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Dolphin Mortality Event in Northwest Florida (2004)

Dolphin Mortality Event Timeline and Present Status

A dolphin mortality event was initially reported from St. Joseph Bay in northwest Florida on March 11 and 12, 2004. A limited number of dead fish and horseshoe crabs were also reported. Water samples were collected from the area on March 11, 12, 16, 18, and 19 and analyzed at the FMRI laboratory. The samples contained no Karenia brevis and low to medium concentrations of Pseudo-nitzschia delicatissima. Samples analyzed from dolphin tissues contained elevated brevetoxin levels and trace amounts of domoic acid.

Dolphin mortalities in this area continued through March 26 but at a slower rate. No additional fish or benthic mortalities were observed. From March 22 to 24, FWC scientists aboard the RV Seminole conducted a research cruise that sampled within St. Joseph Bay and surrounding waters to approximately 30 miles offshore. Temperature, salinity, dissolved oxygen, and chlorophyll a fluoresence were measured, and water samples were collected for phytoplankton identification and pesticides and biotoxins analysis. Samples were returned to FMRI on March 25. All cruise samples from the area outside of St. Joseph Bay had zero to low concentrations of Pseudo-nitzschia delicatissima. No Karenia brevis was detected in any samples.

As of March 31, dolphin mortalities totaled 103. The dolphins recovered during the previous week had been dead for an extended period prior to recovery. Preliminary results on dolphin tissues from the initial event indicated the following:

  • No evidence of viral infection in dolphin tissue was found (reported by the Armed Forces Institute of Pathology).
  • FMRI scientists detected high concentrations of brevetoxin (produced by the Florida red tide dinoflagellate, Karenia brevis) in dolphin tissues (stomach, liver, kidney, lung, cerebellum) and fluids (blood, urine); the highest concentrations of brevetoxins were found in the animals' stomachs. These levels are significantly higher than the levels detected in manatees that died during and shortly after previous red tide blooms in southwest Florida. However, we do not yet know what constitutes a lethal dose of brevetoxin in dolphins, and we are continuing to investigate its role in the die-off.
  • Low concentrations of domoic acid (the biotoxin produced by the diatom Pseudo-nitzschia delicatissima) were detected in the urine and stomachs of dolphins. Concentrations were so low that the role of domoic acid in the mortality event is unclear.

Both Karenia and Pseudo-nitzschia blooms are common in the Gulf of Mexico. Brevetoxin has been previously implicated in manatee mortalities in Florida in 1982, 1996, and 2002 and is also suspected to be the cause of a bottlenose dolphin mortality event in the Florida Panhandle between 1999 and 2000. No significant mortality events have been previously associated with domoic acid in the Gulf of Mexico. Pseudo-nitzschia blooms have been associated with common dolphin (Delphinus delphis) mortalities along the coast of California; however, concentrations of domoic acid found in the bottlenose dolphins (Tursiops truncatus) in the current Panhandle event are much lower. No data are available on the normal levels of domoic acid in the food web; therefore, the significance of low levels of domoic acid in bottlenose dolphins is unknown.

Four new dolphin carcasses were reported between April 10 and 13. An FMRI sampling cruise in the area offshore of St. Joseph Bay on April 7 and 8 found no significant Karenia populations. Water samples collected from a fish kill area within St. Joseph Bay on April 12 contained no Karenia and low concentrations of Pseudo-nitzschia.

No new dolphin deaths or fish kills have been reported since April 13. Water samples collected from St. Joseph Bay on April 16 and 19 contained no Karenia brevis and low concentrations of Pseudo-nitzschia sp. FWC personnel conducted an overflight of the area south of Cape San Blas on April 19. Active sea turtles and dolphins were observed, and no offshore fish kills were located. Based on the absence of K. brevis in the area and toxin levels below the regulatory limit, the St. Joseph Bay Approved Shellfish Harvesting area was opened, effective April 30 at sunrise. Visit Florida Department of Agriculture and Consumer Services (FDACS), Shellfish Harvesting Area Status for more details on shellfish harvesting areas in Florida and up-to-date status information.

As of April 23, dolphin mortalities totaled 107. Water samples continue to be collected from the area, but no Karenia brevis has been found and no new dolphin mortalities have been reported in the area. View the map to see stations sampled during March and April.

A fish kill (trout, redfish, and catfish) and a dead sea turtle were reported May 6 at the southern end of St. Joseph Bay, but water samples collected from the area contained no K. brevis.

An interim report regarding the dolphin mortality event was completed in mid-June by the National Oceanic and Atmospheric Administration's National Marine Fisheries Service (NOAA/NMFS). The report provides information on the initial findings and ongoing analyses in the investigation.