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Maryland Coastal Bays Program crab survey

By Morgan Pilz, Staff Writer

In the coming weeks, visitors to Maryland’s coastal bays and beaches can experience one of the world’s oldest migrations – horseshoe crabs emerging to spawn, as they’ve done for the last 350 million years.

(May 30, 2019) From mid-May to early July, the Maryland Coastal Bays Program and the Maryland Natural Resources Fishing and Boating Services will conduct its annual survey of the horseshoe crab population.

Horseshoe crabs are not crabs as the name would imply, but are most closely related to spiders and scorpions than they are crustaceans such as crabs and shrimp.

Having been around since well before dinosaurs roamed the planet, horseshoe crabs are frequently referred to as living fossils, which isn’t exactly true. Fossils are the preserved remains of a once-living organism, while horse horseshoe crabs continue to wander on their underwater mission to eat, live and procreate.

And in one of the oldest migrations of its kind, horseshoe crabs have been wandering up to coastal beaches for the last 350 million years to do the latter.

“The reason we do this survey is horseshoe crabs are managed for a variety of reasons,” said coastal fishery biologist Steve Doctor of the Department of Natural Resources. “They have a lot of ecological value; they provide food for migrating shore birds and also a lot of fish species.

“Overall, the survey is an indication of quality and quantity of horseshoe crabs spawning in the coastal bays,” Doctor added. “That information is also passed along to the Atlantic State Marine Fisheries Council, which also overlooks the Delaware bay population.”

The greatest number of horseshoe crabs can be found on Maryland beaches during the full moon, June 17 and July 16 and new moons, June 3 and July 2.

During the 2018 spawning survey results, 41 surveys were conducted at five beach sites and produced a total count of 22,140 horseshoe crabs, Doctor said. Those sites included Assateague Island, Skimmer Island, the Oceanic Motel, Gudlesky Park and Sunset Island.

While horseshoe crabs have ecological value, they also have a medicinal value that has risen to global significance in recent years, since their blood reacts to certain infectious bacteria such as E. coli, Legionella and Salmonella and others that are referred to as “gram-negative bacteria.”

“Their blood is very sensitive to gram-negative bacteria,” Doctor said. “It’s used for a test in biomedical applications to test for gram-negative bacteria in human products. It’s a worldwide test now; it used to be national. Anything that has to go through a human has to go through this test first.”

Medicinal breakthroughs such as vaccines, life-altering surgeries, and injections are possible due to the gram-negative bacteria in horseshoe crab blood. The blood is used to test the sterility of medical equipment and injections.

During the full or new moon, when the tide is at its highest, thousands of horseshoe crabs will overtake the beaches to lay and fertilize eggs.

Thousands of eggs will be laid during peak spawning periods. During this time, many eggs end up as food for shorebirds, Doctor said.

Horseshoe crabs are often used as bait or fertilizer, which was a contributor to the species’ drastic decline from 1998 to 2003, according to Doctor.

The Maryland Coastal Bays Program and Maryland Department of Natural Resources Fishing and Boating Services conducted the first horseshoe crab spawning survey in 2002, after unregulated horseshoe crab harvesting led to a significant drop in the population.

However, the population has increased dramatically. The most recent stock assessment has indicated that the population is stable in the Delaware Bay area, including the Maryland Coastal Bays.

“We expect to see close to the same number of crabs as last year,” Doctor said.

While horseshoe crabs may appear menacing with their large exoskeleton and tails, they are harmless and gentle creatures, especially if they are left stuck on their backs.

To help ensure the survival of the species, anyone who spots a horseshoe crab on its back is asked to gently flip the crab over so it can return to the water. The best practice for flipping over a horseshoe crab is to pick it up by its sides using two hands, never by its tail, according to a Maryland Department of Natural Resources press release.

To learn more about the horseshoe crab migration, contact Doctor at or call 410-213-1531.