June 3, 2024 — 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.