Ecosystem Targets and Supporting Indicators

Horseshoe Crab Abundance

This indicator shows the abundance of Horseshoe Crabs in Connecticut and New York.

View Implementation Actions for Horseshoe Crab Abundance

Show/Hide Table Data

Horseshoe Crab Abundance CT
	CT DEEP (kg/tow)	Niantic Bay (Count/tow)
1976	-	0.77
1977	-	0.598
1978	-	0.124
1979	-	0.205
1980	-	0.132
1981	-	0.175
1982	-	0.244
1983	-	0.197
1984	-	0.141
1985	-	0.162
1986	-	0.141
1987	-	0.24
1988	-	0.343
1989	-	0.319
1990	-	0.393
1991	-	0.305
1992	0.65	0.468
1993	0.77	0.543
1994	0.57	0.697
1995	0.20	0.372
1996	0.85	0.402
1997	0.66	0.385
1998	0.69	0.296
1999	0.91	0.248
2000	0.95	0.35
2001	1.11	0.175
2002	1.11	0.038
2003	1.31	0.198
2004	1.31	0.15
2005	0.58	0.043
2006	0.46	0.124
2007	1.06	0.077
2008	0.87	0.073
2009	0.86	0.064
2010	0.52	0.017
2011	1.00	0.047
2012	0.59	0.043
2013	0.89	0.128
2014	0.60	0.156
2015	0.45	0.068
2016	0.46	0.060
2017	0.54	0.051
2018	1.18	0.090
2019	0.73	0.026
2020	-	0.013
2021	1.3	.077
2022	1.23	0.038
2023	1.54	0.038

Horseshoe Crab Abundance NY (Count per tow)
	Peconic East	Manhasset and Little Neck West
1987	0.49	1.22
1988	0.70	1.89
1989	2.68	5.09
1990	1.66	1.54
1991	3.52	4.39
1992	3.60	1.47
1993	2.99	4.93
1994	2.60	0.76
1995	2.16	2.94
1996	2.40	2.43
1997	2.01	7.79
2998	1.26	5.49
1999	1.63	3.90
2000	0.94	5.03
2001	1.16	3.88
2002	0.50	5.33
2003	0.68	6.71
2004	0.73	1.80
2005	0.75	1.64
2006	1.17	2.47
2007	0.63	2.70
2008	0.63	2.41
2009	0.52	1.03
2010	0.23	1.08
2011	0.36	2.58
2012	0.33	2.07
2013	0.30	3.53
2014	0.24	1.52
2015	0.23	0.92
2016	0.13	2.09
2017	0.13	1.35
2018	0.19	1.61
2019	0.20	1.27
2020	0.05*	NA*
2021	0.13	0.73
2022	0.14	2.12
2023	0.26	2.39

WHAT ARE HORSESHOE CRABS?

The horseshoe crab (Limulus polyphemus) is an arthropod more closely related to spiders than other crabs and has a body form that evolved more than 200 million years ago. They are found from Nova Scotia to Mexico and live year-round in Long Island Sound. They are harvested as bait for other fisheries, but are not typically eaten for meat. They come onshore to spawn in May and June, with spawning tending to peak at night around the new and full moons.

WHAT DOES THIS INDICATE?

Since horseshoe crabs rely on beaches and the shallow intertidal environment to produce their young, their abundance is an indicator of the health and productivity of this transitional environment. Horseshoe crab eggs are an essential food source for migrating shorebirds, and their larvae and juveniles are consumed by many fish. They are most valuable to humans for their blood proteins which are extremely sensitive to bacteria. The extracted compound, known as LAL, is used to screen injected drugs and implanted biomedical devices for contamination.

STATUS

CT DEEP’s Long Island Sound Trawl Survey samples throughout the Sound in both Connecticut and New York waters during the spring (April, May, and June) and Fall (September, November, October). The Millstone Environmental Laboratory dataset in Niantic Bay reflects the abundance in the eastern Sound near the Connecticut shoreline. The Manhasset and Little Neck Bays NYSDEC seine survey reflects conditions in western Long Island Sound along the New York shoreline, while the trawl survey in Peconic Bay, which borders Long Island Sound, is indicative of conditions in eastern Long Island Sound near the New York shoreline.

Both the CT and NY indices show a decreasing abundance in Long Island Sound from the early ‘00s. Although American horseshoe crab populations increased in the 1990s, recent years show a fluctuating trend due to various stressors (e.g., loss of habitat and illegal harvesting). To stabilize and restore the horseshoe crab populations, regulations have been implemented such as limiting harvesting permits, closed areas, seasonal closures, commercial quotas, and restricting the timing (lunar closures) and daily number of crabs a harvester can possess.