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Summary of Choctawhatchee Bay Aquatic Animal Mortalities (Updated April 20, 2006)

Based on results of analyses conducted since mid-January 2006, FWC/FWRI researchers have attributed the aquatic animal mortalities in Choctawhatchee Bay to post-bloom brevetoxin exposure.

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Since mid-January 2006, the FWC’s Fish and Wildlife Research Institute (FWC/FWRI) has been investigating an aquatic animal mortality event in Choctawhatchee Bay. The event has been primarily affecting fish in the Garnier Bayou area (NW Choctawhatchee Bay).  Dead and dying species reported to the FWRI Fish Kill Hotline (1-800-636-0511) included Gulf sturgeon (Acipenser oxyrinchus desotoi), bay anchovies (Anchoa mitchilli), skipjack shad (Alosa chrysochloris), and juvenile spot (Leiostomus xanthurus). Reports of dead invertebrates included lion’s mane jellyfish (Cyanea capillata)and blue crabs (Callinectes sapidus). FWRI/FWC staff and volunteers collected samples of the reported species as well as live bivalves for health evaluation. In March 2006, FWC/FWRI staff sampled four dead and one live longnose gar (Lepisosteus osseus), one live mullet (Mugil sp.), and numerous dying juvenile spot fish from further east in Choctaw Beach and Basin Bayou (northern shore of the central Bay). Samples collected on the southern shore of the Bay included bivalves and water from Sandestin and Alligator Point. Incidental bird mortalities were reported and tissue samples were collected and archived for future analysis. Concurrently, water and sediments were sampled throughout the Bay to analyze water quality, potential presence of harmful algal bloom species and potential presence of toxins. Since the fall of 2005, the National Oceanic and Atmospheric Administration (NOAA) with assistance from FWC/FWRI has been investigating a bottlenose dolphin (Tursiops truncatus) mortality event in the Florida Panhandle.

During the fall of 2005, a red tide bloom was present in the Florida Panhandle following an extensive red tide event in west central Florida, which persisted throughout 2005. In late August 2005, transport of the west central Florida bloom initiated the Florida Panhandle bloom. High red tide (Karenia brevis) cell concentrations were detected just north of Cedar Key in late August and in the Apalachicola Bay area one week later. The bloom spread rapidly west.  By September 12, red tide cell populations were detected in Panama City.  By October 3, the bloom spread to waters off Escambia County on the Florida-Alabama border. Bloom concentrations remained elevated in the Panama City region until December 10. Significant red tide cell concentrations were detected in mid-December in the Cedar Key region. Weekly monitoring has not detected any red tide in the northwest Florida region since the end of December 2005.

Through mid-April, no red tide was observed and only background levels of brevetoxin (toxin produced by K. brevis) were present in water samples from the area. Dying fish from the affected areas behaved as if they had been exposed to neurotoxic brevetoxins. High concentrations of brevetoxins found in the internal organs of fish (sturgeon, gar, and multiple samples of juvenile fish) indicate toxin exposure was post-bloom. Most significantly, brevetoxin was detected in several food web components. Toxin levels were higher than would be expected since the last red tide in the area was in December 2005. Based on the results, brevetoxin is considered the primary cause of the fish kills. These findings also indicate that a reservoir of brevetoxin is present in Choctawhatchee Bay.

It has been well documented that brevetoxin has caused extensive aquatic animal mortalities in the Gulf of Mexico. While mortality events usually occur at the same time as red tide blooms, FWC/FWRI researchers have documented that effects can continue after the bloom has ended. Animals can be exposed to lethal doses of brevetoxins weeks to months after a bloom has dissipated. Toxins released from red tides often persist in the environment and circulate through the food web.

No other HAB species or toxins have been identified in connection with the Choctawhatchee Bay aquatic animal mortalities. Although background levels of a potentially toxic diatom (Pseudo-nitzschia sp.) were detected in some samples, no domoic acid (toxin produced by the diatom) was present in any biological or water samples tested. As part of the Choctawhatchee Bay mortality investigation, the Florida Department of Environmental Protection provided data on contaminant sampling from Garnier Bayou. This data did not provide any evidence to suspect any contaminant involvement in the ongoing fish kill.

Reports of “pink water” in the vicinity of Garnier Bayou were not related to red tide.  The “pink water” was likely caused by a high amount of purple bacteria in the water column. These bacteria can be attributed to local environmental conditions and are not considered responsible for the Choctawhatchee Bay mortalities.   FWC/FWRI acknowledges the Association for Bayou Conservation, the Choctawhatchee Basin Alliance, and the Healthy Gulf Coalition for their collaboration and assistance in collection of samples and provision of data.