“Since 1982, DMF has monitored horseshoe crabs along with many other species in our spring and fall trawl surveys. This twice annual survey uses a 72-foot vessel that drags a net (known as an ‘otter trawl’) behind the vessel for 20 minutes at each survey station. The net drags along the bottom to capture fish and invertebrates, including horseshoe crabs, that live on or near the sea floor. The survey occurs throughout state waters and follows a scientific design that allows biologists to estimate the relative abundance of each species caught. We use these data to examine how the abundance of each species changes over time.

Declining horseshoe crab abundance trends were observed in this survey until around 2010, but since then, the trend has reversed. Recently, the survey has seen record high numbers of horseshoe crabs. The strongest increasing trends are coming from the region south of Cape Cod. In spring 2025, more female crabs were caught south of Cape Cod than any other point in the survey’s history.”

From Mass.gov.