The horseshoe crab is an aquatic sea creature that has remained virtually unchanged for over 350 million years. It is not an actual crab, but a close relative of spiders and scorpions. Its armored outer shell provides protection from predators and it uses its long, spiny tail for steering. Horseshoe crabs prey on mollusks and sea worms, grasping them with their six pairs of claws. Threats to the horseshoe crab populations include loss of spawning habitat to development (such as new bulkheads, piers and beach nourishment projects), overharvesting for medical research and use as bait.

Our department, in collaboration with the Maria Mitchell Association, is participating in a region-wide project aimed at identifying where horseshoe crabs spawn in Massachusetts waters. Scientists are concerned that there may be localized population declines of this species and are interested in collecting data to determine if management efforts are necessary. Each spring, from late April through June, horseshoe crabs come ashore to lay their eggs. Although weather conditions, water temperature, and habitat affect where and when crabs gather, spawning generally occurs on high tides near the full and new moons in May and June. Standardized surveys are being conducted on the Foundation’s property at Warren’s Landing (in Madaket Harbor) and in Monomoy (in Nantucket Harbor) during these periods. We are also placing numbered tags on horseshoe crabs to obtain information on their regional movement patterns. If you see one around Nantucket, please call us with the tag number, the date and time observed and the location where you saw it!

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