Friday, August 08, 2014

Scientists observe poor quality water killing fish

Every summer, Save The Bay conducts water quality surveys with the state’s Dissolved Oxygen Strike Force, A.K.A. the Insomniacs, named for the group’s past practice of conducting nighttime surveys  This group of scientists, mainly from Brown University, RI Department of Environmental Management (DEM), URI Graduate School of Oceanography (GSO), and Save The Bay, head out onto Upper Narragansett Bay on early-morning neap tides throughout the summer to monitor the oxygen content in the water column.  Just as for land animals in air, oxygen in the water is critical for sea animals to survive.  Oxygen concentrations below 2 milligrams per liter (termed “hypoxic”) are considered acutely dangerous to sea life, including finfish and shellfish. 

Plentiful oxygen is found in most surface water, from the great oceans to tiny creeks.  However, nutrient pollution, mostly from our own waste products, pet waste, and lawn fertilizers, can cause algae blooms that drain oxygen from the water as the algae decompose.  Additional factors, such as weak tidal flow, lack of wind, warm temperatures, and rain, can set the stage for low oxygen events, characterized by dangerously-low oxygen levels persisting across a substantial volume of water for a significant time, sometimes days or even weeks.  Low oxygen events pose a direct threat to sea life.  The Insomniacs aim to document these events and identify trends that will help us better understand the various factors that cause them, and how they may interact.

This past Tuesday morning, the Insomniacs set out to conduct one of these surveys.  As we motored up the Seekonk River in the upper reaches of the West Passage of the Bay, we began to notice dead and dying adult menhaden in the water and washed up on the shore.  Several fish were gulping for air and swimming upside down in small circles in their last moments of life.  As we made our way further up the river, we saw this sad scene over and over; beautiful fish dying before our eyes.  We were witnessing, firsthand, a fish kill.  As we began monitoring the oxygen levels in the river, it became clear that widespread low oxygen in the river was the cause.  The fish kill continued into Wednesday.  Yesterday (Thursday), I went upriver to check the status and saw no new dead or dying fish. In fact, I saw some fish flipping at the surface the way healthy menhaden normally do.  It seems as though higher tides and some brisk winds the past few days may have brought oxygen concentrations back to tolerable levels.
This trip was a reminder to me of why we do what we do at Save The Bay.  We work hard every day to improve water quality conditions in the Bay so it is healthier for people and sea life.  It’s a huge task that takes an incremental process to address all the stresses that we have imposed on the Bay in the last two hundred years.  But, too many people love the Bay to call this good enough.  We need to keep working until fish kills and other signs of unhealthy Bay conditions are things of the past.

Insomniacs Dave Murray (center) and me with our guest Dr. Courtney Schmidt from the Narragansett Bay Estuary Program.  Dave is preparing the monitoring sonde for deployment in the Upper Bay, while I try to impress Courtney with rope tricks.  Photo courtesy of Tom Borden.

An adult menhaden gulping for air in the Seekonk River this past Tuesday.  Photo courtesy of Tom Borden.

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