Answer: The Long Island Sound horseshoe crab populations are stressed, and habitat quality is one factor stressing the population. Overfishing resulting from the importance of horseshoe crab blood as a medicinal tool is a new stressor. Recently the population increased, perhaps due to regulatory protections from overfishing. However, it is too early to tell if this positive trend will continue. In time and with ongoing effort, we will see if continued habitat conservation, restoration, and protection actions are effective to rebound the Long Island Sound horseshoe crab population.
This indicator tracks the total weight in kilograms of horseshoe crabs per tow in Long Island Sound, conducted by the Connecticut Department of Energy and Environmental Protection’s spring and fall Long Island Sound Trawl Survey. It also tracks the number of horseshoe crabs per tow conducted by the Millstone Environmental Laboratory survey in Niantic, CT specifically reflecting the abundance in the eastern Sound near the Connecticut shoreline. In New York, the indicator tracks the number of horseshoe crabs counted per sample in a New York State Department of Environmental Conservation seine survey at Manhasset and Little Neck Bays, reflecting conditions in the western Long Island Sound along the New York shoreline. A trawl survey conducted by NYSDEC also counts the number of horseshoe crabs per tow in Peconic Bay, which borders Long Island Sound, and is indicative of conditions in eastern Long Island Sound near the New York shoreline.
The population of horseshoe crabs in Long Island Sound can indicate if the Partnership is making progress to achieve the Coastal Habitat Objective of protecting, enhancing, and assessing the extent and health of coastal habitats and their associated wildlife.
Since horseshoe crabs rely on beaches and tidal flats to produce their young, their numbers are an indicator of the health and productivity of this transitional environment. Horseshoe crab eggs are an essential food source for migrating shorebirds, and horseshoe crab juveniles are consumed by many fish. When beaches are raked, horseshoe crab eggs can be raked away, making this important food for birds even more scarce.
The decline in Long Island Sound horseshoe crab populations seen throughout the 2000s is likely due to habitat loss, overfishing, and warming waters. Horseshoe crabs need healthy beaches and tidal flats so their young can hatch and grow. Beaches and tidal flats can be harmed by human development activities that result in more people living and working in these areas.
Horseshoe crabs are also overfished. Horseshoe crabs can be used as bait, and their blood is highly valued in the medical field due to a special protein that medical professionals use to detect contamination in medical devices and medications.
In response to this decline, recent studies, conducted by the Maritime Aquarium, on Long Island Sound’s horseshoe crabs indicate that coordinated action to prevent population decline is an immediate need (Crosby et al., 2025; Raviraj et al., 2025). In 2004, New York voluntarily implemented harvest reductions in the annual quota from 366,272 crabs to 150,000 crabs, which may be a possible explanation for the upward trend in their abundance. Horseshoe crabs have roughly a 10‑year sexual maturity lag, so changes in abundance from those reductions would be expected to show up around 2014 onward. To restore and stabilize the horseshoe crab populations, Connecticut passed a statewide ban on harvesting horseshoe crabs in 2023 and New York in 2025 passed a law to phase out commercial and biomedical harvesting of horseshoe crabs over a three‑year period, with a full ban taking effect in 2029. Read more on the story of Long Island Sound’s horseshoe crabs here: Celebrating the American Horseshoe Crab: Long Island Sound’s Living Fossil.
Impacts from recent management actions should be seen in horseshoe crab populations in approximately ten years after their implementation (i.e., 2033 & 2035) With the introduction of harvesting bans and investments in habitat improvement, an increase in the population of juvenile and young adult horseshoe crabs is expected. To ensure horseshoe crab populations rebound and continue to support healthy coastal habitat ecosystems, the Partnership will continue work to improve habitat health for horseshoe crabs.
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