Anguilla rostrata). As a result of increasing cost for horseshoe crabs for bait, a number of Cape and Island conch fishermen used fine mesh lobster bait bags in their conch pots that allowed fishermen to use smaller pieces of crab as well as to mix other baits such as mussels, scallops and fish in the bags as sweeteners. A Virginia Institute of Marine Science study concluded that bait bags significantly reduced the amount of crab required in a pot without reducing catch. In an effort to further reduce numbers of horseshoe crabs needed for bait, the American Bird Conservancy, Massachusetts bait dealers and MarineFisheries began distributing bait bags supplied by the Delaware-based Ecological Research and Development Group Inc. (ERDG) free to conch fishermen in 2001. A 2002 survey of Massachusetts conch fishermen indicated that 82% used some form of bait bags (See MarineFisheries 2003 Compliance Report to ASMFC).

As the fishery progressed from unregulated to regulated with a management plan that includes requirements to report harvest levels, the Commonwealth's harvest went from 400,000 crabs in 1998 to about 138,600 in 2002.

Many Buzzard Bay conch pot fishermen originally opposed bait bags because they believed it caused bait to spoil to quickly. In 2003, some fishermen began using bait cups and modified containers instead of bait bags. Unlike bait bags, the cups allowed bait to be raised off the bottom of the pot. Fishermen found that the small size of the cup and because the crab didn't wash out, smaller pieces of bait could be used and lasted longer than staked baits.

A 2005 survey showed that nearly all fishermen (97%) use some form of bait bag or cup. Fishermen report that bait cups allowed them to bait as many as six to ten pots with a single crab instead of the two to three pots when crabs were staked, with no decrease in conch catch rate. Introduction of bait bags in 2001 and cups in 2004 have significantly reduced bait harvest to well below the ASMFC Massachusetts quota of 330,377 horseshoe crabs (Figure 1).

In June 2006, ASMFC adopted Addendum IV to the FMP, which with voluntary reductions in landings by Delaware Bay states, greatly reduced supply of out-of-state crabs available to Massachusetts dealers. In previous years, Massachusetts dealers imported about 70,000 crabs annually from dealers in Delaware Bay states. Loss of out-of-state crabs resulted in the Massachusetts harvest more than doubling to 171,646 crabs in 2006 (Figure 1).

Figure 1. Massachusetts Horseshoe Crab Bait Landings 1998-2006.

Pleasant Bay
Increased harvest of horseshoe crabs has been most noticeable in Pleasant Bay on Cape Cod. The eastern shore of the Bay, which falls within the National Seashore, has been closed to bait harvest since 2000. Despite this closure, bait harvest from the rest of Pleasant Bay increased substantially from 194 crabs in 2001 to more than 41,000 crabs in May and June 2006 (Figure 2). Based upon dealer information, horseshoe crabs in 2006 were valued at $1.62 each as bait, resulting in a total ex-vessel value of $61,560 for the Pleasant Bay bait fishery

Figure 2. Pleasant Bay Horseshoe Crab Bait Landings 2001-2006

The National Seashore closure has been limited in its effect on total harvest because crabs move freely in and out of the protected area, thus leaving them vulnerable to harvest most of the year. Two additional qualities of Pleasant Bay may exacerbate the increase in landings. First, a large number of horseshoe crabs appear to remain in the Pleasant Bay/Little Pleasant Bay system year round. By contrast, in other coastal embayments, the crabs enter shallow water areas during the May - June spawning season but then move to nearby deeper water offshore after spawning. Second, shallow depths and the tendency of crabs to congregate in channels of the Bay make high densities of this local population of crabs more easily accessible to year-round harvest. These factors combine to make Pleasant Bay vulnerable to overharvest.

Based upon concerns that bait harvest in the Pleasant Bay Complex had reached a level that may not be sustainable, on July 14, 2006, MarineFisheries , with approval of the Marine Fisheries Advisory Commission, placed an emergency mid-season closure on bait harvest. The closure included the waters of Pleasant Bay, Little Pleasant Bay, Chatham Harbor (North), Pochet Creek, Round Cove, Bassing Harbor, Ryders Cove, Crows Pond, Frostfish Creek, Muddy Creek, Quanset Pond, Namequoit River, Meetinghouse Pond, Kescayogansett Pond and Paw Wah Pond (Figure 3).

