Delaware Bay is home to the world’s largest population of horseshoe crabs worldwide. As a result, each year the Delaware Bay is also host to the second largest population of migrating shorebirds in North America.
Birds including sanderlings, sandpipers, red knots, ruddy turnstones and others arrive from South America to this area late May and use it as resting and feeding grounds. Over 10 to 14 days, migrating birds gain up to 50% of their body weight in fat primarily by feasting on horseshoe crab eggs. The new body fat helps fuel the birds for the next part of their journey northward to breeding grounds in the Arctic, a flight which may include non-stop distances as long as 3,000 miles. Researchers have found 1/3 of the total number of sanderlings that live in the western hemisphere on the beaches of Cape May and up to 70% of the North America red knots on the shores of the Delaware Bay on a single day.
The horseshoe crabs are critical for sustaining this natural phenomenon and the ecotourism industry that has built up around it. In 1988 an estimated $34 million was spent by bird watchers in the Cape May area alone. Because much of these expenditures occur in the off-season, it is particularly valuable to the local economy. The horseshoe crabs are also critical to the health care industry providing blood that is collected non-lethally from adult crabs for the biomedical industry.
Last year about 280,000 crabs were taken from NJ’s spawning beaches alone. Studies are showing a marked decline in both the horseshoe crab populations and in shorebird populations they sustain. Delaware trawl data has shown a 75% decline in the number of horseshoe crabs in 11 years. NJ DEP research shows a statistically significant decline in the number of horseshoe crab eggs available to shorebirds from 2000 to 2002. And data from the NJ Department of Environmental Protection (NJ DEP) conclusively links the rapid disappearance of Red Knot, a state threatened species, and other shorebird species to the overharvest of horseshoe crabs.
Key Shorebird and Horseshoe Crab Facts
1. Nine species of shorebirds, including the state threatened Red Knot, feed on horseshoe crab eggs on Delaware Bay Beaches during their spring migration. The egg-rich diet is needed to gain sufficient weight to migrate north to their Arctic breeding grounds.
2. Shorebirds rely on a superabundance of reproductive age class horseshoe crabs to produce and excavate enough eggs for this weight gain.
3. There has been a precipitous decline in the number of wintering Red Knots in Tierra del Fuego, South America. In 2002, researchers counted 22,172 Red Knots; this is a 25% decline from the 2001 count of 29,745 and a 51% decline since 2000 (45,705 individuals).
4. Many shorebird species have shown a steady population decline on the Delaware Bayshore. The number of Red Knots counted on the Delaware Bay decreased by 12.0% from 2001 to 2002.
5. Delaware survey trawl data shows a 75% decline in horseshoe crabs in 11 years. This is consistent with horseshoe crab egg counts on the Delaware Bay which also show an alarming decline in the amount of eggs available to foraging shorebirds.
6. Horseshoe crabs are a long-lived species, not reaching sexual maturation until 9 years of age. Adult crabs are harvested as bait for eel and conk.
7. Harvesting is allowed to occur even though no stock assessment has been completed for this species. We are harvesting in the absence of sound science.
8. Studies show daily weight gains of Red Knot and Semipalmated Sandpipers have dropped precipitously. The disappearance of horseshoe crabs is the culprit. In fact, many birds leave the Delaware Bay without enough fat reserves to reach the Arctic breeding grounds.
9. The non-lethal ecotourism and biomedical industries out value the fisheries 6 to 1.
a. A report to the NJ Department of Environmental Protection valued the 1998 Delaware Bay ecotourism at $34 million.
b. Horseshoe crabs blood is also collected non-lethally from adult crabs for the biomedical industry. The US Fish & Wildlife Service values this industry as providing $150 million per year.
c. The US Fish & Wildlife Service similarly values the Horseshoe Crab fishery at $11 million per year, and eel and conk fisheries which use the crab as bait at $21 million per year.
To Take Action to Help the Horseshoe Crabs check out our Action Alerts Page or Horseshoe Crab Activities Page