Unlike a lot of other endangered species, the Florida manatee didn't have all that bad a year in 2012. Only 392 manatees were found dead in Florida last year (pdf), according to the Florida Fish and Wildlife Conservation Commission. This figure is a drop from 453 in 2011 (pdf) and well below the record high of 766 in 2010 (pdf). Florida has been tracking manatee deaths since 1974, when the population was maybe 20 percent what it is today and the state recorded just seven fatalities. Numbers of both manatees and fatalities steadily rose through the ensuing decades; last year's deaths are slightly below the annual average for this century. Today an estimated 4,000 to 5,000 manatees currently swim in the waters around Florida and, more rarely, surrounding states.
Florida's manatees are a subspecies of the West Indian manatee (Trichechus manatus) and have been federally protected since 1967, predating the Endangered Species Act. The International Union for Conservation of Nature lists the subspecies (T. m. latirostris) as "endangered," citing a population of fewer than 2,500 mature individuals and predicted declines of at least 20 percent over the next 40 years due to changes in habitat and increased boat traffic.
Watercraft tend to be the most frequent killers of manatees—81 confirmed deaths in 2012, although most manatees bear the scars of nonfatal boat strikes. Stress from colder waters is the second-highest cause of manatee death—78 confirmed cases in 2012. As I wrote in 2010, coastal development in southern Florida has destroyed their native habitats, pushing many of the gentle giants farther north where they are more likely to die of hypothermia when seasonal temperatures drop below 20 degrees Celsius (68 degrees Fahrenheit). (More than 25 percent of the fatalities in 2012 were from undetermined causes.)
Although manatees suffered fewer than average deaths in 2012, the coming weeks could make for a rough start to 2013. On January 3 the Broward County Natural Resources Planning and Management Division warned boaters that twice as many manatees as usual are in the region this month, many of them near the warm-water discharge of a Fort Lauderdale power plant. Broward is one of Florida's southernmost and most populous counties. Boaters there, as in many other areas of the state, must maintain slower speeds in posted manatee zones, which the division credits with keeping manatee deaths low in the county. (In fact, only three manatees were reported killed by watercraft in Broward in 2012, compared with 19 in Lee County on the opposite side of the state, where another unusually large gathering of the animals in search of warm water has amassed in a canal in Cape Coral.)
Cold water and boaters aren't the only threats. Manatees also have a very low genetic diversity, which could leave them vulnerable to inbreeding problems or disease outbreak, according to a study released last month by researchers from the University of Florida and the U.S. Geological Survey. Luckily, the animals do not show any current signs of inbreeding.
And then there's politics. In December a libertarian organization, the Pacific Legal Foundation, petitioned the federal government to change the status of manatees from "endangered" to the less stringently protected classification of "threatened." The petition came on behalf of another group, Save Crystal River, which opposes "onerous federal regulations" that it says endanger the Citrus County fishing and tourist industries. (Manatee deaths have never been very high in Citrus County. Only two manatees were killed by watercraft there in 2012, down from five the previous year, but the state boating regulations are in effect wherever manatees swim.) The organizations base their claim on a 2007 review by the U.S. Fish and Wildlife Service, which suggested that a status change might be warranted, and the service has been collecting additional data ever since. The original endangered species designation was not based on population size (which was unknown 40 years ago) but on the dangers posed by boats and habitat loss.
Scientists do not know how many manatees historically swam in the waters around Florida and other southern states. Today the population enjoys a tenuous recovery. Hopefully we can still say that tomorrow.
Manatee photo by Jim Reid, U.S. Fish and Wildlife Service. Manatee zone sign by Peter Dutton via Flickr, used under Creative Commons license