Ocean City Today

Thousands of horseshoe crabs spotted spawning

By Kara Hallissey | Jun 29, 2017

(June 30, 2017) Every year, the Maryland Coastal Bays Program and the Maryland Department of Natural Resources Fishing and Boating Services team up to conduct horseshoe crab population surveys.

Surveys are taken from mid-May through mid-July, when the prehistoric animals gather and come to shore to spawn and lay eggs during evening high tides on full or new moons. About five excursions take place during that time.

“We are seeing trends and conduct surveys on the same beaches every year,” said Amanda Poskaitis, the watershed program coordinator for the Maryland Coastal Bays Program. “We can tell if they take a dive or [if] they are slowing rising.”

On June 22, 102 males and 29 females were spotted spawning during high tide on the north end of Assateague Island around 7:30 p.m.

“This is typical,” Poskaitis said. “We see 3 to 1 or 5 to 1 ratios. It varies and there are always more males.”

About 15 minutes later, 5,200 horseshoe crabs were counted in a 200-meter stretch using a transect on Skimmer Island. The meter square device helps volunteers estimate the amount of horseshoe crabs along 100 meters of beach. Researchers believe 25,000 total horseshoe crabs are spawning on the entire island.

“Every year we find that island is a wonderful asset [to the survey],” Poskaitis said.

External fertilization or spawning occurs when a number of “satellite” male horseshoe crabs surround one female as she digs down in the sand near the shoreline and deposits hundreds of thousands of eggs, which are fertilized by the males who have formed a cluster around her.

“Initially, these surveys were taken to see what the population numbers were,” said Coastal Fishery Biologist Steve Doctor of the Department of Natural Resources. “Traditionally, horseshoe crabs were used for fertilizer and they were harvesting a lot with no limits. The horseshoe crab [population] became depleted and it affected the migratory shorebirds, and the Red Knot decline.”

The Red Knot makes one of the longest yearly migrations of any bird, traveling approximately 9,300 miles from its Arctic breeding lands to Tierra del Fuego in southern South America with a stopover on mid-Atlantic beaches to reboot their energy.

“The spawning season of horseshoe crabs coincides with the stopover of shorebirds, and millions of horseshoe crab eggs provide an abundant and preferred food source for the shorebirds,” Poskaitis said. “Horseshoe crabs play a key role in coastal ecosystems. It has been suggested that hemispheric populations of shorebirds are dependent upon healthy horseshoe crab populations.”

In 2002, the Maryland Coastal Bays Program and the Maryland Department of Natural Resources Fishing and Boating Services coordinated the first volunteer horseshoe crab spawning survey. Preliminary work began in 1998 and the surveys are beginning to show some trends on the timing and areas horseshoe crabs spawn each year.

“Horseshoe crabs take 10 years to mature so it will take 40 years to get numbers where we’d like them to be,” Doctor said. “They have been stable and slowly increasing.”

At least 11 volunteers have or will be counting horseshoe crabs on Sunset Island on 67th Street, at the Oceanic Motel near the inlet and at Homer Gudelsky Park in West Ocean City.

Horseshoe crabs can live up to 40 years and molt or shed their shells about 10 to 12 times before maturing around 20 years old.

Commercial fishermen use horseshoe crabs as bait for conch and eel while the biomedical industry uses its blood to test for sterility of medical equipment and almost all intravenous drugs, Poskaitis said.

“If they are upside down, flipping them over is always nice,” Poskaitis said. “Do not pick them up by their tails. Always by the side of the shell. They use their tails to flip themselves back over so if they lose that, they are pretty much done for.”

The Maryland Coastal Bays Program has been seeking volunteers to help assist with horseshoe crab strandings.

“Often, when the tides change, groups of horseshoe crabs get caught up in certain landscapes, such as rip-rap and marshes, which ultimately results in death,” Poskaitis said. “We need to keep an eye on those major spawning areas behind rocks at Sunset Island and on rip-rap at the Oceanic Motel. We need volunteers to help rescue.”

If interested in participating, contact Poskaitis at amandap@mdcoastalbays.

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