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Horseshoe Crab Surveys

The Maryland Coastal Bays Program assists the Maryland Department of Natural Resources in conducting annual horseshoe crab surveys to measure spawning abundance in the Coastal Bays. The survey has been in existence since 2002 and provides valuable data used in fisheries management. Surveys start in late May and continue through early July, with sampling taking place once every two weeks.

The surveys are conducted during these months as it is peak spawning (mating) season, and they occur on evening high tides during full and new moons.

Volunteers assist with this program. If you are interested in volunteering, contact Carly Toulan at ctoulan@mdcoastalbays.org.

Many species are dependent on horseshoe crabs for survival, but populations on the East Coast of the United States have decreased. Abundance of horseshoe crabs has not been well defined, but many areas have seen declines.

In addition to being an important food source to many species throughout the Coastal Bays food web, horseshoe crabs provide humans with a valuable resource in regards to public health; Limulus amebocyte lysate (LAL). This substance is extracted from the horseshoe crab’s blue-colored blood, which is blue due to the blood being copper based instead of iron based like human blood. We use LAL in the biomedical industry to test for the presence of bacterial toxins. The discovery of this life-saving substance occurred in 1971. Since then all vaccines, injectable drugs, intravenous solutions, and implantable medical devices that are certified by the Food and Drug Administration are required to be tested using LAL. Horseshoe crabs are also harvested to be used as bait for American eels and whelks.

One way you can help the horseshoe crab is to keep a lookout during spawning season. Many horseshoe crabs get hung up and perish on rip rap barriers installed to protect properties from wave action and erosion.

Horseshoe crabs are ecologically important and harmless to humans. Their tail, called a telson, may look sharp, but it doesn’t sting like a stingray; it is used for maneuvering and helps it to turn upright when he or she gets flipped over. They have very tiny claws on their front legs that are not able to pinch you.

If you see a horseshoe crab stuck in the rocks, pick it up by grabbing each side of the shell and put it back into the water, this will help the little guy out tremendously. Never pick up a horseshoe crab by its telson—this will result in injury and potential death to the animal. We have several locations that could use your assistance if you are interested in stewarding these guys during the season.

Graphs and Data:

Horseshoe Crabs Male To Female Ratios
Total Horseshoe Crabs Numbers
Horseshoe Crabs Presence By Temperature

For more information on the horseshoe crab visit:

Horseshoe Crab Anatomy

The Horseshoe Crab: Limulus polyphemus, A Living Fossil (PDF)

Contribute Online

Become a member of the Coastal Bays Foundation and donate online securely through PayPal. Your financial contribution will go toward protecting our watershed, its habitat, and wildlife. The Maryland Coastal Bays Program Foundation is a 501(c)(3) nonprofit; all donations are tax deductible.