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© Brian Gratwicke, Wikipedia
Connecticut's Department of Energy and Environmental Protection why thousands of fish died in the past week in the state's coastal waters.

Multiple natural fish kills were reported during the past week. The kills were reported in several locations on the Thames River between Norwich and the U.S. Naval Submarine Base in Groton, in the lower Connecticut River, in Clinton Harbor and on the Quinnipiac River.

Thousands of Atlantic menhaden, and smaller numbers of other species were found dead at each location.
The population of Atlantic menhaden has grown in local waters for the past two years, most likely due to limits placed on menhaden harvest along the Atlantic coast.

Menhaden are caught commercially and made into animal feed and used as bait in lobster, crab and other fisheries.

The fish could have died of natural causes according to the DEEP. "These events more commonly occur during the warmer summer months when bluefish attack tightly packed menhaden schools in locations where the oxygen content of the water is also below normal," said David Simpson, Director of the CT DEEP Marine Fisheries Division. "The tightly packed schools rapidly use up the oxygen in the water and suffocate."

Another cause is a viral "whirling" disease which spreads rapidly through the school. In late stages of the disease, fish are commonly seen spinning or whirling at the surface. "This behavior has been described by witnesses in each of the fish kill locations," added Simpson.