Tropical Storm Debby Creates Surge in Florida Manatee Strandings

FWRI researchers, Clearwater Marine Aquarium staff, City of Oldsmar personnel and volunteers use a net to capture a manatee and remove it from the basin.  View additional images from this event on Flickr

After two years of unprecedented cold-related disease and mortality in 2010 and 2011, Florida manatees (Trichechus manatus latirostris) endured another type of extreme weather in the summer of 2012. Tropical Storm Debby formed in the Gulf of Mexico on June 23, and its slow movement and heavy rain contributed to the state’s wettest June on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climate Data Center. Although the storm’s impact on the Florida manatee population, in terms of mortalities, was much less severe than that of the record-breaking cold events, unusual rescue scenarios and carcass response efforts following Debby challenged Fish and Wildlife Research Institute (FWRI) scientists. Furthermore, it was the first time scientists recorded storm-related manatee mortalities with necropsies.

On June 27, biologists at FWRI’s Marine Mammal Pathobiology Laboratory received the first report of a manatee entrapped in a retention pond system in Oldsmar. The manatee swam over a spillway during high water associated with the tropical storm but could not swim out of the retention ponds after the water receded. The following day, FWRI staff discovered that not one, but two manatees were entrapped in the retention ponds. One manatee was rescued that same day, but the team called-off efforts to capture the second because of difficult conditions – size of water system, lack of boat access, snagging of capture nets on bottom substrate and elusive behavior of the animal. The second manatee was successfully rescued the following week with the help of staff from Clearwater Marine Aquarium and the City of Oldsmar’s wastewater treatment plant.

On June 28, a citizen reported manatee sightings in Lake Tarpon. Manatees entered the lake while water control gates were open to flush out excess water from Tropical Storm Debby. Deep murky water and heavy vegetation created challenging rescue conditions, but FWRI biologists and FWC law enforcement officers, with the help of a spotter plane, located and captured two manatees in the month after the storm.

Biologists determined all four manatees were healthy and released them in Pinellas County waters immediately after rescue. There was no immediate threat to the health of the entrapped manatees; however, FWRI staff made it a priority to relocate these animals as soon as possible because of concerns about food availability in the Oldsmar retention ponds and boaters not being aware of manatee presence in Lake Tarpon. Eventually, entrapment would have threatened the manatees by preventing their winter migration to warm-water sites, such as springs and electric power plant outfalls (discharge sites). Prolonged exposure to water temperatures below 68 degrees Fahrenheit can cause manatees to suffer cold-stress syndrome, which can result in death.

The following articles provide more information about manatee cold-stress syndrome: Manatee Mortality Winter 2008-2009 and Cold-Related Mortality Event Winter 2009-2010.

For three manatees stranded in a remote area near Cedar Key, the storm resulted in their deaths. On July 3, a citizen found the three carcasses together, hidden in dry marsh land. FWRI staff performed necropsies on site and determined the manatees became stuck after storm waters receded. Beached in the mud and exposed to the elements, they likely died from hyperthermia (extremely high body temperature).

The three deaths associated with the aftermath of Tropical Storm Debby will have a relatively small effect on the manatee population, but they are of great importance to science. This is the first time researchers documented storm-related manatee mortalities with necropsies. This finding supports observations from photo-identification data of individual manatee sightings through the years, which suggest annual manatee survival rate is lower during years with extreme storms (Langtimm and Beck 2003).

To report a possibly entrapped, distressed or dead manatee, please call the FWC Wildlife Alert Hotline at 888-404-FWCC (3922).

Manatees Affected by Tropical Storm Debby

Reference
Langtimm C.A. and Beck C.A. Lower survival probabilities for adult Florida manatees in years with intense coastal storms. 2003. Ecological Applications 13(1), pp. 257–268.