Inland Bays display hearty but small horseshoe crab population

By Noah Zucker
Posted 3/21/21

The Delaware Bay may be the most famous horseshoe crab destination in the state, but it’s not the only one. Delaware’s Inland Bays are another important breeding ground for the species.

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Inland Bays display hearty but small horseshoe crab population

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The Delaware Bay may be the most famous horseshoe crab destination in the state, but it’s not the only one. Delaware’s Inland Bays are another important breeding ground for the species.

The nonprofit Delaware Center for the Inland Bays has been studying the horseshoe crab population in its area of focus for decades and released new data on the topic Wednesday.

“There’s actually been about a 90% decline in the horseshoe crab population since 1990,” said Dr. Marianne Walch, the organization’s science and restoration coordinator.

The horseshoe crab population in the Inland Bays has remained small but resilient in recent years, after decades of pollution and overharvesting decimated those waterways.

DCIB would like to help it recoup.

“Our mission is to protect and restore the Inland Bays,” said Chris Bason, the organization’s executive director. “One of the important parts of that job is to track the health of the bays over time and our progress on our restoration.”

A key metric in assessing that, he said, is the size and composition of the bays’ seasonal horseshoe crab populations.

“We have five years of data,” from 2015 to 2020, he said Wednesday. “This is the first time we’ll be presenting the data on this environmental indicator.”

Dr. Walch described the population’s size as steady.

“Over the last few years, there have been some ups and downs, but the numbers are really not declining or increasing. But they are still quite low,” she said. “Decades ago, there were certainly far more horseshoe crabs in the Inland Bays than there are currently.”

There is unfettered good news, too, though.

“The density of crabs we see spawning on Inland Bays beaches really approached the densities that are seen at Delaware Bay beaches,” Dr. Walch said. “The Delaware Bay is known for its dense spawning.”

At present, the organization has six survey sites around Sussex County’s Rehoboth and Indian River bays. The beaches at James Pond and Tower Road, two of the sites, have particularly high spawning densities, Dr. Walch said.

She also provided some information about DCIB’s tagging program, which Dennis Bartow, the organization’s senior naturalist, works on.

“We have found our tags as far north as Groton, Connecticut, and as far south as South Carolina,” he said. “I think they get caught up in the currents.”

Mr. Bartow plays a key leadership role in carrying out the survey on the beaches. The self-trained naturalist said the crabs are nothing to fear, even if they do look a bit strange to those unfamiliar.

“They can’t sting. They can’t bite,” he said. “You can put your finger right down in its mouth, and it feels like the soft palate of your mouth. They don’t have jaws that bite.”

Mr. Bartow said he even had a volunteer stick his nose into a crab’s mouth. Although he said this was probably unwise, the volunteer ended up being fine.

Dr. Walch did note that it’s possible to get pinched by the crab’s tail, which is a lever it uses to navigate.

“If you’ve lived in the Delaware area for any amount of time, you know that every May and June, around the full and new moons at night, … tens of thousands of horseshoe crabs gather to mate and to lay their eggs in the sand,” she said.

“This is not just an amazing event to watch,” she said. “(But) these ancient animals actually play a key ecological role in inland bays up and down the coast. They lay billions of these tiny green eggs on the beaches each spring, and these eggs provide a critical food and energy source for the shorebirds that migrate along the Atlantic Flyway, including the endangered red knot.”

They’re also commercially significant.

“They are harvested commercially, primarily as bait for the conch and American eel fisheries,” Dr. Walch said. “Then, their unique blue blood is harvested to use in biomedical applications. It has a particular compound that clots in the presence of (some) bacteria, so that component of their blood can be used to test pharmaceuticals, vaccines, medical devices and so forth for contamination.”

She said that the “important commercial interest has led, over decades, to overharvesting,” which was compounded by many years of pollution.

“That led, in the late ‘90s, to an interstate management plan being developed by the Atlantic States Marine Fisheries Commission,” Dr. Walch said. “That plan now regulates the harvest.”

Mr. Bartow said harvesters, who need a permit from the state, are allowed to take 162,000 crabs each season. Dr. Walch added that only males can be taken, given that it’s important to keep the number of females as high as possible.

One spectator at the presentation Wednesday added that the construction of homes along the Inland Bays has minimized the amount of unaltered beach on which the crabs can spawn.

“We see a lot of our natural shorelines disappearing with all the developments occurring,” Dr. Walch said. “That’s why we’re so keen on promoting the use of living shorelines and nature-based methods as a way to stabilize shorelines as an alternative to bulkheads.”

DCIB’s survey efforts have traditionally been staffed by volunteers, with the exception of 2020, due to the pandemic. Anyone interested should fill out a volunteer application here.

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