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Red Knot and Horseshoe Crabs

Monitoring Horseshoe Crabs, Tagging, and Rescues

Update: February 2024:

Delaware Riverkeeper Network joined Center for Biological Diversity and over 20 conservation allies to draft and submit a petition to urge the US Commerce Dept to list the American Horseshoe Crab as threatened or endangered under the federal Endangered Species Act. Horseshoe crab populations crashed due to overharvesting for bait many years ago, and have not recovered to their historic numbers despite efforts underway by conservation groups.  As a keystone species to the Delaware Bay their continued decline is extremely worrisome cuasing cascading impacts to the flor and fauana of the Delaware Bay and beyond.  Their habitat is rapidly disappearing, they continue to be overharvested for both bait and blood, and their spawning beaches are threatened by development, erosion, pollution, and climate change.

Listing American horseshoe crabs under the Endangered Species Act would provide many important protections to this species and their habitats. This horseshoe crab petition will also initiate a federal review of the species that could provide important data, research, funding, and oversight of ASMFC and state management agencies who continue to attempt to eat away at long hard protections that are science based and essential for the horseshoe crab.  Please stay tuned to this important petition effort and we will update you when it is time to write in letters to support this initial petition.


Delaware Riverkeeper Network will be out along the Bay this coming May and June for horseshoe crab monitoring work.  If you would like to possibly join us in this community science based  volunteer monitoring and tagging effort that we have been a part of each year for over two decades on the New Jersey and Delaware beaches, please contact

For decades, the Delaware Riverkeeper Network along with our colleagues from around the region, country and world have struggled to protect the horseshoe crabs of Delaware Bay from their continuing decline and to protect the shorebirds dependent upon them from going extinct as a result of that decline. In 2010 we had a huge success.  New Jersey passed a moratorium on the harvest of horseshoe crabs until such time as the birds dependent upon them could be deemed to have recovered.  

The Delaware Bay is critical habitat to more than 400 species of birds and migrating shorebirds. In fact, the Delaware Bay “is one of the most important stopover sites in North America for long distance migratory shorebirds.”  Each spring, at least 11 species of birds, including the red knot rufa, stop over on the Delaware Bayshore to feed on the eggs of the horseshoe crab and thereby fuel their annual spring migration. 

Available scientific studies clearly indicate large declines in shorebirds that is directly linked to decreasing shorebird weights and their decreased ability to feed themselves with horseshoe crabs eggs when they arrive along Delaware Bay beaches during their spring migration. Horseshoe crab numbers are at historic lows, resulting in low abundance and availability of horseshoe crab eggs for migratory shorebirds. As horseshoe crabs take 7-10 years to mature, we have a long way to go before historic densities of eggs will once again be found on the beaches of the Delaware Bay. The horseshoe crabs are not only vital for the shorebirds, but they currently provide an irreplaceable substance necessary for testing vaccinations and medical devices to ensure they are safe for human use.  Efforts continue to advocate the biomedical industry replaces this horseshoe crab use of blood with artificial alternatives that have been developed to further take pressure off of the struggling horseshoe crab populations.    

Peak counts of red knots on the Delaware Bay stopover have declined by 70% since 1998. Other shorebirds that rely on horseshoe crab eggs, such as ruddy turnstone, semipalmated sandpiper, sanderling, dunlin and short-billed dowitcher have also declined in number on the Delaware Bay migratory stopover. These species, together with red knots, make up 99 percent of the shorebird concentration in the Delaware Bay. All are dependent upon horseshoe crab eggs for all or most of their diet during the stopover, and all have significantly declined in population.  Sea turtles and other animals also feast on horseshoe crab eggs. 

Much of the recreation and culture of the New Jersey Bayshore is linked to the spawning of the horseshoe crabs and the annual arrival of the migratory shorebirds, including the red knot. The arrival, feasting and migration of the shorebirds supports a multi-million dollar ecotourism industry. Birding and outdoor enthusiasts from all over the world flock to the Delaware Bay shore to watch the spectacular feeding frenzy. During their visits, they buy recreation-related goods and services, stay in the region’s hotels, visit parks and patronize restaurants and local shops. According to one report, horseshoe crab-dependent ecotourism generates between approximately $7 million and $10 million of annual spending in Cape May, New Jersey alone, and creates 120 to 180 related jobs, providing an additional $3 million to $4 million in social welfare value.  According to a New Jersey Department of Fish and Wildlife report, the economic value of the horseshoe crab and migratory bird phenomenon seasonally for the Delaware Bay shore area is over $11.8 million with over $15 million of economic value generated if other beneficiaries beyond New Jersey are included. Annually, it provides $25 million in benefits to the Delaware Bay shore region and $34 million regionally. Because most of these expenditures occur in the “off-season”, they are particularly valuable to local economies. 

The continuing existence of the horseshoe crab and migrating shorebird phenomenon is vital for the related ecotourism industry. Of those surveyed, only 6.6% said that the horseshoe crab and shorebird phenomenon was unimportant to their visitor satisfaction. On average those surveyed said they would be willing to pay as much as $212.45 (in decreased annual household income) annually for a program to protect these resources; and that they would “be willing to tolerate no more than 50.7% decline in Horseshoe Crabs and migratory shorebirds before they would cease visiting the Delaware Bay shore area.” 

About the Petition

In 2005, the Delaware Riverkeeper Network led the creation and submission of a petition to the U.S. Fish and Wildlife Service (USFWS) to list the red knot (Caladris canutus rufa) as an endangered species under the Endangered Species Act.  The USFWS finally on September 30, 2013 took steps to list the Red Knot as “Threatened” under the Endangered Species Act in response to our petition.  Delaware Riverkeeper Network continued to push for “Endangered” listing through the public comment process that ended June 2014 to urge for elevation of protections.   A final USFWS listing rule of “Threatened” for the red knot was published December 11, 2014, with an effective date of January 12, 2015, triggering the full Section 7 consultation requirements of the Endangered Species Act. 

Delaware Riverkeeper Network continues to advocate, collaborate, and assist with monitoring  and tagging projects and stakeholder groups for the protection of the horseshoe crabs and shorebirds as threats emerge and continue for these essential animals that are keystone species to the Delaware Bay.   DRN currently sits on a stakeholder group as part of enforcement of the ESA and Published Biological Opinion (PBO) on the Effects of Existing and Expanded Structural Aquaculture of Native Bivalves in the Delaware Bay to watchdog the impacts that oyster aquaculture farming activities could have on red knots and the horseshoe crabs as this farming footprint operates and continues to seek to expand in the Delaware Bay

View a video from May 2014 showing horseshoe crab tagging with the Delaware Riverkeeper Network and efforts for volunteers to take part in citizen science to help the crabs and shorebirds.