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Delaware's horseshoe crab population is growing

Horseshoe Crab Slaughter Beach
Quinn Kirkpatrick
/
Delaware Public Media

Horseshoe crabs are living fossils, existing nearly unchanged for at least 445 million years, and much of that time has been spent in the Delaware Bay.

The Delaware Bay’s stable environment with proper salinity and tidal ranges, and limited erosion, is perfect for spawning horseshoe crabs.

Horseshoe crabs visit the First State beaches each year to lay eggs, offering a food source for migratory birds - including the red knot, which feeds on the eggs as it travels thousands of miles to the Arctic.

Red knots are considered threatened species under the Endangered Species Act, and in the State of Delaware they are listed as endangered. David Saveikis, Director of the DNREC Division of Fish and Wildlife, says that DNREC is doing everything they can to help.

“Our responsibility, and one thing we can control, is making sure that horseshoe crabs remain and expand their population to provide the eggs on that critical stopover phase in their life cycle,” said Saveikis.

Before horseshoe crabs were managed in a sustainable manner under the Atlantic States Marine Fisheries Commission Adaptive Resource Management framework, their population plummeted, affecting the lives of several migratory bird species.

But DNREC reports the Delaware Bay horseshoe crab population rose to 31.3 million crabs this year. That’s good news for not only migratory shore birds that feed on their eggs, but also the biomedical industry, and the commercial conch fishery.

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Saveikis says while horseshoe crabs are allowed to be harvested, it's carefully monitored by DNREC.

“It’s an important bait in the commercial conch fishery that is done in pots out in Delaware Bay. And there is a limited harvest season. And the harvesters have to report daily their catch to us. And we do have our Natural Resource Police monitoring to ensure compliance,” explained Saveikis. “And once that 162,136 male-only harvest quota is reached, then the season is closed.”

The 162,136 crabs represent less than 1% of the scientifically-estimated total Delaware Bay horseshoe crab population, but is an increase from just over 159,211 in 2019.

Harvesting is not allowed in Delaware until June 8 after migrating shorebirds depart, helping avoid disturbances to their period of feeding and rest during migration.

And while Delaware does not have a horseshoe crab biomedical collection fishery, other states like New Jersey do. Horseshoe crabs are harvested for their blood, which has a rare component that is not found anywhere else in the world.

Saveikis says what makes horseshoe crab blood so unique is the fact that it doesn’t contain white blood cells, it contains amoebocytes.

“That blood is very important in the pharmaceutical testing of vaccines and drugs,” Savekis emphasized. “Essentially, horseshoe crab blood is unique in that its components will, if a vaccine or a drug is contaminated, it will congeal when the horseshoe crab blood is added and that will indicate that it is an unsafe product to release.”

While the biomedical industry conducts a live harvest of horseshoe crabs and releases them back into the wild, there is still mortality associated with extracting up to 30% of the horseshoe crabs' blood for medical use.

But even though synthetic versions of horseshoe crab blood have been developed, the 445 million year old version found in the animal is still the gold standard in the biomedical industry.

Quinn Kirkpatrick was born and raised in Wilmington, Delaware and a graduated of the University of Delaware. She joined Delaware Public Media in June 2021