Manatee impacts from the 2022-2023 red tide bloom
Updated July 17, 2023
Manatee carcass with bloody discharge from the eye, one of the non-specific findings documented in red tide-related carcasses.
Manatee mortality from the recent red tide bloom was first documented in November 2022. Red tide caused elevated mortality in the southwest region during March 2023 when 85 carcasses (preliminary data) were verified in this region (Pinellas, Hillsborough, Manatee, Sarasota, Charlotte, Lee, and Collier counties). Approximately 123 manatee mortalities (out of 241 carcasses total) between November 2022 and June 2023 were attributed to this red tide bloom (2022 preliminary manatee red tide mortality table and 2023 preliminary manatee red tide mortality table). These data will be finalized once all tissue testing for brevetoxin is complete and all carcass information is fully reviewed. A total of 128 carcasses were reported in the southwest region during the spring months (March through May) and the leading cause of death among necropsied carcasses during this time was red tide-related. This mortality event followed the pattern of previous manatee spring red tide events in southwest Florida.
A subadult male manatee with neurological signs from brevetoxicosis receives support from FWC manatee biologists to prevent it from drowning in Saint James City on 26 February. The manatee was rescued and brought into rehabilitation.
Between February 24 and May 6, ten manatees with signs of brevetoxicosis (see below) were rescued and brought into rehabilitation for treatment. Most have already been released back into their natural habitat after they were medically cleared and red tide dissipated in the region.
Brevetoxin is a neurotoxin that can weaken or paralyze a manatee or cause seizures. Necropsy findings include lung edema from drowning or toxic shock. Signs of brevetoxicosis in live manatees include struggling to surface and breathe, seizures, facial tremors, abnormal position in the water (belly up, vertical position head or tail down), weakness, or beaching in shallow water. Manatee exposure to red tide is mostly through ingestion of brevetoxin accumulated in seagrass. Even after red tide dissipates seagrasses can still retain brevetoxins for 1-2 months after a bloom. Mass mortality from red tide typically occurs in the spring, when a red tide bloom coincides with manatee migration away from warm-water sites.
Please report any manatees in distress or carcasses to FWC’s Wildlife Alert Hotline (1-888-404-3922).