At Stage Harbor in Chatham, Derek Perry, the state’s horseshoe crab biologist, walks the shoreline, counting how many horseshoe crabs fall within a 25-square-meter area.

It’s not an easy task, especially when the males in the group are clamoring to reach the limpet-and-seaweed encrusted females. But after a few moments, he’s satisfied with the count.

“That’s 67 crabs in a five-by-five-square-meter quadrat,” Perry said. “So it’s a fair number.”

Of them, 61 are male, and each is trying to latch onto one of the six females in the area. According to Perry, it’s pretty easy to identify the sex of a horseshoe crab at a distance, because the females are 30% bigger, and the males form a “conga line” behind them.

“So a male,” he said, picking one up and flipping it upside down, “will have these legs here. He uses those to attach to the female.”

From Maine to the Yucatan, female horseshoe crabs each will lay about 80,000 eggs a season and bury them in the sand, mostly along the high tide line.

“And the males are trying to jockey for position to get in there and fertilize those eggs,” Perry said.

This is how horseshoe crabs have been reproducing for 450 million years.

But lately, things have gotten harder for them. They’re threatened by climate change, by fishermen using them for bait, and by the biomedical industry catching them to extract their blood for vaccines and drugs. So this year, for the first time, the state of Massachusetts is fully protecting horseshoe crabs from any harvesting while they’re at their most vulnerable.

“We have some new regulations this year. There’s a spawning closure, which goes from April 15 through June 7. So that’s protecting over 90% of the spawning crabs,” Perry said.

Male horseshoe crabs will latch onto females — or other males, or even a lucky volunteer — to fertilize its eggs and reproduce.
Male horseshoe crabs will latch onto females — or other males, or even a lucky volunteer — to fertilize its eggs and reproduce.
Eve Zuckoff

There’s some debate about the population size of horseshoe crabs, but for years, officials and conservationists have worked to keep it strong. Perry said he feels relatively good about the numbers.

“We have 16 beaches that we [survey] in the state,” he said, “and 70% of them have an increasing trend over the last 10 years.”

The state allows only a certain percentage of horseshoe crabs to be harvested by fishermen, and officials work closely with biomedical companies to limit their impact.

But it’s harder to control the natural environment.

Dan McKiernan, director of the state Division of Marine Fisheries, said compared to the rest of New England, Massachusetts has perfect beaches for horseshoe crabs: sandy with warm water.

“Nantucket Sound is this very large, shallow embayment. No other state has such a body of water with such great habitat as we do. And of course, the sandy beaches of Nantucket and Martha’s Vineyard and this side of the Cape, Monomoy, makes this incredibly productive habitat for the species,” he said.

But, McKiernan added, those very same beaches are more vulnerable to the impacts of climate change.

“We have a concern that there are fewer sandy beaches because of coastal erosion.”

In fact, the site in Chatham where the state historically counted horseshoe crabs is no longer accessible because of erosion. This is only the second year that counting is being done at Stage Harbor.

Perry, the biologist, can’t count horseshoe crabs here every day – he’s monitoring 15 other beaches statewide. So he relies on volunteers from organizations that include Mass Audubon, North and South Rivers Watershed Association, Southeastern Massachusetts Pine Barrens Alliance, U.S. Fish and Wildlife Service, Maria Mitchell Association, Nantucket Conservation Foundation, and the Massachusetts Division of Marine Fisheries.

Derek Perry, who grew up on Cape Cod, says climate change has affected the timing of horseshoe crab spawning season. "There's some work that was done in the '40s and '50s in Barnstable. The peak in spawning at that point in time was the third week of June. But we're seeing the same temperatures as the third week of June ... now the second and third week of May. So the peaks are still the same as far as temperature, but not by date."
Derek Perry, who grew up on Cape Cod, says climate change has affected the timing of horseshoe crab spawning season. "There's some work that was done in the '40s and '50s in Barnstable. The peak in spawning at that point in time was the third week of June. But we're seeing the same temperatures as the third week of June ... now the second and third week of May. So the peaks are still the same as far as temperature, but not by date."
Eve Zuckoff

Two of those volunteers came to find him as he walked the beach at Stage Harbor.

“So we have your paperwork from last night,” said Liz Henry, who drove nearly 100 miles from Cambridge to Chatham with her 8-year-old son Taylor. Henry explained that she and Taylor, drenched by fog under a full moon, counted crabs during the midnight-to-2 a.m. high tide.

“We think there were 1,100,” she said. “And I thought we were undercounting, because we couldn’t get very deep.”

While his mom spoke with Perry, Taylor walked down the beach, helping horseshoe crabs by turning them right-side up, and reflecting on what he likes about the species.

“They lived in the dinosaur time,” he said. “They’re just so cool.”

Asked whether he was scared being out in the middle of the night, he was matter-of-fact: “Not really scared. But it was so much work.”

But to Taylor Henry, the late night and all the counting will be worth it, if it helps horseshoe crabs survive — maybe even for another 450 million years.

To become a horseshoe crab volunteer or  learn more, survey coordinator Derek Perry can be reached at  derek.perry@mass.gov. 

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