Why the Florida Manatee is at Risk of Extinction
Multiple Threats are Preventing Significant Growth in the Population
Jan 30, 2009
Increases in harmful algal blooms and the movement of the Florida manatee (Trichechus manatus latirostris) population north out of its optimum habitat are also having an impact on the species. Efforts to stem the decline of the manatee in Southwest Florida and maintain the rest of the state’s population will require some hard choices.
Boat Accidents Kill Florida Manatees
Manatees inhabit coastal waterways and rivers in Florida where there is heavy boat traffic. In the winter the manatees move into rivers, often near the outflow from hydroelectric plants where warm waters are discharged.
The manatees, traveling below the surface, are difficult to see and do not move away from the sound of boat motors. Most adult manatees in Florida bear scars from boat strikes. And for nearly 100 manatees every year boat accidents result in their death.
Manatees Impacted by Harmful Algal Blooms
Harmful algal blooms, commonly called red tides, affect manatees causing respiratory problems along with liver and kidney damage. While harmful algal blooms are considered natural, there has been an increase in the occurrence of these HABs which is likely related to nitrogenous runoff from agriculture and sewage outfalls. In 1996, approximately 150 manatee deaths were positively linked to a harmful algal bloom in Southwest Florida.
Lack of Critical Habitat Protection for Florida’s Manatees
The US Fish and Wildlife Service has acknowledged that critical habitat boundaries need to be updated, particularly in Southwest Florida where the manatee population is declining. Critical habitat designation can be used to reduce the incidence of boat accidents by requiring lower speed limits.
Boat propellers are also a source of damage to the seagrass beds where the manatees feed. Controlling access to those areas will help the seagrass recover. Coastal development and the release of freshwater from Lake Okeechobee have also had impacts on the seagrass beds. While some of the freshwater releases have been part of the effort to restore the Everglades, restoration of other seagrass beds is necessary to balance those losses.
As coastal development continues the number of manatees trapped in canal locks or floodgates is also increasing, especially in areas where the manatees are drawn to the warmer waters near the floodgates or locks.
Reduced Genetic Diversity Threatens Florida Manatees
Genetic diversity within a species is an important factor in maintaining healthy populations. Because the Florida manatee has long been physically separated from the other West Indian manatee populations its gene pool has shrunk. Researchers are looking at whether that low genetic diversity found in the Florida manatee is having an impact on their ability to respond to disease, cold exposure and hazards such as harmful algal blooms.
The scientists are also considering whether introducing manatees from captive populations would help or hinder the recovery of the species. Introducing animals with very similar genetic structure could actually increase inbreeding issues within the population.
In order for the Florida manatee to survive a comprehensive program of reducing human related hazards to the species and ensuring there is sufficient healthy habitat and food is needed. Monitoring genetic variability and ensuring that reintroductions do not contribute to inbreeding will be necessary as well.
Other Resources:
Bossart GD, Baden DG, Ewing RY, Roberts, B., and Wright SD. 1998. Brevetoxicosis in Manatees (Trichechus manatus latirostris) from the 1996 Epizootic:Gross, histologic, and immunohistochemical features. Toxicol. Pathol.26:276-282
Further Information on the Florida Manatee:
Controversy over Endangered Species Status for the Manatee
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