Photos of the Long Island Sound

Status and Trends: LISS Environmental Indicators

Type of Indicators: Health/Condition Response/Performance Socio-Economic Historical/Background

Horseshoe Crab Abundance

  • CT
  • NY

Source: CTDEEP, NYSDEC, and Millstone Environmental Laboratory

Horseshoe Crab Abundance CT
CTDEEP (kg/tow) Millstone (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 0.35 0.468
1993 0.45 0.543
1994 0.6 0.697
1995 0.13 0.372
1996 0.61 0.402
1997 0.33 0.385
1998 0.55 0.296
1999 0.8 0.248
2000 0.74 0.35
2001 0.94 0.175
2002 0.76 0.038
2003 1.33 0.198
2004 0.96 0.15
2005 0.39 0.043
2006 0.25 0.124
2007 0.86 0.074
2008 0.62 0.073
2009 0.65 0.064
2010 0.52 0.017
2011 0.81 0.047
Horseshoe Crab Abundance NY (Count per tow)
Peconic Manhasset
1987 0.4967320261 1.2226098574
1988 0.724137931 1.8883348689
1989 2.8203883495 5.089907415
1990 1.6830357143 1.5365488726
1991 3.6310679612 4.3922712327
1992 3.7572815534 1.4687905618
1993 3.140776699 4.9349019468
1994 2.6490384615 0.7623264005
1995 2.2784090909 2.940724409
1996 2.6363636364 2.42679686
1997 2.046875 7.7879717235
1998 1.2857142857 5.4859981871
1999 1.7024390244 3.9004234346
2000 0.9509803922 5.0274070954
2001 1.1791044776 3.8844332992
2002 0.5120772947 5.6750230089
2003 0.6826923077 6.8042622636
2004 0.8115942029 1.8045133234
2005 0.7650273224 1.6384295331
2006 1.1851851852 2.469281162
2007 0.6378378378 4.1036263166
2008 0.6411764706 2.42
2009 0.5384615385 1.03
2010 0.2377622378 1.079956261
2011 0.359375 2.58

 

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 on shore 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 for the health and productivity of this transitional environment.  Horseshoe crab eggs are an essential food source for migrating shorebirds, and their larvae 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

Both the CT and NY indices show a stable or increasing abundance in western Long Island Sound through the 1990s, with high abundance in 2003, 2007, and 2011.  Although abundance was equally strong in the eastern Sound and Peconic Bay during the early 1990s,  it has declined since 1995, currently reaching among the lowest values in each of the time series.

CTDEEP’s survey samples mainly in the western and central Sound, while the Millstone Environmental Laboratory dataset in Niantic Bay reflects 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 near the New York shoreline, while the seine survey in the Peconics, which borders Long Island Sound, is indicative of conditions in eastern Long Island Sound.

 

Data Note

  • The CTDEEP data is from the spring trawl survey.
  • The survey uses geometric mean instead of arithmetic mean to find the most frequently observed  number of  fish collected per tow. In a natural environment such as Long Island Sound  fish have a “patchy” distribution, i.e. some areas will have a very high abundance of fish, and other areas very low abundance or no fish at all. An arithmetic mean can be easily biased by unusually high or low values so that it doesn’t reflect the true center of a data set.  The geometric mean minimizes the effects of very high or low values using a log transformation and is a better average for this type of biological data.

Show/Hide Table


The horseshoe crab is an arthropod more closely related to spiders than other crabs and has a body form that evolved more than 200 million years ago. Photo of horseshoe crab at Long Wharf Beach, New Haven by Richard Howard.

Learn More

 
Subscribe to receive our e-newsletter, Sound Bytes by providing your email address. Interested in a free copy of our print newsletter, Sound Update? Then also provide your home/company/school address.