Photos of the Long Island Sound

Research & Monitoring


The Long Island Sound Study has launched a new version of the Environmental Indicators section. The data below may be out of date. Please visit and bookmark the new section here to see the most recent data.

Status and Trends: LISS Environmental Indicators

Shad & Blueback Herring—Long Island Sound

CTDEEP Fall Trawl Survey *Data for 2010 unavailable-see note below.

Shad & Blueback Herring—Long Island Sound (count per tow)
Blueback Herring American Shad
1984 0.38 3.13
1985 0.16 0.19
1986 0.07 0.27
1987 0.13 0.29
1988 0.53 2.66
1989 0.34 3.1
1990 0.1 0.65
1991 0.04 0.72
1992 0.08 0.54
1993 0.11 1.11
1994 0.93 1.84
1995 0.27 1.9
1996 0.05 0.27
1997 0.75 0.91
1998 0.16 1.22
1999 0.06 1.73
2000 0.06 0.55
2001 0.2 0.41
2002 0.06 0.76
2003 0.1 0.75
2004 0.09 0.95
2005 0.06 0.54
2006 0.15 0.12
2007 0.24 0.38
2008 0.05 0.41
2009 0.09 0.46
2011 0.08 0.42
2012 0.01 0.44
2013 0.00 0.31
2014 0.04 0.20
2015 0.17 0.71
2016 0.21 0.85
2017 0.24 0.63


River herring is a collective term for the alewife, Alosa pseudoharengus, and blueback herring, Alosa aestivalis, two anadromous fish species that are related to the American shad. Anadromous fish migrate from the ocean to rivers to spawn.  The coastal range of the alewife extends from northeastern Newfoundland to South Carolina, while that of the blueback herring extends from Nova Scotia to Florida. Both species undertake upriver spawning migrations during spring.  The American shad, Alosa sapidissima, is the largest of the herring family, and is a favorite Connecticut River sportfish. It also undertakes upriver spawning migration during spring. The historic range of American shad was from the St. Lawrence River to Florida. Shad are still distributed throughout their historic range but shad are most abundant in east coast rivers between Connecticut and North Carolina.


River herring and shad are important to our freshwater, marine and estuarine ecosystems because adult herring and their young provide food for a variety of predators including freshwater gamefish, marine gamefish, osprey, bald eagle, harbor seals, porpoise, egrets, kingfishers, and river otter.  Shad supported an extremely important fishery from CT’s earliest history. Indians and the earliest colonists relied on the spring shad migrations for food, setting multiple fixed nets on the river banks.  In more recent years, going to watch women bone the fish at ‘shad shacks’ and  spring shad ‘plankings’ or ‘bakes’ were very popular events. The commercial fishery is now reduced to only a small remnant of folks, mostly representatives of the fishing families who used to make a living fishing the lower CT River with drift gill nets.


American shad migrate from the ocean to rivers to spawn. Their year to year populations vary, often depending on differences in recruitment of individual year classes. Blueback herring has declined dramatically in recent years. Striped bass predation may be a factor in declining populations for both species. In Connecticut waters a moratorium on the taking of blueback herring has been in place since 2001.


Both of the above graphs depict data from CTDEEP’s fall 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. In fall 2010, sampling was cancelled because the CTDEEP’s research vessel was out of service due to repairs.

Show/Hide Table

Atlantic salmon (below) and American shad (above) are anadromous fish which return to fresh rivers to spawn. Both species have been negatively impacted by river dams and pollution. These fish were photographed at a fishway (fish ladder) on the Farmington River.

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.