Low oxygen, algae cause of fish kill in Hancock, Harrison
By Echo Staff
Jul 2, 2013, 20:13
A lack of oxygen in the water and algae blooms are the main causes of a fish kill along the Coast , according to the Mississippi Department of Marine Resources (MDMR) and the Mississippi Department of Environmental Quality (MDEQ).
The fish began washing up on the beaches of Harrison and Hancock counties and on Cat Island early Monday.
The MDMR and MDEQ took samples and conducted an aerial survey in an effort to determine the cause of a widespread fish kill. The Gulf Coast Research Lab also worked with the two state agencies.
"We found widespread areas of low dissolved oxygen," said Dr. Kelly Lucas, chief scientific officer for MDMR, adding that oxygen levels are lower in warm water. "In two of the 14 sampling areas, we found high concentrations of a microscopic algae that causes blooms, also known as 'red tide.' This particular species is non-toxic; however it can clog the gills of fish."
Lucas said the MDMR is working with the GCRL to sample the gills.
The lack of oxygen in the Mississippi Sound occurs during the summer months when hot water temperatures result in areas of very low or no oxygen, and fish attempt to get to the surface for oxygen. Oxygen levels generally are lower in warm water.
In response to the event, researchers from the Institute for Marine Mammal Studies, examined a field site in waters near Pass Christian and found their traps filled with dead fish and crabs. As part of an ongoing ecological study examining artificial reef habitats, Dr. Jonathan Pitchford and Dr. Andy Coleman recorded more than 50 dead animals and collected water quality data showing very low oxygen levels in the shallow waters of the Mississippi Sound. However, these low oxygen levels are not a recent or unexpected phenomenon for IMMS researchers.
“Dissolved oxygen has been declining since mid-June as both temperature and salinity have risen. It will be interesting to monitor the conditions to see how long the low levels persist,” said Dr. Pitchford.
While some have proposed the fish kill could be related to red tide and associated biotoxins, Drs. Pitchford and Coleman observed a pod of dolphins displaying normal foraging behavior, suggesting the marine mammals were not being adversely affected by the presence of biotoxins.
This observation coupled with water quality data indicates low oxygen levels to be the most probable cause for the large-scale kill, researchers said.
“Even though Monday’s jubilee appeared to be a large event, we are hopeful its consequences will be short-lived. Either way, IMMS is committed to studying the long-term effects of any type of environmental disturbances on apex predators, such as dolphins and sea turtles, and their habitats,” said Dr. Coleman.