A devasting red tide bloom that started in southwest Florida in September 2012 contributed to the worst year for manatee deaths on record, according to a news release Wednesday from the Save the Manatee Club.
The unprecedented manatee mortality toll climbed to 769 deaths as of Tuesday, surpassing the mark of 766 set in 2010 when hundreds died from cold stress.
The total this year is almost twice the 392 that died in 2012, according to the conservation group.
At least 276 manatees in southwest Florida have died from exposure to red tide year-to-date compared with 33 manatee deaths from red tide in 2012.
Red tide acts as a neurotoxin in manatees, giving them seizures that can result in drowning without human intervention. Manatees exposed to red tide
can be moved out of the affected area by trained biologists and stabilized at a critical care facility.
Dr. Katie Tripp, Save the Manatee Club's director of science and conservation, said red tide and a food source disruption were two unusual mortality events in 2013, coupled with the regular threats manatees face on a daily basis, and are responsible for the unprecedented losses.
"This year's record-breaking manatee mortality is a loud-and-clear signal that our waterways are in trouble," said Tripp in the release.
Other manatee deaths so far this year included 123 stillborn, newborn or young calves less than 5 feet in length, which sets another annual record for this category of mortality.
Of these, at least 49 were found in Brevard County, at the epicenter of the unusual mortality event linked to a variety of algal blooms and the loss of 47,000 acres of seagrass since 2010.
Since 2012, at least 111 manatees have died of unknown but presumed natural causes, possibly from a different toxin or toxic syndrome.
"One theory is that since the seagrass is not available, manatees have switched to a different food source -- a macroalgae called gracilaria -- that is getting into their digestive tract and killing them," according to the news release. "Another theory is that the toxins are found on seaweed that manatees eat."
Veterinarians and scientists at the University of Florida are testing genes and proteins expressed when manatees are exposed to toxins. The study is designed to see if differences between affected and healthy animals carry the biological signature of an immune system responding to toxin exposure -- a signature they can then test for in the Indian River Lagoon manatees.
"With 2013's catastrophic loss of manatee lives coming so close on the heels of the mass mortality suffered during 2010, the already difficult job to ensure the survival of these gentle and defenseless marine mammals has been made all the more challenging, and it's not over yet," said Patrick Rose, aquatic biologist and the executive director of the Save the Manatee Club. "What we put into our waters, how much we pump from our aquifer and draw from our springs and rivers, together with how we use our waterways, all has an impact on our own lives and the lives of every aquatic species. We must be better stewards of our waters and waterways or suffer even more severe consequences going forward."
Manatee treatment centers and officials include those run by the Florida Fish and Wildlife Conservation Commission, Lowry Park Zoo's Manatee Hospital, Lee County Manatee Park and Ellie Schiller Homosassa Springs Wildlife State Park.
Rescue and rehabilitation partners and volunteers put in long hours during the red-tide crisis.
"Because of their help, many manatees were rescued in southwest Florida who otherwise would have perished," according to the Save the Manatee Club press release. "Fortunately, these manatees were found alive and were successfully rescued and transported to a critical care facility.