American Littoral Society Extends Horseshoe Crab Experience to Delaware

An early season pair of horseshoe crabs leaving a nest - Slaughter Beach, DE

By Trevor Metz, Littoral Society Delaware Seasonal Technician

What an exciting month! Extending the American Littoral Society’s advocacy and outreach to the great state of Delaware has been a fun-filled adventure over the past handful of weeks.

As awesome as the experiences of bearing witness to moonlight horseshoe crab spawning and paddling alongside Red Knots have been, the overwhelming feeling is that we are at a pivotal time for protecting these vulnerable coastal species.

I live in Milford, DE and only a short drive away from Slaughter Beach, one of the well-known shorebird stops along the Delaware Bayshore. The Mayor and Town Manager kindly set aside some time for me to introduce myself, explain the American Littoral Society, and talk about some of what we were planning in and around their town. I let them know about our interactive presentations, cooperative tagging efforts, and gave some insight into the Red Knot Fest that would be taking place Memorial Day weekend. 

Future conservationist demonstrates safe handling of a male horseshoe crab during low tide - Slaughter Beach, DE

​With handshakes and information exchanged, I left feeling collaborative and with a few public outreach events on the calendar.

A few times a week we (myself and whichever of my kids I could convince to come along) would head out to the DuPont Nature Center to see what shorebird species could be accounted for. A trip with Delaware Nature Society’s recently retired guru, Jim White, was especially helpful for improving my novice birding skills as well as learning more about the dynamic coastal ecosystem and some local environmental history (Did you know: the Coastal Zone Act, signed into law in 1971, was made a priority by single-term governor Russell Peterson and is responsible for maintaining the undeveloped coastal shoreline we have come to see as valuable habitat?).

With some practice I have become proficient in differentiating a wide variety of birds that convene along our coastal marshes and beaches this time of year.  

Early May is heralded as the “Return of the Red Knot” here as flocks of this mighty migratory shorebird begin their spring stopover. These birds, along with many other migratory shorebirds, have left their wintering grounds in the Southern Hemisphere with a course charted through the Atlantic Flyway, and a stop here at Delaware Bay.

It is also during this time in early May that the first horseshoe crabs begin emerging from the shallows to conduct their age-old spawning ritual during flood tides. An invaluable food supply will soon be available on Delaware Bay beaches in the form of fatty, protein-rich horseshoe crab eggs, and these birds instinctively stop to forage and refuel before continuing their journey north to their breeding grounds in Canada.

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Dunlin, Ruddy Turnstones, Red Knots, and Laughing Gulls forage around horseshoe crabs - Mispillion River, DE

Female horseshoe crabs come to the calm, gently sloping, sandy beaches of the Delaware Bay to deposit their eggs into the upper layers of beach sand.

If you have never seen horseshoe crab eggs, they are greenish BB-sized balls amassed in a cluster (imagine a cup of slightly smaller Dippin’ Dots buried together). An adult female horseshoe crab will continue spawning throughout a single high tide cycle laying multiple clutches to the tune of 20,000 eggs.

​Throughout the spring season she will continue spawning at hightides to deposit somewhere around 80,000 eggs. Multiple females spawning at the same beaches results in nests being disturbed and eggs being unearthed and made available to a litany of species. Readily available food - specifically horseshoe crab eggs - is vital to the survival and successful reproduction of vulnerable migratory shorebirds, including the Red Knot. 

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Male horseshoe crab with a forked telson.

I did my best to talk up an evening beach visit to the family, and during the new moon in early May, I got everyone out to witness the spectacle of horseshoe crabs spawning.

​Our children had a sense of eeriness and awe as they crested the dune and saw for the first time thousands of the pre-historic looking creatures clambering along the water’s edge. It was windy and cool, and they excitedly splashed along the seemingly never-ending line of horseshoe crabs being over-washed by the crashing waves. We spotted a small male crab with a forked telson and another crab that had been previously tagged.

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​Horseshoe crabs spawning during an early May new moon high tide - Slaughter Beach, DE

U.S. Fish and Wildlife Service has established a Cooperative Tagging program to help collect data from a few different marine species. For the horseshoe crab, a plastic disc-like tag is affixed to the left side of their carapace (or shell).

The tag contains a unique ID number along with a URL for anyone who comes across the crab or tag in the future to report their sighting. The information collected helps provide details about horseshoe crab biology and their behavior.

​Having never tagged a crab before, I took an opportunity to practice while crabs were spawning during a daylight high tide ensuring my form was ready to demonstrate and aid volunteers in our upcoming public tagging events.

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Trevor's first horseshoe crab tag - Slaughter Beach, DE

In cooperation with the Milford Public Library, we held an interactive talk at the Slaughter Beach pavilion in mid-May. Interested adults, families, girl scouts, and a serendipitous birder were able to engage with a live horseshoe crab, learn about their history, biology, and ecological importance, and walk along the beach to see their spawning ritual firsthand.

​Later that same week, along the same shoreline, we held our first volunteer tagging event which was attended almost entirely by Slaughter Beach residents. Interested and motivated, the group made short work of tagging 75 crabs!

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Volunteer tagged female horseshoe crab - Slaughter Beach, DE

As May winds down, the horseshoe crab spawn and shorebird migration are at their peak. A group of dedicated, conservation minded participants joined together for the Upstream Alliance’s annual Delaware Bay Expedition.

Along with collaborative discussion around protecting vulnerable species like the Red Knot and horseshoe crab, we joined together to celebrate the timeless synchronization of two world class migrations.

​The weekend was capped off with the first annual Red Knot Fest at Slaughter Beach. This family-friendly event exceeded expectations, and along with Red Knot sightings and thousands of horseshoe crabs spawning, an energized and optimistic feeling is carrying me into another month of outreach, education, and advocacy.    

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Horseshoe crabs spawning during a full moon high tide - Slaughter Beach, DE