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COASTAL BAYS Fish kill a sign of low oxygen levels in bay - October 13, 2010

Most living things require oxygen. Of late, low levels in the coastal bays, particularly in Chincoteague Bay, are cause for concern.

Last week, scientists investigated a large menhaden kill in the headwaters of Gray's Creek, near Ocean City, Maryland. According to Maryland Department of the Environment officials, upwards of 100,000 3-4" fish were scattered throughout the creek. The epicenter of the event was in the headwaters.

The Maryland Department of Natural Resources has continuous monitoring stations throughout the Chesapeake and coastal bays. The station located near the headwaters of Gray’s Creek indicated dissolved oxygen levels were as low as 1.57 on October 2, during the time of the kill. While the cause of the event has not yet been determined, the extreme low levels of dissolved oxygen are of concern.

As Dr. Roman Jesien, Science Coordinator for Maryland Coastal Bays explains, “if fish wind up at the end of a long, dead end canal – a confined space –  there is no place for the fish to go, oxygen consumption goes up and the concentration in the water goes down.” This is not good for fish.

Executive Director Dave Wilson notes, "unfortunately fish kills in long sheltered canals are not uncommon,” and cautions landowners along the canals are diligent about keeping lawn clippings and other materials out of their canals. Polluted water may have reduced amounts of oxygen in it, further depleted by decaying algae and other biomaterials.

Dissolved oxygen (DO) concentration in water is often used to gauge the overall health of aquatic environments. Oxygen is needed to maintain suitable fisheries habitat. When excessive amounts of algae die and sink to the bottom, bacteria decompose the material and consume oxygen. Dissolved oxygen concentrations near the bottom are often lowest. The low levels of DO that result can impair the feeding, growth, and reproduction of aquatic life in the coastal bays. Organisms that cannot move about easily may die.

Maryland State water quality criteria require a minimum DO concentration of 5 mg/L at all times. This water quality standard is needed to support aquatic species in the coastal bays including: hard clams, alewife, blueback herring, white perch, and striped bass. Blue crabs, bay anchovies, and alewife and blueback herring juveniles need a minimum of 3 mg/L DO. More tolerant species such as spot and Atlantic menhaden need a minimum of 2 mg/L and1.1 mg/L, respectively, before significant mortalities occur. While some of these species may survive at such low oxygen values, they will not grow or reproduce. So, recent readings under 2 mg/L serve as a warning, as are living resources are threatened.

In the Maryland Coastal Bays Report Card, released this past summer, Chincoteague Bay received a B-. Although this region received the second highest score of all, that it comprises nearly 64% of the total coastal bays area must be considered. Declining water quality in this largest bay must be reversed. A marked decrease in dissolved oxygen has occurred since the release of the 2008 Report Card.

In 2006, Scenic Maryland (www.scenicmaryland.org) released its Last Chance Scenic Places report which included the coveted gem of the coastal bays—Chincoteague Bay. Their description described the remote bay and its watershed as “a wild, largely undeveloped region dotted with tiny islands, marshes, beaches, and hunting and fishing camps offering a wealth of scenic beauty and diverse habitats.”

Now, large areas of what was thought to be pristine habitat are showing significantly degrading water quality trends and living resource impacts. Despite past improvements, nutrients and phytoplankton have been increasing in recent years throughout Chincoteague Bay. The large-scale changes in water quality trends should be considered as a warning for the estuary and its watershed. Although management actions have occurred on land, it may take decades to see the results. Nutrients, which impact the overall water quality of the Chincoteague Bay, are from widespread sources such as septic tanks, runoff from land, ditches, and groundwater. Changes in water quality will impact Chincoteague Bay’s living resources, as well as those animals and people that depend on the bays for sustenance. Together, we need to act more aggressively to ensure the protection of Chincoteague Bay.

If you’re interested in helping to cleanup our coastal bays, please contact the Maryland Coastal Bays Program at mcbp@mdcoastalbays.org or visit www.mdcoastalbays.org for more information.

Carrie Samis is the Education Coordinator for the Maryland Coastal Bays Program.

 


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