The Florida manatee is a subspecies of the West Indian manatee that occurs only in the southeastern United States. It occupies the northern limit of the species’ range, which extends south along the eastern coast of the Americas to Brazil. All manatees are slow-moving aquatic herbivores that feed on aquatic vegetation in freshwater and estuarine systems. They rarely venture into nearshore ocean waters except to travel between adjacent rivers or estuaries. Prolonged exposure to water temperatures below 18°C (65°F) can be lethal to manatees. During winter, Florida manatees are therefore largely confined to the lower two-thirds of the Florida Peninsula where they aggregate around warm-water springs and thermal outfalls from power plants, or remain in the Everglades at the southern tip of the state. As water temperatures rise in spring and summer, Florida manatees disperse throughout the state and beyond (i.e., north to Virginia and west to Louisiana), but rarely move from one side of the Florida Peninsula to the other.
Although historical information on Florida manatees is sparse, limited archaeological evidence indicates that their abundance was reduced by Native hunting at springs perhaps as early as the arrival of the first humans in Florida some 10,000 years ago. Commercial and subsistence hunting in the 1800s further reduced their numbers to very low levels and limited their distribution to the southern tip of Florida. In 1893, the State of Florida prohibited the killing of manatees making them one of the first U.S. wildlife species to receive protection. Since the 1950s their numbers have increased slowly and their winter range has expanded as they reoccupied some of the natural springs in the central parts of the Florida Peninsula. Vessel strikes, along with environmental stressors including toxins from periodic red tide events in southwest Florida and cold-stress during exceptional cold periods, particularly in east central Florida and southwest Florida, are now the major sources of manatee death.
Since passage of the Endangered Species Act in 1973, West Indian manatees, including the Florida manatee, have been listed as endangered. Lead responsibility for research and management activities on Florida manatees is shared by the Fish and Wildlife Service, the U.S. Geological Survey, and the Florida Fish and Wildlife Commission. A recovery plan for Florida manatees was adopted in 1980 (the first recovery plan for any species listed under the ESA) and revised in 1989, 1996, and 2001.
Table 1. Annua1 number and percentage (in parentheses) of known Florida manatee deaths in the southeastern United States (excluding Puerto Rico): 1978 - 2013. Data provided by the Florida Fish and Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission. (For see FWRI for manatee mortality in Florida only)
In April 2007 the Fish and Wildlife Service completed a five-year status review of West Indian manatees. Such reviews are undertaken for species listed as endangered and threatened under the Endangered Species Act to determine periodically whether they should be reclassified. The 2007 review concluded that both Florida and Antillean manatee populations were stable or increasing throughout all of their range with the possible exception of southwest Florida. In view of those findings, Fish and Wildlife Service staff recommended that pending further analysis of survival rates in southwest Florida, the species be down-listed from endangered to threatened. Subsequent analyses completed in 2012 concluded that the population was robust and growing in all regions, including Southwest Florida. However, because of funding cuts imposed in 2012 by budget sequestration, the staff’s recommendation to reclassify Florida manatees was further deferred.
Also of concern was a series of near or record high mortality years following the 2007 manatee status review. Data available for the 2012 population analysis extended only through 2009, but in 2010, manatee mortality jumped to a record level of 776 manatees - nearly twice the previous annual death toll (see table 1)- due to a cold-stress event in which some 450 manatees were known or suspected to have died following one of the coldest periods of winter weather on record for Florida. Manatee deaths were again well above previous years in 2011 due to another red tide event in southwest Florida and an algal bloom in the Indian River. In light of this unusually high mortality, the Commission wrote to the Service on 21 September 2011 expressing concern about the population’s status. Because the minimum population estimate at the time was 5,076 animals and more 1,000 manatees had died in 2010 and 2011, it noted that the sharp increase in mortality could have had a significant effect on Florida manatee abundance. The Commission therefore recommended that, as part of any reclassification proposal, the Service incorporate an assessment of the effects of reclassification proposal, the Service incorporate an assessment of the effects of the high mortality that occurred in 2010 and 2011 and consider the possibility that mortality events similar to those that have occurred in recent years could continue to occur at least as often in the foreseeable future.
