Recent Fish Kills in Narragansett Bay Are Likely Due to a Combination of Factors, According to RI DEM
PROVIDENCE – Scientists with the Department of Environmental Management believe that the recent spate of fish kills in various parts of Narragansett Bay is likely due to a combination of natural factors and existing water quality conditions. As part of the Department’s ongoing Bay monitoring program, the Department has been tracking Bay conditions and investigating reported problems. Over the past week, fish kills have been reported in Bullocks Cove, between Barrington and East Providence; in the Kickemuit River; and in Wickford Cove. The numbers of dead fish have ranged from as low as a dozen to as many as a thousand.
The fish kills, mostly involving menhaden, are most likely the result of four major factors, acting in combination: low dissolved oxygen associated with excess nutrients and algal blooms, poor tidal exchange caused by recent neap tides; an extremely large biomass of menhaden; and predation pressure from bluefish. A widely held theory is that large schools of hungry bluefish may be chasing the even larger schools of menhaden into shallow cove areas, where the dissolved oxygen levels are typically lower than in deeper, better-flushed areas of the Bay; the areas may also be impacted by pollution sources. The cascading effect of more and more fish drawing oxygen from already depleted shallow cove waters leads to hypoxic (low oxygen) and then anoxic (no oxygen) conditions, which stresses and then kills those fish that are unable to escape.
DEM and its partners maintain network of monitoring stations in the Bay, which regularly record oxygen, temperature, salinity, pH levels, and, in some cases, water clarity and the presence of algal blooms. The monitoring data is supplemented by field observations made by DEM personnel to generate weekly reports on Bay conditions. As of last week, the upper Bay stations were showing signs of low oxygen, especially in portions of the Providence River and Greenwich Bay. DEM will continue to closely track the oxygen levels and provide further notification if the trends worsen and become serious.
The monitoring network is also essential to measuring changes in water quality expected by the upgrades planned for or installed during the last few years at wastewater treatment facilities (WWTFs) in Rhode Island. The additional pollution controls are part of an overall nutrient reduction strategy developed by DEM to restore ambient water quality conditions in upper Narragansett Bay and Greenwich Bay. The strategy includes working with EPA to require and implement nutrient reductions from WWTFs in the Massachusetts portion of the Narragansett Bay watershed.
DEM reminds the public that Bay conditions can be tracked via the Department’s 24-hour Bay Line (222-8888) and via DEM’s Bay Assessment and Response Team (BART) webpage, which includes a regularly updated link to the latest Bay conditions as well as a lot of additional information on the Bay and events such as algal blooms and fish kills. To access the webpage, click on “BART” under “Timely Topics” on the Department’s homepage (www.dem.ri.gov).
Since the fish kills to date have been localized, dispersed throughout the Bay, relatively small in size, and apparently influenced by a combination of natural factors, DEM anticipates that more such events may occur. DEM urges the public to remain vigilant and to continue reporting any major problems by calling the Bay Line and leaving a message. The information received via Bay Line is extremely useful to the Department in tracking and understanding Bay conditions.