Fish kills in MD

With all the fish kills it is a wonder there are any fish left.

Fish kills MD

The Maryland Department of the Environment is mandated by Environmental Article Section 4-405 (c) to oversee the investigation of fish kill incidents throughout the state.
The Fish Kill Investigation Section manages and coordinates the multi-agency, statewide fish kill response program. Staff is on call during the regular workweek and on weekends, holidays and after normal working hours to ensure that all fish kill reports are promptly addressed.

The presence of dead or distressed fish may indicate that a toxic substance has entered the waterway. For this reason, it is very important to quickly ascertain the facts, announce the findings, and institute corrective measures if practical.
Fish kills also result from a combination of natural and human induced stresses in the environment. Several elements may combine and act synergistically to overload stress tolerance levels and induce a fish kill. Typical stress factors may include population stress (crowding), spawning stress, reduced food abundance, excessive temperatures or sudden temperature change, parasite burdens, high or low pH, low oxygen levels caused by sewage or excessive algae (fueled by nutrient enrichment), salinity stress, chronic toxin levels (including metals and organics), and drought. Each incident is categorized according to the dominant stress factor detected.

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A total of 112 fish kills were reported in 2008, of which 84 were considered significant enough to warrant on-site investigations. There were approximately 372,000 fish mortalities confirmed. Five Maryland incidents involved more than 10,000 fish. Two included more than 100,000.
In 2008, a number of fish kills in Chesapeake Bay and the Potomac River occurred in association with blooms of the toxic dinoflagellate, Karlodinium veneficum. This algae species is a long term resident of Chesapeake Bay. Although previously thought to be a non-toxic species, Gyrodinium estuariale, it was associated with fish kills for many years. Recently researchers at the University of Maryland Center of Marine Biotechnology (COMB) corrected the misidentification and successfully isolated potent chemicals (i.e. ichthyotoxins called karlotoxin) released by Karlodinium veneficum . Since 2002, this office has worked to combine pertinent data from fish kill investigations (phytoplankton community, water quality, karlotoxin analysis and dose response data) to diagnose kills caused by karlotoxin.

Algal blooms generally cause poor water quality by depleting the water column of oxygen. As a result it can be difficult to determine whether karlotoxin or low dissolved oxygen is the primary cause when Karlodinium veneficum is present. Occasionally, investigation reveals that karlotoxin levels are high enough to damage fish gills but not high enought to kill fish. Simultaneously, oxygen levels may be depressed but not low enough to be lethal. These events may be attributed to the synergistics effects of low dissolved oxygen (D.O.) and chronic karlotoxin levels. In some cases karlotoxin levels are high enough to kill fish in less than one hour. These cases were attributed strictly to the algal toxin.

Five kills were attributed exclusively to karlotoxin but none were attributed to the synergistic effects of low dissolved oxygen and gill damage resulting from sub-lethal concentrations of karlotoxins. The number of these events is higher than the historical average of two per year, but it is significantly lower than the 2007 results: 7 kills attribnuted to the toxin and 17 attributed to the synergisms with low D.O. No known human health effects are associated with these phenomena.

The largest kill occurred September 16th in Marley Creek, a tributary of the Patapsco River in Glen Burnie, Anne Arundel County. Approximately 101,865 fish, almost exclusively atlantic menhaden, died. A strong bloom of the dinoflagellate, Gryodinium uncatenum, was discoloring the water in the affected area. Low dissolved oxygen associated with nighttime respiration and partial die-off is suspected to be the primary cause of the incident.

The second largest event occurred August 30th in Aberdeen Creek, a tributary of the South River in Annapolis, Anne Arundel County. Investigation revealed that approximately 100,778 atlantic menhaden died. The creek has a very shallow, narrow outlet to the river. The fish likely became stranded during nittime conditions and became overwhelmed from diurnally reduced dissolved oxygen levels and collective respiration from the massive school.

The third largest kill occurred September 23rd in Bear Neck Creek, a tributary of the Rhode River in Mayo, Anne Arundel County. Investigation revealed more than 40,500 atlantic menhaden died in the upstream half of the creek. Low dissolved oxygen induced by a bloom of the dinoflagellate, Gyrodinium uncatenum, was suspected to be the cause of the incident.

The fourth largest kill occurred May 31st in Hollis Creek, a tidal pond near Point Lookout, Saint Mary's County. Investigation revealed that more than 23,000 fish, almost exclusively large white perch, died as a result of low dissolved oxygen during an algal bloom. Over the years, the pond gradually lost its natural connection with the Bay. Periodically, county personnel attempt to reopen the connection to allow for flushing, which also allows for spontaneous fish recruitment from the Bay. In this case, the affected fish were concentrated, became trapped and subsequently subjected to deteriorating water quality.

The fifth largest kill occurred September 20th in Bishopville Prong, a tributary of Assawoman Bay in Worcester County. Investigation revealed that approximately 20,000 atlantic menhaden died due to low dissolved oxygen, initiated by a bloom of bluegreen algae (900,000 cells/ml). A bloom of sulfur bacteria was also detected.

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