On 14 December 2012, the Fish and Wildlife Service received a petition from the Pacific Legal Foundation on behalf of Save the Crystal River, Inc., requesting that the West Indian manatee, including both the Florida and Antillean manatee, be down-listed as had had been recommended by the Service’s staff in 2007. After a subsequent exchange of letters with the applicant, the Service announced on 2 July 2014 that it found the petition to contain information sufficient to indicate the requested action may be warranted (79 Fed. Reg. 37706) and requested public comments on the action as well as information that should be considered during the decision making process on the petition.
On 2 September 2014 , the Commission responded to the request. It noted that since the initial listing West Indian manatees had been divided into two subspecies (i.e. Florida and Antillean manatees), the Service should give strong consideration to listing each subspecies separately. In addition, it noted that each subspecies may consist of multiple distinct population segments, some of which may have increased to a point where they no longer qualify as endangered. Therefore, the Commission recommended that, as part of its response to the petition, the Service should review available genetic, photo-identification, tagging, and other data to identify any distinct population segments and then assess the status of each independently.
With regard to Florida manatees, the Commission noted that record high numbers of manatee deaths between 2009 and 2013 driven largely by an unprecedented series of die-off events caused by red tides and cold weather had resulted in more than 2,900 deaths. Given the species low reproductive rate and a reported minimum population estimate of 4,824 manatees based on a count made in January 2014, it is possible that the number of Florida manatees has declined substantially over the past five years. It also noted that the frequency of red-tide and cold weather die-off events appeared to have been increasing since the early 1980s. The Commission therefore also recommended that before making any decisions to reclassify manatees, the Service complete a review of the effects of recent manatee die-offs and manatee mortality levels on the Florida manatee population size and growth rate, estimate trends in the frequency of such die-offs, and project their possible future effects on the population over time. The Commission’s letter also noted the need to evaluate the adequacy of measures to mitigate the effects of potential power plant closures over the next 30 to 40 years on Florida manatees (see below). Finally, the Commission recommended that the Service respond to the petitioners by noting that recent mortality events and other factors that have arisen since the 2007 recommendation that West Indian manatees be down-listed require a reanalysis before any change in listing status is considered.
To change the listing status of Florida manatees, the Fish and Wildlife Service must assess the severity of existing and foreseeable threats to their survival. As indicated above, virtually all Florida manatees, including those in southernmost Florida, require small localized warm water refuges to survive the coldest winter weather in at least some years (Figure 1) (Laist and Reynolds 2005a). Currently, two-thirds of all manatees now rely on power plant outfalls to survive the coldest winter days (Laist et al 2013). The projected operational lives of power plants currently used by manatees do not extend beyond 35-40 years (Laist and Reynolds 2005b). As power plants are retired, it is unclear whether alternative natural warm-water refuges - principally warm-water springs in the central and northern parts of the state and passive thermal basins in the southern part of the state - will be sufficient to support current numbers of animals. Most natural springs, which are believed to be the best natural winter habitats have either been blocked by dams or other structures, altered by construction, degraded by overuse, used intensively for recreation, or are subject to declining spring flow due to groundwater pumping for human consumption or agricultural use. Nevertheless, about 18 percent of all manatees now use warm-water springs (principally Blue Spring on the St. John’s River and Kings Bay at the head of the Crystal River) to survive cold weather. Increasing the proportion of manatees dependent on natural springs will require extensive work to improve access and conditions at springs over the coming decades to prepare for eventual power plant closures.
Figure 1. Location of warm-water refuges with counts of 50 or more manatees and boundaries of the four Florida manatee subpopulations (●= springs; ▲= power plants; ■ = passive thermal basins; * = power plants that have been retired or no longer support major aggregations of manatees due to reduced operations).
In recent years, the Florida Fish and Wildlife Commission and the Fish and Wildlife Service, have begun efforts to improve access to and protection of natural springs, many of which are currently underutilized by manatees. Major accomplishments in this regard include the following:
In addition the Florida Fish and Wildlife Commission and Fish and Wildlife Service are taking steps to complete a warm-water refuge management plan to identify actions that should be taken to further ensure that manatees will have adequate warm-water refuges when power plant outfalls are eventually retired and closed. When that plan is completed, Florida Power & Light Company plans to convene a workshop to assess actions that will be needed to prepare for eventual power plant closures.
The dependence of manatees on power plants has evolved over the past 50 years; it is anticipate that it will take a substantial period of time to conduct the needed research, take measures to provide manatees access to secure alternative natural refuges, and give manatees the chance to alter their movement patterns to take advantage of the availability of such sites.
Links for Additional Information