Why Should Delaware Care?
Overharvesting once threatened the horseshoe crab population, which is a staple to the Delaware Bay’s ecosystem. But state protections put in place over 20 years ago appear to be helping Delaware’s “living fossil” rebound.
On a windy night in mid-May, about a dozen volunteers gathered at the James Farm Ecological Preserve near Ocean View, wielding charts, thermometers and a white square made of PVC pipe.
The volunteers placed the plastic square on sections of the beach, then counted the number of male and female horseshoe crabs inside of it.
“I like seeing the surprise on everyone’s faces when they see how many there are,” said Lorie Whitehaus, a team lead on the survey.
The scene was part of a statewide effort to monitor the horseshoe crab population in Delaware, run jointly by the Delaware Department of Natural Resources and Environmental Control, and by the Center for the Inland Bays.
And these counts recently have sparked optimism among marine biologists about the 450 million-year-old species, often referred to as “living fossils” because they are one of the oldest living species on the planet, dating back to about 100 million years before dinosaurs appeared.
The Delaware Bay’s horseshoe crab population is close to reaching its historic population, said Jordan Zimmerman, a horseshoe crab biologist for the state of Delaware.
The bay hosts the world’s highest concentration of the species. They also remain a key part of the local estuary ecosystem. But the number of horseshoe crabs in the Delaware bay dipped drastically in the 1990s due to overharvesting.
In response, Delaware and neighboring states imposed restrictions about 30 years ago on harvesting the arthropods. The population has now almost reached its 1990 levels, Zimmerman said.
The rebound marks a rare success story in environmental management.
“We don’t get too many of those,” Zimmerman said. “It’s very difficult to manage natural resources.”
DNREC monitors commercial horseshoe crab fishing through a mandatory reporting system and check stations. There is a cap on the number of male horseshoe crabs that can be harvested. It is illegal to catch and keep females.
How to find a horseshoe crab
The best places to view horseshoe crabs are during high tide at the DuPont Nature Center (from the observation deck or the live cam), Slaughter Beach, Kitts Hummock or Pickering Beach, near the Town of Little Creek, according to DNREC.
Blood harvesting affected population
The drop in the horseshoe crab population happened for two main reasons: fishermen harvested them to be used as bait, and biomedical companies harvested them for their blood.
In the 1960s, scientists discovered horseshoe crab blood contains an extract called limulus amebocyte lysate, or LAL, which clots in the presence of pathogens.
This substance helps scientists detect bacteria and toxins in virtually every drug, making horseshoe crab blood one of the most valuable liquids in the world. LAL can sell for up to $60,000 a gallon.
Scientists collect the blood without killing the animal and return them to the ocean, although studies suggest about 15% of crabs die during the process.
Still, Zimmerman said it is hard to know if that number is accurate because the horseshoe crabs are treated differently in the studies than in the actual blood collection process.
“If we want to get an idea of the industry impacts on them, then we need to use crabs that are handled the exact same way,” he said.
Scientists have also developed a synthetic alternative to the LAL in horseshoe crab blood, which may decrease the need to harvest them.
Last year, the U.S. Pharmacopeia, which helps to ensure drug quality, determined the synthetic alternative is just as effective at detecting pathogens as the extracted material from horseshoe crab blood.
A volunteer effort
Every full or new moon in the horseshoe crabs’ peak mating season of May and June, volunteers go out whenever the tide peaks at night — whether that be 7 p.m. or midnight.
The volunteers often find the beaches covered in dozens or even hundreds of horseshoe crabs.
“There’s nothing that can replace the experience of seeing them in the wild,” said Nivette Pérez-Pérez, manager of community science at the Center for Inland Bays.
People come from all over the country to volunteer, Zimmerman said, hoping to experience the unique phenomenon for themselves.
Center for the Inland Bays volunteer Cathy Hutchins said some people don’t like having horseshoe crabs on their beaches, especially during the surge of mating season.
“But I know if you don’t have them, you’re not going to have the birds,” Hutchins said.
Female horseshoe crabs lay about 80,000 eggs per year, Pérez-Pérez said, providing an important food source for migratory shore birds like red knots or sanderlings.
While the horseshoe crab population is increasing, other factors like climate change, pollution and coastal development could threaten their numbers in the future, Pérez-Pérez said.
The nonprofit Center for Biological Diversity recently filed a lawsuit against the Trump administration for failing to classify horseshoe crabs as a threatened or endangered species.
Pérez-Pérez said the main way people can help horseshoe crabs is by flipping them over if they are on their backs. Many die when they are unable to flip themselves over and become stranded on the beach at low tide.
The best way to flip them over is by grabbing the edge of their shells, not by their tails, she said.
