Fish Kills Discovered at Torquay Canal, Mariners Cove and Arnell Creek

September 09, 2005

The Department of Natural Resources and Environmental Control is investigating three separate fish kills of juvenile Atlantic menhaden discovered yesterday in areas of Rehoboth Bay. Low dissolved oxygen is suspected as the cause or contributing cause in all three fish kills. No lesions or sores were observed on any of the dead fish.

An estimated one million dead juvenile menhaden were discovered at Mariners Cove in Rehoboth Bay off Long Neck Road near Masseys Landing. Another estimated one million dead juvenile Atlantic menhaden were found in Torquay Canal – a circular lagoon upstream from the mouth of Bald Eagle Creek at the head of Rehoboth Bay. A smaller fish kill of approximately 100,000 juvenile Atlantic menhaden were found at Arnell Creek on the northern end of Rehoboth Bay.

According to Craig Shirey, fish kill coordinator, a dissolved oxygen measurement taken at Mariners Cove yesterday morning by a DNREC enforcement officer was low at 2.1 parts per million. Water samples screened at the University of Delaware's College of Marine Studies indicated a harmful algae also present in the water at Mariners Cove. The samples have been sent for further testing for the presence of any toxins to the University of North Carolina, and will be tested for molecular confirmation of the algae at the College of Marine Studies.

The fish kill at Torquay Canal was discovered later in the day during routine sampling of the canal by a DNREC scientist. Dissolved oxygen levels were very high or supersaturated at the surface, which could indicate that dissolved oxygen late Wednesday evening or early Thursday morning had been low enough to cause a fish kill. Other indications of a low dissolved oxygen event were the presence of other live species of fish and invertebrates behaving normally in the area of the dead menhaden. Screening of the water at the College of Marine Studies did not reveal any indications of harmful or abundant algal blooms.

Shirey noted that although no dissolved oxygen samples were taken at the smaller kill at Arnell Creek, “all the symptoms of a dissolved oxygen related kill were present.” Only menhaden – a species vulnerable to low dissolved oxygen – which travel in large dense schools were involved and some live fish and crabs were observed.

Large schools of juvenile menhaden are known to enter the tributaries of Rehoboth and Indian River bays to filter feed on plankton. Dead end lagoons are common in the bays and can develop poor water quality from inadequate tidal flushing, especially at night and into the early morning hours during summer months when dangerously low oxygen levels can be particularly lethal to menhaden.

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