Figure 3. Map showing the Pleasant Bay Complex Area  closed indefinitely to horseshoe crab bait harvest as of May 1, 2007; closure was first enacted temporarily in 2006

The area was kept open for biomedical harvest. The Pleasant Bay system is the only area in the Commonwealth where biomedical harvest of crabs currently occurs. Approximately 50% of crabs used by the biomedical company are harvested by biomedical crab harvesters. The remaining 50% are purchased from bait dealers. The biomedical harvest was allowed to continue, because unlike bait harvest which has a 100% mortality rate, crabs harvested under biomedical permits are returned to the water at the harvest location with 48 hours after being bled.

The sole biomedical company, Associates of Cape Cod, and the biomedical crab harvesters are concerned that the current crab population has diminished to a point were it has become difficult to find enough adult horseshoe crabs to meet needs of the biomedical company. ACC is concerned that if bait harvest is allowed to continue unrestricted, lack of horseshoe crabs in Pleasant Bay could have a significant adverse impact on biomedical operations.

Some crab bait harvesters have objected to the bait harvest closure alleging presence of ample crabs in Pleasant Bay. They cited a report by Dr. Ruth Carmichael for the Friends of Pleasant Bay that estimated the population of adult horseshoe crabs in the Pleasant Bay Complex to be 500,000 + 27% (Carmichael et al. 2003). Some fishermen have reasoned that since 2001, a large number of juvenile crabs (estimated to be 13,500,000 during the 2001 spawning season) should have matured into adult crabs increasing the Bay Complex population to several million crabs. However, the 2001 estimate of 13.5 million juvenile crabs in the Bay includes every stage from newly hatched triblobite larvae to 14th instar (age 6.6 yr). There is a cumulative mortality of 99+% associated with this time period. An additional 22% of surviving crabs are estimated to die between the last juvenile instar (14th) and first adult instar. So only a tiny fraction of those 13.5 million juveniles enter the adult population each year. Carmichael et al. (2003) and Grady and Valiela (2006) both conclude that the Pleasant Bay population is close to stable stage distribution; in other words, the proportion of each size category doesn't change over time (barring an outside force such as harvest or disease). So rather than seeing an increase in the adult population since the 2001 survey was done, we would expect the current population to remain unchanged.

If this assumption is true, then the current adult population of PB is about 500,000 crabs. However, of those crabs, only about 140,000 are spawning females, which dominate the population dynamics. Grady and Valiela (2006) found through modeling that a sustainable harvest level for the population is 5%, a level not atypical for animals that mature slowly (horseshoe crab females do not reach sexual maturity until age 11). Grady recommends focusing harvest on larger females (>220-240mm) because the modeled population was much less sensitive to mortality in this size range than to smaller adults or large juveniles. To a large extent the industry is already doing this, as both the bait and biomedical harvesters prefer larger females (in 2006, 76% of the females harvested from PB were >240 mm and 96% were >220 mm). However, biomedical harvesters noted that ACC has had to reduce the minimum size of crabs they will accept, claiming that all large crabs have been harvested. Pressure on ACC to accept smaller crabs due to a lack of large ones could shift harvest to small adults, the most important sector for maintaining population levels.

All sustainable harvest levels were greatly exceeded by the 2006 harvest of 20,000 female crabs (Table 1), concluding that pre-closure bait harvest levels are not sustainable.

Table 1. Sustainable harvest levels of adult female horseshoe crabs, total and for given size ranges.

Estimated mortality from biomedical harvest of horseshoe crabs in Pleasant Bay falls within range of the maximum sustainable harvest for this complex, particularly since the majority of this harvest occurs in the larger size categories (sustainable yield 2,685-5,510 crabs). If the bait fishery is allowed to resume in Pleasant Bay, harvest levels would be pushed to unsustainable levels, thus threatening future population levels in that embayment. We therefore recommend that bait harvest in the Pleasant Bay Complex be kept closed, and the fishery restricted to biomedical harvest.