January 9, 2007

Photo by Doug Perrine, USFW ©

A preliminary report from the Florida Fish and Wildlife Conservation Commission (FWC) says there were 416 manatee deaths in state waters in 2006. That compares to 396 in 2005.

Scientists are unsure whether the increase reflects manatee population growth, increased mortality or better detection of carcasses. However, the best available science indicates that Florida’s manatee population is stable or growing in all regions of the state except the Southwest, which may contain more than a third of the statewide population.

The FWC report indicates watercraft-related mortalities and red tide contributed to more than half of the total deaths in 2006 in instances where scientists could determine the cause of death.

Researchers classify manatee mortalities in eight categories – watercraft, floodgate/lock, other human, perinatal (newborn), cold stress, other natural, undetermined and unrecovered carcasses. The number of manatee deaths declined in every category except watercraft, undetermined and unrecovered.

“It is always sad to see such high numbers, especially in watercraft-caused mortality, but these numbers shed some light on the measures we can take in our commitment to reducing human-related threats to manatees and possibly other threats,” said FWC Chairman Rodney Barreto. “With continued human population growth and enjoyment of the outdoors, we must all be diligent in the conservation and protection of this gentle animal.”

FWC scientists report that red tide continues to threaten manatees in Southwest Florida, with 37-96 deaths annually in four of the past five years. Preliminary findings suggest red tide may have been responsible for the deaths of 61 manatees in 2006.

The 86 watercraft-related manatee deaths in 2006 are the second highest on record for that category. As a result, FWC law enforcement will enforce a special manatee speed zone detail this weekend. The FWC is urging boaters to abide by manatee speed zones and assuring law-abiding boaters who hit manatees that they will not receive citations if they report such accidents. Accident reports provide valuable information for sharpening manatee protection efforts.

“The FWC’s seizing every option in helping manatees continue to recover,” Barreto said. “We’ll be exploring other options to ensure recovery stays on track.”

For instance, manatee mortality figures provide useful information on why manatees die and the risks they face. Information from necropsies (non-human autopsies) help FWC scientists develop conservation measures to reduce risks to manatees. One such measure is development of the state’s first manatee management plan.

The draft plan (PDF file; Adobe Reader required), which is available for public comment, examines past protections and outlines additional measures such as protection of warm-water refuges to reduce stress on manatees during the winter. It also proposes new measurable biological goals and objectives that will provide benchmarks and timelines to help guide future management decisions.

The number of manatees for which a cause of death could not be determined because of decomposition of carcasses was unusually high in 2006, representing 37 percent or 155 of the total.

“Every year a substantial portion of deaths cannot be attributed to a specific cause because of the advanced decomposition of the carcasses,” said FWC research scientist, Leslie Ward.

Scientists use population models to estimate manatee population growth. Although the most recent analysis indicates manatee numbers have been stable or growing in many parts of the state, some areas may require more attention.

“The FWC is aware of that,” Barreto said. “But the bottom line is the FWC and other parties are taking steps that have moved manatees away from the threat of imminent extinction, and will continue to nurture them along the road to full recovery and use whatever tools it takes.”

Manatee mortality information is maintained by FWC staff at the agency’s Fish and Wildlife Research Institute Marine Mammal Pathobiology Laboratory in St. Petersburg. It is the primary facility in Florida for manatee necropsies. Research done by the biologists at the lab includes aging and life history, skeletal anatomy and biology, pathology and forensics.

For more information on manatee mortality research or to comment on FWC’s manatee management plan, visit the Manatee section of the MyFWC.com web site.